Doctoral Degrees (Plant Breeding)

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Occurrence of cowpea aphid-borne mosaic virus and prospects of improving resistance in local cowpea landraces in Uganda.
(2007) Orawu, Martin.; Melis, Robertus Johannes Maria.
Viral diseases are a major limiting factor to cowpea production in many countries of Africa. In Uganda, studies indicated that the cowpea aphid-borne mosaic virus (CABMV) is common and a potential threat to cowpea production in the region. There have been no efforts to develop cowpea cultivars with resistance to CABMV in Uganda. This work focused on the development of cultivars resistant to CABMV. Production of cowpea in Uganda is constrained by several factors, including a lack of awareness of diseases among the majority of farmers. A participatory rural appraisal (PRA) was conducted to elicit farmers’ indigenous knowledge of cowpea production and also to gain insight into their understanding of viral diseases affecting cowpea in Uganda. PRA tools such as group discussions, transect walks, problem listing and ranking were used to gather information. Insect pests, diseases, low yielding cultivars and the high cost of pesticides were perceived to be the most important production constraints. Farmers were not aware of the problem of virus diseases, but provided descriptive names of symptoms. Only three cowpea cultivars (Ebelat, Ecirikukwai and Blackcowpea) were produced in the area. Seed size and colour were seen as important traits in new varieties. Information about the occurrence, distribution and identity of cowpea viruses is limited in Uganda. The objective of this study was to identify the important cowpea virus diseases occurring naturally in the major cowpea growing regions of Uganda. Surveys were conducted to determine the incidence and severity of virus symptoms in four districts (Soroti, Kumi, Pallisa and Tororo) in 2004 and 2005. The incidence ranged from 40.5 to 94.4% and severity ranged from 15.0 to 30.6% (for Kumi and Pallisa districts, respectively) during the 2004 surveys. In 2005, the incidence ranged from 55.9 to 85.4% and severity ranged from 4.7 to 14.5% (for Tororo and Soroti districts, respectively). The CABMV, cowpea mild mottle virus (CPMMV), cowpea severe mosaic virus (CPSMV) and cucumber mosaic virus (CMV) were serologically detected by double antibody sandwich enzyme- linked immunosorbent assay (DAS-ELISA). Fifty four improved cowpea genotypes were screened for resistance to CABMV during the first season of 2004 at Serere Agricultural and Animal Production Research Institute in Uganda. Further screening was conducted in the second season of 2004 using 27 genotypes. The genotypes were planted in single rows between the rows of the susceptible cultivar, Ebelat. This was to provide high pressure of aphid vector (Aphis craccivora Koch) and CABMV inoculum. In addition, the test genotypes were artificially inoculated with a CABMV extract on fully expanded primary leaves of fourteen day-old seedlings. The CABMV incidence and severity was assessed. Disease severity was assessed on a 0-60% visual estimation scale where 0 = with no symptoms and 60 = with severe symptoms. Serological analysis was conducted using DAS-ELISA. Five genotypes showed good levels of resistance to CABMV, namely MU-93, IT82D-889, IT82D-516-2, IT85F-2841 and SECOW-2W. These resistant lines were crossed with three susceptible local landraces, namely Ebelat, Ecirikukwai and Blackcowpea in a North Carolina II mating design. The F1, F2 and BC1F1 populations and the parents were evaluated in the field to assess the response to CABMV and to study the inheritance of resistance to CABMV. The general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive genetic factors are important in determining the control of CABMV in cowpea. The proportions (%) of the sum of squares for crosses attributable to GCA and SCA for CABMV severity were 51.4% for GCA due to females, 8.4% for GCA due to males and 40.2% for the SCA. The narrow-sense heritability estimates, obtained by regressing F1 on mid-parents was 0.87 and 0.84, F2 on F1 progenies 0.49 and 0.48, and F2 progenies on mid-parents 0.63 and 0.79, for AUDPC and final disease severity, respectively. Single gene conditioned resistance in seven populations, but resistance was quantitatively inherited and involved many genes in eight populations. Observation of transgressive segregation and moderate to high heritability suggests a quantitative mode of gene action and the importance of additive effects. The predominance of GCA variance, high heritability estimates and observation of transgressive segregation suggested that resistance could be improved by selection.
Breeding investigations of finger millet characteristics including blast disease and striga resistance in Western Kenya.
(2008) Oduori, Chrispus O. A.; Derera, John.; Tongoona, Pangirayi.
Finger millet (Eleusine coracana (L.) Gaertn. ssp. coracana) is an important food, food security and cash crop in eastern and southern Africa where small-scale farmers grow it in low input farming systems. The crop has food security, nutritional, cultural, medicinal, and economic value with high industrial potential. Little research and hardly any breeding have been done on the crop leading to low yields and low production. A project was therefore implemented in western Kenya during 2004-2007 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop. The research comprised a social survey, germplasm evaluation, appraisal of ethrel as a chemical hybridising agent (CHA), genetic analysis of yield, and resistance to blast and Striga, and breeding progress in developing new finger millet varieties. A participatory rural appraisal (PRA) was conducted in three districts during 2006 to position finger millet (FM) in the farming systems, production constraints, and variety diversity and farmer preferences. The PRA established the high rating the peasant farmers gave to finger millet among crop enterprises, using it for food, cash, brewing, ceremonies and medicinal purposes. Farmers cultivated many varieties ranging from five to nine in a district, but each district had its own popular variety. Farmers used the following criteria to select new cultivars: high yield potential; early maturity; resistance to blast disease, Striga, birds, drought, and lodging; large head size, dark grain colour, and good taste. This probably indicated the willingness of farmers to adopt new varieties. Farmers identified constraints to production as blast disease, Striga, wild FM, birds, rats, termites, lack of market, labour shortage, and low yield. The farmers’ variety selection criteria and production constraints underscored the need to improve finger millet varieties. Evaluation of 310 accessions for trait variability and association conducted during 2005 long rain (LR) season at two sites revealed wide variation among the accessions for yield and secondary traits. The best accessions grain yield was above the yield potential of 5,000- 6,000kg ha-1 reported in other environments. Accessions KNE 072 (7,833kg ha-1), GBK 028463 (7,085kg ha-1), GBK 029661 (6,666kg ha-1) and FMBT ACC#42 (6,566kg ha-1) were outstanding. The data showed the opportunity to select for yield directly because of its wide variability but indirect selection could also be used to exploit seedling vigour as shown by its high correlation to yield and direct and indirect positive effects on yield through plant height and single plant yield in path analysis. The wide genetic variability among the genotypes for several traits indicated high potential to breed new and better finger millet varieties.
Improving resistance to Fusarium root rot [Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burkholder) W.C. Snyder & H.N. Hans] in common bean (Phaseolus vulgaris L.)
(2008) Mugisha, Clare Mukankusi.; Melis, Robertus Johannes Maria.; Derera, John.; Laing, Mark Delmege.; Buruchara, Robin.
Fusarium root rot (FRR) disease, caused by the fungus Fusarium solani f. sp. phaseoli (FSP), is an important soil-borne disease reducing common bean (Phaseolus vulgaris L.) yields, and hence food security, in Uganda and elsewhere in developing countries where the crop is grown without fungicides. The key aim of this study was to elucidate the significance of bean root rot (BRR), appraise methods for screening germplasm for resistance to FRR, determine the genotypic variability of resistance, and the inheritance of resistance to FRR in common bean. This information was deemed useful in devising an appropriate strategy for breeding FRR resistance in beans. A participatory rural appraisal (PRA) was conducted in south-western and eastern Uganda to ascertain farmers’ awareness of BRR and their influence on preferred bean varieties. Bean root rot is considered to be the most devastating and most recognised disease, especially in south-western Uganda. Control measures for BRR were very minimal, and in some cases, non-existent. Use of resistant varieties to control the disease was not evident, because the most popular varieties were susceptible to the disease. The resistant bean varieties currently available have undesirable characteristics such as small seed size, black seed and late maturity. Large-seeded bean varieties, even though cited as being more susceptible to BRR than the small-seeded varieties, are still very popular. The study highlighted the need for breeding FRR resistance in the large-seeded bean varieties that are highly preferred by farmers. Four isolates of FSP (FSP-1, FSP-2, FSP-3 and FSP-4) were tested for pathogenicity under screenhouse and laboratory conditions. In addition, three methods of storing and maintaining the viability of FSP isolates were appraised. The isolate FSP-3, was found to be the most pathogenic, resulting in 100% disease incidence on all bean varieties tested, with high severity scores. The potato dextrose agar (PDA) slants stored at 5oC were found to be the best method of storage for pathogenic isolates. The FSP-3 isolate was subsequently utilised for screening bean lines for resistance to FRR. The influence of soil composition, irrigation frequency, and inoculation technique on the severity of FRR was studied on six bean lines. Interactions of irrigation frequency, soil composition, and bean lines were not significant. The 50% swamp soil:50% forest soil composition and forest soil alone categorized the varieties most distinctly according to their reaction to FRR. Also, the best distinct classification for the varieties was obtained under treatments that were watered daily and once in a week. Based on economic considerations, the standard forest soil and daily irrigation were subsequently adopted for screening bean germplasm for resistance to FRR. It was also found that sorghum seed as a medium for pathogen inoculation was better than the agar slurry medium. One hundred and forty seven common bean varieties were evaluated for resistance to FRR (isolate FSP-3) under screenhouse conditions. In order to confirm this resistance, 46 common bean lines selected from the screenhouse trial were further evaluated using natural inoculum in a BRR-infested field. Forty-four varieties comprising ten large-seeded, four medium-seeded and 30 small-seeded varieties showed moderate resistance to FRR; but none were resistant or immune to the disease. Based on adaptability, eight moderately resistant varieties were selected for use as parents in the study of inheritance of resistance to FRR. A 12 x 12 diallel mating design was utilised to develop 66 F1 and F2 populations, plus their reciprocal crosses, with the aim of studying the mode of inheritance of resistance to FRR. The F1 and F2 progeny evaluations showed that FRR resistance was mainly governed by additive genes in most populations. However, there were a few crosses which displayed highly significant specific combining ability (SCA) effects, implying that dominant effects were important in some populations. Maternal effects were also highly significant at both the F1 and F2 generations, suggesting that resistance was modified by cytoplasmic genes. The non-maternal effects were also significant in some populations, suggesting that the cytoplasmic genes were interacting with nuclear genes. The number of genes governing resistance to FRR varied from two to nine among the eight sources of resistance. The allelism test of resistant x resistant populations, and the observation of continuous distributions of severity scores, suggested the presence of many loci governing FRR resistance in beans. Broad sense heritability of disease resistance varied from 0.22-0.69, while heritability in the narrow sense was estimated as 0.35-0.49 in the populations. These results suggested that selection and backcrossing to both parents would be the best breeding procedures for improving resistance in the popular large-seeded bean varieties in Uganda. However, there could be complications in breeding for resistance to FRR in beans, because resistance was modified by cytoplasmic gene effects and their interaction with nuclear genes in some of the populations.
