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Masters Degrees (Plant Breeding)

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    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.
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    Evaluation of soybean (Glycine max L. Merr.) lines for grain yield and drought-tolerance.
    (2021) Mathonsi, Thubelihle Lungelo.; Sibiya, Julia.; Kondwakwenda, Aleck.
    Soybean (Glycine max L. Merr.) is ranked as the fourth-highest commercial agronomic seed crop in South Africa. An increase in animal feed demand has mainly driven the significant growth in demand for soybean oilcake and oil. This demand is also contributed by increasing demand for protein-rich foods, especially among the middle class. However, soybean production has always been variable in different seasons in South Africa mainly due to the occurrence of droughts in some provinces causing the yields to decline. Therefore, enhancing grain yield and drought tolerance would preserve farmers’ profits at large and smallscale farms. The present study was undertaken during 2019 and 2020 summer growing seasons in the field and greenhouse trials to: i) screen 36 soybean genotypes for drought-tolerance using morphological and physiological traits, ii) assess drought-tolerance in soybean genotypes using drought-tolerance indices and iii) estimate the variance components and heritability of yield and yield components of soybean under wellwatered and water-stressed. Thirty-six soybean lines obtained from the International Institute of Tropical Agriculture (IITA) were screened for drought-tolerance in the field and greenhouse under water-stressed and well-watered regimes using morphological, physiological traits and yield-based selection indices. The targeted traits were; plant height (PH), stem diameter (STD), leaf width (LW), leaf length (LL), seed moisture content (SMOI), stomatal conductance (STC), chlorophyll content (CC), 100 seed weight (SW) and biomass Yield (BMS). High genetic variation was observed in grain yield and morpho-physiological traits under both well-watered and water-stressed regimes. Genotype effect was significant for PH, LL, LW, STD, BM, SW and GY. The water regime indicated a significant effect for PH, LL, LW, STD, SMOI and GY. The environment effect was significant for all morphological traits PH, LL, LW, STD, FLW, SMOI, SW and GY. The environment by water regime interaction showed a significant effect for PH, FLW, SMOI, SW. A significant reduction in agronomic traits was observed for G10, G12, G22 and G29, which were the best potential genotypes for improving drought-tolerance. The PH, LL, LW, STD; GY, SMOI, BM and SW could effectively be used for selection in the yield improvement of soybeans under water stress conditions, since they were positively correlated with GY. The Principal components analysis (PCA) and cluster plot analysis approach was very helpful in identifying high-yielding, drought-tolerant genotypes, discriminating and grouping genotypes based on their responses to water stress. The principal components indicated that first dimension (Dim1) was consistently correlated with PH, LL, LW and STD. The SW, CC, FLW, STC, SMOI, BM and GY were either associated with second dimension (Dim2) or third dimension (Dim3). The cluster plot showed that G1, G10, G12, G20, G22, G25 and G29 under WS in the field experiment had high means values and were consistency associated with STD, LL, STC, FLW, SMOI, BM, SW and GY based on principal components and cluster plot, represented as cluster II. Whistle, G5, G7, G10, G12, G13, G14, G17, G21, G22, G23, G27, G29 and G31, showed significantly high mean values and association with PH, STD, LW, LL, STC, CC, BM, SW and GY in the greenhouse environment. The selection for drought-tolerance among 36 soybean lines under well-watered and water-stressed regime was performed using yield based selection indices, including Drought intensity index (DII), Stress susceptibility index (SSI), yield index (YI), Stress tolerance index (STI), Mean relative performance (MRP), GMP-Geometric mean of productivity (GMP), Yield stability index (YSI), Mean productivity(MP), TOL-Stress tolerance (TOL), Harmonic mean (HM) and Relative efficiency index (REI). The ANOVA indicated that the main effects due to the environment, genotype and water regime were significant for GY at the level of significance of (P≤0.05), (P≤0.001) and (P≤0.001). The drought-tolerant indices with significantly positive correlation with the grain yield under well-watered and water-stressed regimes were MRP, GMP, MP, MRP, HM and REI (P<0.001-P<0.05). These indices were comparably effective than SSI, YI, STI, YSI and TOL in selecting and predicting better grain-yielding soybean genotypes under a well-watered and water-stressed regime. Most of the soybean genotypes studied resembled water stress tolerance, including G22, G4, G8, G1, G23, G5, G20, G24, G27, G25, G16, G14, G7, G2, G28, G11, G6, G34, G10, G30, G3, G15, G19, G36, G17, G21, G31, G18, G33, G35, G13, based yield reduction rankings. Among these genotypes, G1, G19, G13, G33, G31 showed high mean performance, tolerance and association with SSI, STI, MRP, GMP, MP, TOL, HM and REI. However, G26, G32, G9, G29, G12 were considered moderately susceptible to water stress and G7, G8, G14, G22, G34 had low mean performance values and low association with indexes. The 36 imported lines from the International Institute of Tropical Agriculture (IITA) were assessed in the field and greenhouse environments, using a 6×6 alpha-lattice design with two replications. Water stress was applied up two weeks after 50% flowering for each genotype and a well-watered regime was used as a control treatment. The genotypes were screened using morphological and physiological traits including; PH, STD, LW, SMOI, STC, CC, SW, BM and GY for estimating variance components and broad-sense heritability. The present study showed the existence of genetic variability among 36 soybean genotypes examined. Hence, one can examine the presence of variability in these soybean lines for crop improvement programs through indirect selection. According to the results, a higher genotypic coefficient was observed for grain yield under both water regimes, consistent with wide-ranging heritability. The PCV was higher than the GCV for all traits across environments and water regimes, thereby suggesting the significance of the environmental expression for all traits. The PCV was higher than the GCV for all traits in all environments and water regimes, suggesting the importance of the environmental effect for all traits. The PCV values ranged from 7.03 to 92.84, while the GCV values ranged from 0.07 to 60.77. GY and BM showed high PCV and GCV values in each environment and under the respective water regimes, which signifies a considerable genotypic variation in these traits. Additionally, the phenotypic expression of these traits would help identify genotypic potential and are efficient further to be used to improve breeding plants. Because of the reduced effects of environmental stress, there was no clear trend in the traits examined for heritability in both environments and water households. Heritability estimates under WW ranged from -0.34 to 55%, while under WS, they ranged from -0.29 to 43%. Overall, most traits had low heritability in both water regimes. Consequently, one should be careful in selecting for droughttolerance using the traits examined.
