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POSTERS: Pathogenicity and host specificity

Fitness cost associated with increased aggressiveness of Phytophthora nicotianae on a tobacco genotype with WZ resistance
Jing Jin - North Carolina State University. David Shew- North Carolina State University

Phytophthora nicotianae causes tobacco black shank worldwide. The ability of P. nicotianae to rapidly overcome single-gene resistance was documented following deployment of the Php gene in the 1990s. Increased aggressiveness in P. nicotianae has been observed following exposure to tobacco varieties with varying levels of partial resistance. The WZ genomic region from Nicotiana rustica has been demonstrated to confer a very high level of resistance to P. nicotianae. However, a greenhouse study showed P. nicotianae was able to adapt to WZ resistance within several host generations. Our objective in this study was to investigate the fitness cost of this increased aggressiveness of P. nicotianae on the tobacco genotype K326WZ that has the WZ resistance. We selected an isolate of P. nicotianae adapted on K326WZ for 6 generations and then maintained it on either K326WZ or Hicks (a susceptible cultivar) for an additional six host generations. Hicks-exposed isolates exhibited a decreased aggressiveness on K326WZ comparing to K326WZ-exposed isolates, indicating a fitness cost associated with aggressiveness on tobacco genotype K326WZ. This observation could aid researchers in optimizing resistance deployment strategies, thus increasing the durability of different sources of partial resistance to tobacco black shank.