Development of high yielding pigeonpea (Cajanus cajan) germplasm with resistance to Fusarium wilt (Fusarium udum) in Malawi.
(2007) Changaya, Albert Gideon.
Pigeon pea [Cajanus cajan (L.) Millspaugh] is a very important grain legume crop for food, cash and firewood in Malawi. However, its production is affected by Fusarium wilt (Fusarium udum Butler), which causes up to 100% yield loss. The deployment of resistant varieties would be an economical way to manage the disease, and for this, more information is needed on farmers' preferences for local landraces, how farmers and consumers can be involved in developing new varieties resistant to wilt disease, and the genetics of inheritance of resistance. This information would be used to devise a breeding strategy. A participatory rural appraisal was used in the southern region of Malawi to identify pigeonpea production and marketing constraints. Results showed that Fusarium wilt was the most prevalent and destructive disease of pigeonpea in the area. Other constraints included pests, flower abortion, low yields, and low soil fertility. Local landraces accounted for 84% of the pigeonpea production in Malawi. Local landraces were preferred due to their fast cooking time, taste, and the high prices they earn the farmer. Participatory variety selection was used to identify landraces with desirable traits that could be used in the breeding programme. Farmers and buyers selected ten local landraces which were used in the genetic improvement programme. Pigeonpea local landraces and international Crops Research Institute for the Semi-Arid Tropics (ICRISAT) genotypes were evaluated for wilt resistance, yield, and secondary traits at three sites over three seasons. Most of the landraces were susceptible to wilt and late maturing. However, AP10, a local landrace, was high yielding and resistant to wilt and outperformed ICRISAT varieties. This local landrace showed promise for use as a source material for Fusarium wilt resistance in other locally adapted farmer-preferred varieties lacking resistance. The local landraces needed genetic improvement in wilt resistance, yield, early maturity, number of branches and seeds pod. Laboratory and screenhouse studies were performed to develop a new Fusarium wilt screening technique. Grains of finger millet, sorghum, and wheat were tested as media for multiplying F. udum isolates. Pathogenicity tests were done on Bunda College and Bvumbwe Research Station isolates. The Bunda isolate was then used in an infested-seed inoculation technique against eight differential cultivars. The results showed that finger millet, sorghum and wheat were equally effective for rapid multiplication of F. udum isolates. Wheat grain showed the best results for pathogen multiplication and inoculation, due to the large seed size for easy handling. The inoculation process involved placing infested wheat grain on bruised pigeonpea roots and transplanting into soil in pots. The infested seed inoculation technique, which is the first of its kind for pigeonpea, was effective in screening pigeonpea for wilt resistance. The selected landraces were crossed with wilt resistant testers in a 12 lines x 4 testers mating scheme, and 48 F1 crosses were generated. These F1 crosses were evaluated for wilt resistance, yield, and secondary traits. The variations among F1 crosses for wilt and secondary traits were due to additive gene action in both parents and the dominance effects arising from the interactions of parents. Parental lines, with good combining ability effects for wilt resistance (AP2, AP3, and AP4), days to 50% flowering, seed pod, plant height, stem diameter, and number of primary and secondary branches were identified, while ICEAP00554 (tester) was a good general combiner for wilt resistance and days to 50% flowering. These lines would be useful in breeding for Fusarium wilt resistance in farmer-preferred pigeonpea genotypes in Malawi or similar environments. Specific F1 crosses were identified with significant SCAs for wilt resistance, days to 50% flowering, and secondary branches. The significance of GCA and SCA effects, which indicated importance of both additive and non-additive gene effects, respectively, suggested that both selection and hybridisation would be useful to improve the resistance in farmer-preferred varieties. Segregation analyses were conducted on F2 populations to determine the resistance to susceptibility phenotypic ratios. The Chi-square analyses showed that resistance to wilt was dominant over susceptibility in most F2 populations. The segregation ratios of 3:1, 13:3, 15:1, and 9:7 (R:S) indicated that either one dominant gene, or two inhibitory genes, or two independent dominant genes, or two complementary genes, respectively, were conferring wilt resistance in these crosses. Involvement of only a few genes governing wilt resistance suggested few complications, if any, in breeding for this trait in these locally adapted pigeonpeas. The Pedigree breeding method would be recommended for incorporating these traits.
Genetic improvement of Zambian maize (Zea mays L.) populations for resistance to ear rots and a survey of associated mycotoxins.
(2009) Mweshi, Mukanga.; Tongoona, Pangirayi.; Derera, John.; Laing, Mark Delmege.
Maize ear rots are among the most important impediments to increased maize production in Africa. Besides yield loss, they produce mycotoxins in their host whose contamination has been linked to several human and animal mycoses. The main objectives of the studies reported on in this thesis were (i) to investigate farmer perceptions of maize ear rot disease and prospects for breeding for host plant resistance in Zambia; and (ii) to establish the levels of incidence and extent of maize ear rot infection as well as the level of mycotoxins in the maize crops of smallholder farms in central and southern Zambia; (iii) to appraise the field inoculation techniques and assess them for their suitability for the Zambian environmental conditions, (iv) to determine the combining ability of Zambian maize populations for resistance to ear rot and investigate the genetic basis of this resistance; and (v) to investigate both direct and indirect responses to full-sib selection for ear rot resistance in Zambian maize populations. A participatory rural appraisal (PRA) was conducted in four communities, involving a total of 90 farmers. Participatory methods were used, such as focused group discussions, group interviews, participant scoring and ranking. Farmers ranked and scored the various constraints affecting their maize production in general and the maize ear rots in particular. Ear rots were ranked as the third most important biotic stress and it was evident that although farmers were aware of the disease, they were not aware of mycotoxins. This was reflected in the way they disposed of rotten maize: either by feeding livestock or eating it in periods of hunger. The survey of ear rots and mycotoxins was carried out in the Southern and Central Provinces of Zambia. A total of 114 farms were covered in the survey: maize samples were collected and both ear rot fungi and mycotoxins were isolated. Fusarium and Stenocarpella were the most frequently isolated fungi from smallholder farms. The levels of fumonisins on these farms ranged from 0.05 to 192 ppm, while those of aflatoxins were between 1.5 and 10.6 ppb. In 50% of the farmsteads surveyed, the mycotoxins, i.e. fumonisins and aflatoxins, exceeded the recommended FAO/WHO 1limits of 2 ppm and 2 ppb, respectively. Five field inoculation techniques namely, colonised toothpick, leaf whorl placement, ear top placement, spore suspension spray, and silk channel injection, were evaluated over three seasons in a series of experiments. It was found that the leaf whorl placement of inoculums, followed by colonized toothpick method, gave a constant ranking of genotypes across locations and years compared to the other three methods. In addition, the use of a mixture of ear rots as inoculum was as effective as its principal single species constituents. In the population diallel analysis, five broad-based maize populations were crossed in a diallel and evaluated under artificial ear rot inoculation using an inoculum mixture of three ear rot fungi, Aspergillus flavus, Fusarium verticilloides and Stenocarpella maydis at four locations in Zambia. The purpose was to estimate general (GCA) and specific combining ability (SCA) and investigate genotype x environment interaction. GCA effects were found not to be significant for disease severity but were significant for grain yield across environments. Populations with a strong GCA effect for disease severity across sites included PRA783244c3, Pop25, MMV600, and ZUCASRc2. Across sites, the F1 combinations, MMV600 x Pop25, ZUCASRc2 X Pop25, and Pop25 x PRA783244c2 had strong SCA effects for root lodging, ear drooping, husk cover and ear insect damage. In a related diallel analysis of 10 full-sib families derived from these populations, it was observed that resistant x susceptible families and their reciprocal crosses performed better than their resistant parents, suggesting an over dominant expression of resistance. Both maternal and non maternal effects were observed to be influencing resistance to ear rots. There was a preponderance influence of non-additive gene action. A response to full-sib recurrent selection was conducted in four locations in Central Zambia. Out of the 343 families created in 2005/6 season, 10% were selected from each population and recombined to create five new populations. These, with the original populations, were evaluated in four sites during the 2007/8 season. There was a net reduction in ear rot incidence and rot severity in the new synthetic population. Pop10 had the largest reduction in disease severity. The predicted gain per cycle was -4.1% and realized gain was -2.5% for disease incidence, and 0.19% and 19.4% for grain yield. Genetic variability was maintained though with low heritability estimates. Negative but at times strong association between grain yield and ear rot disease severity was detected suggesting that in general selecting for ear rot resistance would enhance grain yield in the five populations. Overall the importance of the ear rots and mycotoxins in compromising yield and health of the communities in Zambia, respectively, were confirmed and support the call to improve maize varieties for resistance to ear rots. The results indicate that the five populations could be enhanced for ear rot resistance through population improvement procedures such reciprocal recurrent selection that exploit both additive and non-additive variation. Selection might be compromised by the large genotype x environment interaction effects, and large reciprocal effects and their interaction with the environments. To enhance repeatability genotypes should be artificially inoculated, by placing the inoculum in the leaf whorl followed by colonized toothpick inoculation, and screened in many environments to identify genotypes with stable resistance to ear rots.
Mutagenesis and development of herbicide resistance in sorghum for protection against Striga.
