Wheat Blast: Can QTL Mapping Help Stop This Cereal Killer?.

Wheat blast, caused by the fungus Magnaporthe oryzae Triticum, can completely devastate affected fields and fungicide control has proven inconsistent. Therefore, genetic resistance is the most promising sustainable alternative for disease suppression. The objective of this study was to identify quantitative trait loci (QTL) for wheat blast resistance using a double haploid (DH) population with 187 lines from a cross between ‘Sossego’ x ‘Alvorada’, widely grown spring wheat cultivars in Brazil. While ‘Sossego’ has shown moderate levels of wheat blast resistance and carries the 2NS-resistance trait, the cultivar ‘Alvorada’ was chosen as the susceptible parent. The population was evaluated under field conditions in one meter-row plots stablished in a randomized complete block design with three replications during the 2016-2017 wheat-growing season in Quirusillas (Bolivia). Disease incidence and severity were measured at approximately two-day intervals during the watery ripe through soft dough stages of wheat grain development. Parents and DH-lines were genotyped using the 90K SNPchip platform. Standard, composite, and multiple QTL mapping were performed using Haley–Knott regression. Despite the low disease pressure due to the dry and cool season, two QTLs associated with incidence and severity were identified on chromosomes 2AS and 5AL. The QTL on 2AS mapped to the telomeric region in the same interval as the 2NS segment and it explained 30.4% of the phenotypic variation for wheat blast severity. The diagnostic marker ventriup-ln2, which is associated with 2NS, mapped within the QTL interval, confirming that this QTL is in fact the 2NS resistance. The QTL identified on 5AL is likely a novel wheat blast resistance gene and it explained 5.7% for severity. Resistant alleles for both QTLs came from the variety ‘Sossego’. Despite promising preliminary data, the low disease pressure in this season compromises drawing definitive conclusions. Thus, the experiment will be repeated under controlled conditions.