Masters Degrees (Plant Breeding)

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Assessment of maize germplasm lines for genetic diversity, cultivar superiority and combining ability.
(2012) Khoza, Suzan.; Derera, John.; Laing, Mark Delmege.
Maize (Zea mays L.) is an important crop in the world; however, its yield is compromised by new production challenges leading to poor yield in sub-Saharan Africa. This calls for a need to enhance maize adaptation to changing climate and challenging environments. The new maize varieties should be richly endowed with high frequency of genes that confer high yield under stress and non-stress conditions. Currently, such maize is not available, prompting research into development of new germplasm lines for use in developing new hybrids. The objective of the study was to determine i) the level of genetic diversity using SSR molecular markers and phenotypic data in a set of 60 maize inbreds from the breeding program, ii) genotype by environment interaction in maize hybrids, iii) cultivar superiority, iv) combining ability effects, v) the relationship between yield and secondary traits and vi) the relevant genetic parameters that underpin genetic gains in a breeding program. To study genetic diversity present in the germplasm, phenotypic data and 30 SSR markers were used to estimate the genetic distance between the inbreds. The results indicated that inbred lines which were put in the same cluster were related by pedigree and origin. To assess the level of genotype by environment interaction (GXE) and cultivar superiority of the new germplasm lines, hybrids were planted in five environments with two replications. Data were analysed using the REML and AMMI tools in GenStat 14th edition. The results revealed significant differences between hybrids and environments for grain yield. However, GXE interaction was also significant indicating possible challenges which can be encountered in selecting new hybrids. To determine combining ability estimates two different testers were used. The REML tool from GENSTAT was used to perform the line X tester analysis. Results indicated that both additive and non-additive gene action were important for grain yield. The direct selection strategy for yield was recommended because heritability of grain yield was high. Overall, results suggested that the information on genetic diversity will assist in defining heterotic groups; which will enable effective and efficient management of the germplasm lines to produce new maize hybrids.
Breeding investigations for development of specialty green maize hybrids.
(2011) Qwabe, Fikile Nozipho Pricilla.; Derera, John.; Tongoona, Pangirayi.
Green maize (Zea mays L.) provides food security and cash income to rural households in Sub-Saharan Africa (SSA). However, research on green maize varieties is scarcely reported in the literature. Consequently there is no information on suitable genetic materials (germplasm) for green maize production. Additionally there is no data regarding quality attributes of suitable hybrids, which impacts on variety development and management. Breeding investigations were therefore conducted to investigate farmers’ preferences for hybrids and attributes of green maize hybrids in KwaZulu-Natal, in South Africa, and to determine combining ability for green maize traits of experimental inbred lines that were derived from an experimental population. The study also investigated the relationships between green maize traits and some desired agronomic traits; and also sought to identify specific inbred combinations (hybrids) with potential for green maize production. A case study was conducted at Mjindi (MJD) and Ndumo (NDO) Irrigation Schemes in KwaZulu - Natal South Africa, to determine the attributes of the “ideal” hybrid, production constraints, production trends and enterprise viability. Prior to a formal survey some focus group discussions were conducted, then 64 green maize growers were interviewed using a formal questionnaire. The study indicated that the most desired consumer traits were a combination of sweet taste, long shelf life and large ears. The required attributes of the model hybrids were high grain yield potential, high selling ability, flint grain texture, white grain color, medium ear placement, thick and long ears, short maturity period, medium plant height, long shelf life and nonpopping during roasting. This study also showed that the enterprise was viable with average gross margin of about R10,000 per ha which makes it attractive to both small and large-scale commercial farmers with implications for rural development in the second economy. Thus there is a great business potential, but lack of suitable and special hybrids appears to be the major production constraint which should be addressed by research and development. A total of 100 advanced maize inbred lines were crossed in a line x tester mating scheme to generate 200 experimental hybrids. The hybrids with sufficient seed were evaluated for green maize and agronomic traits at three sites in KwaZulu-Natal. Large genotype x environment interaction effects were observed which was reflected by the different ranking of hybrids at each site resulting in selection of different sets of top 15 hybrids with potential for production in each environment. Only a few hybrids exhibited high performance consistently in at least two mega environments. The results showed that hybrids were highly significantly different for the green maize traits such as ear yield, ear length, single ear weight and marketability indices, and also for the agronomic traits. The difference among hybrids for marketing ability indices was attributed to the testers main effects and specific combining ability (SCA) effects. Differences between the general combining ability (GCA) of the lines and testers, and SCA effects were significant for the green maize traits. These findings suggested that the traits are governed by both additive and non-additive gene effects, respectively. Additionally observation of continuous and normal distribution of hybrids for the traits indicated that quantitative minor genes were involved and therefore the base population can be improved by selection for large ears, superior marketability index, and high single ear yield. The observed top performing hybrids were recommended for further testing at many sites. Results confirmed that the current dominant variety is not adapted to summer production conditions in the Mjindi and Ndumo areas which present opportunities for breeding programmes. Future studies should therefore aim to improve both the genetics and production economics of specialty green maize hybrids to further enhance profitability of the enterprise with positive implication for the rural economy in KwaZulu-Natal.
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, genetic gains and path coefficient analyses of maize hybrids developed from maize streak virus and downey mildew resistant recombinant inbred lines.
(2015) Mathew, Isack.; Derera, John.
