Browsing by Author "Sibiya, Julia."

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Assessment of groundnut (Arachis hypogaea L.) for genetic diversity using agro-morphological traits and SSR markers.
(2019) Chipeta, Olivia.; Sibiya, Julia.
Groundnut (Arachis hypogaea L.) offers one of the cheapest sources of proteins and economic empowerment to smallholder farmers in Africa, contributing significantly to world production and trade. Thus, improved groundnut seed with high quality attributes is needed. Therefore, pre-breeding activities involving agro-morphological attributes such as yield, disease tolerance/resistance, plant architecture among others are important in order to develop superior genotypes with the needed quality attributes. This study focused on assessing the performance and level of phenotypic variability and genetic diversity of groundnut genotypes using agronomic and morphological attributes, and simple sequence repeat (SSR) markers. Twenty-seven groundnut genotypes collected from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Malawi) and Chitedze Agricultural Research Station (Malawi) showed highly significant differences in relation to number of branches, days to flowering, leaf color, seed yield and shelling percentage except for aflatoxin content and groundnut rosette disease. Moderate to high broad-sense heritability (0.56-0.71) was observed for number of branches, days to flowering and leafspot disease. The genotypes grouped into three main distinct clusters with those bred for low aflatoxin accumulation falling in the same cluster. Principal component analysis (PCA) had two PCs explaining 57.7% of the total variation with number of branches, flowering and aflatoxin contributing the most to the first PCA. Five genotypes; MP-68, ICGV-94379, ICGV-93305, CDI-1314 and CDI-0009 were identified as high yielding with low aflatoxin concentration hence are recommended for further pre-breeding activities such as increasing yield and resistance to diseases and aflatoxin. Using 20 SSR markers, 39 groundnut genotypes of diverse origin maintained at Agricultural Research Council – Grain Crops Institute in South Africa (ARC-GCI were assessed for genetic diversity. Results showed polymorphic information content (PIC) averaging 0.71, indicating the markers were very informative. A wide genotypic diversity with highest dissimilarity index of 6.4 between genotype pair RG562 and RG288, and smallest dissimilarity index of 0.9 between RG512 and RG562 was observed. Allelic diversity analysis showed high diversity among genotypes from southern Africa and southern America as indicated by the Shannon information index, mean number of observed alleles (Na) and mean number of effective alleles (Ne) which were relatively higher than in other groups. Analysis of molecular variation (AMOVA) results indicated that variation between and within individuals was more significant than between populations. Discrimination of the genotypes was not dependant on the geographical origin as genotypes belonging to different origins clustered in the same groups. Thus, genotypes with wide diversity can be used in breeding programmes as parents.
Assessment of sweet sorghum lines for genetic diversity using quantitative traits and SSR markers.
(2016) Chinyama, Sombo.; Sibiya, Julia.; Odindo, Alfred Oduor.
The increase in energy demand, volatile oil prices and climate change has led South Africa to reduce its dependency on fossil fuels and promote biofuels. Sweet sorghum [Sorghum bicolor (L.) Moench] has been considered as one of the promising crops due to its sugar-rich stalk to supplement sugarcane which is the major feedstock for bioethanol. Establishing genotypic variability for biomass yield and sugar-related traits in sweet sorghum is therefore essential for developing superior cultivars. The objectives of the study were: (i) to assess sweet sorghum lines for agronomic performance and genetic diversity using quantitative morphological traits and (ii) to assess sweet sorghum lines for genetic diversity and interrelationships using simple sequence repeat (SSR) markers. Twenty-five sweet sorghum lines collected from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Kenya) and the African Centre for Crop Improvement (ACCI-South Africa) were evaluated during the 2015/2016 season in KwaZulu-Natal (KZN) province at Ukulinga Research Farm in Pietermaritzburg and Makhathini Research Station in Jozini. Seven agronomic traits; fresh biomass yield, fresh stalk yield, grain yield, plant height, stalk diameter, panicle length and days to 50% flowering, and six quality traits; fibre, dry matter, °brix, °total brix, total fermentable sugars and ethanol were recorded. The sweet sorghum lines revealed highly significant variations for the 13 quantitative characters assessed in this study. The extent of variation was highly influenced by environment and genotype by environment interaction. Genotypes designated as IS 2331, IESV 92008 DL, ICSV 700, AS 244, URJA and SS 27 were identified as suitable genotypes with high plant height, dry matter, fibre, °brix, °total brix, total fermentable sugars and ethanol. The specified genotypes also exhibited medium to late maturity with relatively high fresh biomass and fresh stalk yield. Genotype 91018 LT showed the highest fresh biomass yield, fresh stalk yield, stalk diameter and relatively high grain yield. High levels of trait heritability were observed for fresh stalk yield (98%), stalk diameter (93%), fresh biomass yield (81%), panicle length (76%), fibre (73%) and plant height (66%). Heritability estimates were influenced by the environment and genotype by environment interaction. Principal component analysis resulted in the first three principal components showing 83% of the total variability among the genotypes. Ethanol, total fermentable sugars, °total brix, fresh stalk yield and °brix contributed mainly to PC 1, whereas fresh biomass yield and stalk diameter contributed mainly to PC 2. The dendrogram generated from cluster analysis divided the genotypes into two main clusters and three singletons (ICSB 324, ICSB 654 and ICSV 700). Cluster I comprised 54% of the total germplasm and included only one ACCI genotype (SS 27), while cluster II comprised of 33% of the total variation. The morphological variability analysis of the genotypes was also complimented with the use of molecular markers. The 24 sweet sorghum lines were genotyped with 10 simple sequence repeat (SSR) markers and distance-based method was used to analyze the data. Variation was observed for all the markers with allelic size ranging from 1 to 36 bp. A total of 61 alleles were generated with an average of 6.1 alleles per locus. The polymorphism information content (PIC) values ranged from 0.32 to 0.86 with an overall mean value of 0.62, showing a high discriminating ability of the markers used. The largest genetic distance was observed for AS 244 (GD = 1.9), while IESV 92001 DL and IESV 92008 had the smallest genetic distance (GD = 0.50). The dendrogram generated from cluster analysis using SSR markers classified the 24 sweet sorghum lines into two major clusters. Cluster I comprised of 12.5% of the total genotypes which included URJA, SS 27 and ICSB 654. It was observed that all ACCI genotypes apart from AS 244 were grouped in Cluster I, with URJA and SS 27 being very closely related. Cluster II was observed to be the largest (87.5%) with 21 genotypes, which further formed 3 sub-clusters (A, B and C) and a singleton (AS 244). The results from molecular marker characterization were similar to those obtained using PCA analysis of morphological traits which grouped genotypes into four clusters, with the same type of genotypes in each group. The information obtained in this study coupled with phenotypic characterization can be used by plant breeders to select parents or pure lines that can be used in developing improved cultivars. This will therefore contribute to the production of sweet sorghum and promotion of its use for bioethanol in South Africa.
Breeding for ascochyta blight [Phoma exigua var. diversispora (Bubak) Boerema] resistance of the common bean (Phaseolus vulgaris L.) in Rwanda.
(2017) Urinzwenimana, Clement.; Melis, Robertus Johannes Maria.; Sibiya, Julia.
Abstract available in PDF file.
Breeding for durable resistance to angular leaf spot (Pseudocercospora griseola) in common bean (Phaseolus vulgaris) in Kenya.
(2014) Njoki, Ng'ayu-Wanjau Beatrice.; Melis, Robertus Johannes Maria.; Mwangi, Githiri.; Sibiya, Julia.
