Establishment of an Efficient Screening Method for Resistant Cultivar of Chili Pepper to Bacterial Spot Caused by Xanthomonas euvesicatoria

Abstract

Bacterial spot caused by Xanthomonas euvesicatoria is one of the most economically important diseases affecting chili pepper production worldwide. This study was conducted to establish a reliable screening method for evaluating resistance of chili pepper to bacterial spot. Seven isolates of X. euvesicatoria were characterized for race and virulence. One isolate belonged to race 1, whereas three isolates each belonged to races 7 and 8. KACC 11165 exhibited the highest virulence, followed by KACC 11164, KACC 11154, and XCV1523. Based on its disease response on susceptible and resistant cultivars, KACC 11164 was selected to develop the screening method. The effects of seedling growth stage, inoculum concentration, and post-inoculation incubation temperature on disease development were evaluated using three pepper cultivars differing in resistance. The optimal screening conditions consisted of inoculating 30-day-old seedlings at the fully expanded four-leaf stage with a bacterial suspension of KACC 11164 (1×108 CFU/ml), followed by incubation at 30°C under saturated humidity for 48 hr and subsequent growth at 25°C. Using this protocol, 147 commercial chili pepper cultivars were evaluated, of which five were resistant, 86 moderately resistant, and 56 susceptible cultivars to bacterial spot. The screening method established in this study provides a reliable and reproducible tool for resistance evaluation in chili pepper breeding programs.