Farmers in SSA continue to obtain low yields (less than two tonnes per hectare) despite the high potential yield (about 14 tonnes per hectare) that can be achieved. The development of improved and high yielding hybrids can help to reduce this gap significantly. Characterisation of maize inbred lines is crucial for developing high yielding maize hybrids. A line x tester analysis involving 38 crosses generated by crossing 19 maize inbred lines with two tropical testers was conducted for different agronomic traits. The maize inbred lines used in this study were sampled from a bi-parental inbred population developed by a shuttle breeding program at University of KwaZulu Natal. The objectives of the study were to estimate combining ability of inbred lines and hybrids, to evaluate the performance of the hybrids in agronomic traits and grain yield, to calculate breeding gains achieved through selection and to deduce the relationship between secondary traits and grain yield. In total 50 hybrids, including control hybrids were evaluated in the trial. The hybrids were planted in the summer season of 2014/15 under rainfed conditions at three sites, Cedara, Dundee and Ukulinga in five metre row plots and replicated twice in 5X10 alpha lattice design under recommended agronomic practices for maize. Data was collected using a CIMMYT protocol and subjected to statistical analyses using ANOVA and REML packages in GENSTAT 14th edition and PATHSAS macros in SAS 9.3 computer software. The results showed varying performances between the lines, crosses and control hybrids at the different sites. Inbred lines DMSR-8, DMSR-13, DMSR-30 and DMSR-35-5 were shown to have good combining ability while DMSR-21 and DMSR-73 showed positive specific combining ability. Selection across sites improved grain yield by 9.32% over the population mean and by 10.22% and 12.73% at Cedara and Dundee, respectively over commercial hybrids. Ranking by mean yield identified hybrids 15XH16, 15XH20 and 15XH28 at Cedara, Dundee and Ukulinga respectively, as the highest yielding hybrids for that particular environment. GGE biplot and AMMI analyses revealed that hybrids 15XH10, 15XH13, 15XH20, 15XH25, 15XH28, 15XH34 and 15XH39 were the most stable hybrids. Secondary traits were found to be associated with grain yield potential of hybrids. Ear prolificacy had the most important relationship with grain yield and was recommended for selection in grain yield improvement programs.
Efficacy of mon 89034 bt trait in conferring fall armyworm resistance in high yielding three-way and single-cross maize hybrids.
(2020) Chingombe, Pretty Nyaradzo.; Derera, John.; Yobo, Kwasi Sackey.
Maize production, especially in tropical sub-Saharan Africa, is hampered by the fall armyworm (FAW) posing a serious threat to food security and livelihoods. Many methods of control including pesticide use have been tried against FAW but without sustainable success. The main objective of this study was to investigate whether or not the Bt trait (MON89034) could be successfully integrated in high yielding tropical hybrids and confer effective resistance to FAW when deployed in three-way and single cross hybrids. The study was conducted under natural FAW hotspot conditions and under field conditions representative of farmer’s situation. Conventional non-genetically modified (non-GM) tropical single cross hybrids and inbred lines were crossed to four WEMA Bt lines. The resultant three-way and single cross hybrids were evaluated at three sites, in South Africa. The results indicated adequate discrimination of hybrids according to FAW resistance and grain yield, under both FAW infestation and at two other sites with limited FAW pressure. The experimental Bt hybrids displayed high yields exceeding 5 t/ha and higher FAW resistance, which was comparable to standard genetically modified (GM) control hybrids. In sharp contrast, the conventional non-GM control hybrids recorded yield as low as 0 t/ha, under FAW infestation. They were highly susceptible to FAW which was indicated by high damage scores. Therefore, the event MON89034 was effective in conferring FAW resistance in both three-way and single cross hybrids. Although the environment main effects were highly significant (P<0.001) for grain yield, the three-way cross hybrids were relatively stable and showed non-significant (P>0.05) genotype x environment interaction (GxE) effects. In sharp contrast, GxE effects were highly significant (P<0.001) for grain yield of single cross hybrids, indicating that they were less stable than their three-way counterparts. New Bt hybrids with high cultivar superiority index and combining high yield potential and FAW resistance were identified. These included (H3WX3167Bt) (HSX5054Bt), (HSX5368Bt) and (H3WX3194Bt). The three-way experimental hybrid (H3WX3167Bt) had yield advantage of 64% above WEMA GM checks, 33% above local GM hybrid checks and 22% above conventional non-GM checks. The single cross experimental hybrid (HSX5368Bt) exhibited yield advantage of 127% above mean of conventional non-GM checks, 100% above mean of WEMA checks and 99% above mean of local GM checks, under FAW infestation. In addition, secondary traits, such as ear prolificacy and number of ears harvested per plot, which had significant direct and indirect effects for grain yield under FAW infestation were identified for use in construction of a viable selection index. Overall, the study was successful and showed efficacy of the Bt trait (MON89034) in conferring FAW resistance when deployed in tropical high yielding three-way and single cross hybrids. The best performing experimental Bt hybrids with high yield and high FAW resistance, and out-yielded both GM and non-GM standard commercial hybrids, would be advanced in the breeding program that targets the GM market segment in tropical Africa. A survey of the literature has not revealed prior studies on evaluation of FAW resistance in three-way cross hybrids. The trait is deployed predominantly in single cross hybrids, in the GM maize production lead countries, such as Argentina, Brazil, China, South Africa and USA. Therefore, this study formed a significant baseline for revealing useful information on the efficacy of the Bt trait in conferring FAW resistance in three-way cross hybrids which are predominantly deployed to smallholder farmers in tropical Africa.
Genetic analysis of agronomic and quality traits in popcorn hybrids.
(2012) Jele, Collinet Phumelele.; Derera, John.; Siwela, Muthulisi.