Common bean (Phaseolus vulgaris L.) is an important legume crop in Kenya and is a cheap source of proteins. The small scale farmers in Kenya produce common bean under low agricultural input systems and this predisposes the crop to pests and diseases. Among the diseases, angular leaf spot (ALS) is a major constraint to common bean production and contributes to yield losses as high as 80%. The causative pathogen Pseudocercospora griseola (Sacc.) Crous & Braun is highly variable and several races have been reported. There are few common bean genotypes with resistance to this disease. Therefore breeding for resistance to ALS is important for the country. This study was carried out to; i) evaluate the common bean production systems, constraints and farmer varietal preferences in Kenya, ii) evaluate local landraces and selected introductions of common bean for yield performance and reaction to ALS, iii) study the genetics of resistance to ALS in common bean and iv) develop a breeding method for durable resistance to ALS in common bean. To determine the common bean production systems, farmers’ preferred traits and their knowledge on common bean constraints including ALS, a survey was conducted in Kiambu county using a semi-structured questionnaire, interviews, and focus group discussions. The study revealed that farmers cultivate common beans during the short and long rain seasons. However, they experience better yields in the short rains due to reduced disease incidence. The majority of the farmers (71%) intercrop common bean and this ensures maximum utilisation of space. A high percentage (70%) of the farmers utilise their retained seed for production. The farmers identified ALS as one of the most important constraints to production. The only preventative measure they undertake to control the disease is weeding. The farmers reported that they would prefer improved varieties that were resistant to ALS. Farmers have a preference for particular common bean traits that include high yield (80%), resistance to insect-pests and diseases (72%), type I growth habit (52%), early maturity (68%), seed size and colour (21%) and cooking time (20%). These should be incorporated in breeding programmes. Two hundred common bean landraces and market class varieties were evaluated for ALS resistance in a nethouse at University of Nairobi, Kabete Field Station and for ALS resistance and yield in the field in KARI-Tigoni. The results showed that disease severity scores for the genotypes were similar in the two locations, with the top three resistant genotypes being Minoire, GBK 028123 and Murangazi with disease severity scores of 2.9, 2.9 and 3.2 in Kabete and 2.6, 2.8, and 2.9 in Thika respectively. These resistant genotypes can be used as sources of resistance in a breeding programme or they can be used as resistant varieties. All the market class varieties were susceptible to ALS (disease severity score 6.7-8.0). There was a non-significant correlation between disease and yield most likely because most of the resistant genotypes were exotic and hence not adapted to the local conditions. There was also a non-significant correlation between disease and seed size. The two hundred common bean genotypes were evaluated for yield at University of Nairobi, Kabete Field Station and KARI-Thika. The results indicated that the 2011 and 2012 seasons had similar mean yields and that yields at Kabete were higher than at KARI-Thika. The highest yielding genotypes across the two locations were; GLP 2 (766 kg ha-1), Nyirakanyobure (660 kg ha-1), GBK 028110 (654 kg ha-1), GLP 585 (630 kg ha-1) and Mukwararaye (630 kg ha-1). There was a significant genotype x environment interaction and hence it is important for breeders to carry out stability analysis, so as to recommend varieties for a wide range of environments. To study the genetics of ALS resistance in common bean, three inter-gene pool crosses: Super-rosecoco x Mexico 54, Wairimu x G10909 and Wairimu x Mexico 54 were made. The resistant genotypes were Mexico 54 and G10909, while Super-rosecoco and Wairimu were susceptible. The generations F1, F2, BC1P1 and BC1P2 for each of the crosses were developed. The parents P1, P2 and the five generations of each cross were evaluated for resistance to ALS in Kabete Field Station. Results showed that both dominance and additive gene action were important in the expression of resistance to ALS. However, additive gene action was predominant over dominance gene action. There was a moderately high narrow sense heritability estimate (52.9-71.7%). The minimum number of genes controlling resistance to ALS was between 2 and 3. The predominance of additive gene effects and the moderately high narrow sense heritability estimates recorded imply that progress in resistance to ALS could be made through selection in the early segregating generations. A double cross followed by selection against resistant genotypes was used to develop a method to breed for durable resistance to ALS in common bean. The method was used to accumulate minor genes of ALS resistance into single genotypes. Four intermediate resistant landraces were used to develop a double cross population that was screened using a mixture of ALS races. Selection in F1 and F2 population was done on the basis of intermediate resistance (disease severity score 4.0-6.0), while selection from F3 population was based on resistance (disease severity score 1.0-3.0). Ten advanced F4 lines along with their parents were evaluated for ALS resistance. The F4 advanced lines had a significantly improved resistance to ALS compared to their parents. Hence the method was successful in accumulating minor genes for resistance thus showing significant breeding progress in breeding for durable resistance.
Breeding for durable resistance to Cercospora Leaf Spot diseases in groundnuts (Arachis hypogaea L.) in Tanzania.
(2018) Kongola, Eliud Francis.; Sibiya, Julia.; Melis, Robertus Johannes Maria.
Lack of high yielding groundnut cultivars tolerant to Cercospora leaf spot disease (CLD) and stable across different environments is one of the challenges to groundnut production by smallholder farmers in Tanzania. This makes selection of adaptable high yielding stable varieties under the different agro-ecological zones before release a very important part of the breeding program as this has an impact on the adoption and productivity of the cultivar. The objectives of this study were to evaluate and select genotypes that are tolerant to CLD, high yielding and identify environments that can be used for selection. A total of 24 groundnut genotypes comprising of six double cross population, twelve single cross parents and six checks from the three botanical groups (Valencia, Virginia and Spanish) were evaluated over six environments (viz Tumbi in Tabora region, Mlali, Ilindi and Hombolo in Dodoma region, Njoro in Manyara region and Ikhanoda in Singida region in Tanzania in the 2016/17 cropping season. The experiment was laid out in a 6x4 alpha lattice design replicated twice. Additive main effect and multiplicative interaction (AMMI) model was used in analysis. The study result revealed that, Tumbi (E1) was the most discriminating environment followed by Ilindi (E3), Mlali (E2), Hombolo (E4), Njoro (E5) and Ikhanoda (E6) respectively. The Hombolo (E4), Njoro (E5) and Ikhanoda (E6) environments showed a high correlation, therefore, indirect selection can be applied across the environments. The existence of such unique correlation among test environments has the advantage of reducing the number of sites used for evaluation and thus reducing cost of evaluating the genotypes. Using the first and second interaction principal component axis (IPCA1 and IPCA 2) genotype G2, G5, G11, G7, G3 and G8 was identified as the best performing genotypes however, G7 had relative stability and adaptability across the testing environments. These crosses will be advanced through selfing and selection of CLD tolerant progenies that are yielding high. Key words: AMMI, Cercospora leaf spot disease, Environments, Groundnuts, IPCA1, IPCA2, Stability, Adaptability.
Breeding for high leaf yield and minerals content in Gynandropsis gynandra (L.) Briq.
(2022) Houdegbe, Aristide Carlos.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
Gynandropsis gynandra (Spider plant) is an African leafy vegetable rich in minerals, vitamins, and health-promoting compounds with great potential in addressing malnutrition. The species is used as food and medicine and provides substantial incomes for smallholder’s farmers with an increasing interest for its cultivation in Africa. Spider plant is also an important resource for pharmaceutical industries. However, its production is still hampered by low leaf yield, early flowering, pests and disease and poor seed germination, resulting from the lack of improved cultivars. Our study intended to develop high yielding and nutrient-dense cultivars for farmers through merging modern molecular and classical plant breeding tools to increase income generation and improve nutrition and health. Specifically, the study: i) assessed the phenotypic variability among advanced lines of spider plant using biomass and related traits; ii) profiled the leaf mineral content among advanced lines of G. gynandra; iii) determined the combining ability, gene action and heterosis of mineral content in spider plant; iv) identified the genetics of the inheritance of biomass and related traits in spider plant; and v) deciphered genomic regions associated with combining ability and heterosis of biomass and related traits in G. gynandra. The evaluation of 71 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa using biomass and related traits revealed significant difference among lines and principal component analysis grouped them into three clusters: Asia (Cluster 1), West Africa (Cluster 2), and East/Southern Africa (Cluster 3). The West and East/Southern African groups were comparable in biomass productivity and superior to the Asian group. Specifically, the West African group had high dry matter content and flowered early while the East/Southern African group was characterized by broad leaves and late flowering. The maintenance of lines’ membership to their group of origin strengthens the hypothesis of geographical signature in cleome diversity as genetic driver of the observed variation. The leaf mineral profile of 70 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa revealed significant variation among lines and zinc, calcium, phosphorus, copper, magnesium, and manganese as landmark elements in the genotypes. East and Southern African genotypes were clustered together in group 1 with higher phosphorus, copper and zinc contents than Asian and West African lines, which clustered in group 2 and were characterized by higher calcium, magnesium and manganese contents. An additional outstanding group 3 of six genotypes (three, two, and one from Asia, Southern Africa and Eastern Africa, respectively) was identified with high iron, zinc, magnesium, manganese and calcium contents and potential candidates for cultivar release. Significant differences (P < 0.001) were observed among and between experimental hybrids and parents for the levels of all mineral contents. Significant general and specific combining ability effects together with variance components analysis revealed that both additive and nonadditive gene action controlled mineral content with a predominance of nonadditive gene action. Mid- and best-parent heterosis ranged from -84.98 and 404.79% for minerals. Parents with good general combining ability were identified, as well as crosses with high specific combining ability and heterosis. There were significant and moderate to strong correlations between mean hybrid performance, specific combining ability effects and heterosis levels and low to moderate correlations between general combining ability and mean parents’ performance. Similar to leaf mineral content, significant differences (P < 0.001) were observed among and between hybrids and parents for fourteen agronomic traits. Hybrids outperformed their parents with more than 50% for total and edible fresh biomass, showing the existence of hybrid vigour. Mid- and best-parent heterosis varied between -51.89% and 192.10% with only positive heterosis effects for leaf area and total fresh biomass, characterized by an average mid-parent heterosis greater than 50%. Significant general and specific combining ability (GCA and SCA) effects together with variance component analysis revealed that both additive and nonadditive gene action, controlled biomass and related traits in the species with the predominance of additive gene action. Moderate to high broad- and narrow-sense heritability was observed for most agronomic traits, except for dry matter content. The environment significantly interacted with genotype, GCA and SCA. Parents with good GCA and crosses with high SCA and heterosis were identified. There were significant changes from parents to hybrids in the association of harvest index and time to 50% flowering with biomass per plant and leaf traits on the one hand and between harvest index and dry matter content on the other hand. A core set of 594 diversity array technology sequencing (DArt-seq) markers were identified and differentiated the 38 parental lines into three clusters linked with the provenance of the original accession. Using this set of markers, a genome-wide association analysis revealed two markers linked to heterosis level for flowering time, a single marker for edible biomass, one marker for total fresh biomass and one marker for the number of primary branches. Specifically, the marker MABiomLa1 was a pleiotropic marker and was associated with heterosis level for biomass and leaf area. In contrast, no consistent markers associated with combining ability were observed for general combining ability and might be due to the low number of parents and the density of markers used. The study thus revealed that reciprocal recurrent selection would be a sound breeding strategy for G. gynandra improvement with the development of hybrid cultivars to exploit heterosis. These findings showed that G. gynandra could be used as a model plant to study the genetic mechanism underlying heterosis in orphan leafy vegetables. The identified markers open room for implementing marker-assisted selection in the species for better exploitation of heterosis.