(2009) Ndung'u, David Kamundia.; Tongoona, Pangirayi.; Derera, John.
Sorghum (Sorghum bicolor) is an important cereal crop in sub-Saharan Africa. The parasitic weed Striga hermonthica is a major biotic constraint to sorghum production. A novel technology where planting seeds are coated with herbicide to kill Striga that attach to the roots of the host has been shown to be effective in protecting the cereal crop from Striga damage. However, the host plant must have herbicide tolerance. This technology has not been tested in sorghum because there are no herbicide tolerant sorghum varieties available in Kenya and is, therefore, unavailable for subsistence farmers. One of the ways in which genetic variation can be enhanced and herbicide resistance developed is through chemical mutagenesis with ethyl methane sulfonate (EMS). The objectives of this project, therefore, were to: 1) identify sorghum production constraints through farmer PRA in order to determine breeding priorities.in two Striga endemic districts in western Kenya; 2) develop an EMS mutagenesis protocol for sorghum and to enhance the genetic variability of the crop using chemical mutagenesis; 3) evaluate EMS-derived sorghum mutants for improved agronomic performance; 4) develop acetolactate synthase (ALS) herbicide resistance in sorghum and to characterize the mode of inheritance of the trait; 5) determine the effect of herbicide coating of seed of herbicide tolerant sorghum on Striga infestation. In order to determine breeding priorities and constraints in sorghum production and the likelihood of adoption of herbicide seed coating technology, a survey involving 213 farmers was conducted in two Striga endemic rural districts of Nyanza province in Kenya. Results indicated that local landraces like Ochuti, and Nyakabala were grown by more farmers (> 60%) than the improved varieties like Seredo and Serena (48%). Popularity of the landraces was linked to Striga tolerance, resistance to drought, bird damage and storage pests, yield stability and high satiety value. Major constraints to sorghum production were drought, Striga weed, storage pests, bird damage and poverty among the rural farmers. Important characteristics farmers wanted in new varieties were Striga and drought resistance, earliness, resistance to bird and weevil damage and good taste. Striga infestations in sorghum fields were > 70%. Cultural Striga control options were considered inadequate while inorganic fertilization and chemical control were considered effective but unaffordable. Farmers’ willingness to pay a premium of over 30% for a Striga solution gave indication that herbicide seed coating if effective could be adopted by farmers. As a prerequisite to development of herbicide resistance, a comparative study was carried out to determine optimum conditions for mutagenesis and to induce genetic variation in the sorghum. Two sorghum varieties were mutagenized using varying concentrations (0.1 to 1.5% v/v) of EMS and two exposure times (6h and 12h). In laboratory and greenhouse experiments, severe reduction of sorghum root and shoot lengths indicated effective mutagenesis. The LD50 based on shoot length reduction was 0.35% and 0.4% EMS for 6h for Seredo and Kari/mtama-1, respectively. The highest mutation frequency based on chlorophyll abnormalities was 56% for 0.3% EMS for 6h. In the M2 generation, phenotypic variances for panicle characteristics were increased on treatment with EMS. However, significant effects of exposure time and variety indicated the necessity of genotype optimization for some traits. In order to determine the significance of mutation breeding in sorghum, 78 mutant lines derived from EMS mutagenesis, their wild type progenitor (Seredo) and two local checks (Kari/mtama-1 and Serena) were evaluated for agronomic performance in two locations in Kenya. There were significant (P = 0.05) effects among entries for grain yield, 1000-seed weight and visual scores for height uniformity, head exertion, head architecture and overall desirability. The highest yielding entry-mutant line “SB2M13” had a yield of 160% and 152% relative to the wild type (Seredo) and the best check Kari/mtama-1, respectively. Mutant line “tag27” had the highest 1000-seed weight which was 133% relative to the wild type. Seven mutant lines were rated superior to the wild type for panicle characteristics, head exertion and overall desirability. However, the majority of mutants were inferior to the wild type for most characteristics. Superior mutant lines may be developed into direct mutant varieties after multi-location trials or used as breeding material for sorghum improvement. In order to develop acetolactate synthase (ALS) herbicide resistance in sorghum, over 50,000 seeds of Seredo were mutagenized with 0.3% EMS. Over four million M2 plants were screened using 20g ha-1 of the ALS herbicide, sulfosulfuron. Five mutants (hb46 hb12, hb462, hb56 and hb8) survived the herbicide treatment and were confirmed to be tolerant. Mutant lines displayed differential herbicide tolerance, and the general order of tolerance after spray or seed coat application was hb46 > hb12 > hb462 ~ hb56 > hb8. The LD50 values for herbicide application as a spray, or seed coat, showed mutant lines to be up to 20 and 170 fold, respectively, more resistant than the wild type. Chi square analysis of data from herbicide screening of F2 generation of mutant X wild type crosses indicated no difference from the Mendelian segregation of 1:2:1 indicating the herbicide tolerance was inherited as a single semi-dominant gene. Mutant X mutant crosses did not show allelism indicating that the tolerance in all five mutants could be a result of the same gene mutation. To determine effect of herbicide seed coating on Striga infestation, the five herbicide tolerant mutant lines, hb46, hb12, hb462, hb56 and hb8 and the wild type progenitor Seredo were coated with varying concentrations (0.5-1.5% g ha-1) of sulfosulfuron and planted in a Striga endemic field. There were significant (P=0.05) effects of herbicide concentration on Striga density, Striga flowering and seed set, and sorghum plant stand and biomass. All treatments with herbicide coated on sorghum seeds had lower Striga emergence. Coating sorghum seed with 1g ha-1 sulfosulfuron reduced Striga infestation, Striga flowering and Striga seed set by 47%, 52% and 77%, respectively, and was considered the most effective rate as it did not result in sorghum biomass reduction. Mutants displayed differential herbicide tolerance and Striga resistance. Combining seed coating with high herbicide tolerance and inherent Striga resistance would be most effective for Striga control. Overall, the study showed that EMS mutagenesis is effective in inducing variation in sorghum for several traits including herbicide resistance. The mutants developed in this study will be important for sorghum breeding and for protection of sorghum against the Striga weed.
Breeding, evaluation and selection of Cassava for high starch content and yield in Tanzania.
(2009) Mtunda, Kiddo J.; Shanahan, Paul Edward.; Melis, Robertus Johannes Maria.
High starch content is an important component of root quantity and quality for almost all uses of cassava (flour, chips, and industrial raw material). However, there is scanty information on genetic variability for dry matter and starch contents and relatively little attention has been paid to genetic improvement of root dry matter content and starch content in Tanzania. The major objective of this research was to develop improved cassava varieties that are high yielding, with high dry matter and starch content for Tanzania and specifically to: i) identify farmers’ preferences and selection criteria for cassava storage root quality characteristics and other traits of agronomic relevance for research intervention through a participatory rural appraisal; ii) determine the genotypic variability for starch quantity and dry matter content evaluated for three harvesting times in four sites; iii) determine the inheritance of dry matter and starch content in cassava genotypes; and iv) develop and evaluate clones for high storage root yield, high dry matter content and starch. Attributes desired by farmers were yield, earliness, tolerance to pests and diseases. The complementing attributes associated with culinary qualities were sweetness, good cookability, high dry matter content or mealyness and marketability. The preliminary study conducted to evaluate the variability in root dry matter content (RDMC) and starch quantity and yield of ten cassava cultivars indicated that RDMC ranged from 29 to 40% with the mean of 34.3%. The RDMC at 7 months after planting (MAP) was higher than at 11 and 14 MAP. Starch content (StC) ranged from 20.3% to 24.9% with the mean of 22.8%. The StC differed significantly between cultivars, harvesting time and sites. An increase in StC was observed between 0 and 7 MAP, followed by a decline between 7 and 11 MAP, and finally an increase again noted between 11 and 14 MAP. However, for most of the cultivars at Kibaha an increase in StC between 11 and 14 MAP could not surpass values recorded at 7 MAP. At Kizimbani, cultivar Kalolo and Vumbi could not increase in StC after 11 MAP. At Chambezi and Hombolo, a dramatic gain in StC was observed for most of the cultivars between 11 and 14 MAP. Starch yield ranged from 0.54 to 4.09 t ha-1. Both StC and fresh storage root yield are important traits when selecting for commercial cultivars for starch production. Generation of the F1 population was done using a 10 x 10 half diallel design, followed by evaluation of genotypes using a 4 x 10 á-lattice. Results from the diallel analysis indicated that significant differences in fresh storage root yield (FSRY), fresh biomass (FBM), storage root number (SRN), RDMC, starch content (StC), and starch yield (StY), and cassava brown streak disease root necrosis (CBSRN) were observed between families and progeny. The FSRY for the families ranged from 15.0 to 36.3 t ha-1; StC ranged from 23.0 to 29.9%; RDMC ranged from 31.4 to 40.1%; and StY ranged from 3.3 to 8.3 t ha-1. The cassava mosaic disease (CMD) severity ranged from 1.7 to 2.7, while cassava brown streak disease (CBSD) severity for above ground symptoms ranged from 1.0 to 1.9. Additive genetic effects were predominant over non-additive genetic effects for RDMC, StC, and CBSRN, while for FSRY, FBM, SRN, and StY non-additive genetic effects predominated. Negative and non-significant correlation between RDMC and FSRY was observed at the seedling stage (r=-0.018), while at clonal stage the correlation was positive but not significant (0.01). The RDMC and StC were positive and significantly correlated (r=0.55***) at clonal stage. However, the StC negatively and non-significantly correlated with FSRY (r=- 0.01). High, positive and significant correlation (r=0.94; p.0.001) was observed between the StY and FSRY at clonal stage. High, positive and significant correlations between the seedling and clonal stage in FSRM (r=0.50; p.0.01), RDMC (r=0.67; p.0.001), HI (r=0.69; p.0.001), and SRN (r=0.52; p.0.01) were observed, suggesting that indirect selection could start at seedling stage for FSRM, RDMC, HI, and SRN. The best overall genotype for StC was 6256 (40.9%) from family Kiroba x Namikonga followed by genotype 6731 (40.6%; Vumbi x Namikonga). Among the parents, Kiroba and Namikonga were identified as the best combiners in terms of GCA effects for StC. Genotype 6879 from family Vumbi x AR 42-3 had the highest StY value of 34.8 t ha-1 followed by genotype 6086 (30.4 t ha-1; Kalolo x AR 40-6). Among the parents, Kalolo and AR 42-3 were identified as good combiners for the trait. Mid-parent heterosis for StC ranged from 41.6 to 134.1%, while best parent heterosis ranged from 30.4 to 119.6%. Genotype KBH/08/6807 from family Vumbi x TMS 30001 had the highest mid-and best parent heterosis percentage for StC. For StY, mid-parent and best parent heterosis ranged from 168.0 to 1391.0%, and from 140.4 to 1079.0%, respectively, with the genotype 6879 (Vumbi x AR 42-3) exhibiting the highest mid- and best parent heterosis percentage for StY. Improvement for StC, RDMC, and CBSRN may be realized by selecting parents with the highest GCA effects for the traits and hybridize with those that combine well to maximize the positive SCA effects for the StC, RDMC and CBSRN. Selected genotypes from the clonal stage will be evaluated in preliminary yield trial and advanced further to multi-locational trials while implementing participatory approaches involving farmers and processors in selection. New promising lines should be tested at different sites and the best harvesting dates should be established.