Popcorn is increasingly becoming popular as a snack and is consumed widely all over the world. It is a high value crop, with possible multiplier effects like income generation for the under-resourced communities in the second economy. Despite its popularity, developing countries are battling to meet the demand and rely on importing popcorn grain due to challenges which include poor agronomic traits and slow breeding progress. Most of the imported varieties are not adapted to stress-prone local environments, which are prevalent in tropical sub-Saharan Africa. The objective of the study was to evaluate newly developed hybrids and inbred lines for agronomic and popping quality traits with the possibility for commercialization in future. The study aimed at determining variability for popping ability in inbred lines and hybrids, grain yield and its secondary traits, the nature of gene action, relationships among agronomic and popping quality traits, effect of genotype x environment interaction on agronomic traits and popping method x genotype interaction effects. To determine popping ability, 128 inbred lines were evaluated at the University of KwaZulu-Natal, South Africa, in June 2011 using two popping methods, the microwave method and the hot-air method. The popping quality attributes measured were flake volume, popping fold, number of unpopped kernels, kernel size and quality score. Variability among inbred lines was significant (P<0.05) for all traits. Flake volume ranged from 63 cm3 to 850 cm3, popping fold ranged from 2.5 to 34 times the original volume. Kernel size had a significant positive correlation (r= 0.49) with the number of unpopped kernels. There was a significant strong and negative correlation between flake volume and the number of unpopped kernels (r= -0.62), indicating that either of the two traits would be effective for measuring popping ability. Experimental hybrids were then developed from 87 out of the possible 128 inbred lines. Only the inbred lines with sufficient seed were crossed to develop hybrids. Random crosses were generated at Makhathini Research Station during the winter season of 2011. Crosses were made at random among parents that managed to synchronize their flowering dates, resulting in 119 hybrids with sufficient seed for planting in trials. To determine agronomic superiority, the 119 experimental hybrids and the standard check P618 were evaluated at the Cedara Research Station and Ukulinga Research Farm in the Midlands of KwaZulu-Natal during the summer of 2011/2012. The experiments were laid out as 10 x 12 alpha lattice design, with two replications at each site. Standard cultural practices for maize were followed. The data were subjected to analysis of variance and line x tester analysis in Genstat and SAS statistical programmes. Results indicated that hybrids were significantly different for all agronomic traits. Means for grain yield ranged from 1.0 t/ha to 5.2 t/ ha. General combining ability effects were significant for all agronomic traits, suggesting that additive gene effects were governing these traits. Specific combining ability effects were significant for ear length, number of ears per plant and yield indicating, that non-additive gene effects were influential for these traits. Generally, agronomic traits were highly heritable. Grain yield showed significant and positive correlation with ear length, plant height, ear position, shelling percentage and number of ears per plant, indicating that these were the major yield-determining secondary traits which should be enhanced in popcorn. Although site main effects were highly significant for secondary traits, the hybrid x site interaction was not significant. The results therefore indicate that the hybrids were ranked similarly at both sites. The 119 experimental hybrids and the standard check P618 were evaluated for popping quality, using the microwave and the hot-air popping method. There was a significant variability observed among hybrids for popping quality traits. Flake volume across sites and across popping methods ranged from 734 cm3 to 1288 cm3. Popping fold ranged from 14.69 to 25.75 times the original volume. Additive gene action was more prominent than non-additive action for all popping quality traits. The SCA effects were significant for flake volume, popping fold and number of kernels per 10 g. All popping quality traits had high heritability, indicating that selection would be effective to improve popping. Flake volume was negatively correlated to quality score, indicating that popping expansion is reflected on the quality score and a significant negative correlation between flake volume and number of unpopped kernels. There was significant and strong positive correlation between kernel size and number of unpopped kernels. Hybrid x site interaction was only significant for quality score and kernel size. Hybrid x method interaction was not significant, indicating that popping ability was not dependent on the method. Inbred lines showed significant variation for popping quality and therefore have utility for hybrid development. Significant genotypic variation was also observed among hybrids for agronomic and popping quality traits. Additive gene action was predominantly responsible for both agronomic and popping quality traits. Both agronomic and popping quality traits were highly heritable and positive relationships were identified among traits. Overall, the study indicates opportunities for further breeding progress through selection.
Genetic and economic value of a shuttle breeding programme for enhancing adaptability of tropical maize germplasm in South Africa.
(2013) Musundire, Lennin.; Derera, John.; Tongoona, Pangirayi.