Breeding for resistance against angular leaf spot disease of common bean in the Southern Highlands of Tanzania.
(2016) Mongi, Rose John.; Tongoona, Pangirayi.; Shimelis, Hussein Ali.; Sibiya, Julia.
Abstract available in PDF file.
Breeding groundnut for resistance to rosette disease and its aphid vector, Aphis craccivora Koch in Malawi.
(2013) Chintu, Justus Mtendere Martin.; Githri, Mwangi.; Laing, Mark Delmege.; Sibiya, Julia.; Monyo, Emmanuel.
Groundnut (Arachis hypogaea L.) is one of the most important legume crops in Malawi. However, production among smallholder farmers has declined in recent years. One of the constraints affecting groundnut production is groundnut rosette disease (GRD). Therefore, the main objective of this study was to develop appropriate groundnut cultivars that are resistant to GRD, combined with other traits preferred by farmers, in order to improve income and food security of smallholder farmers in Malawi and beyond. The specific aims were; (i) to assess groundnut cropping systems used by smallholder farmers in Malawi, their varietal preferences, and production challenges (ii) to assess the genetic diversity among groundnut germplasm collected from ICRISAT, the Chitedze gene bank and farmers (iii) to identify sources of resistance to GRD and to its aphid vector (iv) and to understand the type of gene action governing GRD resistance, and to identify groundnut genotypes suitable for use as parents in breeding for GRD resistance. Assessment of groundnut cropping systems used by smallholder farmers, their varietal preferences, and production challenges was done by using a field survey and participatory rural appraisal (PRA) tools. The field survey was done in Lilongwe, Mchinji and Salima while the PRA was done in Kasungu, Lilongwe, and Salima. The assessment of genetic diversity among 106 groundnut genotypes collected from ICRISAT, Chitedze gene bank and farmers was done using 19 SSR markers. High throughput DNA extraction was done followed by polymerase chain reactions (PCR) after which the amplified products were analyzed. Evaluation of genotypes to identify new sources of resistance to GRD and its aphid vector was conducted under two test situations, one with high inoculum levels and one with low inoculum levels. Under high inoculum level, the infector row technique developed by Bock and Nigam (1990) which employs a susceptible variety as a disease spreader was used. While under low inoculum level, an aphid resistant variety instead of the infector row was used to control the aphids. Aphid resistance was studied under field and glasshouse conditions. Plants were planted in rows and at 14 DAS, 2 aphids were place on each plant. Aphid resistance was determined by observing the increase in number of the aphid population on the test plants. Gene action governing inheritance of resistance to GRD was studied under high disease pressure created by using viruliferous aphids. Parents and F2 generations and their reciprocals were used in the study. The trials were laid out in a glasshouse and aphids were infested a week after germination and were killed after 7 days using Dimethoate. Disease data was collected at 7, 14, 21 and 28 days after aphid infestation. The study on groundnut cropping systems, varietal preferences and production challenges revealed that most farmers grew groundnut alongside maize (Zea mayis L.) and beans (Phaseolus vulgaris L.) as food crops and tobacco (Nicotiana tabacum L.) and cotton (Gossypium hirsutum L.) as cash crops. The most preferred groundnut varieties grown by farmers were Chalimbana and CG 7. GRD was observed in half of the fields visited. However, 98% of the farmers interviwed had experienced it in their fields at some point, and 63.3% of the farmers believed that GRD was a major problem. Other challenges noted by farmers included lack of quality seed, poor extension support, lack of inputs, manipulation of the markets by buyers, and the failure of groundnut crops to meet the high standards required by the market. The examination of genetic diversity among 106 groundnut genotypes revealed a total number of 316 alleles with a mean of 17 alleles per locus. Polymorphic information content (PIC) and gene diversity values were high, which indicated that genetic diversity among the groundnut genotypes was high. The analysis of molecular variance indicated that 72.9% of the genetic variation observed in the genotypes was due to the variation between individuals within rather than between specific population groups. The evaluation of genotypes for resistance to GRD revealed five highly resistant genotypes namely ICG 9449, ICG 14705, ICGV-SM 05701, MW 2672 and MW 2694. Farmer preferred genotypes were rated as either moderately resistant or susceptible to GRD. Aphid resistance was only recorded in ICG 12991. Yield and GRD incidence were negatively and moderately correlated, which confirmed that GRD has the potential to reduce yield in groundnuts. The highly resistant genotypes were also high yielding except for genotype ICG 9449. Farmer preferred genotypes CG 7, Chalimbana and Tchayilosi, also gave above average yields, despite high disease incidence levels, which showed that these genotypes have tolerance to GRD. The study on gene action governing GRD resistance revealed information on combining ability effects of GRD resistance. The diallel analysis showed that GCA, SCA, reciprocal, maternal and non-maternal effects were all significant, which indicated that both additive and non-additive gene effects played a role in governing GRD resistance. The significance of SCA and reciprocal effects indicated that maternal parents played an important role in the expression of GRD resistance. However, the additive effects were predominant over non-additive gene effects. Four of the resistant genotypes, ICG 14705, MW 2694, ICGV-SM 05701, and MW 2672, were the best combiners for GRD resistance. Generally, the study indicates that there is still a need to develop new varieties with resistance to GRD having traits preferred by farmers to enhance adoption. There is also a need for breeders to work with extension staff in promoting new varieties and also there is need for extension staff to actively provide information to farmers on production and marketing of groundnut. Groundnut is widely known to have a narrow genetic base which has been a bottleneck to its improvement. However, the high genetic diversity observed in this study provides a basis for selection of appropriate parental genotypes for breeding programmes which can enhance further the broadening of the groundnut genetic base. Identification of the genotypes with high resistance to GRD in this study provides an opportunity to breed more GRD resistant materials. The observation that additive gene effects are predominant in governing GRD resistance means that GRD resistant materials can be improved by introgressing additive genes using recurrent selection breeding procedures. There is also a need to employ molecular techniques which can help in shortening the entire breeding process.
Breeding investigations and validation of molecular markers linked with spot blotch disease resistance in wheat (Triticum aestivum L.) germplasm for the rain-fed conditions of Zambia.
(2015) Tembo, Batiseba.; Sibiya, Julia.
