Role of Blossom Colonization in Pepper Seed Infestation by Xanthomonas euvesicatoria

Abstract

Colonization of Xanthomonas euvesicatoria was investigated in pepper blossoms and the relationship between inoculum concentrations and seed infestation was determined. Inoculation of blossoms resulted in asymptomatic pepper fruit. However, real-time polymerase chain reaction detected X. euvesicatoria in 39% of the seed lots assayed and viable colonies were recovered from 35% of them. Successful transmission occurred in 16% of the seed lots tested. In a separate experiment, X. euvesicatoria reached populations of up to 1 × 105 CFU/blossom on stigmas 96 h after inoculation. Bacteria colonized stylar and ovary tissues with populations ranging from 1 × 105 to 1 × 106 CFU/blossom 96 h after inoculation. A positive correlation existed between inoculum concentration and percentage of infested seedlots. Blossoms inoculated with Acidovorax citrulli also resulted in infested pepper seedlots. Furthermore, A. citrulli colonized pepper blossoms significantly better than X. euvesicatoria by 96 h postinoculation. It was concluded that pepper blossoms can be a potential site of ingress for X. euvesicatoria into seed, and blossom colonization may be involved in pepper seed infestation. Data also indicated that seed infestation via blossoms may be nonspecific because nonhost plants can be colonized by incompatible pathogens. Thus, host–pathogen interactions may not be important for bacterial ingress through blossoms.