Maize is the principal crop for food security and livestock feed in South Africa. It is also an industrial crop and the produce is exported to many countries in the world. Therefore there is high seed demand which prompts competition for breeding productive hybrids. However direct introduction of tropical hybrids into the warm temperate South African environments has not been successful. Competitive advantages can be obtained by implementing a “shuttle breeding” programme whereby part of the breeding is done in Zimbabwe and South Africa to minimise research and production costs. Introgression of temperate germplasm in tropical elite inbred lines can also be pursued to obtain adapted hybrids. The aim of this study was therefore to assess the effectiveness of introgression of temperate germplasm into tropical elite maize inbred lines as a strategy to enhance adaptability of new hybrids to South Africa, and also to determine both breeding and economic value of a “shuttle breeding” programme. To this end, the introgressed inbred lines and their hybrid progenies were evaluated in South Africa to determine the effect of the selection environment on their performance and genetic variation. Both genetic and economic gains were evaluated with a view to make recommendations to the small and medium scale enterprises with interests in the market. Introgression of temperate germplasm into tropical germplasm elite lines did not disrupt the heterotic groupings because most of the introgressed lines (86%) fitted into known existing heterotic groups. Only 14% of the introgressed lines did not show any inclination to towards the known heterotic clusters of their founder tropical parents. These lines were considered to be new recombinant inbred lines that showed little resemblance with their founder parents. Selection environment did not influence heterotic clustering of the introgressed lines, and genetic diversity was identified among introgressed lines developed in the same environment. Genetic variation was observed for the major economic traits and heritability of 21% to 91%. The introgression was effective for improving grain yield potential and ear prolificacy. Spearman’s rank correlation analysis on grain yield and ear prolificacy data showed significant positive correlation between selection environments such as Ukulinga in South Africa and Kadoma Research Centre in Zimbabwe. Therefore Kadoma Research Centre will be recommended for use in breeding new maize germplasm lines for South Africa. Correlation among traits showed that ear prolificacy and plant height had significant (P<0.05) direct effects on grain yield thus direct selection of these traits will be emphasised in breeding new hybrids. Introgression of temperate germplasm into tropical elite maize inbred lines was effective for improving their adaptation to warm temperate environments. Positive genetic gains of 5-58% were realised for grain yield potential and 26-46% for ear prolificacy. Whereas 1% to 37% gains were realised for secondary traits such as plant and ear height, anthesis and silking days there was barely any improvement for root and stalk lodging, and grain moisture content at harvest. However, introgressed lines displayed impressive performance per se and inter se indicating potential for commercial production. The new inbred line 71-DMLF7_88 combined early physiological maturity, high ear prolificacy and grain yield potential qualifying it as a perfect parent for the warm temperate environments. At least six hybrids were stable and adaptable while four were considered to be ideal genotypes relative to standard commercial hybrids such as PAN6Q445B which is a market leader. The exceptional hybrids, 12C20264, 12C22766, 13XH349 and 11C11774 will be advanced in South Africa. The study also indicated significant economic gains when a shuttle programme is implemented to breed new hybrids following the introgression strategy. The “Shuttle breeding” programme attained a positive net present value (NPV) of $1, 834, 166. 00. This indicated an increase in shareholder value through an opportunity cost of 17% and 3% relative to conventional breeding programmes which are based in South Africa and Zimbabwe, respectively. Positive NPV and genetic gain achieved using the “shuttle breeding” programme makes it a viable option for small and medium scale seed companies with intention to breed and commercialise competitive products in South African. In general, the study revealed that introgression of temperate germplasm into tropical elite inbred lines using a “shuttle breeding” programme was effective for enhancing adaptability of tropical germplasm to the South African warm temperate environments.
Genetic characterization of pro-vitamin A and quality protein maize inbred lines and their derived hybrids.
Phakathi, Lindokuhle.; Derera, John.; Gasura, Edmore.
Maize is one of the most important crop plant, valued both as cereal and forage crop because of high nutrition and palatability. Sub-Saharan Africa (SSA) countries are highly dependent on maize compared to other African countries and there is preference of white maize over orange maize, which leads to Vitamin A deficiency (VAD) crisis. Vitamin A deficiency can be alleviated by increasing pro-Vitamin A maize consumption rate in the population. In orange maize, Vitamin A is in the form of pro-Vitamin A, therefore crops with high content of pro-Vitamin A carotenoids are a promising strategy to alleviate Vitamin A content among disadvantaged populations. Lack of quality proteins in maize is another challenge faced the consumers of this staple crop in SSA. Therefore maize requires improvement in this regard. Quality protein maize (QPM) was developed from mutant maize with an opaque- 2 gene that improves amino acids; lysine and tryptophan. Lysine and tryptophan allow the body to manufacture complete proteins, and tryptophan lessens the prevalence of kwashiorkor in children. Studies clearly show that QPM could be superior to normal maize (NM) if used in the diet of humans. The objectives of this study were therefore to analyze the genetic diversity among the Pro-Vitamin A lines, Quality Protein Maize lines, and Normal Maize lines; to identify potential heterotic groups, and to evaluate their F1 hybrids. Twenty maize inbred lines were used in the study, comprising 13 Pro-Vitamin A; four QPM and three normal lines. The lines were genotyped with 93 SNP markers at the DNA Landmarks Laboratory in Canada. Data was analyzed using the PowerMarker version 3.25 statistical package. The hybrids were generated in a 4 X 10 North Carolina design II with reciprocal mating which resulted in 78 experimental hybrids with adequate seed for planting in trials. Three commercial hybrids were included as controls. The 81 hybrids was evaluated in a 9 x 9 alpha-lattice design with two replications at four sites in KwaZulu-Natal, South Africa. The data collected was analyzed using Genstat. Out of 93 SNPs markers used, six of them were monomorphic and 87 polymorphic. The use of SNP markers was effective; the data set reflected the homogenously homozygous state of inbred lines and was able to determine the genetic diversity and distance. Inbred lines that showed the highest genetic distance were normal maize (DPVA17) and pro-Vitamin A (DPVA12) which was 0.54; and lowest genetic distance was observed between normal maize (DPVA19) and normal maize (DPVA18) which was 0.11. In the current study the higher genetic diversity was observed between previously identified groups and six potential heterotic groups were identified. Grain yield of the hybrids was highly significant at Cedara and Dundee, and not significant at Jozini and Ukulinga. The three economic traits (ear aspect, number of ears per plant, and grain moisture content) were significant at all sites. Genotype x environment interaction effects were observed. Performance of hybrids varied with sites. At Cedara, the highest performing experimental hybrid was 14PVAH-29, Dundee; 14PVAH-166, Jozini; 14PVAH-8, and Ukulinga; 14PVAH-50, respectively. Hybrid 14PVAH-139, 14PVAH-129, 14PVAH-149, and 14PVAH-10 were placed by three methods in top 10% stable hybrids, thus they are considered as the most stable hybrids. The current study showed that traits such as number of ears per plant, plant height, and ear aspect are strongly associated positively with yield, and that stem lodging, root lodging, and ear rot are negatively associated to yield. Although DNA molecular markers can be used in identifying heterotic groups, the relationship of genetic distance and hybrid vigour is still not well understood. Therefore, both molecular markers and conventional field trials (phenotyping) must be used to identify heterotic groups among pro-Vitamin A and quality protein maize. This would be crucial for devising breeding strategies for developing nutritionally rich maize hybrids.
