Genetic Structure and Spatiotemporal Dynamics of Pyricularia oryzae Triticum in Minas Gerais, Brazil

Wheat blast is a major threat to wheat production in tropical and subtropical regions of Brazil, yet the influence of epidemiological processes and population genetic structure on epidemic development remains unclear. Therefore, this study aimed to investigate, across different temporal and spatial scales, the genetic dynamics of Pyricularia oryzae Triticum lineage populations and their potential role in shaping wheat head blast epidemics. To investigate temporal genetic dynamics, we analyzed 270 isolates collected from wheat and co-occurring grasses at different crop growth stages within a single field. To evaluate potential tissue specialization and regional genetic structuring, an additional 97 isolates from leaves and spikes were sampled in two distinct regions of Minas Gerais. The analyses revealed a predominantly clonal population structure, with identical multilocus genotypes occurring within the same field, across geographic regions, and between plant tissues. The absence of genetic differentiation between leaf- and spike-derived isolates indicates a lack of tissue specialization, suggesting that the same genotypes can infect multiple organs throughout the crop cycle. Moreover, the detection of Pyricularia oryzae Triticum-positive grasses both before and during wheat development highlights the potential contribution of grass-associated inoculum early in the epidemic. These findings support a scenario of low recombination, strong clonal expansion, and widespread dissemination of a few adapted genotypes, suggesting that early foliar infections and grass-associated inoculum may play a key role in initiating and sustaining wheat blast epidemics.