Biosurveillance of Invasive Southern Corn Rust: Insights Into Recent Migration Patterns and Virulence Variation.

Emerging pathogen races spreading via long-distance migration increasingly threaten global agricultural ecosystems. Understanding how pathogens migrate and adapt to new hosts via virulence evolution is crucial for developing strategies to mitigate future crop damage. Here we performed biosurveillance of Puccinia polysora, a global fungal pathogen causing southern corn rust (SCR), across China, Thailand and the Philippines. By analysing 193 field transcriptomic data, we detected both epidemic and endemic lineages co-circulating in each country and elucidated the crucial role of host selection in driving the diversification of endemic lineages. Gene flow assessments and trajectory tracking indicated that the SCR infection source in northern China is likely of domestic origin and pathogen migration from the Philippines/Thailand into China is restricted to Hainan, coastal Guangdong and southern Yunnan. We detected country-specific variants in 32 effector genes, with AvrRppC exhibiting the strongest positive selection. A phylogenetically distinct Luzon Island lineage (Philippines), carrying a novel AvrRppC allele capable of overcoming RppC-mediated resistance and represents a potentially invasive threat. Finally, we reviewed the global migration history of P. polysora in light of our findings. Our work represents the first step toward establishing an international surveillance network for P. polysora and emphasised a comprehensive control strategy integrating local governance and invasion prevention of international races.