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    Genetic analysis of maize streak virus disease resistance on tropical maize.
    (2021) Chisikaurayi, Barbra.; Mafongoya, Paramu L.; Magorokosho, Cosmos.
    Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila) is a major contributing factor to low maize yields in Africa. The disease threatens maize production in Zimbabwe, thus the importance of breeding Zimbabwe maize varieties that carry resistance to this disease. Cimmyt has developed inbred lines, good for other traits, for example, high general combining ability (GCA) effects for grain yield performance, but susceptible to MSV hence efforts are being made in CIMMYT to introduce MSV resistance genes from MSV resistant donor lines known to be good for important traits, especially yield, but bad for MSV resistance. This study was designed to assess newly developed tropical maize inbred lines with complete resistance to MSV and to compare disease progression between the MSV susceptible and resistant inbred lines artificially infect plants with virulent leafhoppers. Breeders usually cross two resistant parents to exploit the potential contribution of beneficial resistance alleles originating from them to generate transgressive segregation that can lead the development of new maize inbred lines with much higher levels of resistance to MSVD and desirable agronomic traits. Twelve inbred lines from CIMMYT were evaluated to determine their level of resistance. Genotype effects on MSV scores were significant from week 1-6 as well as for the average (p < 0.05). Significant effects on MSV scores were also observed on each week interval, except for week 4. Broad-sense heritability (H2) estimates for MSV scores was high (<50%) on each week interval as well as for the average MSV score. Genotypic effects showed to be more important than the environmental variances on each week MSV recordings were taken. This study showed that inbred line CML536 was highly resistant confirming previous observations made with artificial infection in Zimbabwe. Candidate lines CL1210634 and CL1210635 showed complete resistance to MSV meaning they may share the same major gene Msv1 with CML539 and CML536 check inbred. The data we obtained provide quantification of conclusions of visual observations: (a) some varieties bred for resistance are less affected by MSD than others, even when infected at the same stage; (b) early infection is more damaging than late infection, but resistant varieties differ in their response, and; (c) varieties carrying no resistance can be little damaged if infected late. In order to avoid the over-dependence on Msv1, further studies should be carried out to identify a second gene for MSD resistance to compliment Msv1 gene in conferring enhanced and durable resistance to MSD. Enhanced resistance through additional phenotypic selection will also help prevent possible breakdown of Msv1.
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    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.
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    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
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    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.
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    An investigative study of the drought tolerance of F1 maize (Zea mays L.) single crosses derived from PANNAR and CIMMYT inbred lines.
    (2015) Muyambo, Caiphas.; Shanahan, Paul Edward.
    Drought is the most devastating abiotic stress limiting the production of maize (Zea mays L.) worldwide. The effect of drought stress is greatest in sub-Saharan Africa (SSA) where most small scale farmers rely on open pollinated varieties (OPVs); rather than certified hybrid seed grown under dryland1 conditions. Small scale farmers perceive OPVs to be drought tolerant and yet the yields are as low as 1-2 t ha-1 . In many parts of SSA, therefore, hybrid adoption rate is still below 20%. With the projected population growth in SSA, food insecurity is likely to worsen. However, the development of drought tolerant maize hybrids to help address declining food security is a relevant strategy in SSA. This is so because, drought tolerant hybrids will out yield OPVs. The main objective of this study was to investigate the drought tolerance of F1 single cross maize hybrids developed from CIMMYT drought tolerant donor inbred lines and PANNAR elite inbred lines. The hybrids were tested under random and managed drought stress environments. The first set of F1 hybrids was produced using a 12x12 North Carolina factorial mating design during winter (April-August 2012) and the second set of hybrids was produced in summer (November 2012-March 2013). Seventy F1 hybrids were tested during the summer season (November 2012- April 2013) under random drought stress (RDS) environments in South Africa and Zimbabwe. One hundred hybrids were tested during the winter season (April – September 2013) in Zimbabwe at CIMMYT experimental stations in Save Valley and Chisumbanje under managed drought stress (MDS). The main traits measured included grain yield (GY), ear plant-1 (EPP), anthesis-silking interval (ASI) and days to anthesis (DTA). Statistical analysis of collected data was conducted using GenStat 16th edition. Significant differences between hybrids and environments for grain yield and secondary traits were obtained. The genotype x environment (GxE) interactions was significant under both RDS and MDS environments indicating the differential performance of hybrids across environments. Using stability indices, the relatively stable hybrids were identified. General and specific Combining ability (GCA and SCA) analysis revealed lines that could be used as potential parents in development of hybrids. However, the presence of GCAxE and SCAxE interactions indicated that selection of inbred lines and their hybrid crosses should be done at target environments. Under RDS and MDS, EH79 and EH24 appeared to be the best performing hybrids, respectively, whereas inbred lines DT2, DT7 and UT8 had the best GCA and SCA under both RDS and MDS. Further efforts are required to develop potential drought tolerant hybrids and test for adaption in target environments.
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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.
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    Evaluation of early maturing maize (zea mays L.) hybrids for multiple-stress tolerance.
    (2018) Ndlala, Lucia Zinzi.; Sibiya, Julia.; Mashingaidze, Kingstone.
