Negative impacts of Phytophthora nicotianae race 1 on highly resistant tobacco variety KT215LC in the greenhouse

Phytophthora nicotianae, a soilborne oomycete, causes one of the most economically devastating diseases of tobacco known as black shank. In the past several years, burley tobacco growers have reported declining yields. Phytophthora nicotianae has two important races (race 0 and 1) with race 1 currently being the predominant race in tobacco growing areas across the U.S. Black shank is managed through a combination of crop rotation, fungicides, and selection of resistant varieties. We hypothesize that P. nicotianae race 1 could be contributing to burley tobacco yield decline in race 1-resistant varieties despite remaining mostly asymptomatic in the presence of black shank. A greenhouse trial was established to evaluate growth parameters of the resistant variety ‘KT215LC’ which is fully resistant to race 0 (level 10/10 resistance) and highly resistant to race 1 (level 9/10 resistance). Hybrid 404LC, which is fully susceptible to races 0 and 1, was used as a check to ensure inoculum virulence. Race 1 reduced plant height, stem diameter, leaf length, leaf number, and leaf, stem, and root mass in ‘KT215LC’. These results suggest that P. nicotianae may be contributing to yield decline on varieties with high resistance to race 1. Knowledge gained from these results could help burley tobacco growers make more informed decisions when managing their tobacco crop to maximize their profits and reduce losses due to black shank.