APS Homepage

Poster: Biology & Disease Mgmt: Chemical Control


Production of Phytophthora nicotianae isolates resistant to oxathiapiprolin
R. BITTNER (1), A. Mila (1) (1) North Carolina State University, U.S.A.

Black shank, caused by Phytophthora nicotianae (Pn), is a devastating disease of tobacco throughout the world. Oxathiapiprolin (OXA), a newly discovered fungicide, has shown efficacy against numerous oomycetes including Pn, but the potential for OXA resistance is unknown. The generation of resistance to OXA was attempted using UV light mutagenesis and mycelial adaptation with four Pn isolates. UV mutagenesis generated two isolates (EdgeB7-M1 and YadA28-M1) with mycelial resistance to OXA. Sporangia production of both UV mutants also showed increased insensitivity to OXA. Resistance produced by UV mutagenesis was stable after five consecutive transfers on non-amended medium. In greenhouse studies, EdgeB7-M1 remained pathogenic to tobacco, while YadA28-M1 was nonpathogenic. For mycelial adaptation, 48 colonies, twelve replicates from each of the four isolates, were transferred fifteen times on OXA medium. After the 15th transfer, twelve colonies from the initial 48 had a significant increase in mycelial insensitivity to OXA, compared to the wild-type isolates. Increased insensitivity from mycelial adaptation was not stable. Sixty-six percent of the isolates lost their insensitivity after fifteen successive transfers on a non-amended medium. Of the twelve adapted isolates, one remained pathogenic on tobacco. Our results show that the generation of OXA resistant Pn isolates is possible; however resistance may be associated with fitness penalties.