    Maize (Zea mays L.) is the most important cereal in Africa, but a number of constraints including biotic, abiotic and socio-economic factors affect its production. The abiotic factors such as drought, low nitrogen (N) and heat contribute to the low grain yield production, which creates a challenge that needs to be addressed by researchers. Thus, development and use of early maturing maize hybrids could help in stabilizing maize production. Early maturing maize hybrids help in reducing the growing period to escape some of the abiotic stresses that contains variability for high yield potential and adaptive traits. This study, therefore, was aimed at breeding and identifying early maturing maize hybrids cultivars that are tolerant to drought and low N stresses. Fifty early maturing maize hybrids including six commercial checks were evaluated under stress and non-stress environments during the 2016/17 maize growing season in South Africa. The objectives were (i) to estimate variance components, correlation and path coefficients among grain yield and secondary traits in early maturing maize hybrids across stress and non-stress environments and (ii) to evaluate genotype by environment interaction effects and stability for grain yield performance in early maturing maize hybrids across stress and non-stress environments. To estimate the variance components, correlation and path coefficients among grain yield and secondary traits in early maturing maize hybrids across stress and non-stress environments, quantitative traits data including grain yield and its secondary components were recorded. Statistical analyses revealed that the effect of genotype, environment and genotype by environment interaction were significant (P<0.01) for all the traits. Hybrids CZH16084, CZH16064 and CZH16095 under managed drought, low N and optimum environments, respectively, were identified as the outstanding genotypes for grain yield and recommended for further testing, release and registration. High magnitude of phenotypic and genotypic coefficient of variation as well as high heritability were recorded for each single environment for anthesis days, silking days, ear height and plant height, suggesting that those traits interacted with the environment. Grain yield was positively correlated with anthesis days and ear height, field weight, grain moisture at Potchefstroom while at Lutzville and Cedara had negative correlation with those traits, suggesting that the genotypes differed significantly for most of the phenotypic traits. Path coefficient analyses revealed that anthesis days and anthesis-silking interval had positive direct effects while silking days, plant height and ear per plant had a negative direct effect on grain yield in all the environments. These traits are recommended for effective selection to the improvement of maize grain yield. To evaluate genotype by environment interaction effects and stability for grain yield performance in early maturing maize hybrids across stress and non-stress environments, data collected from all environments which were Lutzville (managed drought), Potchefstroom (optimum), Cedara (optimum) and Cedara (low nitrogen) during the 2016/17 summer planting season, were subjected to ANOVA and GGE biplot analyses. Analysis of variance for individual environments showed that the genotype mean squares were significant at P<0.01. The ANOVA across environments showed that the genotype, environment and genotype by environment interaction mean squares were significant at P<0.01 for grain yield. From the GGE biplot analysis, the two principal components (PC1 and PC2) contributed 64.8% of the total variability due to genotypes plus genotype by environment interaction, with PC1 and PC2 accounting for 35.97% and 28.83%, respectively. The use of GGE biplot analyses provided a clear basis for determining the stability and performance of the 50 early maize hybrids and ranked them according to order. The best performing genotypes were G13 (CZH15448), G46 (CZH15574), G15 (local check 2), G33 (CZH16094), G7 (CZH16083), G20 (CZH16090) and G4 (CZH16089). The following hybrids were adapted to specific environments as follows: G26 (CZH16070), G34 (CZH16074), G9 (CZH15499) and G18(CZH16071) at Cedara (optimum) conditions; G46 (CZH15574), G40 (CZH16069) and G12 (CZH16080) excluding the checks G23 (local check 1) and G14 (SC301) at Potchefstroom (optimum); G22 (CZH16093), G6 (CZH15575), G49 (CZH16068) and G17 (CZH15600) excluding the check G15 (local check 2) at Cedara (low N) and G33 (CZH16094), G37 (CZH15184), G41 (CZH16082), G28 (CZH16076) and G8 (CZH16065) at Lutzville (managed drought). The GGE biplot analysis also identified nine stable and high yielding genotypes, which included G6 (CZH15575), G46 (CZH15574), G22 (CZH16093), G49 (CZH16068), G12 (CZH16080), G17 (CZH15600), G28 (CZH16076), G47 (CZH15452), and G8 (CZH16065). These genotypes will contribute to high maize yields and stable grain production in specific and across environments and are therefore, recommended for further testing and release.
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    The physiology of germination and dormancy in seeds of Gynandropsi gynandra L. Briq syn Cleome gynandra L. (Cleomaceae).
    (2018) Blalogoe, Seho Jelila.; Odindo, Alfred Oduor.
    The “spider plant” Gynandropsis gynandra L. Briq,” is an important traditional leafy vegetable in many parts of Africa. The species is considered underutilized and has been mainly neglected by research systems. Yields are generally low and this has been attributed to a number of factors including low and non-uniform seed germination. This study sought to gain a deeper understanding of factors influencing germination and dormancy in spider plant seeds. The specific objectives were to, (i) describe and document the phenotypic characteristics and mineral composition of seeds of 29 G. gynandra accessions from diverse regions, (ii) determine the pattern of seed germination and dormancy development in seeds of different spider plant accessions and their crosses and (iii) assess the storage potential of spider plant seeds using artificial aging. To achieve these objectives, accessions originating from West Africa, East Africa and Asia were used. In the first experiment, seeds of the accessions from the three regions were subjected to scanning electron microscopy to study seed structure and mineral composition. In the second experiment, seeds from different accessions were planted in pots in a tunnel and data recorded at bi-weekly intervals during development until maturity on the following variables: seed fresh and dry mass, seed moisture content, germination capacity, mean germination time (MGT) and electrical conductivity (EC). In the third experiment, seeds that had been stored for four months and freshly harvested were subjected to the accelerated aging to test for storage potential. The same variables that were in the second experiment were measured in the third experiment in addition to tetrazolium test (TZ). Data analysis was done using R software version 3.5.1. Eight mineral elements were identified in the seeds of spider plant, and the internal and external structure of the seed was revealed. The results showed significant differences among spider plants accessions with regard to shape, size, mineral composition, germination percentage and mean germination with Asian accessions showing a higher germination percentage. The study revealed that spider plant fresh seeds exhibited a physiological dormancy which can be broken by heating at 41°C for 3 days and/or gibberellic acid (0.001%), depending on the genotype. However, the degree of dormancy varied from one genotype to another as follows: weak (% germination >50%), intermediate (% germination>6%<50%) and strong (% germination<6%). Moreover, the study found that a saturated solution of 40% NaCl for 48 h could be used to evaluate the physiological quality in spider plant seeds during storage. It is suggested that further experiments using the diversity observed in the species be conducted to select genotypes with weak dormancy in order to improve the germination capacity in the species.
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    Genotypey by environment interaction, genetic variability and path analysis for grain yield in elite soybean [Glycine max (L.) Merrill] lines.
    (2018) Mwiinga, Bubala.; Sibiya, Julia.; Chigeza, Godfree.
