Genomic and Pathogenic Insights into the Geographic Range Expansion of Wheat Blast into Uruguay.

Wheat blast, caused by Magnaporthe oryzae pathotype Triticum (MoT), is one of the most destructive and emerging diseases affecting global wheat production. Although it is endemic to South America and has significantly affected Brazil, Paraguay, and Bolivia, it had not been reported in Uruguay until 2023. During that season, climatic conditions similar to those associated with Brazilian MoT outbreaks, particularly in northwestern Uruguay, prompted intensive monitoring of this disease. In October 2023, 17 wheat spike samples with blast-like symptoms were collected from 11 fields; nine were positive for M. oryzae based on morphology. Four monosporic isolates were recovered, and three were subjected to molecular and genomic characterization. PCR confirmed their identity as MoT, and pathogenicity tests demonstrated their ability to cause disease in both leaves and spikes of susceptible wheat genotypes. Phylogenetic comparisons among 57 Triticum, Lolium, and Eleusine M. oryzae strains, including strains from the B71 branch responsible for outbreaks in Bangladesh and Zambia, indicated that the Uruguayan strains are closely related to some Brazilian strains and are genetically distinct from the B71 branch. Specifically, PyrUy10.1 and PyrUy14.1 shared 99.9% of their SNPs, whereas PyrUy11.1 showed only 73% similarity to these strains, suggesting more than one introduction of the pathogen into Uruguay and the presence of distinct lineages. These findings confirm the presence of MoT in Uruguay and suggest that its introduction likely occurred through airborne dispersal due to its geographic proximity to Brazil. This study highlights the need for continuous surveillance and monitoring in Uruguayan regions with conducive environmental conditions for wheat blast, as the detection of multiple genetic lineages suggests the presence of strains with distinct adaptations. This genetic diversity poses a significant challenge for effective wheat blast management in Uruguay and may have important implications for national wheat production as the pathogen continues to evolve locally.