Optimising the bioformulation of beneficial bacteria for biological control of Xanthomonas euvesicatoria in pepper

Abstract

Capsicum annuum L., commonly known as pepper, is a cultivated species within the Solanaceae family, and its fruit is of significant importance among the vegetables consumed globally. One of the primary phytopathological challenges facing pepper cultivation is bacterial spot disease, which is caused by Xanthomonas euvesicatoria. This study aimed to optimise the production and formulation of several definitively identified beneficial bacterial (BB) isolates that have demonstrated efficacy in biological control against the bacterial pathogen Xanthomonas euvesicatoria (Xe). To achieve the objectives of this research, the optimal ratios of various nitrogen and carbon sources were determined by identifying the optimum development time at which three beneficial bacterial isolates - Pantoea agglomerans KD80/2, Pantoea agglomerans KD84/3, and Pseudomonas putida KD91/1 - exhibited maximum viability. The shelf life of the BB isolates was monitored under different storage conditions for six months following freeze-drying. Both -80 degrees C deep freezing and -20 degrees C freezing conditions were identified as the most suitable for storage; however, there was a minimal difference in viability loss between these two conditions. The biocontrol efficacy against Xe on the capia pepper plant was evaluated under in vivo conditions. BB formulations were systematically applied in two distinct methods: seed coating and foliar application. In terms of disease suppression levels, in both in vivo trials, a dosage of 109 cfu ml-1 for P. putida KD91/1 was consistently among the most effective treatments in both seed and foliar applications.