    Soybean [Glycine max (L.) Merrill] is the world’s leading source of protein and vegetable oil. However, its productivity is still low in the region due to limited availability of stable and high yielding cultivars. Therefore, the objectives of this study were: (1) to determine the magnitude of genotype by environment interaction and stability of elite soybean lines for seed yield, (2) to establish trait profiles of 25 soybean genotypes and to study the associations among characters, their direct and indirect effects on grain yield and (3) to estimate genetic parameters of traits related to seed yield and to analyse genetic diversity among elite soybean lines. To achieve these objectives, 25 genotypes (20 elite soybean lines and five commercial checks) were evaluated in multi-location trials conducted in the 2017/18 rainy season using six sites in four countries viz. Zambia, Malawi, Zimbabwe and Mozambique. Both AMMI and GGE biplot analyses indicated Lusaka West as the highest yielding and most informative environment and could be useful for selecting specifically adapted genotypes. Rattray Arnold Research Station was the most ideal environment as it was both informative and highly representative. The soybean lines TGx2002-17DM, TGx2001-10DM, TGx2001-18DM, TGx2014-24FM, TGx2001-6FM and TGx2002-3DM exhibited specific adaptation. Both GGE and AMMI models showed that TGx2014-5GM was more stable than the checks and was second to the highest yielding check. The genotype by trait (GT) and correlation coefficient analyses revealed that pod number per plant and hundred seed weight were the most positively correlated traits with grain yield, while days to 50% flowering had a negative association with grain yield. Sequential path analysis, showed that the number of pods per plant and hundred seed weight had the highest positive and significant direct effects on seed yield, implying that these two traits could be used as selection criteria for seed yield in soybean. The soybean lines TGx2014-5GM and TGx2002-23DM had good combinations of high yields with large seed size and high pod number. The analysis of genetic variability showed small differences between PCV and GCV values for all the traits except for pod clearance. This implied that there were minimal effects of the environment and high contribution of the genes in the phenotypic expression of the traits, except for pod clearance, which was more affected by the environment. Moderate GCV values of 13.45% and 13.49%, high heritability values of 70% and 69% and GAM values of 23.24% and 23.04% were recorded for grain yield and number of pods per plant, respectively. Only two principal components, PC1 and PC2 accounted for the variation, with a cumulative contribution of 68.25%. All the seven traits were useful in discriminating the genotypes as they had high eigenvalues in either PC1 or PC2. The 25 soybean genotypes were grouped into two main clusters, which were further sub-divided into eight sub-clusters based on the seven morphological characters. The genotypes TGx2014-5GM, checks SC Safari and SC Squire in sub-cluster 6 had the highest means of the most desirable traits (large seed size, high pod number per plant and seed yield). The three genotypes could be used in hybridisation programmes for improvement of grain yield, seed size and number of pods of the genotypes. Overall, the study identified soybean lines that could potentially be released as cultivars in the four southern African countries or used as parents in future soybean improvement programmes. It also revealed traits that could be used for indirect selection of seed yield and high genetic diversity among the genotypes for possible exploitation in soybean breeding programmes to increase seed yield.
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    Evaluation of soybean [Glycine max (L.) Merrill] genotypes for grain yield and associated agronomic traits under low and high phosphorus environments.
    (2018) Pedro, Joao António.; Sibiya, Julia.; Chigeza, Godfree.
    Phosphorus is an important element for growth, development and seed formation in soybean and other plant species. This element is less available for plants. The capacity of absorbing phosphorus in the soil varies from one genotype to another, so that, the selection of phosphorus use efficient soybean lines is crucial in order to enhance the production. The main objectives of this study were: i) to identify soybean varieties that are tolerant to phosphorus deficiency ii) to determine the agronomic characters that contribute directly and indirectly to the yield improvement by correlation and path coefficient analysis and iii) to determine genotype x environment interaction effects and stability of soybean genotypes in respect to grain yield across low and optimum phosphorous environments. Thirty advanced soybean lines were evaluated in an alpha-lattice design, with two replications during 2016/2017cropping season under low phosphorus (0 kg/ha) and high phosphorus (100 kg/ha) levels in seven environments. Data were collected for fifteen phenotypic traits (both quantitative and qualitative) and analysed using SAS, breeding view (BV) in breeding management system (BMS), and Excel. Correlation and path coefficient analysis were done to determine the traits that contributed directly and indirectly to yield. Results for correlation and path coefficient analysis demonstrated strong and significant associations of yield with yield components. Harvest index was highly significant and positively correlated with grain yield but negatively with plant height, days to maturity and days to flowering. Path analysis revealed that under low P environment, total dry biomass, harvest index, number of pods could be used to screen soybean lines for low P, likewise in high P, harvest index, 100-seed weight, and plant height could be used in selection for high P use efficiency. Plant height, number of pods and nodule weight were identified as the traits that could be used for selection of the lines across all environments. The yield was high under high phosphorus (1551.20 kg/ha) than under low phosphorus environment (1154.30 kg/ha). The best yielding genotypes under high phosphorus were TGx2025-9E, TGx2025-6E and TGx2016-3E. Likewise, for low phosphorus the best genotypes were TGx2025-9E TGx2016-3E and TGx2023-3E. Across the two environments, genotypes TGx2025-9E and TGx2016-4E were the best. The genotypes were clustered into six groups with the maximum dissimilarity index of 0.6. In AMMI analysis, genotype TGx2025-9E, was the most stable and high yielding, suggesting the potential value of the variety as an alternative for soybean production across all environments. GGE biplot resulted in three mega-environments from the seven environments; Kabwe1, Lilongwe1, Lilongwe2 and Lusaka composed mega environment one, Gurue1 and Gurue2 formed mega environment two and Kabwe2 mega environment three. The best performing genotypes in these mega-environments were SCSAFARI and TGx2019-1E (mega-environment 1), TGx2025-9E (mega-environment 2) and TGx2025-6E (mega-environment 3). These findings highlighted the need for increased GxE studies to enhance efficiencies of breeding for broad adaptability in respect to responsiveness to low phosphorus.
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    Evaluation of rice genotypes for grain yield and resistance to bacterial leaf blight (Xanthomonas oryzae pv.oryzae) disease.
    (2018) Tesha, Claudia Andrew.; Sibiya, Julia.; Musvosvi, Cousin.