Wheat (Triticum aestivum L.) is an important cereal crop, second after maize in Zambia. Its production during summer rainy season is hampered by several abiotic and biotic constraints. Among the biotic constraints, spot blotch disease caused by Bipolaris sorokiniana (Sacc.) Shoem is the most devastating causing large wheat yield losses and grain quality deterioration. Under severe cases complete crop losses result. This is because resistance to spot blotch disease in most of the genotypes in Zambia is inadequate. Breeding for high yielding disease resistant genotypes is the most cost effective and sustainable way of increasing summer rain-fed wheat yields and achieving sustainable wheat production. The study was, therefore, undertaken to: a) determine farmers` preferences for rain-fed wheat cultivars and identify production constraints, b) assess genetic diversity using agro-morphological traits, c) screen germplasm for resistance to spot blotch, d) determine gene action controlling the inheritance of resistance to spot blotch disease, and e) validate simple sequence repeat (SSR) molecular markers previously reported to be linked with resistance to spot blotch disease. A participatory rural appraisal established that wheat was an important crop among the small-scale farmers as it was a dual purpose crop used for home consumption and income generation. Coucal was the only wheat variety grown by the farmers under rain-fed conditions. The major constraints affecting summer wheat production in order of importance were; lack of good wheat seed, bird damage, weeds, termite damage, diseases (spot blotch being the most important), lack of markets and drought. High yielding cultivars with white coloured grain, combined with resistance to spot blotch disease, resistance to bird damage, termite damage and drought were the traits most preferred by the farmers. The genetic diversity study revealed the existence of genetic variability amongst the genotypes. Principal component analysis identified plant height, tillers/m2, peduncle length, days to heading, days to maturity and grain yield as the main traits that described the variability among the genotypes. The 150 genotypes tested were clustered into five groups based on Ward’s method, indicating that they were from different genetic backgrounds. This suggests that superior genotype combinations could be obtained by crossing genotypes in the opposing groups. The study also established that hectolitre weight, tillers/plant, thousand grain weight (TGW), grains/spike, peduncle length, and tillers/m2 could be effective selection criteria for high yield as they exhibited positive direct effects on yield and also significant and positive association with yield. One hundred and fifty wheat genotypes from Zambia and CIMMYT-Mexico were screened for resistance to spot blotch disease. The study revealed significant variability among the genotypes in their reaction to spot blotch disease. Genotypes were classified as resistant, moderately resistant, moderately susceptible, and susceptible. Genotypes 19HRWSN6 (Kenya Heroe), 19HRWSN7 (Prontia federal) were amongst the genotypes that were resistant across seasons. Most of the genotypes obtained from Zambia were moderately susceptible to susceptible across seasons. Nonetheless, eight genotypes with varying resistant reactions were selected for genetic analysis studies. A genetic analysis using Hayman diallel approach of 8 × 8 mating design and generation mean (GMA) analysis of six generations (P1, P2, F1, F2, BCP1 and BCP2) of two cross combinations was conducted. The two biometrical methods revealed the importance of additive gene effects in controlling resistance to spot blotch disease. The absence of maternal and non-maternal reciprocal effects indicated that choice of female parent was not important in breeding for resistance to this disease. Epistatic gene effects were absent in the inheritance of resistance suggesting that selection would be effective in early generation. Resistance exhibited partial dominance. Both diallel and GMA revealed moderately narrow sense heritability of 56.0% and 55.5%, respectively, an indication that the trait could be improved through selection. The Wr/Vr graph showed that parents 30SAWSN10 (P1), 30SAWSN5 (P3) and Coucal (P4) displayed the maximum number of dominant genes hence can be used in breeding for resistance to spot blotch. The molecular markers Xgwm570, Xgwm544 and Xgwm437 previously reported to be linked with resistance to Bipolaris sorokiniana were validated and their association with resistance confirmed. The markers amplified fragments in resistant parental genotypes that were similar to the F2 resistant and moderately resistant lines but not in susceptible ones. The significant relationship between the marker and resistance to Bipolaris sorokiniana was also established considering the significance of regression analysis (Xgwm570, P=0.003; Xgwm544, P=0.03 and Xgwm437, P=0.03). The adjusted R2 values observed (Xgwm570 =11.0%; Xgwm544=10.0% and Xgwm437=7.0%) further revealed the association between the marker and resistance. The study, therefore, shows that the markers can be useful in Zambia as they would increase the efficiency for the identification of resistant genotypes. This implies that screening of the genotypes could be done even in the absence of the disease epidemic. Overall, the results from this study indicate that the opportunity of improving resistance to spot blotch disease exists by utilizing the information generated. This information could be important during planning and implementation of breeding for resistance.
Breeding investigations for resistance to Phaeosphaeria Leaf Spot (PLS) and other important foliar diseases and a study of yield stability in African maize germplasm.
(2009) Sibiya, Julia.; Tongoona, Pangirayi.; Derera, John.
Maize (Zea mays L.) yields in the smallholder (SH) farming sector in Southern Africa have remained low. despite the availability of many improved varieties. Among the major constraints contributing to tow yields and threatening food security in the region are diseases which include grey leaf spot (GLS). common rust, northern corn leaf blight (NLB) and Phaeosphaeria leaf spot (PLS). These diseases are highly unpredictable in their occurrence every season, making them difficult to control. In addition, the majority of SH farmers cannot afford to control the diseases due to limited access to chemicals. Therefore, maize cultivars with high levels of disease resistance and tolerance to abiotic stresses would provide a long-term solution to addressing the problem of low yields, especially in the smallholder-farming sector. The objectives of this study were therefore to: i) establish farmers' perceptions on diseases, key limiting production constraints and preferred traits of maize cultivars. ii) screen germplasm adapted to tropical environments for resistance to PLS, iii) determine gene action for resistance to PLS and GLS, iv) estimate combining ability effects for resistance to PLS, GLS, NLB and common rust diseases, and v) determine grain yield stability of F, hybrids derived from crosses among selected tropical advanced maize inbred lines. These studies were conducted from 2006/7 to 2008/9 seasons at various sites in South Africa, Zimbabwe, Zambia and Uganda. Structured surveys and participatory rural appraisal (PRA) conducted in Obonjaneni. Busingatha and Okhombe villages of Amazizi district in the Northern Drakensberg established maize as the principal crop grown in the area. All the farmers who participated grew the local variety (landrace) they called Natal-8- row or Is/Zulu. The adoption of hybrids and improved open pollinated varieties (OPVs) was tow. Farmers preferred the local variety ahead of hybrids and improved OPVs mainly for its taste, tolerance to abiotic stresses and yield stability. Characteristics of maize varieties preferred by the farmers included: inexpensive seed, high yield, early maturity and tow input costs. Pests/d is eases and drought were not ranked highly, as farmers planted early to escape diseases and drought. Abiotic stresses were amongst the top four constraints faced by the farmers. The local varieties exhibited high yield potential and genetic variability fordisease resistance. Evaluation of maize germplasm adapted to tropical and subtropical environments of Africa for PLS resistance indicated significant (PS0.05) variation among the inbreds. populations and hybrids. In general, 63% of the inbreds/populations were resistant to PLS. Regionally important inbred lines; SC and N3 and CIMMYT's most successful lines such as CML395. CML444. CML202. CML312. and CML488 were resistant to PLS. Fifty- four percent of the single-cross experimental hybrids were also resistant to PLS. Correlation coefficients for area under disease progress curve (AUDPC) values for disease severity with PLS final disease severity scores were significant (P<0.001) and positive, implying that ranking of the genotypes for AUDPC and final PLS disease severity score was by and large similar. Forty five F, hybrids generated by crossing ten advanced maize inbred lines in a half diallel mating scheme were evaluated in two to six environments to determine combining ability, gene action and heterosis estimates for grain yield and resistance to PLS. GLS. NLB and common rust diseases. Highly significant (PS0.001) general combining ability (GCA) and specific combining ability (SCA) effects were observed for PLS. GLS. NLB. common rust, grain yield and other agronomic traits. The GCA effects were more important than SCA effects, indicating the predominance of additive over non-additive gene action for all the traits studied in these inbred lines. The inbred lines with good GCA for PLS resistance were: A12204, N3. A16. MP18 and CML488. and for GLS resistance were A1220-4. CZL00009. CZL00001. CML205 and CML443. Lines A16 and CML443 had good GCA for NLB and common rust resistance, lines