Towards enhancement of B-carotene content of high dry mass sweetpotato genotypes in Zambia.
(2009) Chiona, Martin.; Shanahan, Paul Edward.; Melis, Robertus Johannes Maria.; Laing, Mark Delmege.
The enrichment of B-carotene, a precursor to vitamin A, in the local sweetpotato (Ipomoea batatas L.) cultivars is an attractive option in order to improve vitamin A intake in Zambia. The study was conducted to: 1) identify sweetpotato genotypes high in B-carotene content and high root dry mass (RDM) and to determine their combining ability, as measured through their progeny performance; and 2) screen progeny for root characteristics, yield, B-carotene content, and RDM. Firstly, a participatory rural appraisal (PRA) was conducted to determine the consumer preferences for sweetpotato. These preferences would form the basis for selecting desirable genotypes. Secondly, five selected parents were crossed in a full diallel for genetic variance studies. A selected subset of the diallel progeny were evaluated in three environments. Thirdly, 15 polycross progeny were evaluated for stability in five environments using additive main effect and multiplicative interaction (AMMI). The PRA revealed that consumers preferred high RDM combined with high fresh root yield. The diallel crosses recorded significant general combining ability (GCA) and specific combining ability (SCA) effects for B-carotene, RDM, harvest index (HI) and root fresh yield (RFY). The ratios of GCA to SCA variances were large (0.68-0.92). Two high B-carotene parents exhibited positive high GCA effects, indicating that additive gene effects were predominant in the inheritance of B-carotene. Reciprocal mean squares were not significant for RDM but they were significant (p=0.01) for B-carotene content. The estimate of narrow sense heritability of RDM (76.3%) was high; but heritability of B-carotene (20.9%), HI (29.1%) and RFY (34.9%) were much lower. These results suggest that rapid genetic gains should be possible with mass selection breeding techniques based on the phenotype of the parent for RDM but progress will be slow for B-carotene content HI, and RFY. The AMMI analysis identified progeny G2 (B-carotene content = 5.0 mg 100 g-1 and RDM = 37%), G6 (B-carotene content = 4.7 mg 100 g-1 and RDM = 37%), and G8 (B-carotene content = 4.7 mg 100 g-1, RDM = 35%) from the polycross as stable across environments for both B-carotene content and RDM. Genotype G3 was best suited to one of the test environments and had the highest B-carotene content (9.421 mg 100 g-1) and a high RDM (35.47%).
Breeding investigations for black Sigatoka resistance and associated traits in diploids, tetraploids and the triploid progenies of bananas in Uganda.
(2009) Barekye, Alex.; Tongoona, Pangirayi.; Laing, Mark Delmege.; Derera, John.
Reduced banana yield owing to black Sigatoka Mycosphaerella fijiensis Morelet is a threat to the livelihoods of Ugandan subsistence farmers who depend entirely on the banana crop for food security. The objectives of this investigation were to: (i) assess farmers’ knowledge of black Sigatoka disease in central Uganda; (ii) document the qualities farmers would desire in the banana genotypes to be developed for black Sigatoka resistance; (iii) appraise the methods for assessing black Sigatoka resistance in diploid banana populations; (iv) determine the phenotypic variation for black Sigatoka resistance and agronomic traits in diploid and tetraploid bananas; (v) determine the influence of tetraploid and diploid parents on the black Sigatoka resistance and agronomic traits in the triploid progenies; and (vi) evaluate 2x by 2x banana progenies for yield and black Sigatoka resistance. A survey that focused on low and medium banana production zones in Uganda established that there was limited awareness of black Sigatoka disease as a constraint on banana production in the areas surveyed. It was also established that farmers liked local bananas because of their superior taste, early maturity, and marketability. There were farmers who had been exposed to new black Sigatoka resistant materials but never liked these new banana materials because of poor taste and lack of market. Farmers desired new banana materials with good taste on cooking, heavy bunches, resistance to pests and diseases, drought tolerance, and early maturing capacity in that order. The results indicated that the banana farmers in Uganda attached more importance to food quality attributes than to production attributes especially when considering new banana materials. This suggested that farmers mainly grow bananas for consumption. Three black Sigatoka assessment methods, youngest leaf spotted, disease development time and area under disease progress curve (AUDPC) were appraised using a diploid population. All the three methods were able to classify the diploid accessions into resistant and susceptible clones. The cultivar rankings of AUDPC correlated strongly with the rankings of disease development time. The cultivar rankings of AUDPC correlated positively with the rankings of youngest leaf spotted method. The youngest leaf spotted at flowering and AUDPC predicted significantly total number of leaves at flowering (R2 = 0.53). Overall AUDPC had the highest coefficient of determination (R2=0.84) in assessment of banana diploids for black Sigatoka resistance indicating that it accounted for the highest variation in disease response observed among the diploid clones. From this investigation it was recommended that AUDPC should be used to assess resistance on black Sigatoka in Musa species. A phenotypic analysis on the diploid and synthetic tetraploids, and a molecular analysis using RAPD markers on the tetraploid population were conducted. Results indicated that the diploid population had significant (P<0.001) variation for plant height, plant girth, days from flowering to harvest, bunch weight, number of suckers, youngest leaf spotted, total leaves at flowering, area under disease progress curve, and number of functional leaves at harvest. Principal component analysis showed that plant height and girth explained most of the variation observed in the diploid population. In the tetraploid population, significant differences were observed for plant height, plant girth, and number of suckers (P<0.05). In the tetraploids principal component analysis, indicated that youngest leaf spotted and total leaves at flowering had higher loadings on principal component one. Genetic distances computed from RAPD markers indicated limited genetic variability in the tetraploid population. Another investigation was also carried out to determine the influence of tetraploid and diploid parents on black Sigatoka resistance and agronomic traits in the triploid progenies generated from tetraploid-diploid crosses. The results indicated that diploids transferred black Sigatoka resistance to triploid progenies as measured by disease development over time, the number of functional leaves at flowering and at harvest. On the other hand, the female synthetic tetraploids influenced plant height and bunch weight in the triploid progenies generated from tetraploid-diploid crosses as observed from triploid progeny correlations and parent-offspring regressions. Therefore, it is important to select tetraploids with heavy bunch weights to generate high yielding triploids in tetraploid-diploid crosses. Lastly, this thesis investigated the relationship between bunch weight and black Sigatoka resistance traits in 2x by 2x progenies generated using a random polycross design. Phenotypic correlations revealed strong positive relationships between bunch weight with total leaves at flowering, youngest leaf spotted, plant girth, and days from planting to flowering among the 2x by 2x progenies. Linear regression analysis indicated that girth, total fingers and finger length significantly predicted bunch weight (R2=0.67). However, days from planting to flowering, and total leaves at flowering had strong indirect effects on bunch weight via plant girth. The results imply that selection for parents with good combining ability for girth, finger length and total fingers can improve bunch weight in a diploid population.
Recurrent selection for gray leaf spot (GLS) and phaeosphaeria leaf spot (PLS) resistance in four maize populations and heterotic classification of maize germplasm from western Kenya.
(2007) Kwena, Philip Onyimbo.; Derera, John.; Tongoona, Pangirayi.; Odongo, Omari Mumani.
