STRATEGIC RESOURCE DEVELOPMENT AND DEPLOYMENT TO LIMIT THE SPREAD OF WHEAT BLAST

Wheat blast is caused by a recently-emerged exotic population of Magnaporthe oryzae, the same fungus that causes the ancient blast diseases on rice and many cultivated and wild grasses in the U.S. and worldwide. The M. oryzae Triticum pathotype (MoT) subpopulation causing wheat blast emerged in Brazil in 1985 and is currently devastating wheat in several South American countries. Wheat blast moved into Bangladesh in 2016 and into Zambia in 2017, most likely through import of this seed-borne fungus in infected wheat seed. It is critical to keep MoT from establishing in U.S. wheat, but a better understanding of disease biology and development of resources for disease detection and control are needed. Our recent results show that the MoT population had a complex origin from diverse strains apparently derived from the same progenitor that gave rise to the devastating new turfgrass disease first reported in the U.S. in 1992 (caused the Lolium pathotype, MoL). The MoT and MoL genomes are admixtures of DNA segments inherited from other host-specialized forms, presumably via sexual recombination. Thus, current diagnostic probes, although effective in identifying MoT to date, target sequences also present in other host-adapted populations that are currently in the U.S. Additionally, we showed that MoT is still evolving to overcome resistance and become a more aggressive pathogen of wheat. With previous NIFA support, we identified the 2NS head blast resistance plus other putative blast resistance genes using MoT strains isolated in Brazil in 1988; but wheat lines containing the non-2NS resistances failed to show any resistance to MoT isolates from 2011 to 2015. We have identified one strain from Brazil in 2016 that appears to have overcome the 2NS-resistance. Therefore, it is critical to understand if the MoT population as a whole is evolving to overcome the 2NS-resistance and to find new wheat resistance genes to stack with the 2NS-resistance. Based on these needs, we are working on the following specific objectives: Objective 1 -- Develop a widely applicable "Plug and Play" bioinformatics pipeline that leverages genome sequence data and phylogenomic information for rapid identification of diagnostic probes for lineage/pathotype-level detection of diverse pathogens. Objective 2 -- Identify accurate diagnostic probe sets to identify strains from the exotic Triticum and native Lolium pathotypes. Objective 3 -- Monitor wheat pathogen evolution through genomic and phenotypic analyses of strains causing recent and current epidemics. Objective 4 -- Identify blast resistance genes in two promising wheat lines. Our bioinformatics pipeline from Objective 1 will become a valuable resource for diverse pathogens including Fusarium species and Colletotrichum species. Knowledge and resources from this research will guide future response to controlling wheat blast and stopping further spread, as well as training of first responders and wheat stakeholders.