Genetic variation and associations among adaptive traits in a recombinant maize inbred line population.
(2012) Sithole, Mxolisi Percival Sibongeleni.; Derera, John.; Odindo, Alfred Oduor.
Maize production in Africa is constrained by abiotic and biotic stresses. Breeders need to have information on the nature of combining ability of parents, their traits and performance in hybrid combination. This requires careful determination of genetic variability of parents, and studying associations between grain yield and adaptive traits to breed superior cultivars which are better able to withstand such stresses. Therefore, this study was aimed at selecting parental testers with best combining ability in hybrid combination with recombinant inbred lines (RILs); and studying the correlation between grain yield and its components in eastern and western South Africa. It was also aimed at determining genetic variation and associations among adaptive traits in hybrids involving RILs. The final objectives of the study were to determine cultivar superiority of testcrosses involving RILs, and to select the best cultivars within and across four different environments. The 42 RILs were crossed to 9 Zimbabwean tropical testers resulting in 1009 hybrids with sufficient seed for planting in trials. From these a sample of 87 hybrids with adequate seed were selected and planted at four sites for combining ability analysis. The hybrids were evaluated at four sites in two regions; western region (Potchefstroom research station) and eastern region (Cedara, Ukulinga and Dundee research stations), during 2011/12 season. The experiments were laid out as augmented alpha lattice design. Trials were managed in accordance with production culture for each region. All quantitative data was subjected to GenStat and SAS statistical softwares. The results from combining ability study indicated that the line general combining ability (GCA) effects played a non-significant role (p > 0.05) in determining grain yield, grain moisture and anthesis date, while they were significant (p ≤ 0.05) for the other traits such as ear prolificacy. The tester main effects were significant for all the traits except ear prolificacy and plant height. Results also revealed that all the traits were controlled by both additive and non-additive genes, where additive gene action had the most contribution to the traits. The non-additive gene action played a minor role suggesting the total GCA effects attributed to both lines and testers predominantly higher over the specific combining ability (SCA) for all traits. In general the additive effects were preponderant over the non-additive gene effects. One cross (L114 x T12) had a significant and positive SCA effect for grain yield. The correlation between grain yield and secondary traits (number of ears per plant, grain moisture content, ear height, plant height, ear position and anthesis date) suggested that indirect selection can be employed to enhance grain yield by breeding for these particular adaptive traits. Path analysis showed that plant height had the highest direct and indirect effect on grain yield indicating its importance among other secondary traits for grain yield enhancement. Phenotypic coefficient of variation (PCV) was higher than genotypic coefficient of variation (GCV) for all the studied traits across all the four environments. All the traits displayed high heritability at Potchefstroom except anthesis date which was highly heritable at Ukulinga. Cedara was the second best site for heritability of all the traits except for the number of ears per plant. The genetic advance for grain yield was the highest at Cedara followed by Potchefstroom, Dundee and Ukulinga. The hybrids exhibited different patterns of variation and distribution for all the traits. This indicated that selection strategies to exploit GCA should be emphasised. Association studies among grain yield and secondary traits such as ear length, number of ears per plant, plant height, anthesis date, silking date and ear leaf area revealed that there were significant phenotypic correlations between grain yield and secondary traits, and among the secondary traits. Ear length had the highest direct effect on grain yield at Ukulinga; number of ears per plant had the highest direct effect on grain yield at Cedara and Potchefstroom; whereas plant height had the highest direct effect on grain yield at Dundee. Grain yield was least affected by indirect factors at all the sites except Ukulinga, where anthesis date had the highest indirect effect on grain yield through silking date followed by plant height through leaf area. The study reveals that there is significant variation among the hybrids for mean performance, indicating that there is opportunity for selection. Overall the findings suggest that direct selection would be appropriate to enhance grain yield. Path analysis revealed that plant height had the highest direct and indirect effects on grain yield, indicating that plant height can be further exploited as the main trait in future breeding programmes for grain yield increment. Hybrid 10MAK10-1/N3 was the best hybrid at Ukulinga in terms of grain yield, relative yield and economic traits. Whereas hybrid T17/L83 was the best hybrid at Cedara in terms of grain yield and relative yield; however, T11/L102 was selected as the most elite hybrid with respect to grain yield, relative yield and economic traits. Hybrid T3/L48 was identified as thebest hybrid at Dundee with respect to grain yield, relative yield and prolificacy. At Potchefstroom the standard check PAN6611 was identified as the best hybrid in terms of grain yield and relative yield followed by developmental hybrid T1/L28; however, developmental hybrid T1/L28 was the best in terms of earliness, prolificacy and ear aspect. Stability coefficients and cultivar superiority index across the sites revealed that four developmental hybrids were identified as best hybrids and they performed better than the standard check. These hybrids will be recommended for further testing in advanced trials. With respect to cultivar superiority, the desired hybrids are required to combine high grain yield with economic and adaptive traits such as high ear prolificacy, low grain moisture, and low ear aspect score (desired) for them to adapt to production environments in South Africa. There was significant variation among the top 25 yielding hybrids. At least 5 hybrids combined high grain yield with the desired complimentary adaptive traits such as quick moisture dry down, prolificacy and ear aspect. The results showed that there is variation in the performance of high yielding genotypes within all the sites, and that agronomically superior cultivars can be identified. The study shows that there is significant variation among the RILs since they interacted differently with the 9 tropical testers. Even among the top 25 selections of RILs in each environment there was still variation for combinations of the desired traits. Significant associations among grain yield and other economic and adaptive traits were observed with implications for breeding strategy. Above all the significant variation gives large score for future breeding of new unique lines.
