Human-Mediated Gene Flow Contributes to Metapopulation Genetic Structure of the Pathogenic Fungus Alternaria alternata from Potato

Jing-Wen Meng, Dun-Chun He, Wen Zhu, Li-Na Yang, E-Jiao Wu, Jia-Hui Xie, Li-Ping Shang, Jiasui Zhan

Metapopulation structure generated by recurrent extinctions and recolonizations plays an important role in the evolution of species but is rarely considered in agricultural systems. In this study, generation and mechanism of metapopulation structure were investigated by microsatellite assaying 725 isolates ofAlternaria alternatasampled from potato hosts at 16 locations across China. We found a single major cluster, no isolate-geography associations and no bottlenecks in theA. alternataisolates, suggesting a metapopulation genetic structure of the pathogen. We also found weak isolation-by-distance, lower among than within cropping region population differentiation, concordant moving directions of potato products and net gene flow and the highest gene diversity in the region with the most potato imports. These results indicate that in addition to natural dispersal, human-mediated gene flow also contributes to the generation and dynamics of the metapopulation genetic structure ofA. alternatain China. Metapopulation structure increases the adaptive capacity of the plant pathogen as a result of enhanced genetic variation and reduced population fragmentation. Consequently, rigid quarantine regulations may be required to reduce population connectivity and the evolutionary potential ofA. alternataand other pathogens with a similar population dynamics for a sustainable plant disease management.