Maize (Zea mays L.) production is constrained by a number of stresses, amongst the most important are gray leaf spot (GLS) caused by a fungus Cercospora zeaemaydis Tehon and E.Y. Daniels and Phaeosphaeria leaf spot (PLS) caused by Phaeosphaeria maydis (Henn.). The diverse germplasm comprising farmer collections and exotic material used in the medium and highland altitudes maize breeding programmes in western Kenya has not been improved for resistance to the two diseases. Heterotic patterns of germplasm from this region have also not been studied. Therefore, the objectives of this study were to (i) assess the prevalence, importance, and farmers’ perceptions of GLS and PLS, (ii) characterize maize germplasm collections into their heterotic groups and (iii) improve four maize populations for GLS and PLS resistance through recurrent selection. The participatory rural appraisal (PRA) was conducted at three sites in western Kenya during the 2005/2006 cropping season. Data was generated using a checklist in group discussions with 109 male and 123 female farmers as well as key informants. Constraints were identified and prioritised. The five most limiting, in order of importance, were low soil fertility, poor varieties and seed, drought, Striga, pests and diseases (GLS and PLS). Gray leaf spot and PLS were reported in all sites but farmers did not know the causes of these diseases. Farmers preferred local varieties Tiriki, Anzika and Kipindi due to their greater resistance to diseases than commercial hybrids. Farmer criteria for variety selection were low fertilizer, Striga and disease resistance, drought tolerance, closed tips, and high yield potential. Due to the high cost of hybrid seed farmers selected and planted their own seed from advanced generations from previous seasons. Across all the sites, yield gap between on-farm and expected yield potential was estimated as ranging from 4.73t ha-1 to 5.3t ha-1 mainly due to the identified constraints. Therefore maize breeding should focus on addressing important maize production constraints and farmers’ preferences identified in this study in developing varieties that will increase maize yields on-farm. During 2005/2006, seventy 77 testcrosses were developed through crossing 47 germplasm collections with four population testers, Kitale synthetic II (KSII), Ecuador 573 (EC 573), Pool A and Pool B. Crosses and testers were evaluated at Kakamega during 2006/2007 in a 9 x 9 triple lattice design. Significant (p < 0.05) differences in grain yield, ear height, days to 50% anthesis, GLS and PLS resistance were observed. Both general and specific combining ability effects (GCA and SCA, respectively) were significant (p < 0.01), with SCA accounting for more than 50% of the variation for GLS, PLS and yield and less than 50% for ear height, days to 50% anthesis and silk. This indicated that both additive and non-additive gene effects were important but non-additive gene effects were more important in conditioning these traits. High SCA effects indicated high heterosis between collections and populations. Both yield heterosis and SCA were used to study heterotic patterns, but percentage yield heterosis data was used to classify these materials into heterotic groups. Based on significance (p < 0.05) of percentage yield heterosis as a primary factor for classification, seven collections were classified to Pool A, 17 to Pool B, 12 to KSII and 6 to EC 573 heterotic groups. The study indicated that germplasm collections belong to distinct heterotic groups therefore they can be infused into these populations (Pool A, Pool B, KSII and EC 573). Four populations, KSII, EC 573, Pool A and Pool B were subjected to one cycle of reciprocal recurrent selection (RRS) and two cycles of simple recurrent selection (SRS) during the 2004-2006 cropping seasons at Kakamega. Response to selection was assessed by evaluating C0, C1 and C2 and four commercial checks in a randomised complete block design in three replications at Kakamega and Kitale during 2007. All cycles except C0 of Pool A were more resistant to GLS than the three checks, H623, KSTP94 and PHB3253. Response to selection for GLS was significant (p < 0.01) in the desired direction. Gains ranged from -32.2% to 6.4% cycle-1 for RRS and 0.0% to -61.3% cycle-1 for SRS. Heritability estimates of between 59% and 76.3% for GLS and 39% and 80% for PLS were observed indicating that both GLS and PLS can be improved through selection. Significant negative correlations between GLS and yield were observed in Pool A C0 (r = -0.947, p < 0.01) and between yield and PLS in Pool A C0 (r = -0.926, p < 0.01). These indicated gain in yield as GLS and PLS were selected against. Generally, SRS out performed RRS method both in genetic gain and time, as indicated by gain of -61% for SRS and -32.2% for RRS, respectively. Two cycles of selection were achieved in two years with SRS as compared to only one with RRS. These results clearly demonstrated that it is possible to improve for GLS resistance using simple and reciprocal recurrent selection methods. The main constraints to maize production in Western Kenya were low soil fertility, Striga, drought, lack of seed and diseases. Farmers preferred varieties that can do well under the constraints mentioned. Local collections belonged to distinct heterotic groups with good resistance to GLS and PLS and were highly heterotic to four maize population testers with both SCA and GCA effects being important in conditioning GLS and PLS resistance. Recurrent selection methods were found to improve maize resistance to GLS and PLS. Breeding should therefore, focus in development of hybrids and improvement of populations using these local collections by employing SRS and RRS selection methods with identified constraints and farmer preferences in mind.
Combining ability and heterosis for stem sugar traits and grain yield components in dual-purpose sorghum (Sorghum bicolor L. Moench) germplasm.
(2009) Makanda, Itai.; Tongoona, Pangirayi.; Derera, John.
Sorghum is the fifth most important cereal crop in the world and ranks third in Africa, and it is potentially the number one cereal for the semi-arid environments in sub-Saharan Africa. Sorghum varieties have been developed specifically for grain, fodder or stem sugar but not for dual-purpose combining grain and stem sugar. Such varieties could be beneficial to the resource-poor farmers by providing grain for food and sugar rich stalks that can be sold for bioethanol production. However, there are no suitable dual-purpose cultivars on the market. There is also limited information about the combining ability, gene action and genetic effects and relationships between stem sugar and grain yield which is required in devising appropriate strategies for developing dual-purpose sorghum varieties. Furthermore, there is also lack of information about the perceptions of resource-poor, small-scale farmers and other important stakeholders on the potential of dual-purpose sorghum production and the value chain. Therefore, the objectives of this study were to: (i) investigate the awareness of the farmers, industry and other stakeholders on the dual-purpose sorghum varietal development and its feasibility, (ii) screen germplasm for use as source materials useful for grain yield and stem sugar traits, (iii) investigate the inheritance and heterosis levels attainable in grain yield components and stem sugar traits in dual-purpose sorghums, (iv) determine the relationships between stem sugar traits and grain yield components in dual-purpose sorghums, and (v) investigate the fertility restoration capacities of selected male-fertile lines used as male parents through the evaluating seed set in experimental dual-purpose hybrids. Two surveys were conducted to establish stakeholders’ level of awareness and perceptions on the potential and feasibility of developing and utilising dual-purpose sorghums in Southern Africa. One survey was carried out in the semi-arid tropical lowlands in Zimbabwe under the conditions of small-scale and resource-poor farmers while the other, which targeted sugar industries, plant breeders, engineers, political leaders, economists and extension workers, was conducted in South Africa and Zimbabwe. Data were analysed using SPSS computer package. Results showed that both farmers and the non-farmer stakeholders were in agreement on the view that dual-purpose sorghum would be a viable enterprise that could alleviate poverty, enhance food security, create rural employment and boost rural development in southern African countries. Farmers were willing to adopt the cultivars if they were made available. The stakeholders also suggested mechanisms to overcome the infrastructural, economic and technical challenges associated with the technology. Screening of regional and international germplasm collection held at the University of KwaZulu- Natal in South Africa revealed high genetic variability for grain yield, stem brix and stem biomass yield that can be exploited in dual-purpose sorghum cultivar development. Ten lines were selected for inclusion as parents in the dual-purpose sorghum breeding programme. The selections were crossed to eight cytoplasmic male-sterile lines originating from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in accordance with a North Carolina Design II mating scheme. The 18 parents, together with the 80 experimental hybrids generated and two check varieties were evaluated for grain yield and stem sugar traits in six tropical low- and mid-altitude environments in Mozambique, South Africa and Zimbabwe. Stem sugar concentration and stem biomass were measured at the hard dough stage of each entry due to maturity differences between the genotypes. Grain yield was measured and adjusted to 12.5% moisture content. Data were analysed in GenStat computer package following a fixed effects model. Both additive and non-additive gene effects were important in controlling stem brix, stem biomass, grain yield and the associated traits in dual-purpose sorghum. This showed that breeding progress can be achieved through hybridisation and selection. Cultivars showing high stability, and high standard and better-parent heterosis for the three traits were identified implying that breeding for general adaptation was an option and that productivity could be enhanced by breeding hybrid cultivars. The relationships between traits were estimated using correlation and path-coefficients analysis. Grain yield was found to be negatively and significantly associated with stem brix but was positively and significantly associated with stem biomass. This implied that breeding for high stem brix might compromise grain yield but selection for high stem biomass improved grain yield. Stem biomass and stem brix were not significantly correlated. The general negative relationship between grain and stem brix was attributed to the predominance of entries with contrasting performances for the two traits. However, the relationship between grain yield and stem brix of the top 20 performing entries showed a non-significant relationship between stem brix and grain yield suggesting that the traits were independent of each other. This finding was confirmed by the presence of crosses that combined high performance for both stem brix and grain yield as well as stem biomass among the hybrids. The relationships between stem brix and stem biomass for the top 20 performers remained non-significant while that between stem biomass and grain yield became stronger, positive and significant. Direct selection for stem brix and grain yield was shown to be more important than indirect selection, while selection for stem biomass improves grain yield but had no effect on stem brix. Therefore, it is possible to breed dualpurpose sorghum cultivars and the identification of genotypes combining the desirable traits is prudent in addition to general relationships information. The study on fertility restoration capacities as evaluated through hybrid seed set showed that fertility restoration was under the control of genes with both additive and non-additive action. Since restoration is conferred by a single dominant gene (Rf1), this could have arisen from the action of the modifier genes that have been previously reported to influence it. This showed that fertility restoration can be improved through breeding. Hybrid combinations showing complete seed set and high performance for grain, stem brix and stem biomass were identified and are potential dual-purpose sorghum cultivars. Overall, the study showed that development of dualpurpose sorghum cultivars would be feasible and genotypes identified as potential cultivars in this study will be forwarded for further testing across many sites and seasons in the target environments.
A study of bruchid resistance and its inheritance in Malawian dry bean germplasm.
(2007) Kananji, Geoffrey Acrey Duncan.; Melis, Robertus Johannes Maria.; Derera, John.; Laing, Mark Delmege.
