48th TWC, Tob. Work. Conf., 2018, abstr. 40

Characterizing the adaption of Pytophthora nicotianae to partial resistance in tobacco

North Carolina State University, Raleigh NC USA

Phytophthora nicotianae causes tobacco black shank worldwide. The ability of P. nicotianae to rapidly overcome single-gene resistance was documented following the widespread deployment of the Php gene in tobacco cultivars in the 1990s. Increased levels of aggressiveness in P. nicotianae have been documented following exposure to tobacco varieties with high levels of partial resistance. In a previous study, isolates of P. nicotianae were adapted on multiple sources and levels of partial resistance by inoculating and reisolating isolates from a given resistance type and level for six consecutive host generations. A single isolate was obtained from each host after each generation of adaptation and these six isolates were characterized for their level of aggressiveness. Our objective in this study was to characterize the adaptation to partial resistance using phenotypic and molecular approaches. We used in vivo inoculum production and rate of lesion expansion to quantify the adaptation by P. nicotianae and found adapted isolates not only have higher infection rates and produce more sporangia, but also cause larger lesions on tobacco stems. The adapted isolates also were subjected to double digest restriction site associated DNA sequencing to identify genetic changes during adaptation. Understanding how P. nicotianae adapts to partial resistance in tobacco will inform better resistance deployment strategies and may increase the durability of partial resistance. (Reprinted with permission)