    Rice (Oryza sativa L.) is a staple food crop in many African countries including Tanzania. However, both regional and national rice production have failed to meet demand due to several constraints, among which is the bacterial leaf blight (BLB) disease caused by Xanthomonas oryzae pv. oryzae. Moreover, attempts to increase rice production through the introduction of modern cultivars has motivated farmers to leave local land races for high yielding, but often susceptible varieties. The overall goal of this study was to increase and strengthen rice production in Tanzania through development of high yielding and BLB resistant varieties. The specific objectives were: to i) analyse genotype x environment interaction (GEI) effects for reaction to bacterial leaf blight under natural infection and rice grain yield performance across different environments in Tanzania ;ii) assess the heritability, variability and efficiency of indirect selection using secondary traits for grain yield improvement among rice genotypes; and iii) assess relationship among traits using correlation, path coefficients and genotype-by-trait associations in rice. The study was conducted at three sites namely Katrin, Igurusi and Kyela, all in Tanzania. Thirty rice genotypes, which include two checks, Txd 306 (susceptible check) and IR- 24 (resistant check), were evaluated. The experimental design was a 6 x 5 alpha lattice design with three replications. Data was collected on early vigour, days to early flowering, plant height (cm), panicle length(cm), number of tillers per hill, dead heart, bacterial leaf blight scoring, lodging percent, days to maturity, dry straw weight (kg), spikelets per panicle, grain length (mm), grain width (mm), 1000-grain weight (g), harvest index (%) and yield per plot (kg). Data were analysed using SAS version 9.4 and GenStat 17th edition. ANOVA was used to detect the significance of GEI. The Additive Main Effect and Multiplicative Interaction (AMMI) and the Genotype plus Genotype by Environment Interaction (GGE) biplot models were used for further analysis of GEI and stability. From the results, genotypes NERICA 4 followed by IR-24 were the most resistant to BLB while Supa India was the most susceptible. Dakawa 83 was the most resistant at Katrin while NERICA 4 was the most resistant at Igurusi and Kyela. Genotypes NERICA 2 and LOWLAND NERICA 6 were the most stable across environments for BLB resistance, while IR54 and Txd 306 were the most unstable. Based on the GGE biplot analysis, the three environments fell into two mega environments where as at Kyela, NERICA 4 and IR-24 were identified as the most resistant genotypes while at Katrin Dakawa 83 and NERICA 1 were identified as the most resistant genotypes. Genotype by Environment Interaction effect for grain yield was not significant and as a result, genotype comparison for the same trait was based solely on mean performance across all the environments. The best three genotypes for grain yield were Txd 306, Txd 88 and WITA 10, but in contrast, NERICA 4, Supa India and Mwanza were the worst performers for the same trait. As for broad sense heritability estimates, days to early flowering had the highest estimate of 99.67%, indicating less influence of the environment, while lodging% had 0.00% heritability indicating high influence of the environment. For variability, the phenotypic coefficient of variation (PCV %) values were higher than the genotypic coefficient of variation (GCV %) for all the traits. The highest PCV(%) was for lodging percent (5325.463) followed by number of spikelets per panicles (1005.352)and the lowest was for grain width (1.197) followed by grain length(2.406).The GCV (%) was highest for number of spikelets per panicle (419.902) followed by plant height (97.843) and the lowest was for lodging percent (0.000) followed by grain yield (0.314), genetic advance (GA) was highest for spikelets per panicles (66.79) and lowest for lodging percent (0.000), while for genetic advance as a percentage of mean (GAM %) the highest was for yield per plot (104.13) followed by dry straw weight (92.11) and the lowest was for lodging percent (0.00) followed by panicle length (8.89).Not all the traits under consideration could be used for indirect selection for yield per plot since none of them had a relative selection efficiency equal to or greater than unity. Regarding diversity assessment, cluster analysis based on Euclidian distance indices revealed that Txd 88 and SATO IX were the most similar pair, followed by IR-56 and IR54, which were also similar to each other, and the most divergent genotypes were Txd 306 and Wahiwahi followed by Wahiwahi and Txd 85. Diverse genotypes can be targeted for hybridization since progenies of diverse parents are often more heterotic than those of related parents. The assessment of relationship among traits using correlation and path analysis the traits which were positive and highly significantly correlated to grain yield were harvest index (0.77***) followed by dry straw weight (0.46***), while negative significant correlations were observed for early vigour (-0.22*). Direct effects on grain yield were positive for harvest index (0.80) and dry straw weight (0.51), while indirect effects were highest for days to maturity through harvest index (0.25) followed by number of tillers per hill through harvest index (0.23). For genotype-by-trait associations, genotypes NERICA 1, NERICA 2, NERICA 4, WAB 450-12-12-BL1- and IR-24 were associated with BLB resistance; on the other hand Txd 306, WITA 10, Txd 88, Txd 85, and SATO I were associated with high yield, although Txd 306 was also associated with susceptibility to BLB, whereby WITA 10 was high yield and resistance to bacterial leaf blight. Moreover this study provided information on the presence of genotype by environment interaction in Tanzanian rice growing environment, valuable blight resistance and high yielding genotypes such as WITA 10 and moderate BLB resistance with high yield for genotypes such as Kalalu, Txd (88) and Txd (85), which could be used in rice breeding improvement and conservation efforts of rice.
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    Genetic variability, path coefficient and marker-trait association analysis for resistance to rosette disease in groundnut.
    (2019-02) Mubai, Nelson Hilário.; Mwololo, James.; Sibiya, Julia.
    Several abiotic, biotic and socio-economic aspects constrain the production of groundnut (Arachis hypogea L.). Groundnut rosette disease (GRD) which can cause yield losses of up to 100% in susceptible cultivars, is among the most important biotic stresses. The use of resistant cultivars is the most viable method to control the disease, therefore, breeding for high yielding and GRD resistant cultivars is needed and should be a priority. The present study was conducted to: (i) determine genetic variability for GRD response and yield traits in selected groundnut accessions under natural infestation, (ii) assess the relationship between seed yield and its related traits, and analyse agro-morphological diversity in selected groundnut accessions under natural GRD infestation and (iii) evaluate groundnut recombinant inbred lines for resistance to GRD and perform SNP marker-trait association analysis. Twentyfive groundnut accessions and three controls were evaluated under natural GRD infestation to assess genetic variability for GRD response and yield related traits. Seed yield, number of pods per plant, plant height, GRD incidence and number of secondary branches showed high phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV), while moderate variation (PCV and GCV) was observed for days to flowering and pod width. A combination of high heritability and genetic advance was recorded for number of secondary branches, plant height, seed yield and GRD incidence, indicating that phenotypic selection based on the mean would be successful in improving these traits. Phenotypic correlations and sequential path analysis indicated that high seed yield was directly associated with taller genotypes, higher number of pods per plant and hundred seed weight, which were a result of higher pod width and lower GRD incidence. Based on morphological traits, the evaluated accessions were grouped into four clusters. Days to flowering and maturity, number of branches, plant height, number of pods per plant, pod width and length, seed yield and GRD incidence, largely influenced this variation. Principal component analysis (PCA) biplot was effective in showing the genetic distance among the accessions with results consistent to those of the cluster analysis. Moreover, Shannon-Weaver diversity indices (0.949-0.9996) for qualitative traits also indicated the existence of high diversity among the accessions. A total of 25 groundnut genotypes, which comprised 21 RILs derived from a bi-parental cross, both parents, and two susceptible controls (CG7 and JL24) were evaluated and used to perform SNP marker-trait association analysis for resistance to GRD. There were significant differences among the lines in all recorded traits, indicating the existence of genetic variability and possibility of effective selection. Interaction of genotype and environment was significant for disease incidence and the glasshouse environment had higher disease pressure, providing the best discrimination among the tested genotypes. ICGV-SM 15605, ICGV-SM 15621, ICGV-SM 15618, ICGV-SM 15604 and ICGV-SM 15615 were among the resistant and high yielding RILs. Twenty-two highly significant marker-trait associations were identified, which will add to previously reported genomic regions influencing GRD and the aphid vector resistance. Overall, the study showed that taller genotypes, higher number of pods per plant and hundred seed weight can be used to improve seed yield in groundnut, particularly under GRD infestation. The genetic diversity among the accessions provides an opportunity for parent selection that can be used for breeding high yielding and GRD resistant cultivars. In addition, the SNP markers will be useful in classifying groundnut germplasm based on the GRD response and for their use in marker-assisted selection, once validated.