Dry bean (Phaseolus vulgaris L.) is economically and nutritionally an important legume, not only in Malawi, but in many parts of Africa and Latin America. Unfortunately, two bruchid species (Acanthoscelides obtectus Say, and Zabrotes subfasciatus Boheman) are known to cause extensive damage in storage, reducing the economic importance, food value and planting value of the crop. The aim of this study was to: i) ascertain farmers’ perceptions of the importance of bruchids as storage pests, and to identify their preferred varietal traits in dry beans; ii) screen Malawian dry bean landraces for effective and adaptable sources of resistance to the two bruchid species; iii) determine the gene action and inheritance of bruchid resistance. Farmers’ perceptions on the importance of the two bruchid species to beans both in the field and in storage were established using a participatory rural appraisal (PRA) in three extension planning areas (EPAs) in Lilongwe agricultural development division (ADD). Results confirmed that the two bruchid species are important storage pests, causing serious storage losses among smallholder farmers. In the absence of any control measures, farmers indicated that more than 50% of their stored beans could be lost to bruchids. Indigenous bruchid control measures are not very effective, making it necessary to search for other control methods. It was also clear from the PRA results that breeders need to consider both agronomic and culinary traits in bean cultivar development. This would enhance uptake of newly developed varieties. To address the problem of bruchid damage experienced by smallholder farmers, a total of 135 dry bean genotypes, comprising 77 landraces and 58 improved varieties (obtained from collaborating partners) were tested under laboratory infestation (nochoice test methods) and field infestation (free-choice test methods). The objective of this study was to identify effective sources of resistance to the two bruchid species. Results of the study showed that there was a wide variation among the genotypes for resistance to the two bruchid species. Overall results showed that 88% of the genotypes ranged from susceptible to highly susceptible to Z. subfasciatus and only 12% of the genotypes were moderately resistant to resistant. Genotype screening for resistance to A. obtectus showed that only 12.5% were resistant, whereas 87.5% were moderately to highly susceptible. All of the improved genotypes were 100% susceptible to A. obtectus in storage. One landrace, KK35, consistently showed a high level of resistance to both bruchids under laboratory infestation, with results similar to the resistant checks (SMARC 2 and SMARC 4), while another landrace, KK90, displayed stable resistance under both laboratory and field infestation. However, performance of most genotypes was not consistent with field and laboratory screenings, suggesting that mechanisms of bruchid resistance in the field are different from that in the laboratory and field screening should always be used to validate laboratory screening. Resistance in the field was not influenced by morphological traits. The seed coat played a significant role in conferring resistance to both bruchid species in the laboratory, whereas arcelin did not play any significant role in conferring resistance in the landraces. The inheritance of resistance to A. obtectus was studied in a 6 x 6 complete diallel mating design, involving crosses of selected Malawian dry bean landraces. The F1 crosses, their reciprocals, and six parents were infested with seven F1 generation (1 to 3 d old) insects of A. obtectus in a laboratory, no-choice test. There were significant differences among genotypes for general combining ability (GCA) and specific combining ability (SCA). However, SCA accounted for 81% of the sum of squares for the crosses, indicating predominance of the non-additive gene action contributing to bruchid resistance. A chi-square test for a single gene model showed that 5 of the 13 F2 populations fitted the 1:2:1 segregation ratio of resistant, intermediate and susceptible classes, respectively indicating partial dominance. The eight F2 populations did not conform to the two gene model of 1:4:6:4:1 segregation ratio of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes, respectively. Average degree of dominance was in the partial dominance range in five F3 populations, but in general resistance was controlled by over-dominance gene action in the F2 populations. The additive-dominance model was adequate to explain the variation among genotypes indicating that epistatic effects were not important in controlling the bruchid resistance. The frequency distribution of the 13 F3 populations for resistance to A. obtectus provided evidence for transgressive segregation, suggesting that resistance is conditioned by more than one gene. Reciprocal differences were not significant in the F2 generation seed; but were significant in four crosses in the F3 generation seed for adult bruchid emergence, suggesting that maternal effects or cytoplasmic gene effects also played a role in the inheritance of resistance to the common bean weevil. Through this study, important sources of bruchid resistance in dry bean have been identified in Malawian landraces (KK35, KK90 and KK73). These resistant sources will be used in a breeding programme to develop bruchid resistant bean cultivars, as well as improve resistance in susceptible commercial bean cultivars currently grown by farmers in Malawi.
Genetic studies of grain and morphological traits in early generation crosses of Malawi rice (Oryza sativa L.) Landraces and NERICA varieties.
(2010) Mzengeza, Tenyson.; Tongoona, Pangirayi.; Derera, John.
Rice (Oryza sativa L.) is the second most important cereal crop in Malawi. Rice productivity in the dominant (85%) rainfed ecosystem is very low, with mean yield of only 1.4 t ha-1. Farmers plant traditional landraces that have low yield potential and are susceptible to various stresses such as drought and diseases. Development and introduction of improved rice varieties, with stress tolerance traits from introduced varieties, such as the New Rice for Africa (NERICAs), could significantly increase productivity. Previous attempts to introduce high yielding irrigated varieties into the dominant rainfed ecosystem in Malawi have not been successful because farmers basically did not adopt the varieties, claiming that the varieties were lacking in grain traits that they preferred but that the traits were present in their landraces. The notable traits mentioned, through previous informal surveys, were long grains, medium to slender shape and aromatic grain with intermediate gelatinization temperature. No formal study has been conducted to ascertain the preferences, and the genetic control of the traits, including yield and yield related traits, have not been studied. The objectives of this study were to: 1) confirm farmers’ preferences for grain traits using participatory rural appraisal; 2) determine amount of genetic variability for yield and yield related traits in Malawi rice landraces, 3) determine the genetic control and correlations of grain length, grain shape and 1000-grain weight, 4) determine the inheritance of aroma and gelatinization temperature and, 5) determine the genetic control, correlations and path coefficients of yield and yield related traits, in F2 generations of Malawi rice landraces and NERICA varieties crosses. To confirm the farmers’ preferences for grain traits, a participatory rural appraisal was conducted in 2006 in two villages that were representative of rainfed rice growing areas in Malawi. The villages were Liundi and Nawanga in Machinga and Salima Districts, respectively. Qualitative and quantitative data were collected through questionnaires and discussions with 190 respondents, as well as through observations. To determine variability among Malawi rice landraces, 19 landraces were planted at Lifuwu in a Randomized Complete Block Design with three replicates in 2006. Data on plant height, days to 50% flowering, number of panicles per hill, panicle length, number of filled grains per panicle, 1000-grain weight, panicle weight, grain length and grain yield were collected and analyzed. Four Malawi rice landraces were crossed to four NERICA varieties in 2006 in a North Carolina Design II mating scheme to determine the genetic control of grain size. F1 plants were raised in 2007 and in 2008, 16 F2 populations together with their parents were planted in a Randomized Complete Block Design with three replicates at Lifuwu. Data on grain length, grain shape and 1000-grain weight were collected and analyzed. To determine the inheritance of aroma and gelatinization temperature, four Malawi rice landraces were crossed to four NERICA varieties in 2006 and F1 plants were raised in 2007. In 2008, 16 F2 populations together with their parents were planted in a Randomized Complete Block Design with three replicates at Lifuwu. Aroma and gelatinization temperature were evaluated. To determine the gene action of yield and yield related traits, four Malawi rice landraces were crossed to four NERICA varieties in 2006 in a North Carolina Design II mating scheme and F1 plants were raised in 2007. In 2008, 16 F2 populations together with their parents were planted in a Randomized Complete Block Design with three replicates at Lifuwu. Data on grain yield, the number of panicles per hill, days to 50% flowering, panicle length, panicle weight and 1000-grain weight were collected and analyzed The participatory rural appraisal confirmed that that long, slender or medium shape grains, with aroma and intermediate gelatinization temperature were the key traits preferred by farmers. Therefore the farmer preferred traits of long, slender grains, with aroma and medium gelatinization temperature, must be selected for in any high yielding varieties to be developed for the rainfed rice ecosystem. Results showed that differences were significant (P=0.05) for all the traits that were studied. Heritability estimates were low to moderate: 18.3% for panicle weight, 40.0% for panicles per hill and 56.3% for days to 50% flowering date. The high genetic variability among the landraces could be used in a breeding programme to develop improved varieties for various morphological traits. The number of panicles per hill and 1000-grain weight combined moderate heritabilities with relatively high genetic advance and therefore could be reliable traits for yield improvement. Genetic analysis of grain size showed that Malawi rice landraces were variable for all three grain size characteristics, namely grain length, grain shape and 1000-grain weight. NERICA varieties were variable for 1000-grain weight. Sixteen F2 progenies were variable for all three characteristics, and the variability was significant (P=0.05). Heritability estimates were high (45.4%) for grain length and low for grain shape (12.3%) and for 1000-grain weight (14.3%) suggesting that early generation selection would be effective for grain length. Predominance of additive gene action for grain length and grain shape suggested that early generation selection would be effective for these traits. Selection for 1000-grain weight would be more effective in later generations because of preponderance of non-additive gene action in the control of this trait. The correlation between grain length and grain shape was positive (r=0.769) and highly significant (P=0.01) suggesting that breeders would choose to select for both traits simultaneously, or they would choose one of the traits to develop varieties with long grains and medium shape. Crosses between aromatic and non-aromatic varieties had non-aromatic F1. The F2 progenies segregated into 3:1 ratio for non-aromatic: aromatic suggesting that, in the Malawi rice landraces, aroma was probably simply inherited through a single recessive gene. F1 progenies, between parents with high and intermediate gelatinization temperatures had intermediate gelatinization temperature. F2 progenies segregated into 1:3 ratios for high; intermediate gelatinization temperature in three out of four crosses suggesting control by one dominant gene. The segregation pattern in one cross was not significantly different from 3:13 ratio for high: intermediate suggesting that two dominant genes, one an inhibitor, were controlling the trait. Breeding and selecting for aroma and intermediate gelatinization temperature could be accomplished relatively easily because the traits are simply inherited. The genetic variability for yield and yield related traits was wide and significant (P=0.05) in the F2 populations of Malawi rice landraces and NERICA varieties crosses indicating that the populations would be valuable sources to develop varieties with improved yield. Panicle weight and the number of panicles per hill were positively correlated with, and had high direct effects on grain yield, therefore they could be used to indirectly select for high yield. Grain yield, the number of panicles per hill and plant height were predominantly controlled by additive gene action suggesting that bulk breeding methods would be adopted for these traits. The days to 50% flowering, panicle weight and 1000-grain weight were predominantly under the control of nonadditive gene action suggesting that hybrid development would be profitable for these traits. Faya Mpata, Faya Zidyana and NERICA 3 could be the best parents for improving yield and yield related traits because they had high general combining abilities for the traits.
Genetic diversity of proprietary inbred lines of sunflower, determined by mapped SSR markers and total protein analysis.
(2008) Erasmus, Tertia Elizabeth.; Laing, Mark Delmege.
