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Characterizing the adaptation of Phytophthora nicotianae to partial resistance in tobacco

Jing Jin: North Carolina State University

<div><em>Phytophthora nicotianae</em> causes tobacco black shank worldwide. The ability of <em>P. nicotianae</em> to rapidly overcome single-gene resistance was documented following the widespread deployment of the <em>Php</em> gene in tobacco cultivars in the 1990s. Increased levels of aggressiveness in <em>P. nicotianae</em> have been observed following exposure to tobacco varieties with high levels of partial resistance. Our objective in this study was to characterize the adaptation of <em>P. nicotianae</em> to partial resistance in tobacco using phenotypic and molecular approaches. We used <em>in vivo</em> inoculum production and rate of lesion expansion to quantify the adaptation by <em>P. nicotianae</em> and found adapted isolates not only have higher infection rates and produce more sporangia than non-adapted isolates, but also cause larger lesions on tobacco stems. The adapted isolates also were subjected to double digest restriction-site associated DNA sequencing (ddRADseq) to identify genetic changes during adaptation. No changes in population structure could be attributed to adaptation on multiple tobacco genotypes; however, to our surprise, isolates showed extremely high diversity given <em>P. nicotianae</em> was predominately undergoing asexual reproduction during adaptation. Understanding how <em>P. nicotianae</em> adapts to partial resistance in tobacco will inform better resistance deployment strategies and may increase the durability of partial resistance.</div>