Pyricularia pennisetigena and Pyricularia oryzae isolates from Paraguay's wheat-growing regions and the impact on wheat

The Pyricularia genus includes species causing blast disease in monocots, posing significant challenges for disease management due to their ability to infect multiple hosts. This study aimed to identify the pathogenicity and species identity of Pyricularia isolates from 11 plant species in wheat-growing regions of Paraguay and assess their capacity to infect wheat. Twenty-four monosporic isolates were analyzed based on macroscopic and microscopic and phylogenetic characteristics. Three phylogenetic clades corresponding to P. oryzae, P. grisea, and P. pennisetigena were identified through five barcoding genes. For the first time, wheat blast was reported in San Pedro Department, and blast disease was observed in weeds in Cordillera and Central Departments. In greenhouse trials, P. oryzae isolates from wheat successfully infected both susceptible and resistant wheat cultivars, whereas isolates from non-wheat hosts did not elicit symptoms. Notably, P. pennisetigena isolates derived from Cenchrus echinatus were capable of infecting wheat spikes, producing typical blast symptoms, highlighting the potential for cross-species pathogen transmission. This finding suggests P. pennisetigena may pose an emerging threat to wheat in Paraguay, as its primary host is prevalent near wheat fields. These results highlight the critical importance of integrated disease management strategies, particularly the identification of inoculum sources, to mitigate cross-species pathogen transmission. This approach aligns with the One Health paradigm by addressing interconnected risks to plant health, food security, and environmental sustainability.