Protein Preparations from Xanthomonas euvesicatoria Obtained Under Putative Hrp-Inducing Conditions Enhance Resistance Responses in Capsicum annuum Against Bacterial Spot

In plants, pathogen-associated molecular patterns (PAMPs) activate pattern-triggered immunity and can contribute to resistance against phytopathogenic infections. Identifying novel microbial elicitors is important for developing resistance-inducing strategies that reduce reliance on pesticides. This study evaluated BV801-derived protein preparations obtained from Xanthomonas euvesicatoria strain BV801 grown in host-associated media containing lyophilized Solanum lycopersicum or Capsicum annuum tissue. Six treatments were evaluated in C. annuum against bacterial spot caused by X. euvesicatoria (BSX) under in vitro conditions: SP-AWSL and SP-AWCA (obtained from BV801 grown in the host-associated AWSL and AWCA media), SP-NYGA and SP-M9 (obtained from BV801 grown in rich and minimal control media), and two commercial reference inducers, Actigard® 50 GS (acibenzolar-S-methyl) and Messenger Gold® (commercial harpin formulation). Plants were treated 48 h before pathogen inoculation. SDS-PAGE revealed protein bands in the 12–26 kDa range that were enriched in SP-AWSL and SP-AWCA relative to the control-media preparations. Several BV801-derived preparations produced localized necrosis in N. tabacum leaves consistent with a hypersensitive-response-like reaction. SP-AWSL and SP-AWCA reduced BSX severity in chili pepper by up to 67% compared with the diseased control (Kruskal–Wallis, p ≤ 0.05) and significantly reduced bacterial proliferation (Tukey, p ≤ 0.05). At the final sampling point, plants pretreated with BV801-derived protein preparations and subsequently challenged with X. euvesicatoria showed higher CaBPR1 expression than corresponding pretreated but unchallenged plants, a pattern consistent with a priming-like defense response. These findings support the potential of BV801-derived protein preparations obtained under putative Hrp-inducing conditions as candidates for sustainable resistance-inducing strategies against bacterial spot in chili pepper.