This study compared DNA based SSR markers with total seed protein markers, used to evaluate genetic diversity of sunflower. The multiplex-ability, cost effectiveness and applicability of microsatellites as molecular markers for a genetic diversity study were investigated and evaluated based on pedigree data of the sunflower germplasm. A solution for oil and fat interference in ultrathin iso-electric focusing gels was investigated, in order to make imaging and interpretation easier and clearer. Total protein analysis was utilized for the determination of genetic diversity on the same inbred material used for the DNA analysis. Finally a correlation is made between the data obtained on DNA vs Protein compared with phenotype and expected pedigree data. A set of 73 SSR markers with known mapped positions were utilized to determine genetic similarity in a group of sunflower inbred lines. Cluster analysis of genetic similarity revealed an excellent correlation with the breeding background and source information obtained from breeders on all inbred lines used in this study. Cluster analysis gave a clear differentiation between B and R-lines, showing clearly defined heterotic groups of the proprietary set of inbred lines. The most outstanding single-locus SSR markers in the set used for this study were identified and used as a core set. Multiplex assays were designed and optimized for the most cost and time effective method for rapid variety identification. The selected markers produced robust PCR products, amplified a single locus each, were polymorphic among the elite inbred lines and supplied a good, genome-wide framework of completely co-dominant, single-locus DNA markers for molecular breeding. The use of a fluorescent-tailed primer technique resulted in a considerable cost saving. Furthermore, the SSR markers can be multiplexed through optimization, in order to avoid undesirable primer-primer interactions and non-specific amplification. First stage iso-electric focusing of total protein extracts were used to analyze sunflower looking at genetic purity and genetic variety verification on diverse sunflower germplasm. Severe visual interference was visible on most seed storage protein extracts of sunflower. This interference was visible as a distortion in the gel matrix on the anodal end of the gel, and caused important proteins to denature in the presence of heightened field strength and the absence of a uniform matrix. Adjustment of the extraction solutions removed this interference. Total protein profiles were generated with the use ultrathin layer iso-electric focusing (UTLIEF) to assess the level of genetic diversity on the same set of sunflower lines used for the SSR analysis. Finally, the genetic diversity of the sunflower germplasm was analysed by comparing proteomic, genomic and pedigree data from the same germplasm. A total of 295 alleles were amplified with a set of 73 SSR markers with known mapped positions. These were utilized to determine the genetic relatedness of a group of B-lines and R-lines of sunflower. In parallel, a total of 68 protein bands were visualized using protein samples of two types of seed storage proteins derived from exactly the same sunflower lines. Cluster analysis clearly differentiated between the B-lines and R-lines, identifying defined heterotic groups of this proprietary set of lines. The comparison of DNA and protein data for the application of genetic diversity studies is analysed, as well as the general comparison on the use of the two different molecules as markers.
Optimising aspects of a soybean breeding programme.
(2008) Jarvie, John Antony.
Abstract not available.
Recurrent selection for drought tolerance in Maize (Zea mays L. and study of heterotic patterns of maize populations from Eastern Kenya.
(2007) Leley, Philip Kipkoech.; Tongoona, Pangirayi.; Derera, John.; Ininda, Jane.
There are few maize varieties that are drought tolerant in semi-arid eastern Kenya and farmer perceptions of drought tolerant maize cultivars have not been studied in this region. Farmers in this region use maize landraces that have not been studied for their potential future hybridization. The main objectives of this study were therefore to: (i) study farmer perceptions of drought and preference for maize varieties, (ii) improve drought tolerance in maize populations in the semi-arid eastern Kenya using S1 family recurrent selection, and (iii) classify maize landraces according to their heterotic patterns. A participatory rural appraisal (PRA) was conducted in Machakos and Makueni districts in semi-arid eastern Kenya. A total of 175 farmers were involved in focus group discussions. An open ended questionnaire and a checklist were used to guide the farmers during the discussion sessions. Scoring and ranking techniques were used to assess farmers’ preferences of maize varieties and constraints to maize production. The farmers grew maize as their major crop followed by beans. Nearly 60% of the farmers grew local maize landraces, whose seed they recycled from season to season; 40% grew improved varieties, but mainly composites rather than hybrids. The key farmers’ criteria for choosing a maize variety in order of importance were drought tolerance, early maturity, high yield, and disease resistance. The major constraints to maize production were drought, lack of technical know-how, pests, poor soils, and inadequate seed supply. Maize traits preferred by farmers in a drought tolerant variety included high yield, recovery after a dry spell and the stay green characteristic. Two maize landrace populations MKS and KTU from semi-arid eastern Kenya and three CIMMYT populations V032, ZM423, and ZM523 were subjected to two cycles of S1 progeny recurrent selection for drought tolerance in yield and traits indicative of drought tolerance were measured during flowering and grain filling from February 2005 to September 2007. Evaluation to determine selection gains was done in one trial replicated five times. It was laid out as a 4x4 lattice design and drought was imposed at reproductive stage by withholding irrigation one week before flowering and resumed during grain filling. The trial was repeated under well-watered conditions which served as a control experiment. After two cycles of selection under drought stress conditions, KTU population had a realized gain in yield of 0.2 t ha-1, MKS population 1.2 t ha-1 and ZM423 0.4 t ha-1, whereas in V032 and ZM523, grain yield reduced by 1.1 t ha-1 and 0.6 t ha-1, respectively. Under well watered conditions, the realized gains in grain yield were positive in all the populations except V032, where there was a reduction of 0.1 t ha-1. Selection increased the genetic variability and heritability estimates for yield in S1 lines of MKS and ZM423 populations, but decreased in KTU, V032 and ZM523 populations. The research to identify heterotic patterns was undertaken using ten maize landraces from the semi-arid eastern Kenya, six maize landraces from coastal Kenya, and three maize populations from CIMMYT. These populations were planted at Kiboko Research Farm during the short rains of October-December 2005 and crossed to two population testers, Embu 11 and Embu 12. The evaluation of the test crosses was done during the long rains of March-June 2006. Percentage heterosis for yield ranged from -17.7% to 397.4%, -79.4 to 22.2% for anthesis-silking interval, -23.9% to 29.2% for ear height, -0.1 to 1.1 for ear diameter, -7.1 to 21.2% for ear length and -5.9% to 30.3% for plant height. iii General combining ability (GCA) effects were significant (p=0.05) for all the traits, while specific combining ability (SCA) effects were not significant (p>0.05), implying that variation among these crosses was mainly due to additive rather than nonadditive gene effects. Since SCA was not significant (p>0.05) for yield, maize populations were classified based on percentage heterosis for yield alone. The maize populations therefore, were grouped into three different heterotic groups P, Q and R. Twelve landrace populations and two CIMMYT populations showed heterosis with Embu 11 and no heterosis with Embu 12 were put in one group P. Two landrace populations that showed no heterosis with either tester were put in group Q. Two landrace populations and one CIMMYT population showed heterosis with both testers were put in group R. None of the populations showed heterosis only with Embu 12 and no heterosis with Embu 11. The main constraint to maize production was drought and the farmers preferred their landraces whose seed they recycled season to season. After two cycles of recurrent selection, the landrace populations showed improved progress in yield. Thus, further selection will be beneficial in the populations where genetic variability increased. Therefore, these populations can further be improved per se and released as varieties and/or incorporated into the existing maize germplasm to broaden their genetic base, given that their heterotic patterns have been identified. Considering that farmers recycle seed, breeding should be towards the development of open-pollinated varieties which are drought tolerant.
Breeding investigations of maize (Zea mays L.) genotypes for tolerance to low nitrogen and drought in Zambia.
(2007) Miti, Francisco.
Low soil nitrogen (N) and drought impede maize production in the small-scale farming sector in Zambia; and adoption of new cultivars with improved tolerance might enhance production. This study: a) assessed farmer preferences for maize cultivars; b) determined genotype x environment interaction effects among popular maize cultivars under contrasting soil fertility levels and; c) investigated landraces for tolerance to low N and drought using S1 selection. The study was carried out in Zambia from 2004-07. Farmer preference influencing the adoption of maize cultivars was investigated using both formal and informal surveys in Luangwa, Chibombo and Lufwanyama rural districts representing the three agro-ecological regions of Zambia. Focus group discussions and personal interviews were used to collect data on issues that affected maize production in these areas. It has been found that although farmers perceived landraces to be low yielding, they believed that they were superior to improved cultivars for: tolerance to drought; tolerance to low soil fertility; grain palatability; grain storability; and poundability. The need for food security, their inability to apply fertiliser, and their need for drought tolerant cultivars significantly (p ≤ 0.05) influenced farmers in adopting cultivars. The farmers would readily adopt cultivars that address these concerns. The predominant use of certain landraces (76%) reflected their superiority in meeting some of these needs. The performance of nine popular cultivars (three for each of hybrids, OPVs and landraces) under contrasting levels of soil fertility, across six environments (ENVs) in the three agro-eological regions, was evaluated. An ENV was defined as season x location combination. The fertilizer treatments were full fertilization, basal dressing, top dressing and nil fertilization. The cultivars exhibited significant non-crossover type of genotype x fertilisation interaction effects at three ENVs, while the genotype x fertilisation interaction effects, were non-significant at the other three ENVs. The cultivars exhibited dynamic stability by increasing grain yield (GY) when fertilization was increased. Landraces yielded higher than all open pollinated varieties and were generally higher yielding than two hybrids. Based on average rank for GY, the five highest yielding cultivars were MRI724, Gankata, MM603, Kazungula and Pandawe. Superiority of landraces revealed their genetic potential for GY under low soil fertility and they should be used as germplasm in developing cultivars targeting such environments. Ninety-six local landraces were selfed to generate S1 lines (2004/05 season) which were crossed to a tester (2005/06 season). Testcrosses were evaluated under optimal, low N, and drought conditions (2006/07 season). Data on GY, anthesis-silking interval, number of ears per plant, leaf senescence, leaf rolling, tassel size and grain texture were recorded in all the trials during the study period. Testcrosses, their S1 parents and landraces that were superior under low N, drought, optimal conditions and across environments were identified; these should be used to develop varieties targeted to a particular environment. Selection for tolerance to drought also selected for tolerance to low N. Selection for low N tolerance also selected for GY under drought and optimal conditions. Therefore, in selecting for tolerance to abiotic stresses, use of optimal and managed stress environments was effective. The following landraces were superior at 10% selection intensity: LR38, LR84 and LR86 (optimal, low N and drought conditions); LR11, LR35 and LR76 (low N and drought conditions); LR12 (optimal and drought conditions); LR40 and LR93 (low N conditions only); LR79 (drought conditions only) and; LR74 and LR85 (optimal conditions only). These landraces should be used as source germplasm targeting respective environments. Significant (p ≤ 0.05) positive general combining ability effects for GY under both low N and drought conditions were found implying that additive gene action conditioned GY under the abiotic stresses. The heritability for GY under low N (0.38), and drought (0.17) conditions, was low suggesting that selection based on GY alone was not effective. The genetic correlation for GY between optimal, and either low N (rG=0.458), or drought (rG = 0.03) environments, was low (rG < 0.5) suggesting that indirect selection would not be effective either. Therefore, use of secondary traits for selection is discussed. The study established that most farmers depended on local landraces for seed and would adopt low input improved varieties that yield higher than the landraces. Some landraces were found superior to some improved cultivars under contrasting fertilisation regimes. The study also found that landraces had genetic variation for tolerance to low N and drought. Landraces, S1 lines and testcrosses superior under low N, drought, optimal conditions and across environments were selected and they should be used to develop cultivars targeting respective environments. Policy implications of these results are discussed.