A1220-4, N3, CML205, A16, and CML443 contributed towards high yield. Lines A1220-4 and A16 were late maturing, whereas CZL00009 displayed eariy maturity. High mid-parent and better-parent heterosis for high grain yield and resistance to all the diseases were observed. Generation mean analysis was used to deteimine the inheritance of PLS and GLS resistance in populations involving six tropical advanced maize inbred lines. Reciprocal crosses and backcross progenies were generated among inbreds A1220-4, A15, B17 (resistant. R), CML445 (moderately resistant. MR). CML441 and CZL00001 (susceptible. S) for PLS inheritance, and among inbreds A1220-4. A15, CML441 (resistant. R). and N3 and B17 (susceptible. S), for GLS inheritance. Results indicated highly significant additive effects (P<0.001) for PLS and GLS resistance, with dominance effects accounting forSH%of the variation in all the crosses for PLS and only A15 x B17 cross for GLS. Epistasis and cytoplasmic gene effects in favour of PLS resistance in F, crosses when the more susceptible parent was used as female were significant. For GLS resistance, epistasis was observed only in CML441 x N3 and A1220-4 x B17 crosses, while no cytoplasmic gene effects were detected. Resistance for PLS was medium to highly heritable and conditioned by less than four genes which exhibited incomplete dominance. In general resistance to GLS was controlled by two to three genes exhibiting zero to partial dominance and was moderate to highly heritable. Stability analysis of the hybrids was done over 11 environments using the additive main effects and multiplicative interaction (AMMI) and the genotype and genotype by environment (GGE) biplot analyses. Both AMMI and GGE biplot analyses selected hybrids H21 (CZL00009 x A16). H14 (A1220-4 x A16). S63 (SeedCo hybrid check). N72 (MP72/N3) and H26 (CZL00001 x A16) as stable and high yielding. Hybrids H1 (CML445 x A1220-4), H44 (CZL00009 x CML443) and H18 (CZL00009 x CZL00001) were identified by both methods as unstable but high yielding. AMMI and GGE biplot analyses identified ZAM08, C108, RAO9 and C09 as the most representative environments which were high yielding and relatively stable. In general, the study has revealed that based on the farmers ranking of the constraints in their area, breeding opportunities do exist for incorporating tolerance to both biotic and abiotic stresses in their varieties. It also identified maize lines resistant to the main foliar diseases, with good combining ability and heterosis for resistance and high grain yield. Hybrids with wide adaptation and high yields across environments were also observed. The experimental hybrids that exhibited high levels of resistance can be recommended for further testing and release. On the whole, highly significant additive effects and moderate to high heritability estimates observed for all the diseases and grain yield implied progress would be made through selection, although significant epistasis and dominance could slow progress. Dominance effects towards resistance and high yield could be exploited in developing single cross maize hybrids among these inbreds when only one parent is resistant.
Breeding investigations for resistance to Phaeosphaeria Leaf Spot (PLS) and other important foliar diseases and a study of yield stability in African maize germplasm.
(2009) Sibiya, Julia.; Tongoona, Pangirayi.; Derera, John.
Abstract not available.
Breeding sweetpotato (Ipomoea batatas [L.] Lam.) for drought tolerance in Kenya.
(2013) Kivuva, Benjamin Musembi.; Mwangi, Stephen Githiri.; Yencho, George Craig.; Sibiya, Julia.
Sweetpotato (Ipomoea batatas (L.) Lam.) is an important food crop in East Africa including Kenya. The crop incurs high yield losses in production due to biotic (insect pests and diseases) and abiotic (drought, and heat) constraints. Among abiotic constraints, drought is the most important. Prolonged periods of drought in arid and semi-arid areas of Kenya have led to reduced quantity and quality of sweetpotato storage roots and in severe cases caused total crop failure. The objectives of this study were to: 1) determine sweetpotato production system constraints and farmers’ coping strategies; 2) evaluate sweetpotato clones for yield performance and drought tolerance; 3) analyse genotype x environment interaction and stability for storage root yield of selected clones, 4) determine mechanisms of drought tolerance in sweetpotato, and 5) determine combining ability and heterosis for yield and drought tolerance traits under managed drought stress conditions. To determine the production constraints and farmers’ coping strategies, a survey was conducted in central, eastern and western Kenya. Out of 345 farmers interviewed, 60% were women, and 40% men. Farm sizes ranged from 0.4-0.8 ha, with 90% of sweetpotato cultivated on 0.2 ha or less. The main sweetpotato varieties were Vitaa, Kabonde and Bungoma and the majority of farmer’s used their own conserved planting material which was conserved by leaving them in the field after harvest. About 35% of the farmers identified weevils as the major pest, and sweetpotato virus disease (SPVD) as the major disease, while 28% of the farmers identified drought as a major constraint. The farmers used clean seed, high yielding varieties, high planting density, and manure application as the main strategies to cope with sweetpotato production constraints. Eighty four sweetpotato clones were evaluated under managed drought stress environments at KARI-Kiboko and KARI-Thika. Drought reduced the fresh weight of storage roots (FSR) (72.5%), fresh biomass weight (FB) (74.0%), marketable fresh storage root (MFSR) (80.7%), number of storage roots (NSR) (24.5%), days to permanent wilting point (DPWP) (0.3%), but seemed to increase percent root dry matter (% RDM) (-4.7%), harvest index (HI) (-2.6%), and chlorophyll content (CC) (-2.7%). Across the environments, genotypes 194555.7 (1.06), 421066 (1.05), Chingovu (0.94), 420014 (0.91), Excel (0.9), 199062.1 (0.87) and Unawazambane06-01 (0.81) gave higher FSR yields (kg plant-1) than the local checks. Genotypes Nyarmalo and Polista were among the lowest yielding in the irrigated and non-irrigated conditions. Clones W119, 441725, and Xiadla-xa-kau were the highest yielding under the drought stress conditions. The performance of 24 improved clones was evaluated in replicated trials at KARI-Thika and KARI-Kiboko using 24 sweetpotato clones grown under managed drought stress conditions for two seasons. AMMI, GGE biplots and regression analyses were conducted to determine stability of the clones. Mean FSR was significantly different (P < 0.001) in the two research sites with the environment contributing to 92.7% of the total variation, genotype 1.8%, and interactions 0.4%. AMMI and GGE biplots, and regression indicated the most stable clones to be 441725, Unawazambane06-01 and 189150.1, while Xiadla-xa-kau was the least stable. To gather more information on drought tolerance mechanisms expressed in the sweetpotato genotypes, an experiment was conducted in the greenhouse using clones expressing different levels of drought tolerance in the field. The results showed more under-developed roots (pencil roots) in the drought stressed regimes than in the irrigated regimes and in the drought susceptible genotypes. Drought tolerant genotypes produced more FSR and NSR. The number of vine branches (NVB), vine tip pubescence (VTP) and mature leaf pubescence (MLP) increased with reduction of drought stress however, drought tolerant clones had reduced NVB. Drought stressed clones had shorter basal vine length (BVL), reduced CC, and reduced leaf growth (LG). Drought stress reduced growth of vines in terms of internodes length, internodes diameter, vine length, petioles length, and leaf CC. Overall, for the first time, the study demonstrated that drought stress in the first three months after planting, leads to the proliferation of non-edible pencil roots, which do not become edible storage roots even when drought stress is removed. Therefore, water is critical during this period for improved sweetpotato storage root yield, probably as a drought tolerant mechanism. Combining ability for yield and drought tolerance of 15 F1 sweetpotato families generated through a half diallel mating of six parents was evaluated at KARI-Kiboko in 2012. Significant (P≤0.05) general combining ability (GCA) and specific combining ability (SCA) effects were recorded for root yield in both drought stress and no stress conditions, indicating that both additive and dominance gene effects were important in the inheritance of resistance to drought stress. Progenies from families G2, G5, G7, G8, G10, G12 and G15 had good SCA for fresh storage root yield, total biomass, number of days to permanent wilting point (DPWP), harvest index, and drought stress index (DSI). Progeny 8 from family G4, 5 and 8 from G15, had the highest mid and best parent heterotic effect (117-270%) for fresh storage root yield in both drought stress and no stress conditions. Progeny 6, and 7 from family G10, had the highest mid and best parent heterotic effect (165-234%) for fresh total biomass yield under no drought stress conditions. In conclusion, the progenies from families G2, G5, G7, G8, G10, G12 and G15 that had high yield and biomass specific combining ability under drought and no drought stress indicated that they could be having drought tolerant genes, and therefore could be incorporated into advanced drought screening trials with the aim of releasing the best performing drought tolerant varieties. Secondly, the findings in this study lay a foundation for sweetpotato breeding programmes on drought tolerance. Thirdly, for the first time, this study uniquely combines yield performance, combining ability estimates, days to permanent wilting point and heterosis under contrasting moisture regimes to unmask the gene action of drought tolerance in sweetpotato, a milestone in science.
