Studies in Argentina warn about the risk of infection of wheat and barley cultivars with Pyricularia oryzae Triticum pathotype.

Abstract

Wheat blast, or brusone, caused by Pyricularia oryzae pathotype Triticum (PoT), is an emerging fungal disease expanding into major tropical and subtropical cereal-producing regions and causing substantial yield losses under hot and humid conditions. We evaluated the response of wheat and barley cultivars to PoT isolates at seedling and heading stages. All tested PoT isolates were pathogenic to wheat and barley. Significant differences in pathogenicity were observed among wheat-derived isolates inoculated on barley reflected variation in disease severity. The 14 wheat cultivars assayed exhibited different blast responses depending on the PoT isolate and phenological stage assessed. Disease severity on barley seedlings ranged from 16.21 to 86.43% across isolate–cultivar combinations, with reaction types 3–5 (on a 0–5 scale) indicating a predominance of susceptible responses. Fluorescence microscopy on barley leaves enabled characterization of early infection sites, which were categorized into five stages from appressorium formation to complete mesophyll collapse. These observations confirmed successful infection of barley by wheat-derived PoT isolates. The results highlight the current risk of wheat blast under favorable conditions for disease outbreaks. PoT is already capable of infecting wheat and barley materials used in Argentina, with greater impact at the adult plant stages, making resistance breeding and early surveillance a priority before further regional spread.