Puccinia polysora, the invasive fungal pathogen causing southern corn rust (SCR), has posed a significant threat to global maize production. The early epidemics of SCR were mainly reported in tropical areas, such as West Africa, the southern USA, and Southeast Asia. In recent decades, SCR has penetrated the temperate zones of China and the USA. However, the migratory pattern and virulence dynamics of P. polysora in the current epidemic centres remain poorly resolved.
A team of scientists from the Institute of Microbiology, Chinese Academy of Sciences, performed biosurveillance of P. polysora in China, Thailand, and the Philippines. They employed field transcriptomic data, a cost-effective alternative to traditional spore purification and proliferation methods, to analyse the dispersal network, virulence variation, and regional impacts of P. polysora. By integrating genetic and atmospheric trajectory analyses, they detected only limited ingress from Southeast Asia into China, indicating that local selection on host cultivars, rather than continual foreign influx, drives Chinese epidemics. Region-specific resistance breeding is therefore the immediate control priority.
Image: Closely related isolates were sampled from hosts with similar genetic backgrounds, and the Mantel test indicated that the maize lineage exerts a significant influence on the lineage divergence of P. polysora.
Re-examining the global invasion history, the authors trace the pathogen’s origin to Central America and its post-WWII jump to West Africa via US sweet corn shipments. The disease subsequently spread to the East Coast and entered the Indian Ocean region, then further eastward to Southeast Asia and Australia, possibly with airline aid within five years (1951-1956), a pattern consistent with clonal lineage dissemination. Surprisingly, a highly divergent lineage (PH1) now dominates Luzon Island, implying either genetic drift of historical lineages or a second, unrecorded introduction of contemporary exotic lineages. It hints at a possible greater global genetic diversity of P. polysora than currently recognised. PH1 carries new AvrRppC alleles capable of evading RppC-mediated resistance, flagging a latent biosecurity threat to neighbouring regions.
As a pioneering effort in global surveillance of corn rust pathogens, this work provides a crucial piece of the puzzle for the global migration map of P. polysora and argues for a comprehensive control strategy integrating internal management and external prevention.
Yuanjie Li, Wiruda Pootakham, Supawadee Ingsriswang, Fe Dela Cueva, Benjamine William Cordez, Yusufjion Gafforov, Jintana Unartngam, Lin Liu, Guozhi Bi, Peng Zhao, Clement K. M. Tsui, Junmin Liang, Lei Cai published this study in Molecular Plant Pathology Journal:
Biosurveillance of Invasive Southern Corn Rust: Insights Into Recent Migration Patterns and Virulence Variation
Cover image: Global invasion history and two current epidemic centres of P. polysora
