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To be host or not to be: the role of asymptomatic hosts in the management of Verticillium wilt of potato

Laura Bautista-Jalon: The Pennsylvania State University

<div>Sustainable management of Verticillium wilt of potato is challenged by <em>Verticillium dahliae</em> (<em>Vd</em>) broad host range and long-term persistence in soil, and the lack of host resistance. Crop rotations are essential for disease management but they do not always render the expected results due to the ability of <em>Vd</em> to infect weeds and rotational crops as an endophyte. Our goal was to assess the genetic structure of <em>Vd</em> populations infecting symptomatic and asymptomatic host plants recovered from potato fields affected by Verticillium wilt in the US and Israel. Our hypothesis was that populations that infect hosts as endophytes may represent lineages that are genetically distinct from those pathogenic to potato. A phylogeny inferred from 26,934 SNPs among 144<em> Vd</em> isolates displayed a highly clonal structure correlated with VCGs, and isolates grouped in lineages 2A, 2B<sup>824</sup>, 4A and 4B. Lineage 4A, highly virulent to potato, was found only among US isolates from symptomatic potato. Isolates from asymptomatic hosts grouped mainly within lineage 4B and were not genetically differentiated by host. Phylogeny of 4B revealed a higher diversity in the US compared to Israel and coalescent analysis from 174 SNPs showed a divergent genealogy based on geographic origin indicating a single introduction of this lineage in Israel. We conclude that asymptomatic secondary hosts can serve as reservoirs to maintain <em>Vd</em> populations of lineage 4B, which are pathogenic to many cultivated hosts.</div>