A comparative analysis of conventional and marker assisted selection methods in screening for resistance to maize (Zea mays L.) streak virus disease.
(2006) Abalo, Grace.; Tongoona, Pangirayi.; Derera, John.
Maize (Zea mays L.) streak virus disease (MSD) is the most important virus disease in Africa but farmers are unaware of its status. A project was initiated to assess the current status of MSD and to breed for its resistance. Four populations comprised of two BC1F1 and two F2 progenies developed by backcrossing and selfing the F1 progenies of two crosses between a donor line (CMl 202) and two susceptible lines (CMl 321 and CMl 384) were developed. Conventional and molecular marker assisted selection (MAS) methods were used to screen for resistance to MSD in each of the four populations. To facilitate unbiased comparison, separate screening nurseries were established for MAS and conventional screening. The objectives of the study were five-fold; 1) to assess the status of MSD in Uganda and understand farmers' preferences and varietal selection criteria for maize using a participatory rural appraisal (PRA), 2) to screen for MSD resistance in early generations of segregating maize populations using conventional method, 3) to screen for resistance to MSD using SSR marker assisted selection , 4) to compare the effectiveness of marker assisted selection and conventional methods for selection for resistance to MSD, and 5) to compare costs associated with MAS and conventional selection methods. Results of PRA showed that unreliable rainfall and insect pests were the dominant constraints to maize productivity in Uganda. Diseases were ranked fifth among the production constraints . Maize streak virus disease was considered the most important disease constraint. Farmers showed common preference for high yielding and early maturing cultivars. However, farmers had other special preferences which were diverse and included large, white and high test density kernels for marketing, and sweet taste, particularly for home consumption. Farmers' research priorities included tolerance to drought, resistance to insect pests and diseases, sweetness, prolificacy, resistance to lodging, and drooping leaves because theyt cover the soil fast and prevent weed growth. Conventional screening for resistance to MSD showed that backcross and selfing populations segregated in 1:1 and 3:1 Mendelian ratios confirming the presence of one major gene with simple inheritance . Severity and incidence of disease were positively correlated suggesting a non-reference by the insects. In the selfing populations, the presence of complete esistance against MSD was suggested because frequency distribution patterns were highly skewed in favour of resistance. There was a decrease in disease severities with selection from BC1F1 to BC2F1 and from F2 to F3 generations indicating that high response to selection was achieved. On the other hand, one marker, umc1917, consistently polymorphic and eo-dominant was selected and used in MAS protocol. Results showed that the observed outcomes fitted the expected ratio of 1:2:1 for a F2 population and 1:1 for a BC1F1 population (X2 not significant). Evaluation of F3 and BC2F1 progeny selected using markers showed low disease severity suggesting that marker assisted selection was effective. However, the study showed that the presence of the O'Tl, was not consistent with symptom expression in the field. Evaluation of lines in three-way crosses identified ten potential lines that were high yielding, highly resistant to MSD and stable across three locations. Both MAS and conventional selection were equally effective in identifying high yielding lines although resistance was higher under MAS. Costs of MAS and conventional method varied depending on the units for comparison. The total costs of conventional method were higher than that of MAS in both first and second selection cycles. Comparing costs per row for conventional and costs per plant or data point for MAS showed that conventional selection was 2.4 times more expensive than costs per sample for MAS. However, costs per plant for MAS were 6.6 times higher than for conventional selection.
Participatory-based development of early bulking cassava varieties for the semi-arid areas of Eastern Kenya.
(2006) Kamau, Joseph Wainaina.; Melis, Robertus Johannes Maria.; Laing, Mark Delmege.; Shanahan, Paul Edward.
Cassava (Manihot esculenta Crantz) is an important food security crop in the semi-arid areas of Eastern Kenya. It provides food for more days in a calendar year than any other crop grown. Kenya has relied on varieties bred in other countries and because of this, local breeding methodologies and expertise are lacking. Access to appropriate varieties and adequate planting materials are major limiting factors to cassava production. Farmers grow late bulking landraces that take up to 18 mo to harvest. Efforts to introduce early bulking genotypes from IITA failed because of poor end-use quality. Local cassava breeding is necessary to alleviate the production constraints. Before a local breeding program can be established, farmers' preferences and production constraints must be identified and methodology appropriate to the Kenyan environment must be developed. The aims of this study were to identify farmer production constraints and preferences, to develop methods appropriate for cassava breeding in the semi-arid areas of Kenya, develop a population segregating for bulking period to estimate genetic variances that would explain the gene effects controlling yield components, and through participatory selection identify varieties that combine early bulking and preferred end-user traits. PRA tools, focus groups and individual interviews were used to identify production constraints and farmer preferences for cassava varieties. The PRA found that farmers grow 13 landraces in the area and 11 production constraints were identified and prioritised. The four most limiting in the order of importance were drought, lack of planting material, pests and diseases. Crosses between cassava varieties often do not produce much seed and the seed produced does not germinate well. Germination studies were done with open pollinated seeds to identify conditions favourable for seed germination in Kenya. The highest germination of the seeds was at 36°C. The control seeds had a higher germination percent (77%) compared to the seeds which were pre-heated at 36°C (57%). Crosses were made between selected IITA and local Kenyan genotypes following the NC 11 mating design to develop new genotypes which combine early bulking along with other farmer/end-user preferred characteristics. The hybrid progenies were evaluated in a seedling trial and clone genotypes advanced to a clonal trial and performance trial. The clonal trial was destroyed by red spider mites and cassava green mites, and only the tolerant 225 genotypes were planted in a performance trial that was harvested at 6, 7 and 8 mo after planting. The SCA effects were estimated to be 57% to 75% for most of the traits, except root number, which was mainly controlled by GCA effects (55%). Participatory selection of genotypes that combined early bulking and end-user qualities at the 7 and 8 mo after planting was done by farmers. Thirty genotypes that combined early bulking and end-user qualities were identified and ranked according to their performance in both agronomic and end-use traits using a selection index. A number of selected genotypes yielded more than three times the yield of the best parents, showing strong progress in breeding. Combining the farmers' preference aggregate score and the selection index based on the agronomic data, assisted in the final identification of the best genotypes developed in the breeding process. These results clearly demonstrated that it is possible to breed early bulking varieties with good end-use quality in the semiarid areas.
Study of anthracnose (Colletotrichum lindemuthianum) resistance and its inheritance in Ugandan dry bean germplasm.
(2006) Nkalubo, Stanley.; Melis, Robertus Johannes Maria.; Laing, Mark Delmege.
The common bean (Phaseolus vulgaris L.) is an important crop grown widely in Uganda. It is also an important source of income for smallholder farmers particularly women. Despite its importance, production in the cool highland regions is constrained by anthracnose disease which causes losses in both the quantity and the quality of beans produced. The principal aim of this research was to elucidate on the status of dry bean anthracnose and the genetics governing its resistance. A participatory rural appraisal study was conducted to explore farmers' knowledge, experience, problems and cultivar preferences in association with managing dry bean anthracnose disease. This study revealed that anthracnose is an important constraint to production which is not controlled in any way. Although farmers have varying cultivar preferences, they use mostly home saved seed and only 1% could access improved seed. The study suggested the need for practical approaches in the provision of quality anthracnose resistant seed in consideration of farmers' preferences and the dynamics of their rural livelihoods. A study was conducted to determine the variability of the anthracnose (Colletotrichum lindemuthianum) pathogen in some of the major bean growing regions of Uganda. Use was made of a set of 12 internationally accepted anthracnose differential cultivars to identify the physiological races present. The results obtained indicated the presence of eight races with one race (767) being dominant and most aggressive. Differential cultivars AB 136 and G2333 were resistant to all the eight races, and can be utilised as potential sources of resistant genes. A germplasm collection of mostly Ugandan accessions was screened for anthracnose resistance. Using the area under disease progression curve as the tool for assessing disease severity, eleven accessions were identified that posses good levels of anthracnose resistance. The yield loss attributed to the anthracnose disease was determined on three susceptible Ugandan market-class dry bean cultivars and two resistant cultivars. The results showed that the yield of susceptible cultivars was reduced by about 40% and an almost equivalent yield was lost due to poor quality seed. In comparison, the yield lost by the resistant cultivars was not significant. The study suggested the use of resistant cultivars as the best solution in combating anthracnose resistance. Three susceptible Ugandan market class dry bean cultivars and six resistant cultivars were used for the study of the inheritance of resistance to the anthracnose pathotype 767 in a complete 9x9 diallel design. The results clearly indicated that the resistance was predominately conditioned by additive gene action. It was also established that epistatic gene action was important. More than one pair of genes displaying partial dominance were responsible for determining resistance and the maternal effect did not have an influence on resistance. Additionally, the result showed that some of susceptible cultivars combined very well with the resistant cultivars and that anthracnose resistance heritability estimates in both the narrow and broad sense were high. These results suggested that the use of simple pedigree breeding procedures such as backcross selection could be useful in improving anthracnose resistance levels in the Ugandan market class varieties.

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