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    Evaluation of maize hybrids for low-nitrogen stress tolerance, yield stability and genetic purity.
    (2019) Josia, Chimwemwe Chabulika.; Sibiya, Julia.; Mashingaidze, Kingstone.
    Nitrogen stress is among the major abiotic constraints that impede maize production in Africa. Therefore, development of maize varieties that are tolerant to low N stress conditions and stable across environments is needed. Assessment of genetic purity of inbred lines and their F1 hybrids is among the quality control measures in hybrid breeding, seed production, variety release as well as intellectual property protection (IP). The objectives of this research were, therefore: a) to assess the grain yield performance, genetic parameter estimates, correlations and conduct path coefficient analysis for grain yield and related traits under low N and optimum conditions, b) to assess the magnitude of genotype by environmental interaction (GEI) and hybrid yield stability under low N and optimum conditions and c) to assess the genetic purity of maize parental lines and their F1 hybrids. To achieve these objectives, 170 single cross maize hybrids were evaluated across low N and optimum environments at three locations in South Africa (SA) during 2017/18 summer season viz. Potchefstroom, Vaalharts and Cedara. The experimental setup comprised of five-production conditions across these three locations. The collected data was subjected to analyses using Genstat software 18th edition, SPSS version 25 and SAS version 9.3. For genetic purity analysis, 158 single-cross maize hybrids along with 30 elite parental inbred lines were genotyped using 92 SNPs markers and the molecular data was analysed using GenAlex software. Results revealed that variance due to environment, genotype and GEI were highly significant (P<0.001) for all the traits under low N and optimum conditions. Lower heritability values were observed for grain yield (0.29) compared to secondary traits including days to anthesis, plant height, ear height and anthesis-silking interval, which had heritability estimates of 0.85, 0.43, 0.38 and 0.52, respectively. Higher phenotypic coefficient of variation (PCV) as compared to genotypic coefficient of variation (GCV) were observed under low N and optimum environments, respectively. Under low N, grain yield was positively correlated with field weight, plant height and ear height, but negatively correlated with days to silking, anthesis-silking interval and leaf senescence. Under optimum environment, grain yield was positively correlated with field weight and ears per plant, and negatively correlated with days to anthesis, days to silking, anthesis- silking interval, plant height and ear height. Highest positive direct effect on grain yield was observed for days to silking and field weight under low N, while under optimum, field weight and days to anthesis exhibited the highest direct effects. AMMI and GGE biplot analyses revealed high yielding hybrids in each specific environment and high yielding and stable hybrids across the environments. Five high yielding and stable hybrids across environments; G134 (I-42/CKDHL0295), G12 (CB399/CML442), G24 (CK21/CML216), G33 (CKDHL0089/CML442) and G102 (CML544/I-42) are recommended for further evaluation and release. Using SNP markers, 66.7% of maize parental lines genotyped were considered pure with residual heterozygosity of <5%, while the remaining 33.3% had residual heterozygosity levels of > 5% hence not pure. Cluster analysis effectively discriminated the parental lines into three distinct genetic clusters. Parent-offspring test conducted on 158 hybrids resulted to the elimination of 38% of the hybrids due to genetic contamination of their parental inbred lines. Of the 68 hybrids that passed the parent-offspring test, seven hybrids, including SCHP29, SCHP95, SCHP94, SCHP134, SCHP44, SCHP114 and SCHP126, were selected as potential candidates for further evaluation and possible release in South Africa due to their outstanding yield performance.
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    Genetic analysis and improvement of groundnut (Arachis hypgaea L.) for drought tolerance and seed yield in Malawi.
    (2018) Sultan, Masoud Salehe.; Sibiya, Julia.; Odindo, Alfred Oduor.
