Clarifying the Source of Black Shank Resistance in Flue-cured Tobacco

Abstract

Widespread use of resistance to race 0 of Phytophthora nicotianae in flue-cured tobacco (Nicotiana tabacum) has increased problems with race 1 in commercial fields. The RAPD marker UBC30, tightly linked to the Ph gene for resistance to race 0, was used to clarify the presence of the Ph gene in specific cultivars to enable farmers to more appropriately match cultivar resistance to the pathogen races predominating in their fields. The marker UBC30 was present in 20 of the 31 flue-cured tobacco cultivars tested, including CC 27, GL 350, NC 196, SP 220, SP 225, SP 227, and NC 810. These cultivars were previously thought to not possess the Ph gene. Presence of UBC30 was highly correlated (r = 0.93; P ≤ 0.001) with survival in fields infested primarily with race 0, and with greater survival in fields infested primarily with race 0 versus race 1 of the pathogen (r = 0.76; P ≤ 0.001). The likely presence of the Ph gene in so many currently grown flue-cured tobacco cultivars may limit farmers' ability to shift pathogen populations back to race 0 from race 1 via the recommended cultivar rotation strategy. Accepted for publication 27 February 2008. Published 18 June 2008.