Breeding sweetpotato for improved yield and related traits and resistance to sweetpotato virus disease in Eastern Tanzania.
(2015) Ngailo, Stephan Eliuth.; Shimelis, Hussein Ali.; Sibiya, Julia.
Sweetpotato production contributes significantly to food security and incomes of subsistence farmers in Tanzania. However, productivity of the crop is constrained by several biotic, abiotic and socio-economic factors. Amongst the biotic constraints, the sweetpotato virus disease (SPVD) causes significant yield losses in the country. Improved cultivars and landraces that are grown succumb to SPVD. Both chemical and biological control methods are not fully effective against SPVD. The use of resistant varieties remains the most effective and cheapest method for subsistence farmers. Therefore, breeding for SPVD resistance and high yields is an important consideration to develop and release improved sweetpotato varieties with end users preferences. Therefore, the objectives of the study were to: 1) assess the present sweetpotato farming systems, farmers’ preferences, production constraints and breeding priorities in eastern Tanzania, 2) determine genetic variation among diverse sweetpotato germplasm with regards to yield, dry matter content and SPVD resistance and to identify suitable clones for breeding, 3) investigate the genetic diversity of 48 Tanzanian sweetpotato genotypes using nine selected polymorphic simple sequence repeat (SSR) markers and to determine genetic relationship and select unique parents for breeding, 4) determine the general combining ability (GCA) and specific combining ability (SCA) effects of selected sweetpotato clones for the number of storage roots, fresh storage root yield, dry matter content (DMC) and resistance to sweetpotato virus disease (SPVD) for further selection and breeding, and 5) determine the magnitude of genotype-by-environment and stability for yield and yield related traits and SPVD resistance among newly developed sweetpotato clones in eastern Tanzania. Participatory rural appraisal study was conducted involving 138 and 149 farmers sampled for household interviews and focus group discussion, respectively at Gairo, Kilosa and Kilombero districts of Morogoro Region and Mkuranga district of the Coast Region of Tanzania. More than 94% of the respondents depended on crop farming for their livelihoods. Farmers preferred sweetpotato varieties with high yields, high dry matter content, tolerance to diseases and early maturing. Sweetpotato virus disease and pests, drought, unavailability of markets, lack of transport, low prices, inadequate extension services and post-harvest losses were identified by farmers being the most important production constraints. Improved extension service delivery, SPVD tolerant cultivars and reliable and coordinated market systems of sweetpotato were the most immediate needs for improved sweetpotato production and productivity. Field experiments consisting 144 sweetpotato genotypes were conducted at two sites in Tanzania using a 12x12 simple lattice design in 2013 to screen genotypes for yield, dry matter content and sweetpotato virus disease resistance and to identify suitable clones for breeding. The genotypes differed in time to 50% flowering, number of roots per plant, root yield, dry matter content and resistance to SPVD. Seven clones including Simama, Ukerewe, Mataya, Resisto, 03-03, Ex-Msimbi-1 and Gairo were selected as potential parents for sweetpotato breeding for high storage root yield and related traits or SPVD resistance. Nine polymorphic simple sequence repeat markers (SSR) were used to determine genetic relationship among 48 Tanzanian sweetpotato genotypes to identify unique parents useful for future breeding. The SSR markers were highly polymorphic and allocated the genotypes into three major genetic clusters. Ex-Ramadhani, Kibakuli, Mkombozi, Mjomba, Ex-Halima-3 and Kabuchenji were identified as genetically unrelated and complementary genotypes and recommended for future breeding programmes. Eight genotypes contrasting for their yield, dry matter content or SPVD resistance were selected and crossed using an 8x8 half diallel mating design. The families were evaluated in the field using a 6x6 triple lattice design at Sugarcane Research Institute (SRI) at Kibaha, Kilombero Agricultural Training and Research Institute (KATRIN) and Sokoine University of Agriculture (SUA) in Tanzania. There were highly significant differences among families (P< 0.001) for all studied traits across sites. Clonal parents with highest general combining ability (GCA) were 03-03 and Resisto for storage root yield, Ukerewe for dry matter content (DMC) and Ex-Msimbu-1 which displayed negative and significant GCA effect for SPVD resistance. Therefore, the parents Resisto, Ukerewe and Ex-Msimbu-1 could be used for future sweetpotato breeding programmes to improve yield, DMC or resistance to SPVD. The following crosses were best combiners displaying positive and significant SCA effects: Mataya x Gairo and Simama x Gairo for number of roots per plant, Mataya x Ex-Msimbu-1 and 03-03 x Ex-Msimbu-1 for root yield and, Mataya x 03-03, 03-03 x Ukerewe and Resisto x SPKBH008 for DMC, and Mataya x SPKBH008 and Mataya x Gairo had negative and significant SCA effect for resistance to SPVD. The selected parents and crosses were the best candidates to develop improved sweetpotato varieties with high root yield, DMC or SPVD resistance. The magnitude of genotype-by-environment interaction for yield and related traits and SPVD resistance of 26 selected sweetpotato clones was investigated across six diverse environments; namely Gairo, Kilombero Agricultural Training Research Institute (KATRIN), Sokoine University of Agriculture (SUA), Sugarcane Research Institute (SRI), Chambezi and Mkuranga. The Additive Main Effect and Multiplicative Interaction (AMMI) and genotype and genotype-by-environment interaction (GGE) biplot analyses were used to determine the GxE interaction and stability of the genotypes. The genotypes were ranked differently for yield and related traits and SPVD resistance. AMMI and GGE biplot analyses identified the following genotypes: G5, G11, G23, G9, G7, G18 and G17 being high yielding and resistant to SPVD which could be further evaluated in multi-environment yield trials (MEYTs) in eastern Tanzania. Also, the genotypes G22 and G3 were isolated as high yielding and resistant to SPVD but specifically suited to Chambezi and Gairo. Test environments sufficiently discriminated the candidate genotypes for the traits studied. MEYTs are required for selection and recommendation of high yielding, SPVD resistant and stable sweetpotato clones for eastern Tanzanian or similar environments. Overall, the study identified valuable sweetpotato parents and families with high combining ability for number and yield of storage roots, dry matter content and SPVD resistance from which new clones can be selected for future evaluation and release as new cultivars.
Characterisation of cowpea accessions based on agro-morphological traits, nutritional quality and molecular markers.
(2017) Ringo, Goodluck Douglass.; Sibiya, Julia.; Odindo, Alfred Oduor.
Abstract available in PDF file.
Characterisation of sweet sorghum germplasm based on agro-morphological traits, molecular markers and juice related traits.
(2018) Nundwe, McDonald.; Sibiya, Julia.; Shargie, Nemera Geleta.
