MOLD & COLD: THE SOLUTION IS SWEET IN WINTER WHEAT

Abstract

Winter conditions necessitate tolerance of snow mold and freezing cold among winter wheat plants. These traits involve numerous quantitative trait loci (QTL), environmental interactions, and mechanisms such as carbohydrate tolerance and gene regulation, that complicate efforts to select for improved tolerance. To identify molecular markers associated with these traits, QTL analysis was performed using a population of 155 F2:5 recombinant inbred lines (RILs) from a cross between soft white wheat cultivars 'Finch' and 'Eltan', which differ in their tolerance to each of these stressors. Two novel QTL for freezing tolerance were identified on chromosomes 5A and 4B, one QTL for snow mold tolerance was identified on chromosome 6B, and a QTL conferring tolerance both mold and cold was detected on 5A and was determined to co-locate with the Fr-A2 (Frost-Resistance A2) locus. Twenty-six additional QTL for snow mold tolerance were detected in a RIL population from a cross between 'Xerpha' and 'Münstertaler'. This RIL population was also compared to a marker-assisted selection subpopulation, derived from the same cross, and was used for genomic selection to investigate the effectiveness of these selection tools. Although both methods failed to improve snow mold tolerance in the Xerpha-Münstertaler population, genomic prediction had good accuracy in the Finch-Eltan RIL population. To investigate the contribution of carbohydrate accumulation to snow mold and cold tolerance in the Finch-Eltan RIL population, eight lines, representing four combinations of tolerance, were analyzed for carbohydrate content over the cold-acclimation period. The lack of significant differences in carbohydrate content between these categories suggests that other traits are responsible for the observed segregation. RNA-seq was performed to investigate differential gene expression, which could account for the segregation. The knowledge derived from this study will facilitate efforts to breed for tolerance to snow mold and freezing cold by improving the understanding of the quantitative nature of these traits and enabling better leveraging of selection methods.