The major physiological determinants of wheat (Triticum aestivum L.) phenology in a given area are a response to vernalization temperature and day length, which are at least in part, regulated by the allelic variation at the vernalization (VRN) and photoperiod (PPD) loci, respectively. Characterization of the existing genetic variation for plant phenology in winter wheat can assist breeding programs improve adaptation to local environments and to optimize wheat phenology for the changing climate. The objectives of this research were to characterize the allelic variation at the major VRN and PPD loci in a diverse panel of high latitude winter wheat genotypes (n = 203) and to associate the allelic variation with phenologic, agronomic and adaptation traits. The panel was genotyped using allele-specific markers at vernalization (VRN-A1, VRN-B1, VRN-D1 and VRN-B3) and photoperiod (PPD-A1, PPD-B1, and PPD-D1) loci and phenotyped for agronomically-important traits. Though photoperiod sensitivity was more prevalent, most of the variation in the phenology of the winter wheat panel was explained by allelic variation at PPD-D1, PPD-A1, and the interaction between these loci. While a typical high latitude winter wheat genotype is one that carries winter alleles at all major VRN loci and photoperiod sensitive alleles at the major PPD loci, in lower latitudes where winters are milder, the presence of one or two photoperiod insensitive alleles seems to contribute to higher yield and wider adaptation.

Fusarium head blight (FHB), caused by several Fusarium spp., is a worldwide problem that severely impacts cereal grain yield and poses major risks to human and animal health due to production of the mycotoxin deoxynivalenol (DON) and its acetylated forms, 3-acetyl-DON (3-ADON) and 15-acetyl-DON (15-ADON). Recent studies suggest an inconsistent effect of F. graminearum chemotypes and resistance of wheat (Triticum aestivum) genotypes. To gain insight into the interaction effects of F. graminearum chemotypes and spring wheat genotypes on FHB resistance response, 10 spring wheat genotypes with varying levels of FHB resistance were inoculated with 10 F. graminearum isolates, consisting of 5 3-ADON- and 5 15-ADON-producing isolates and evaluated in type I (spray inoculation) and type II (point inoculation) resistance assays. Wheat genotypes carrying the resistance allele of the Fhb1 quantitative trait locus on chromosome 3BS had lower disease in type II evaluations, regardless of F. graminearum isolate or chemotype. Isolates of F. graminearum were also significantly different for disease aggressiveness. In addition, the 3-ADON-producing isolates were 18% more aggressive than the 15-ADON isolates in type I resistance assays. No difference in aggressiveness of the two chemotypes was observed, when tested in type II resistance assays. There was no interaction effect between F. graminearum chemotypes and spring wheat genotypes, suggesting that screening of germplasm for resistance can be performed with limited number of aggressive isolates.

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.