    Groundnut (Arachis hypogaea L,) is one of the major sources of food and income for smallholder farmers in Malawi. It is a valuable food security crop that supplies fats and proteins to the predominantly maize–based Malawian diet. Although, groundnut production is a profitable venture for smallholder farmers in Malawi, its productivity is low averaging 250 – 800 kg/ha as compared to a yield of about 4.0 t/ha obtained at research stations. The decline in productivity of groundnuts is due to several abiotic and biotic constraints that smallholder farmers encounter, among them drought due to inadequate and highly variable rainfall in the country. Information on response of different genotypes to drought stress and the explanation of these variabilities is an important requirement in breeding for drought tolerance improvement in groundnut. The main objectives of the study were: (i) to determine the effect of drought stress on the growth performance of groundnut genotypes with respect to morpho-physiological traits,(ii) to identify the relevant traits related to drought tolerance and their relationship to seed yield under drought stress conditions, (iii) to estimate the relative importance of additive and non-additive gene action in controlling the inheritance of drought tolerance traits under moisture stressed conditions and (iv) to investigate the genetic variation existing among genotypes in relation to morpho-physiological traits related to drought tolerance. Twenty-five genotypes from the International Crops Research Institute for Semi-Arid Tropics (ICRISAT) Malawi were evaluated during 2016/17 under rainfed field condition at the drought-testing site of Ngabu Agricultural Research Station. The results indicated high genotypic coefficient of variation (GCV) coupled with high genetic advance (GA), genetic advance as percent of mean (GAM) and heritability estimates for days to maturity (DM), seed yield (SY), relative water content (RWC), biomass (BM), number of filled pods (FP) and pod yield (PY). Seed yield was highly significant and positively correlated with shelling percentage (SHP), hundred seed weight (HSW), SPAD chlorophyll meter reading (SCMR), days to maturity (DM), biomass (BM), relative water content (RWC) and harvest index (HI). Furthermore, path analysis showed that harvest index, biomass, pod yield, shelling percentage, SPAD chlorophyll meter reading, relative water content and days to maturity had the highest direct and indirect effects on seed yield. General combining ability effects were significant for almost all studied traits indicating the importance of additive gene action. Specific combining ability effects were also significant for days to maturity, seed yield, biomass, harvest index, number of field pod and pod yield indicating importance of non-additive gene action controlling the inheritance of these traits. This suggests that both additive and non-additive gene action were important in controlling the majority of the traits. However, additive gene action was more predominant for all traits studied as it was evidenced by its significant (P<0.05) positive GCA effects coupled with high variance components as compared to its interactions. This also, was supported by a high Baker’s ratio of close to unity (X>0.5) ranging from 0.78 to 0.96 for all measured traits. Among male parents, ICGV-SM 02724 and ICGV-SM 94139 were identified as good combiners, whereas among females, CG 7 and ICGV-SM 01721 were good combiners. These parents have outstanding breeding value as proven by their high and significant GCA effects. The crosses Pendo x Akwa, ICGV-SM 99555 x ICGV-SM 02724, ICGV – SM 99551 x Baka and ICGV-SM 01721 x ICGV-SM 94139 had significant SCA effects for seed yield, number of filled pod, harvest index and pod yield. The cross, Pendo x ICGV-SM 02724 was identified as potentially useful for developing early maturing varieties. These crosses could be used for further selection in breeding programmes for developing drought tolerant cultivars. Genotypes also showed different degrees of tolerance where seven genotypes with high yield, favourable adaptive traits and useful for breeding were selected. The principal component analysis under moisture stressed condition also showed that specific leaf area, days to maturity, biomass, number of filled pod, hundred seed weight and pod yield had more influence during selection. Based on the current results, breeding for drought tolerance for the material studied will be possible by focussing on relative water content, shelling percentage, number of filled pod, SPAD chlorophyll meter reading, pod yield and hundred seed weight as selection criteria, accompanied with extensive evaluation of the material under multi-located trials.
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    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.
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    Characterisation of selected bread wheat (Triticum aestivum L.) genotypes for drought tolerance based on SSR markers, morpho-physiological traits and drought indices.
    (2018) Mdluli, Sibusiswangaye Yolanda.; Shimelis, Hussein Ali.
    Bread wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum) are staple cereal food crops worldwide. In South Africa, bread wheat is the second most economically important cereal after maize. Drought stress associated with climate change is a major cause of the yield gap in wheat production in South Africa. Drought tolerant wheat cultivars are yet to be developed and released in the country. Wheat improvement for drought tolerance is one of the major breeding goals in South Africa. Integrative pre-breeding techniques involving genotypic and phenotypic characterisation ensure an accurate selection of potential drought tolerant parents for breeding. Therefore, the specific objectives of the current study were: 1) to determine the genetic diversity and population structure of forty-seven diverse bread wheat genotypes introduced from the International Maize and Wheat Improvement Center (CIMMYT) using ten selected polymorphic Simple Sequence Repeat (SSR) markers, 2) to characterise fifteen bread wheat genotypes introduced from CIMMYT using physiological and morphological traits, and 3) to assess drought tolerance amongst fifteen selected bread wheat genotypes using nine drought tolerance indices. Genetic diversity and population structure of 47 CIMMYT derived bread wheat genotypes were examined using 10 SSR molecular markers. All the SSR markers used in the study were highly polymorphic. The highest PIC values were recorded for XGWM 132, WMS 179 and WMS 30 with 0.93, 0.89 and 0.89, respectively. Cluster analysis detected 3 distinct clusters with Clusters A and C consisting of most diverse genotypes. Two distinct heterotic patterns were identified to select unique parents for crosses. Analysis of molecular variance (AMOVA) detected significant genetic diversity among populations, among individuals and within individuals with explained percentage variance of 3%, 37% and 60%, respectively. Genetic diversity and population stratification was mainly due to private alleles detected. Based on detected genetic variability, a total of 15 genotypes were selected and subjected for phenotypic characterisation. The selected genotypes included SYM2016-037, SYM2016-038, SYM2016-029, SYM2016-010 and SYM2016-012 from Cluster A, SYM2016-044, SYM2016-004, SYM2016-016, SYM2016-019, SYM2016-014, SYM2016-008, SYM2016-006 and SYM2016-047 from Cluster B and SYM2016-042 and SYM2016-027 from Cluster C. The above selected 15 bread wheat genotypes were evaluated under field and greenhouse conditions using a randomised complete block design with 3 replications. Drought stress was imposed as follows: 1 week before 50% heading (WBH) and 1 week after 50% heading (WAH). A fully-irrigated water regime (NS, non-stress) was used as a comparative control. Genotypes were evaluated using 2 physiological and 8 morphological traits. Significant differences (P < 0.05) were detected among genotypes and genotype x test environment interaction. Genotype effect was significant for days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 grain weight. Genotype x test environment interaction was significant for canopy temperature, days to flowering, days to maturity, plant height, number of spikelets per spike, grain number, 100 seed weight and the yield. Significant correlations were detected between yield and days to flowering, days to maturity, plant height, number of productive tillers, number of spikelets per spike, grain number and 100 seed weight under greenhouse condition. The number of productive tillers per plant and the number of spikelets per spike were positively associated with yield under field evaluation. Principal component analysis revealed PC1 to be consistently associated with yield, 100 seed weight and number of spikelets per spike. Days to flowering and maturing, plant height and canopy temperature were positively associated with either PC2 or PC3 under greenhouse and field conditions. A yield penalty was noted for early flowering and maturing genotypes such as SYM2016-014, SYM2016-027 and SYM2016-029 relative to late flowering and maturing genotypes SYM2016-016, SYM2016-037 and SYM2016-006. Crossing of these complementary lines and continuous selection of progenies is essential to develop early maturing genotypes with stable and high yield potential. In this study, days to flowering and maturity, plant height, canopy temperature and 100 seed weight were favourable traits to screen genotypes for drought tolerance. Screening for drought tolerance under greenhouse condition was more reliable than under field evaluation. The above 15 wheat genotypes were evaluated using 9 drought tolerance indices based on yield data. The drought indices used were drought resistance (DR), mean productivity (MP), harmonic mean of yield (HM), stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), yield index (YI), yield reduction index (YR) and yield stability index (YSI). Analysis of variance detected significant differences among genotypes (P < 0.001) and genotype by water regime interaction (P < 0.01) affecting yield response. Significant differences were also recorded among genotypes (P < 0.05) for DR, HM, MP, STI, YI and YSI. Consistent mean genotype ranking was recorded for HM, MP, STI, SSI and YI enabling selection of genotypes SYM2016-006, SYM2016-016 and SYM2016-037. PC analysis detected high variation of 82.2% among genotypes, with percentage variation partitioned as follows: 42.64% for PC1, 22.37% for PC2 and 12.18% for PC3. Both PC and bi-plot analyses revealed strong associations between HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. High yielding genotypes such as SYM2016-006, SYM2016-016 and SYM2016-037 scored higher values for HM, MP, STI, YI and yield under drought stressed and non-stressed conditions. DR was associated with early maturing genotypes such as SYM2016-014, SYM2016-029 and SYM2016-38. These genotypes were considered as potential parents for future wheat breeding programmes emphasizing drought tolerance.
