Stability of Lack of Fitness Cost Associated with G143A Mutation in Pyricularia oryzae Triticum

Wheat blast, caused by Pyricularia oryzae Triticum lineage (PoTl), is one of the most destructive and significant fungal diseases affecting wheat crops. The stability of the G143A mutation in the cytB gene, which confers resistance to Quinone outside inhibitor fungicides (QoIs) in PoTl isolates, has not been extensively studied. This study was conducted to evaluate the stability of fungicide resistance, fitness, and competitive ability of the QoI-resistant (R) PoTl isolates group over nine and five consecutive transfer cycles in vitro and in vivo, respectively, without fungicide exposure. No changes in azoxystrobin sensitivity were observed in either the QoI-resistant or sensitive (S) PoTl isolate groups after the successive transfer cycles in vitro and in vivo. The mycelial growth of the QoI-R PoTl isolate group remained stable, while the conidial germination capacity increased over time. For the QoI-resistant isolates, leaf and head disease, conidial production, and the latent period on wheat leaves did not change between the first and fifth infection cycles. In each transfer cycle, the highest levels of leaf and head disease, as well as the largest quantities of conidia collected from wheat leaves, were observed in isolate mixtures. Also, the G143A mutation responsible for QoI resistance remained stable after five transfer cycles of the QoI-resistant (0S:100R) isolate on wheat leaves. Our findings indicate that the G143A mutation remains stable, and there are adaptive benefits in QoI-R PoTl isolates. We discuss the ecological implications of the wheat blast population’s adaptation and PoTl QoIs resistance stability in wheat-cropping areas in Brazil.