GGE-Biplot and genetic diversity analysis of maize hybrids and inbred lines from the breeding programme at UKZN.
(2016) Makongwana, Mandisa Precious.; Derera, John.
Maize (Zea mays L.) is the most important cereal crop in southern Africa. It is classified as a major staple food for human consumption. It is also used for animal feed in the livestock industry. Therefore, maize plays a crucial role in ensuring food security. However, production of maize is outstripped by consumption. Therefore, there is a yield gap that needs to be closed by increasing maize yields. Unfortunately, the adequate production of the crop is affected by lack of highly stable and highly productive hybrids. Hybrids that combine these two attributes are highly desired in the small scale sector where resources are usually limiting. Hybrids can be exploited to increase productivity of maize; however, a study of diversity between the parent lines is required because hybrid heterosis is obtained when the lines are divergent and complimentary. Therefore, the current study investigated genetic diversity and genetic gains that were realized by the breeding program at the UKZN. Thirty-one experimental hybrids from the program were tested alongside eleven commercial hybrids across 6 locations in South Africa. Hybrids 11C3201, 13C7082, 11C3417, 14XH149 and 14XH146 were among the best four hybrids across 6 locations. They combined high levels of stability and productivity, qualifying them as potential candidates for advancement. The study indicated that the program was successful at breeding new hybrids with the potential to compete with current commercial hybrids. With respect to diversity, 51 inbred lines were genotyped with 396 SNP markers at the LGC genomics, UK. Therefore, PIC, genetic diversity, availability, inbreeding coefficient, heterozygosity and genetic distance were determined. SNP markers indicated there was large diversity between the lines as reflected by two major clusters at the truncation level of 0.14 in the coefficient scale. Under the second major cluster, there were eight sub-clusters (sub-cluster B-J) identified which indicated wide range of the genetic diversity within inbred lines. Genetic distance between lines ranged from 0.05 to 0.35. This indicates the program was successful at generating new inbred lines that can be used to breed new hybrids.
Heterosis, genetic distance and path coefficient analysis in dent, flint and popcorn hybrids.
(2013) Mhoswa, Lorraine.; Derera, John.; Odindo, Alfred Oduor.
Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA); however its production is constrained by many factors. Grain yield is compromised by poor genetic performance and poor agronomic management. This calls for need to develop hybrids and exploiting heterosis of single crosses which are adapted to challenging environments. Currently, there is no popcorn hybrids developed in South Africa which is adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale farmers in marginal environments. The objectives of the study were to determine i) standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship between traits in widely grown selected hybrids in Southern Africa; and vii) to compare effectiveness of phenotypic analysis models for determining genetic distances between hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed using SAS, Genstat and Power marker statistical packages. The results revealed that the relationship between genetic distance and heterosis is dependent on the environment. Hybrids in top 10 at both sites were different indicating that there was a significant genotype x environment interaction. 13 new heterotic patterns that performed better than the controls can be utilized in heterosis breeding; however there is need to test them in different environments to check on their stability. Grain texture cannot be used to discriminate hybrids for yield because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10 hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield qualifying them as potential testers for specific combining ability in future studies. Heterosis in popcorn hybrids that performed better than the mid-parent can be utilized in heterosis breeding to exploit vigour, though there is need to test the hybrids in a number of different environments. The main direct factors contributing to yield were ear prolificacy, ear aspect, number of plants and shelling percentages qualifying them to be selected to boost grain yield. Phenotypic data and 91 SNP markers were used to estimate the genetic distance between the hybrids. The results indicated that hybrids that were in the same cluster belong to the same brand and were related in origin and pedigree. Both molecular and phenotypic data were effective in discriminating the hybrids into different clusters according to genetic background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight clusters and five-trait model revealed six clusters at 85% genetic distance. The study indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids.
Introgression of aflatoxin and fumonisin contamination resistance genes in maize hybrids.
(2014) Chiuraise, Nyashadzashe.; Derera, John.; Yobo, Kwasi Sackey.
