Abstract
Nepal is facing more intense early-season drought stress associated with climate change. The introgression of reduced height (Rht) alleles to enable stem dwarfism in bread wheat (Triticum aestivum L.) inadvertently reduced coleoptile length and growth plasticity in seedlings, making improved varieties less suitable for deep seeding; these alleles may have also reduced seedling root length. Therefore, with the long-term objective of breeding wheat for early-season drought stress, a Nepali spring wheat panel was evaluated to assess allelic variation at the most common dwarfing-associated loci (Rht-B1, Rht-D1) and their impact on coleoptile/seedling root traits, and to identify accessions with longer and/or more GA-responsive coleoptiles as parents for future breeding. Here, Kompetitive Allele Specific PCR (KASP) was used to genotype accessions. The panel was phenotyped using the cigar-roll method in the presence/absence of GA3. Plant height was measured under field conditions. The results showed that Nepali landraces had a significantly higher frequency of the non-dwarfing allele Rht-B1a. The dwarfing alleles Rht-B1b and Rht-D1b had negative effects on coleoptile length but positive effects on the length of the longest seedling root. However, 40 potential semi-dwarf accessions (possessing Rht-B1b and/or Rht-D1b alleles) with long and/or more plastic coleoptiles suited for deep sowing were identified. This included 12 accessions that exhibited significant changes in coleoptile length in response to GA3 treatment.
Highlights
The coleoptile is the structure that covers the first leaf before it emerges from the soil surface during germination
The three objectives of this study were: (1) to measure allelic variation at the reduced height (Rht)-B1 and Rht-D1 loci in the Nepali Wheat Diversity Panel (NWDP); (2) to assess the NWDP for variation in the seedling vigor traits associated with early-season drought stress and the impact of the Rht alleles on these traits; and (3) to identify candidate accessions that possess the dwarfing alleles Rht-B1b and Rht-D1b yet have a longer and/or more GA-responsive coleoptile as potential parents for future breeding programs
The National Agriculture Genetic Resource Centre (NAGRC, Nepal) provided the landrace seeds; the Nepal Agriculture Research Council (NARC) and the National Wheat Research Program (NWRP, Nepal) of NARC provided the seeds of the released varieties
Summary
The coleoptile is the structure that covers the first leaf before it emerges from the soil surface during germination. Wheat accessions having longer coleoptiles are better suited to areas with drought stress or drought at the early growth stage of the crop [4,5,9]. In this context, breeding wheat for longer coleoptiles is a strategy to cope with these challenges [4,9,10,11]. In addition to the coleoptile, different root architectural traits, including longer roots, contribute to improving drought stress tolerance in wheat [6,12,13]. The phenotypic assessment of wheat root traits can be useful when selecting accessions for drought stress tolerance [15]
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