Novel sources of disease resistance in pepper against bacterial spot pathogen, Xanthomonas gardneri
N. POTNIS (1), P. Wechter (1) (1) USDA-ARS, U.S.A.

Significant outbreaks of bacterial spot on tomato and pepper in the Midwest USA have led to major economic losses for growers and producers. Of the four species responsible for bacterial spot, Xanthomonas gardneri has been found to be responsible for these outbreaks. X. gardneri is notorious for its aggressiveness. A characteristic symptom of X. gardneri is a star-shaped fruit, which leads to an unmarketable product. We verified X. gardneri as a causal agent of these outbreaks by characterizing pure cultures of isolates using 16S rRNA sequencing, a greenhouse pathogenicity assay, and repetitive element-polymerase chain reaction (Rep-PCR) using the BOX-A1R primer. Our goal is to develop marker assisted and genome wide selection strategies to generate bacterial spot resistant varieties using the knowledge of pathogen diversity. Although our strain characterization revealed a monomorphic pathogen population, the strains differed in the extent of virulence on susceptible pepper cv. Early California Wonder, with the more aggressive strains causing extensive watersoaking and necrosis accompanied by defoliation. The most aggressive strain was then chosen to screen core pepper germplasm available from the Plant Genetic Resources Conservation Unit. Phenotypic evaluation including leaf symptoms, overall disease and defoliation scores identified several Plant Introductions as resistant to X. gardneri. PCR screening using markers for classically defined resistance loci indicated presence of novel sources of resistance against X. gardneri.

Abstract Number: P17-588
Session Type: Poster