Genotypic and virulence dynamics of Phytophthora infestans populations in southwestern China

The oomycete pathogen Phytophthora infestans causes late blight disease that severely reduces potato production worldwide. Monitoring the genotypic and virulence dynamics of P. infestans populations is vital for management of late blight. Phytophthora infestans populations in southwestern China diversify in genotypes and virulence, but the most recent status of these populations remains elusive. In this study, 218 isolates collected from six locations in southwestern China from 2019 to 2022 were analyzed for genotypic and virulence dynamics as well as effective management strategies. Phylogenetic analysis of simple sequence repeats-classified multi-locus genotypes (MLGs) revealed that these populations comprise three lineages, of which the EU lineage is dominant. These populations had overcome the resistance mediated by R3a, R3b and Rpi-blb3 and had an increased trend in overcoming the resistance mediated by Rpi-blb2, R8, Rpi-blb1 and Rpi-vnt1.1. The EU lineage consisted of 19 MLGs and the predominant genotype MLG24 significantly contributed to the pathotypic diversity of the EU lineage. In addition, two independent MLG24 isolates, CQ-22-16-1 and CQ-22-20-1, overcame the resistance mediated by all seven resistance genes and were virulent on 30 potato cultivars. Notably, two Solanum candolleanum relatives were highly resistant to these two highly virulent isolates. Furthermore, these two isolates could be controlled by three fungicides. In summary, this study elucidates the genotypic and virulence dynamics of P. infestans populations in southwestern China and provides valuable insights into effective control measures.