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    Pre-breeding of architectural traits related to direct harvesting in dry bean.
    (2017) Mulube, Mwiinga.; Melis, Robertus Johannes Maria.; Fourie, Deidré.
    Dry bean (Phaseolus Vulgaris L.) is an important crop for direct human consumption worldwide. In South Africa, it is a major source of plant proteins and income among growers. The crop is mainly grown by commercial producers for the market in Mpumalanga, Gauteng, Northwest, Free State, Limpopo, KwaZulu-Natal and the Eastern Cape provinces. Dry bean is known to be one of the most labour intensive field crops, especially the harvesting operation. In order to maximise profits, commercial producers prefer using the direct harvesting system that has the advantages of labour efficiency and saving time, compared to the pull/cut and window followed by threshing harvesting system. However, the success of the direct harvesting system requires a cultivar with a suitable upright architecture. The upright bean architecture suitable for direct harvesting is a complex trait that may only be improved through indirect selection for sub-component morphological traits associated with the trait. It is therefore important to evaluate diverse genotypes for morphological traits associated with the upright bean architecture to improve the trait. This study was aimed at (1) evaluating architectural traits related to direct harvesting and establishing relationships amongst traits on selected genotypes from the Andean gene pool, (2) estimating the phenotypic and genotypic variation, heritability, and genetic gain of traits related to direct harvesting on selected genotypes from the Andean gene pool, and (3) evaluating the architectural traits related to direct harvesting and establish the relationships amongst traits in local South African genotypes. The evaluation of architectural traits related to direct harvesting and establishing relationships amongst traits, was carried out on 30 Type I genotypes from the Andean gene pool. The trial was evaluated under field conditions in a 10 × 3 alpha lattice design at two sites. The traits collected were the days to physiological maturity, upright plant score, lodging, stem diameter, plant height, shattering, number of branches per plant, number of pods per plant, seed weight and seed yield. The analysis of variance showed highly significant differences (p ≤ 0.001) on genotypes across all traits, except for the number of branches, which was moderately significant (p ≤ 0.05). Superior genotypes were identified in each trait based on the grand mean. The stem diameter was identified to be important for multiple selections, because of its correlations with the upright plant architecture score, lodging, the days to physiological maturity and seed yield. Three principal components were extracted, accounting for 78.55% of total variation. Selection for the seed yield, stem diameter and plant height would be essential for improving the suitability to direct harvesting. The genotypes ADP 35, ADP 166, ADP 211, ADP 36, ADP 395, ADP 436, ADP 455, ADP 458, ADP 661, Mbomvu and Ukulinga were found to have thicker stem diameters and non-shattering, and therefore, they may be useful in improving both seed yield and the upright architecture suitable for direct harvesting. The estimation of the phenotypic and genotypic variation, heritability and genetic gain of traits related to direct harvesting was also carried out on 30 Type I genotypes from the Andean gene pool. The trial was evaluated in a 10 × 3 alpha lattice design at two sites. The traits collected were the days to physiological maturity, upright plant score, lodging, stem diameter, plant height, shattering, number of branches per plant, number of pods per plant, seed weight and seed yield. The analysis of variance showed highly significant differences among genotypes on all traits except the number of branches per plant, which showed moderately significant differences. The highly significant differences indicate the presence of genetic variability in the data set. A significant interaction of genotype with the site was observed on days to physiological maturity, lodging, plant height and seed weight. The phenotypic coefficient of variation was slightly higher than the genotypic coefficient of variation for all traits, showing little environmental influence on the expression of traits. Generally, a high variability was observed in the population. Broad sense heritability estimates ranged from moderate to high, except for the number of branches per plant, which recorded a low heritability value of 29%. The moderate to high heritability and expected genetic gains observed in the population could be exploited through selection and hybridisation during the improvement of the upright bean architecture suitable for direct harvesting. The evaluation of architectural traits related to direct harvesting, and establishing relationships amongst traits on local South African genotypes, was carried out on twenty four genotypes. The trial was laid out in a 6×4 alpha lattice design at Ukulinga Research Farm. The traits collected were, the days to 50% flowering, days to physiological maturity, upright plant score, lodging, stem diameter, plant height, shattering, number of branches per plant, number of pods per plant, seed weight and seed yield. The analysis of variance showed highly significant differences for the number of days to physiological maturity, days to 50% flowering, lodging, number of branches per plant, plant height, number of pods per plant, seed weight and the upright plant score, while it was very significant for the first pod insertion height and moderate for stem diameter, shattering and seed yield. Superior genotypes were identified using the grand means of the different traits and these genotypes may be used in a breeding programme to improve the suitability to combine harvesting. The correlation analysis showed that plant height would be useful in selection. However, an optimum height, to reduce lodging and improve the upright architecture should be selected for. The factor analysis revealed that seed yield, upright plant score, first pod insertion height, plant height and lodging had more influence on the variation in the data set and as such may be considered during selection. The cluster analysis grouped genotypes in two groups, while two genotypes were stand alone and the four principal components accounted for 78.55% of variation.
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    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.