Low nitrogen and phosphorus effects on wheat Fe, Zn, phytic acid and phenotypic traits

In sub-Saharan Africa, crops are often grown under low nitrogen (N) and low phosphorus (P) conditions, which may impact on the nutritional components of the grains. The aim of this study was to investigate the effect of low N and low P and a combination of the two on iron (Fe), zinc (Zn) and phytic acid content in two commercial South African spring wheat cultivars (PAN3497 and SST806). Phenotypic traits were also investigated. Although cultivar effects were not significant, treatment effects were highly significant for the phenotypic and nutritional traits. Low P stress increased Fe and Zn levels, whereas low N stress had the opposite effect. In addition, low P stress inhibited phytic acid accumulation the most, suggesting that under this treatment, Fe and Zn were more available because of less interaction with phytic acid. Compared to the low N treatment, the low P treatment led to lower reductions in the number of tillers, plant height, stem thickness, number of seeds, weight of seeds and dry weight for both cultivars. While low P had positive effects on the nutritional value of wheat, the combination of low N and P treatment had a negative impact on most of the measured characteristics. Low N conditions had more negative effects on all measured characteristics than low P conditions and was very detrimental to wheat nutritional value and yield.Significance: Results from this study emphasise the impact of fertilisation and the impact of insufficient nitrogen and phosphorus fertiliser on wheat productivity. Low nitrogen and phosphorus fertilisation impact grain microelement content and bioavailability which impact nutritional value

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

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

SNP-based genetic diversity among few-branched-1 (Fbr1) maize lines and its relationship with heterosis, combining ability and grain yield of testcross hybrids

Single nucleotide polymorphism (SNP) markers are regarded as efficient,compared to other marker types in genetic characterization of maize (Zea mays L.) germplasm because of their vast coverage of the maize genome. The objectives of this study were to (a) genetically fingerprint few-branched-1’ (Fbr1) and normal tasselled CIMMYT elite lines using SNP markers, to assess their relatedness and level of homozygosity and (b) to determine SNP-based genetic distance among these maize lines and to find association of genetic distances with specific combining ability (SCA), mid-parent heterosis (MPH), high-parent heterosis (HPH) and mean grain yield of the hybrids. Twenty-six CIMMYT maize lines (12 with the Fbr1 gene, and 14 normal-tasselled) were genotyped using 1074 SNP marker loci. Fifteen of these lines were used in two separate diallel mating designs: a 9x9 and 6x6 crossing set-up, to make hybrids for yield evaluation. Average residual heterozygosity of SNP loci ranged from 0.2-36.1%, with an average of 8.2%, well above the expected ranges for residual heterozygosity found in maize inbred lines. The polymorphic information content (PIC) for the 1074 SNP loci ranged from 0.015-0.50, with an average of 0.25. Mean genetic distance for all pair wise comparisons of lines was lower (0.30) suggesting a high level of relatedness among lines. A number of elite CIMMYT lines were successfully converted to Fbr1, and were homozygous for the 1074 SNP loci, thus could be used in breeding programmes involving these new tassel mutants. The unweighted paired group method using arithmetic averages (UPGMA) cluster analysis revealed two discrete clusters for the inbred lines, reflecting heterotic groups used by CIMMYT. In the principal component (PC) analysis, PC1 and PC2 explained 10.87 and 9.08% respectively, of the molecular variance in tassel size for the 1074 SNPs. The results confirmed molecular markers as a powerful complement for use in genetic characterization, in assigning lines into defined heterotic groups and in examining the relationships among inbred lines at deoxyribonucleic acid (DNA) level. Marker-based genetic distances were positively correlated with hybrid performance, SCA and heterosis indicating that they could accurately predict hybrid performance in this set of germplasm. Grain yield for the hybrids ranged from 0.49-2.48 kg/plot, with an average of 1.80 kg/plot. Hybrids from closely related parental lines (according to SNP-based genetic distances) had the lowest mean grain yield, lowest SCA effects for grain yield, and had the lowest heterosis values. Thus, SNP-based genetic distance information would be useful for effective selection by avoiding genetically similar lines when selecting parents for breeding programmes that require genetically diverse lines as parents

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