QTL Pyramiding Provides Marginal Improvement in 2N^vS-Based Wheat Blast Resistance

Wheat blast, caused by the fungus Magnaporthe oryzae Triticum pathotype (MoT), is a devastating disease affecting South America, Bangladesh, and Zambia. Resistance to wheat blast has strongly relied on the 2N^vS translocation; however, newer MoT isolates have increased aggressiveness, threatening the 2N^vS translocation's effectiveness and durability. To identify genomic regions associated with wheat blast resistance, we performed a quantitative trait loci (QTL) mapping study using 187 double-haploid (DH) lines from a cross between the Brazilian wheat cultivars 'TBIO Alvorada' and 'TBIO Sossego', which are moderately resistant and susceptible to blast, respectively. The DH population was evaluated in a greenhouse in Brazil and Bolivia, and field conditions in Bolivia. Contrasting models best explained the relationship between traits evaluated according to differences in disease levels and the presence of the 2N^vS. A large effect-locus, derived from 'TBIO Sossego', was identified on chromosome 2AS, which was confirmed to be 2N^vS translocation and explained 33.5 to 82.4% of the phenotypic variance. Additional significant loci were identified on 5AL, 1DS, 4DS, 5DL, and 6DL chromosome arms with phenotypic variance <6%, but they were not consistent across trait-environment combinations. QTL pyramiding analyses showed that some specific loci had an additive effect when combined with the 2N^vS, suggesting that stacking multiple loci may be an effective strategy to help manage wheat blast. The markers associated with the 2N^vS can be used as dominant diagnostic markers for this alien translocation. Additional characterization of these loci using a broader set of MoT isolates is critical to validate their effectiveness against current MoT populations.