Maize is the principal crop in Africa, particularly in southern Africa. However, food security in the region is constantly threatened by the contamination of maize grain through mycotoxins, such as aflatoxins and fumonisins caused by Aspergillus flavus and Fusarium verticillioides, respectively. Food security is defined as the capacity of a nation to ensure that all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life. Aflatoxins and fumonisins are carcinogenic, teratogenic, mutagenic and immunosuppressive to both humans and livestock. Presently, breeding for reduced mycotoxin contamination is one of the best strategies to reduce aflatoxin and fumonisin contamination in maize grain. Although mycotoxin resistant maize inbred lines have been identified, currently, there are no aflatoxin and fumonisin resistant commercial maize hybrids available to farmers in southern Africa. Decades of research have resulted in the identification of maize inbred lines that are resistant to either aflatoxin or fumonisin accumulation but not to both. Therefore the current study aimed at stacking resistance genes to the two toxins in one germplasm line or hybrid. The first objective of this study was to determine the current picture of mycotoxin contamination in southern African maize germplasm. Thus, a survey on South African and regional experimental hybrids was carried out during 2012/13 and 2013/14 seasons to determine the natural incidences of different types of ear rots and to identify the associated fungi. The second objective was to stack the resistance genes in a single product through introgression of aflatoxin and fumonisin resistance genes from tropical inbred lines into adapted inbred lines used in the subtropical and temperate conditions of southern Africa. Consequently, the resultant 72 single cross hybrids were evaluated for fumonisin contamination and 44 three-way cross hybrids and their progenies (146 S2:3 families) were evaluated for both aflatoxin and fumonisin contamination under artificial inoculation, in South Africa. Survey results showed that F. verticillioides was the most prevalent ear rot causing fungi followed by Stenocarpella maydis, Fusarium graminearum and A. flavus. These pathogens have potential to cause fumonisins, dipliotoxins, vomitoxins and aflatoxins. Assessment of experimental hybrids indicated a significant variation (P <0.001) among hybrids for ear rot incidence, and contamination by mycotoxins. Five single cross hybrids accumulated consistently low fumonisin levels (<4 ppm) both in the greenhouse and field trials. Three 3-way cross hybrids displayed a combined low contamination level for both aflatoxins (<5ppb) and fumonisins demonstrating potential for stacking resistance genes in the end product. Four S2:3 families also accumulated low levels of both aflatoxins and fumonisins below the legal limits of 5 ppb and 4 ppm, respectively, further demonstrating that new maize inbred lines can be developed by stacking mycotoxin genes. Therefore the study indicated a significant progress towards breeding mycotoxin resistant hybrids. Recommendations for upscaling this achievement are discussed.
Investigation of the genetic basis of high yield potential of a new maize hybrid, "exphybrid6"
(2023) Senzere, Phanuel Farai.; Sibiya, Julia.; Derera, John.
Abstract available in PDF.
Path coefficient analysis and combining ability between quality protein and pro-vitamin - a maize lines for yield and secondary traits.
(2016) Kumbula, Patience.; Derera, John.; Sibiya, Julia.
In most countries, white maize varieties are more preferred than the yellow/orange maize. Unfortunately, normal yellow and white maize lacks vitamin A which is crucial mainly for sight as well as growth and immunity. Sub-Saharan African (SSA) countries are largely dependent on maize as their meals are predominantly made from maize, and vitamin A deficiency (VAD) is a progressing problem in these countries. In the biofortified orange maize, vitamin A occurs in the form of pro-vitamin A (PVA) carotenoids. This pro-vitamin A maize is being used to alleviate the problem of VAD. Normal maize is also deficient in two essential amino acids, namely lysine and tryptophan that cannot be synthesised by the body. Quality protein maize (QPM) was developed from a mutant maize type that is rich in the essential amino acids, tryptophan and lysine. These two essential amino acids are required in the body for the formation of proteins which reduces the occurrence of protein deficiencies such as kwashiorkor in children. In addition to the nutritional insecurity that is being faced in SSA countries, maize that is being produced remains insufficient to sustain the populations as they are increasing tremendously. Development of high yielding and adaptable maize hybrids with better nutritional quality in terms of vitamin A and quality protein traits by stacking genes for vitamin A and quality protein in single cross maize hybrids will help alleviate this problem. This study was conducted to establish the combining ability of exotic PVA with locally adapted QPM lines, combining ability of the locally adapted PVA maize with QPM lines and contribution of secondary traits to yield in PVA and QPM hybrids. Line by tester analysis was conducted for two experiments. The maize inbred lines used in this study were developed by a shuttle breeding programme at University of KwaZulu-Natal. In the first experiment, 26 lines were crossed to four testers and 70 selected hybrids, including one check which was repeated twice, were evaluated in another trial. The hybrids were planted at Ukulinga in the summer season of 2015/2016. A 10 X 7 row by column design was used. In the second experiment, 12 lines were crossed to four testers and 44 selected hybrids, including one check, were evaluated in a trial. The hybrids were planted at two sites, Cedara and Ukulinga in summer season of 2015/2016. A 4 X 11 row by column design was used. Recommended agronomic practices were implemented for all the sites. Data was collected using a CIMMYT iii protocol and subjected to statistical analyses using Breeding Management System which is linked to Breeding View package, ANOVA and REML packages in GENSTAT 17th edition. The experimental hybrids performed competitively against the check that was used. The outstanding performance of the hybrids was also displayed by the high genetic gains that were realized for the selected hybrids in both the trials. In the first experiment, hybrid 16XH49 was ranked as the highest yielding. In the second experiment, hybrids 16XP11 and 16XP33 were ranked the highest yielding for Ukulinga and Cedara, respectively. The general combining ability effects of lines were significant for grain yield and shelling percentage for both sites. Cultivar Superiority Analysis revealed that hybrids 16XP33, 16XP11 and 16XP29 were the most stable. Path coefficient analysis revealed significant association of secondary traits with grain yield. Traits such as ear height, plant height, field weight, number of ears per plot, shelling percentage, 100-grain weight and plant stand exhibited positive direct effects on grain yield. Selection of these traits would effectively cause an increase in grain yield. Field weight was found to be the most important trait contributing towards grain yield.
Phenotypic and genotypic characterisation of F₄ families derived from a temperate X tropical maize population.
(2016) Mzobe, Sanelisiwe.; Derera, John.; Sibiya, Julia.
Abstract available in PDF file.