There is rising interest for alternative energy sources because of the decline in fossil fuel production and concern over environmental pollution. Currently most biofuel is based on maize and sugar cane as raw materials. However, the use of feedstocks has triggered concerns related to food security, while sugar cane has a high-water consumption and high production requirements amongst other drawbacks. A crop which meets several requirements for biofuel (such as high biomass yield and growth rate, perennial growth, low input requirements, adaptation to the marginal areas, and tolerance to multiple stresses) is sweet sorghum. This study, therefore, aimed at characterising sweet sorghum germplasm using agro-morphological traits and molecular markers (single nucleotide polymorphisms (SNP) during the 2016-2017 summer season at two sites (Ukulinga farm and Potchefstroom). Fourteen quantitative traits were evaluated in an alpha lattice (10 x 5) design with three replications. Analysis of variance for the quantitative traits revealed high levels of genetic variability. This implies that morphological traits differed greatly with a significant G x E interaction across the two sites. Most of the accessions yielded high at Ukulinga than Potchefstroom on juice yield and %brix with a mean yield of 9 605 l/ha and 16.3%, respectively. Most of the accessions studied were early to medium maturing, as evidenced by the mean number of days to 50% flowering (74 days). Analysis of principle components showed that the first four principle components (PC) accounted for 79.12% of the total variation and that some quantitative traits were significantly positively correlated. The estimates for phenotypic coefficient of variation (PCV) were higher than those of genetic coefficient of variation (GCV) for all the traits, indicating the influence of the environment on these traits. However, GCV values for days to 50% flowering, plant height, stalk diameter and stalk yield were very close to PCV. This indicated minimal influence of the environment on the phenotypic expression of these traits. The highest broad sense heritability (H2) of 99.2% was recorded for plant height. Juice volume had the highest expected genetic advance, expressed as a percentage of mean (GAM) of 131.2%. Days to 50% flowering were significantly and positively correlated to plant height, stalk diameter, number of leaves, stalk yield, brix, juice volume and bagasse weight, but negatively significantly correlated to panicle length, panicle width, panicle weight and 1000 grain weight. Plant height was significantly positively correlated to stalk diameter, number of leaves per plant, stalk yield, juice volume and fresh bagasse weight. Bagasse weight, brix, stalk diameter, plant height and number of leaves had a highly positive and direct contribution on juice yield. Several traits had a highly positively and indirect contribution on juice yield via these traits which had a direct contribution. This revealed primary and secondary traits with practical relevance to sweet sorghum improvement programme, because they showed direct and indirect effects on juice yield (volume), which ultimately translates to sugar yield for ethanol production. Kompetitive Allele Specific Polymorphism (KASP) genotyping using 137 SNP markers revealed a considerable level of genetic diversity among the sweet sorghum accessions. Three populations were generated from the analysis. The expected heterozygosity (He) values ranged from 0.236 to 0.291 with a mean of 0.266. The mean of effective alleles across populations was of 1.438. The percentage of polymorphic loci ranged from 80.29% to 91.24% with a mean of 86.86%. Dissimilarity indices ranged from 0.000 to 0.583 with a mean of 0.296. The highest dissimilarity index was observed between SA 2193 and SA 2014, which implied a considerable amount of genetic diversity. Accessions were clustered into three main groups based on dissimilarity indices. The study identified SA 4490, SA 2400, SA 4495, SA 2193 and SA 4479 as superior accessions in juice yield. These accessions should be used as parents in sweet sorghum improvement programme.
Combining ability analysis of maize inbred lines and genotype x environment interaction of hybrids for grain yield and maize streak virus resistance.
(2018) Juma, Sheila Natividade.; Derera, John.; Sibiya, Julia.
Abstract available in PDF file.
Combining ability and genotype-by-environment Interaction analyses among early-to-medium maturing maize hybrids under drought and non-drought environments.
(2021) Dlamini, Mandisa Noxolo.; Sibiya, Julia.; Musvosvi, Cousin.
Developing high yielding early to medium maturing maize hybrids for Southern Africa represents an effective way to contribute to improving crop productivity in the face of climate change and unpredictable weather patterns. The objectives of this study were: (i) to determine combining ability and gene action among germplasm lines for grain yield (GY) and other traits under drought and non-drought conditions using the line x tester mating design (ii) to explore genotype-by-environment interaction (GEI) patterns of the developed hybrids and identify broadly and specifically adapted entries, with the intention of developing early to medium maturing hybrids for South Africa and the sub region. Twenty-three white maize inbred lines sourced from the International Maize and Wheat Improvement Center (CIMMYT) were crossed in a line x tester mating design involving 13 lines (females) and 10 testers (males), resulting in 122 successful single-cross (SC) hybrids. The SC hybrids and six commercial hybrid checks were evaluated in a 13x10 alpha lattice design, replicated twice under drought and non-drought conditions across three sites viz: Cedara Research Station, Ukulinga Research Farm and Makhathini Research Station over three seasons, (2018-2019 summer growing season, the 2019 offseason, and 2019-2020 summer growing season). Data for grain yield and its related traits was collected. Genetic analysis of the line x tester data followed a fixed effects model. The parents differed in general combining ability (GCA) effects for GY and other traits under drought and non-drought conditions. Likewise, the crosses varied in specific combining ability (SCA) effects for GY and other traits under the drought and non-drought regimes. Line CZL1380 and tester CML539 were good general combiners for GY under drought. Lines CML568, CKDHL0378, CKDHL0467, CML672, and CZL1380 and testers CML312 and CML547 had good GCA effect across non-drought regime. Two crosses, CML540 x CML547 and CKDHL0467 x CML312 had high SCA values for GY under drought and non-drought regimes. The additive type of gene action was predominant for days to anthesis (AD), days to silking (SD), anthesis-silking interval (ASI) plant height (PH), ear position (EPO), ears per plant (EPP), ear aspect (EA), grain texture (GTX), grain moisture (GMH), kernel row number (KRN), and shelling percentage (SHL) under drought, and for AD, SD, ear height (EH), EPO, EPP, EA, GTX, GMH, ear length (EL), kernels per ear row (KER), ear weight (EW), and hundred kernel weight (HKW) across non-drought conditions. Non-additive gene action prevailed for EH, EL, ear diameter (ED), KER, EW, HKW, and GY under drought and for ASI, PH, ED, KRN, SHL, and GY across non-drought conditions. The identified hybrids could be targeted for release as cultivars, and the types of gene action are practically relevant for improvement of early to medium maturing maize germplasm for Southern Africa. Grain yield data from the five environments was analysed to explore genotype by environment (GEI) among the developed hybrids and checks. Analysis of variance across all the environments showed huge environmental, genotypic and GEI effects, with the environment contributing the largest proportion of the variation followed by genotype and lastly GEI. The additive main and multiplicative interaction effects (AMMI) and the genotype and genotype-by-environment interaction (GGE) methods were employed on selected 62 entries to visualize the GEI patterns. The AMMI revealed that two interaction principal component axes (IPCA1 and IPCA2) were significant, and these contributed 50.32 % and 20.84%, respectively, to the total GEI variation. The AMMI1 revealed that hybrid MAK1-122 x CML545 was specifically adapted to drought conditions whereas hybrids CKDHL0467 x CML312 and CZL1380 x CML547 were broadly adapted. The identified two high yielding and broadly adapted experimental hybrids were superior to the best check WE3127 across all environments. Hybrids CML569 x CML566 and CKDHL0467 x CML547 were specifically adapted to irrigated conditions. The GGE-biplots had two principal components, PC1 and PC2, which together explained 69.87% of variation due to genotype and GEI. The GGE-biplots showed similar GEI patterns as AMMI, with the same hybrids identified as broadly and specifically adapted. The identified hybrids could be assessed further in multi-environmental and multiple stress trials to confirm their suitability under high and low input production systems in South Africa and the sub-region.
Developing pre-breeding tools for the miracle plant [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: implications for genomic selection strategies optimization = Ukuthuthukisa amathuluzi okuzalanisa ngaphambilini esitshalo esiyisimangaliso [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: imithelela yokuthuthukisa amasu okukhetha i-genomic.
