Identification of LMA-tolerance QTL in a biparental winter wheat mapping population (Xerpha/Bobtail)

Abstract

Late-maturity α-amylase (LMA) is an emerging cause of low falling numbers in US wheat (Triticum aestivum L.) causing financial losses for growers. Quantitative trait loci (QTLs) associated with α-amylase expression during mid-late grain fill, characteristic of LMA, have been mapped across all three wheat genomes. To facilitate breeding for tolerance in soft white winter wheat, QTLs were mapped in a recombinant inbred line population derived from a cross between LMA-susceptible Xerpha and LMA-tolerant Bobtail. The population was characterized for kernel α-amylase activity with cool-temperature LMA-induction (Lind) and without (Lcon) in field plots from 2019 to 2021. Broad-sense heritability (H²) was estimated at 0.81 and 0.66 for untreated and induced replicates, respectively, suggesting a genetically inherited trait. A novel major QTL, QLind-wsu-7A.2, was mapped to chromosome 7AS and contributed up to 15% of the total phenotypic variation for α-amylase activity in LMA-induced material. Five additional QTLs associated with α-amylase activity after LMA induction, and four QTLs associated with lower α-amylase level in untreated controls, were identified on chromosomes 2A, 3A, 3B, 5B, 6B, 7A, and 7D. All QTLs associated with higher α-amylase levels in untreated material carried the Xerpha allele, and most QTLs associated with lower α-amylase levels following cool-induction carried the Bobtail allele. The Rht-B1b (where Rht is reduced height) and Rht-D1b gibberellin A-insensitive semidwarf alleles, known to be associated with LMA tolerance, reduced α-amylase levels in untreated material. Interestingly, the Rht-B1b/Rht-D1b double dwarfs consistently expressed higher α-amylase levels with LMA induction, suggesting a complex role for GA signaling in LMA.