Phenotypic characterization of mycotoxins resistant maize inbred families and regional hybrids under Aspergillus flavus and Fusarium verticillioides infestation.
(2015) Masemola, Bogaleng Milcah.; Derera, John.
Most South African households depend on maize as source of their staple food and daily calories intake, especially the rural communities which depend on the crop to maintain their livelihood. Despite the importance of maize, numerous factors either biotic or abiotic factors affect its production worldwide. Ear rot is one of the common diseases that affect maize production and productivity worldwide. Aspergillus flavus (Raper and Fennel) and Fusarium verticillioides (Sacc.) are two of the serious ear rot-causing maize fungi. These fungi secrete mycotoxins which are hazardous when consumed by humans or animals. The study was executed to characterize mycotoxins resistant maize inbred families at the phenotypic level and to determine the level of natural incidences of ear rot diseases which are associated with mycotoxins contamination. Understanding architecture of genetic of these resistant maize inbred families would greatly aid in breeding high yielding and stable ear rot and mycotoxins resistant hybrids. Experimental trials were conducted at Ukulinga and Cedara Research Stations, during the 2014 to 2015 growing seasons. Further evaluation was conducted at the Makhathini Research Station during the winter season of 2015. The study was conducted using two experiments. The first experiment was assessment of natural ear rot incidences on regional maize hybrids. These hybrids represented a sample of varieties which are grown in the Southern African region. In the second experiment, S3:4 families, which were derived from three way crosses among, A. flavus and F. verticillioides resistant maize families, were artificially inoculated with A. flavus and F. verticillioides. Grain yield and agronomic traits were measured in both experiments. The grains were evaluated for ear rot infection at harvest. The analysis of variance and correlation analysis were conducted using Genstat 14th edition (Payne et al 2007) and Agronomix Generation II (2000), while the multivariate analyses were conducted using the NCSS (2004) statistical computer program. The assessment of natural ear rot incidences on regional hybrids revealed that ear rot causing fungi is a challenge. The results revealed four fungi that were responsible for the natural incidences of ear rots. The fungi included A. flavus (Raper and Fennel), Stenocarpella maydis (Berk.), Fusarium graminearum (Schwein.) and F. verticillioides (Sacc.). Incidences of F. verticillioides were the highest during the two seasons. This might be due to hot dry weather conditions that occurred after flowering. Early maturing hybrids showed lower incidences of ear rots than hybrids that matured late. Although early maturing hybrids encountered less incidences of mycotoxin causing fungi, the results revealed early maturity period had a significant strong negative correlation with grain yield. This trend was consistent with previous studies. Phenotypic characterization study revealed a significant variability among the mycotoxins resistant maize inbred families for resistance to Aspergillus ear rot, Fusarium ear rot and other selected secondary traits except husk cover, insect damage and days to mid maturity. Generally heritability (H2) estimates were large for most traits, indicating an opportunity for selection of the best inbred families for advancement in the breeding programme. Plant height, ear height and primary tassel branches recorded higher heritability values (>80%) compared to the other traits. This was followed by Fusarium ear rot and Aspergillus ear rot resistance scores (≥77%) and grain yield (73%). The results revealed five principal components contributing more than 69% of the total variation and the traits responsible to this variation are Fusarium ear rot, Aspergillus ear rot, plant height, ear height, days to mid maturity, husk cover, insect damage and primary tassel branches. The inbred families were grouped into five principal component groups based on their phenotypic characteristics. Lines to be derived from these grouped families would be exploited to make heterotic combinations by crossing lines from the different phenotypic clusters.
Why SR52 is such a great maize hybrid.
(2013) Musimwa, Tatenda Rambi.; Derera, John.
Maize is Africa’s most important food crop. Unfortunately a yield gap currently exists in Africa which can be attributed to the use of inferior maize varieties such as open-pollinated varieties, double and three-way cross hybrids. Single cross maize hybrids, such as the world’s first commercial hybrid, SR52, have a higher yield potential, which is reflected by the doubling of maize yields in southern and eastern Africa by SR52, within a decade of its release. The main objective of this study was to determine the genetic basis behind SR52’s high yield potential and heterosis. This was established through a generation mean and path coefficient analysis of the SR52 maize hybrid. Research to determine genetic basis of yield and secondary trait was conducted using a randomized complete block design at two sites during the 2012/13 season, in South Africa. Six derivative generations of SR52 namely, its two parents N3 and SC, F1 and F2, and F1 backcross progenies (BC1N3 and BC1SC) were evaluated. A generation mean analysis was performed using PROC GLM procedures in SAS computer software program. High levels of mid-parent heterosis for grain yield potential was confirmed and ranged from 140% at Cedara to 311% at Ukulinga. The additive-dominance model was not adequate to explain the yield potential of SR52. Although negligible (less than 10%), epistatic gene effects were also influential (P<0.01) on grain yield and its components in SR52. The dominance and additive gene effects were highly significant (P<0.01), but dominance effects were the most influential. Correlation and path coefficient analysis of SR52’s segregating F2 and BC1 populations was performed in SAS. Most secondary traits, such as ear mass, ear length, total number of kernels per ear and plant height, were significant (P<0.05) and positively correlated with yield. However, the ear length, number of kernel rows, kernels per row and 100-kernel mass displayed the largest direct effects on yield of SR52, while indirect effects of secondary traits were small. The presence of genetic variation, as well as transgressive segregants for the yield components indicates possibility for extracting new germplasm lines with the desired QTL’s. It is concluded that SR52 is such an exceptional hybrid because of dominance gene action and direct contribution of superior cob length, number of kernel rows and mass of kernels to yield.

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