(2022) Tchokponhoué, Dèdéou Apocalypse.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
The miracle plant [Synsepalum dulcificum (Schumach & Thonn) Daniell] is an evergreen orphan shrub species originating in West Africa that produces red berries known as miracle fruits. As a unique natural source of miraculin, miracle fruits stand as a singular natural sweetener with huge applications and economic potential. Unfortunately, the lack of systematic breeding history in the species currently hinders the full exploitation of the species potential at both the local and international levels. This study was undertaken with the goal of generating information that can be used to initiate a proper breeding and large-scale cultivation program of the species in its center of origin, West Africa, with a focus on three countries (Ghana, Togo, and the Republic of Benin). The objectives of the study were: i) to determine current management practices and end-users’ preferred traits to identify key breeding traits and formulate sound breeding objectives, ii) to evaluate the natural phenotypic diversity in the species to identify potential parental lines/populations for breeding purposes, to assess genomic diversity and population structure in the species to reshape breeding strategies, and to model the determinants of the local communities’ willingness to invest in the species cultivation to articulate promotion strategies in the species. To assess trait preferences by the miracle plant end-users (farmers, consumers, and processing companies) in the study area, semi-structured interviews and focus-group discussions were held with 300 individual respondents from various socio-cultural backgrounds and one processing company each in Benin and Ghana. The results revealed that farmers in Ghana currently manage the species better than their counterparts in Benin, with men being overall the main owners of the species. Our results offer an impetus for West Africa region-wide cultivar development, as both farmers’ and consumers’ preferences for breeding traits were >80% similar among the six sociolinguistic groups and the three agroecological zones considered in the study area. The preference for breeding traits was 60% similar among farmer, consumer and processing company user groups. Out of the 23 potential breeding traits identified in the study area, fruit size, fruit miraculin content, fruit yielding, early maturity, fruit edible ratio and seed part ratio represent priority breeding traits. Interestingly the traits (fruit size and miraculin content) were consistently ranked as the top two desired traits by all three end-user groups of the species. The classification conducted on 203 individual trees (accessions) sampled from seven populations in the Upper Guinea forest block (Ghana) and the Dahomey Gap (Ghana, Togo, and Benin) block revealed the existence of three natural phenotypic groups in the species. While in terms of population performance, the Volta population in the Dahomey Gap outperformed the six other populations for almost all the end-users’ desired traits assessed. Cluster 3, which encompassed accessions from all seven populations sampled, presented the best performance based on end-users’ preferences and, therefore, represents a potential source of elite accessions. Overall, variability ranged from low to moderate in traits evaluated [coefficient of variation: 9.65% (fruit length) – 53.34% (tree diameter at ground level] and the inferred core collection points to the Dahomey Gap as a center of diversity of the miracle plant. Despite the expected heterozygosity of HS = 0.14 suggesting a low diversity in the miracle plant, the molecular assessment done on 322 individuals revealed a strong population differentiation in the species (FST =0.69). Populations in the Upper Guinea forest block strongly diverged from those in the Dahomey Gap block, and our data supported the existence of a barrier (which we speculated to be the Lake Volta in Ghana) disrupting connectivity between those two West African rainforest block populations of the miracle plant. Corroborating the findings of the phenotypic assessment, the genome-wide diversity analysis also defined three genetic groups. Conveying a higher resolution to the population structuring, the genomic analysis highlighted an ecoregional structuring of the miracle plant population in the study area. The DNA polymorphism and demographic history analyses indicated the Western Dahomey Gap as the likely centre of origin of the miracle plant, thus refining the previously postulated West Africa origin of the species. The Volta population was confirmed as an exceptional breeding population with regards to its high allelic richness and heterozygosity. Our findings also suggest that sociolinguistic groups in Benin valued the miracle plant more than those in Ghana, to the extent that the species diversity was affected, as fitness organs such as roots and bark were highly targeted for medicinal uses. Nonetheless, these sociolinguistic groups in Benin were also more willing to engage in the miracle plant cultivation compared with those in Ghana. However, for this to be effective, market structuring and improved variety (early fruiting) development combined with awareness raising are needed to accelerate local community engagement in the species cultivation in the entire study area. Collectively, these results advance our knowledge of the miracle plant and form the basis for breeding initiatives in the species. The implications of these findings regarding optimization of a genomic selection strategy for accelerated genetic gains achievement in agronomic and functional traits of this species is discussed. Iqoqa Isitshalo esiyisimanga [Synsepalum dulcificum (Schumach & Thonn.) Daniell] wuhlobo lwembewu yesihlahla esingavamile esidabuka eNtshonalanga ne-Afrika, esaziwa ngokuthi siwumsuka ohlukile wemiracuin, isinandisi seglycoprotein esisetshenziswa ngezindlela ezahlukene. Yize kunjalo ukugqama kwaso kahle kukhinyabezwa ukungabi bikho kokuchuma kahle kwaso emlandweni wezimbewu. Lapha, injulalwazi emgwaqohlaka onezigaba zokuzalana kwale mbewu kuyacaciswa kanye nokubaluleka kokugxila esizindeni sokuqoqa ukuthuthuka kwaso ngenhloso yokuqondisisa, kwavezwa. Indlela enokubambisana yasetshenziswa ukuhlonza ubukhulu balesi sithelo, okuqukethwe yisithelo okuyimiraculin, ukuthela kwesitshalo, inani lokukhula kwesithelo, ukuvunwa kwesithelo singakashayi isikhathi, impilo yesitshalo eshalofini, kanye nobuncwaba besithelo njengezinto ezinqala ezidingeka ezitshalweni kulabo abazisebenzisayo eNtsonalanga ne-Afrika. Kwaqapheleka izinga eliphezulu elincamelekayo elifanayo lembewu, hhayi nje kuphela kubatshali, kepha nakubathengi bezitshalo ezahlukene ze-agroecological zones nakulabo abavela kwizindawonhlalo zolimi olwahlukene. Amaqoqo amathathu afanayo acwaningwa kulesi sitshalo eNtshonalanga ne-Afrika, kuphindelelwa ukusebenza kwaso kusezingeni eliphezulu u-0.8. Imiphumela yaveza iDahomey Gap njengomongo wokwehluka kwembewu. Le mininingo efuzene ibe isifakazelana ngesingle nucleotide polymorphism (SNP) markers eyizi-2704 iyinye. Yize-ke noma ukwehluka kwamamolekhyuli kube sezingeni eliphansi embewini (He = 0.14), kwase kuqina ukwehluka emiphakathini phakathi kwe-upper Guinea kanye neDahomey Gap, lokhu kwaze kwafakazelwa ukuhlaziywa KOHLAKA, okwaqagula ulibofuzo oluthathu esixhokweni esihambelana ne-Upper Guinea (UG), neWestern Dahomy Gap (WDG) neCentral Dahomy Gap (CDG). Imiphumela yethu yeseka umlando oguqukayo kulolu libofuzo lapho khona imiphakathi ye-UG ne-CDG kungenzeka ithole ukunwebeka kanti i-WDG iphakathi nendawo. Ekugcineni, yize noma imbewu yayiningi eGhana uma iqhathaniswa neBenin, amaqoqo enhlalolimi eBenin ayikhathalele imbewu kakhulu kunalabo baseGhana. Ulwazi olumangazayo ngembewu nobukhona bohwebo kuqaguleke njengezinye zezinto ezilawula inhlalosiko yokutshalwa kwale mbewu eNtshonalanga ne-Afrika. Le miphumela yethula ulwazi olubalulekile olungasetshenziswa ezinhlelweni zokuzalaniswa kwembewu.
Development of high yielding and early maturing potato (Solanum tuberosum L.) genotypes with resistance to Phytophthora infestans in Uganda.
(2017) Namugga, Prossy.; Sibiya, Julia.; Melis, Robertus Johannes Maria.
Abstract available in PDF file.
Effect of insect pollinator species deployment and interactions with parental inbred lines in hybrid carrot seed production.
(2021) Skosana, Tebogo Lucky.; Sibiya, Julia.; Musvosvi, Cousin.
Insect pollinator species are highly valued for their contribution towards cross-pollination in many vegetable crops for food and seed production. Honeybees (Apis mellifera) are a significant main pollinator not only in entomophilous crop, but for many other plants in their natural habitats. Moreover, attempts to increase seed production through the introduction of an alternative pollinator species (such as Calliphorides flies) throughout the world have encouraged growers and breeders to think more precisely about the management of these pollinators for the future. However, several constraints, including climate, have resulted in low success of pollinators, thereby failing to meet pollination demand for hybrid carrot seed production, both nationally and internationally. The goal of this study was to identify alternative non-bee insect species that can be used as agents of pollination in commercial hybrid carrot seed production. The research experiment was conducted in Matjiesrivier farm (33o23'31.86" S and 22o05'14.91" E) that is situated under the Oudtshoorn district municipality, which is a Cango valley of Western Cape Province. Carrot parents were three cytoplasmic male sterile (CMS) lines, which were pollinated by two pollen donor-male inbred lines. Two insect species, honeybees (Apis mellifera) and Calliphorid flies (Chrysomya chloropyga), were used as agents of pollination. The experiment was arranged in a 2x2x3 factorial with two replications. The weight of umbels, seed weight and germination percentage data were collected to achieve research study objectives. Statistical analysis for all data was done using SAS (SAS Institute Inc, 2018) and R (R Core Team, 2019) statistical computation software. The data were subjected to analysis of variance (ANOVA) for individual umbel level (order) harvests. The TUKEY post hoc test was done at a 5% level of probability to compare the treatments. From the results, flies were comparably effective as honeybees during pollination, while analysis of variance for quantitative traits (germination percentage, seed weight, and umbels weight) was highly significant implying that the traits differed among the advanced lines and the deployment of the two species during pollination. The trait variability was influenced by the umbel stages of different CMS lines and their interaction with pollinator by male fertile and male sterile lines. This information will be useful in a breeding program that focuses on hybrid seed production in carrots and a combination of the two insect pollinators’ deployments to improve cross breeding for future management would be essential