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 × 10(5) CFU/blossom on stigmas 96 h after inoculation. Bacteria colonized stylar and ovary tissues with populations ranging from 1 × 10(5) to 1 × 10(6) 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.

Interactions of Seedborne Bacterial Pathogens with Host and Non-Host Plants in Relation to Seed Infestation and Seedling Transmission

“…Bacterial colonization of the flower (in particular stigma and style) is one of the most critical steps in seed infestation through the floral pathway [9], [11], [45]. In the present study, successful seed infestation was achieved by inoculating host/non-host flowers with 1×10 6 CFU.…”

“…Symptomatic seedling transmission of pathogens from infested seeds with compatible interactions has been observed for many phytobacterial pathosystem [5], [9], [10], [11], [20], [28], [45]. In addition, asymptomatic transmission of pathogens as epiphytes on a compatible host has been reported earlier [7], [8].…”

“…Previous reports of flower colonization of A. citrulli , X. campestris pv. campestris and X. euvesicatoria on watermelon, cauliflower and pepper, respectively showed that populations of these bacterial species can reach up to 1×10 5 to 1×10 8 CFU/flower by 96 hpi, when inoculated with 1×10 2 CFU/flower without inciting disease symptoms [9], [11], [45]. In the present study, despite populations of all bacterial species on host/non-flowers reaching a level of ≥1×10 4 CFU/flower within 96 hpi, disease symptoms or hypersensitivity reactions were never observed on developing fruits.…”

“…In addition, the authors clearly demonstrated that the flowers of a non-host plant can result in infested seeds upon inoculation with an incompatible pathogen [7]. Recently, it was observed that A. citrulli can also efficiently colonize pepper flowers and could result in infestation of pepper seeds [11]. However, the transmission of A. citrulli in pepper seedlings was not evaluated as in the above study.…”

Impact of bacterial spot outbreaks on the phytosanitary quality of tomato and pepper seeds

“…The latter is particularly aggressive against pepper (Ignjatov et al ., ). These bacteria are spread through contaminated/infected seeds as the primary source of inoculum (Dutta et al ., ) and are listed as quarantine organisms by the European Plant Protection Organization (EPPO). These pathogens can survive in seeds for extended periods (Bashan et al ., ); such survival ability allows long‐distance dissemination and facilitates their introduction into pathogen‐free areas through seed trade.…”