Effects of different fertilization levels on the concentration of high molecular weight-glutenin subunits of two spring, hard red bread wheat cultivars

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Assessment of genetic diversity in sorghum accessions using amplified fragment length polymorphism (AFLP) analysis

Amplified fragment length polymorphism (AFLP) analysis was used to assess the genetic relationships among 46 accessions of sorghum (Sorghum bicolor (L.) Moench) collected from the north-western, western and central parts of Ethiopia as well as South Africa. Six AFLP primer combinations were used for the analysis of DNA fragment amplification. Dice similarity coefficients were calculated and a dendrogram was constructed following the UPGMA method of cluster analysis. A total of 186 fragments were amplified of which 78 (43.10%) were polymorphic. The number of polymorphic fragments amplified per primer combination varied from 9 to 21. Genetic polymorphism present among sorghum accessions was low, as evidenced by the high level of similarity in the AFLP marker profiles of different sorghum accessions. Pair-wise genetic similarity coefficients ranged from 0.87 to 0.99, with an average of 0.92. This indicates low levels of genetic diversity among tested sorghum accessions. The landraces were genetically very similar, while the differences between landraces, the Ethiopian cultivars and the South African cultivars were relatively higher. Genetic similarity within the South African and the Ethiopian cultivars was very high. Almost all accessions clustered according to the geographical origin. Results of this study indicate that the landraces were related, and this most likely results from the exchange of seeds between farmers in the collection regions, although no duplications were found in the material.Key words: Amplified fragment length polymorphism (AFLP), accessions, genetic diversity, sorghum

Seedling Shoot and Root Growth Responses among Soybean (Glycine max) Genotypes to Drought Stress

Drought stress is a major limiting factor in soybean production in South Africa. The development of soybean varieties with enhanced tolerance to soil waterlimited induced stress (WLIS) is one sustainable way to deal with drought. Root traits have shown strong potential for improvement of drought tolerance through breeding. The objectives of this study were to evaluate seedling shoot- and root growth responses under WLIS in order to study root morphology as a mechanism to cope with drought stress and to determine if there were genotypic differences in shoot- and root morphology between drought tolerant and -sensitive soybean genotypes. Seedlings of three drought tolerant and one sensitive genotype were subjected to soil WLIS in deep-root-pots for 21 days. Results suggested significant genotypic differences for shoot length, number of leaves, tap root length and root-to-shoot length ratio. Soybean tolerant genotypes were associated with moderate shoot biomass, deep rooting abilities and maintained a large root-to-shoot ratio under WLIS conditions. In contrast, the sensitive genotype was associated with a reduced root-to-shoot ratio and shallower root system. Soybean genotypes showed varying seedling root growth responses to soil WLIS, while shoot biomass characteristics were similar

Solvent Retention Capacity and Gluten Protein Composition of Durum Wheat Flour as Influenced by Drought and Heat Stress

Drought and temperature stress can cause considerable gluten protein accumulation changes during grain-filling, resulting in variations in wheat quality. The contribution of functional polymeric components of flour to its overall functionality and quality can be measured using solvent retention capacity (SRC). The aim of this study was to determine the effect of moderate and severe drought and heat stress on SRC and swelling index of glutenin (SIG) in six durum wheat cultivars with the same glutenin subunit composition and its relation with gluten protein fractions from size exclusion high performance liquid chromatography. Distilled water, sodium carbonate and sucrose SRC reacted similarly to stress conditions, with moderate heat causing the lowest values. Lactic acid SRC and SIG reacted similarly, where severe heat stress highly significantly increased the values. SIG was significantly correlated with sodium dodecyl sulphate sedimentation (SDSS) and flour protein content (FPC) under all conditions. Lactic acid SRC was highly correlated with FPC under optimal and moderate heat stress and with SDSS under moderate drought and severe heat. SIG was negatively correlated with low molecular weight glutenins under optimal and drought conditions, and combined for all treatments. The relationship between SRC and gluten proteins was inconsistent under different stress conditions

Predicting zinc-enhanced maize hybrid performance under stress conditions

The low yield potential of most biofortified maize is a barrier to its full adoption and reduces its potential to curb various macro- and micronutrient deficiencies highly prevalent in low-income regions of the world, such as sub-Saharan Africa (SSA). By crossing biofortified inbred lines with different nutritional attributes such as zinc (Zn), provitamin A and protein quality, breeders are attempting to develop agronomically superior and stable multi-nutrient maize of different genetic backgrounds. A key question, however, is the relationship between the biofortified inbred lines per se and hybrid performance under stress and non-stress conditions. In this study, inbred line per se and testcross performance were evaluated for grain yield and secondary traits of Zn-enhanced normal, provitamin A and quality protein maize (QPM) hybrids and estimated heterosis under combined heat and drought (HMDS) and well-watered (WW) conditions. Responses of all secondary traits, except for the number of days to mid-anthesis, significantly differed for HMDS and WW conditions. The contribution of heterosis to grain yield was highly significant under both management levels, although higher mid and high-parent heterosis was observed under WW than HMDS conditions. However, the findings suggest that inbred line performance was the best determinant of hybrid performance under HMDS. Strong correlations were observed between grain yield and secondary traits for both parents and hybrids, and between secondary traits of inbred lines and hybrids under both management levels, indicating that hybrid performance can be predicted based on intrinsic inbred line performance. Phenotypic correlation between grain yield of inbred lines and hybrids was higher under HMDS than WW conditions. This study demonstrated that under HMDS conditions, performance of Zn-enhanced hybrids could be predicted based on the performance of their corresponding inbred lines. However, the parental inbred lines should be systematically selected for desirable secondary traits correlated with HMDS tolerance during inbred line development

Combining ability and testcross performance of multi-nutrient maize under stress and non-stress environments

While significant progress has been made by several international breeding institutions in improving maize nutritional quality, stacking of nutritional traits like zinc (Zn), quality protein, and provitamin A has not received much attention. In this study, 11 newly introduced Zn-enhanced inbred lines were inter-mated with seven testers from normal, provitamin A and quality protein maize (QPM) nutritional backgrounds in order to estimate the general combining ability (GCA) and specific combining ability (SCA) for grain yield (GY) and secondary traits under stress conditions [(combined heat and drought stress (HMDS) and managed low nitrogen (LN)] and non-stress conditions [(summer rainfed; OPT) and well-watered (irrigated winter; WW)] in Zimbabwe. Lines L6 and L7 had positive GCA effects for GY and secondary traits under OPT and LN conditions, and L8 and L9 were good general combiners for GY under HMDS conditions. Superior hybrids with high GY and desirable secondary traits were identified as L10/T7 and L9/T7 (Zn x normal), L2/T4, L4/T4, L3/T5 (Zn x provitamin A), and L8/T6 and L11/T3 (Zn x QPM), suggesting the possibility of developing Zn-enhanced hybrids with high yield potential using different nutritional backgrounds. Both additive and dominance gene effects were important in controlling most of the measured traits. This suggests that selecting for desirable traits during inbred line development followed by hybridization and testing of specific crosses under different management conditions could optimize the breeding strategy for stacked nutritionally-enhanced maize genotypes

Influence of low soil nitrogen and phosphorus on gluten polymeric and monomeric protein distribution in two high quality spring wheat cultivars

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