In bread wheat (Triticum aestivum L.), flowering time and plant stature are important phenological and agronomic traits for adaptation, yield potential, and yield stability. Timely flowering is critical for production, and the flowering window has to be late enough to avoid early season frosts but early enough to avoid late season stresses such as heat and terminal drought. Flowering time is controlled mainly by vernalization, photoperiod response, and earliness per se genes, which can be exploited to fine-tune growth and tailor flowering time for the production of desirable wheat cultivars. Tailoring flowering time could help reduce preharvest sprouting problems by escaping high temperatures and late season rainfall, which promote preharvest sprouting, hence yield loss. Concisely summarizing available information on flowering time and identifying research gaps could provide direction for future research. This chapter, therefore, discusses: (i) the progress made in discovering genes involved and the impact of their extensive allelic variation on flowering time, (ii) the potential benefits of tailoring wheat's flowering time to improve yield, and (iii) the benefits of introgressing genes for other complimentary traits, such as semidwarf and preharvest sprouting resistance on advanced lines to achieve higher yield, thus, sustainable food security.
Grain yield is a quantitatively inherited complex trait that is strongly influenced by interacting genetic and environmental factors. The identification of major quantitative trait loci (QTL) for plant height (PH) and yield component traits (YCT) is important for improving yield potential through wheat breeding. We performed a QTL analysis for PH and YCT in the Tugela-DN × Elands doubled haploid (DH) population using a genotype-by-sequence single nucleotide polymorphism and a silicoDArT-based genetic map. Field trials were conducted under rain-fed conditions across five environments in the Free State Province of South Africa during the 2017–2018 and 2018–2019 cropping seasons. Analysis of variance revealed significant differences (p < 0.001) among DH lines and the environments. However, for G × E interactions, significant differences (p < 0.05) were only observed for spikelet number per spike. Broad-sense heritability estimates of all traits ranged between 0.44 and 0.81. Nine QTL, viz. QPh.sgi-6A.2 and QPh.sgi-4D for PH, QSl.sgi-6A.2 and QSl.sgi-7A for spike length, QGns.sgi-3B for grain number per spike (GNS), QGwps.sgi-7B for grain weight per spike (GWPS), QGw.sgi-2A and QGw.sgi-7A for grain width, and QGl.sgi-3B for grain length (GL), were identified on chromosomes 2A, 3B, 4D, 6A, 7A, and 7B, in two or more environments. Some of these QTL exhibited pleiotropic effects. The QPh.sgi-6A.2 QTL for PH and QGwps.sgi-7B for GWPS appear to be novel QTL, while the rest of the reported QTL validated previously identified QTL for PH and YCT. The study also reported a trade-off between GL and GNS. The findings of this study will be useful in elucidating the genetic architecture of yield component traits contributing to the development of new dryland wheat varieties with high and stable yield.
The current and projected climate change that is represented by increasing temperatures and humidity levels and irregular rainfall patterns promotes the occurrence of preharvest sprouting (PHS) in wheat. PHS results in significant economic losses, globally, which necessitates the need for high-yielding cultivars with increased PHS tolerance; hence, this study was conducted. The current study evaluated two doubled-haploid (DH) wheat populations of Tugela-Dn × Elands and Elands × Flamink across six environments in the Free State Province of South Africa to select genotypes with increased PHS tolerance and further map the underlying loci. Significant effects of DH lines (194) and environments (6) were observed for PHS tolerance. The results of this study validate previous findings that PHS is only expressed when environmental conditions are conducive. Quantitative trait loci (QTL) mapping using single-nucleotide polymorphism (SNP) and silicoDArT markers revealed three additive QTLs with major effects on chromosomes 5B and 7B, and these QTLs were detected more than once, when conditions were favourable. These QTLs explained a phenotypic variation (PVE) varying between 10.08% and 20.30% (LOD = 2.73–3.11). About 16.50% of DH lines performed to the level of Elands (the PHS-tolerant parent) and are recommended for further selection in a pre-breeding or breeding programme. The findings of this study are expected to expedite the on-going breeding efforts for PHS tolerance in winter wheat, which will facilitate the development of PHS-tolerant cultivars adapted to the South African environment.
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