Expression of Arabidopsis NPR1 in Transgenic Cotton Confers Resistance to Non‐defoliating Isolates of Verticillium dahliae but not the Defoliating Isolates

Verticillium wilt, caused by Verticillium dahliae Kleb., causes severe yield and quality losses in most cotton growing areas of the world. Only moderate resistance has been achieved by traditional breeding. Therefore, transgenic approaches offer a possible alternative to obtain resistance against this disease. Overexpression of a homologous or heterologous NPR1 gene has been effective in conferring broad-spectrum resistance to diverse pathogens in a variety of plants. We investigated the resistance of cotton plants, expressing the Arabidopsis NPR1 (ATNPR1) gene, to defoliating and non-defoliating pathotypes of V. dahliae. The transgenic cotton plants showed significant resistance against two non-defoliating V. dahliae isolates. Both visual symptoms and pathogen colonization were reduced, indicating that disease progression was curtailed in the AtNPR1-transformants. In contrast, the same transgenic lines showed little, if any, resistance to two defoliating isolates. The NPR1-mediated activation of cotton's defences apparently is not sufficient to counter the disease mechanism(s) utilized by the defoliating pathotype of V. dahliae.