Bio-Intensive Role of Endophytic Bacteria for the Management of Bacterial Leaf Spot of Grapevine

Bacterial leaf spot caused by Xanthomonas citri pv. viticola (Xcv) in India is of economic importance. The objective of the investigation was to isolate and characterize bacterial antagonists from different tissues of the grapevine. Fifty endophytes were isolated from the leaves, stems, and roots of 15 different varieties of grapevine. The primary identification of the isolates was done by microscopic and biochemical characterizations. These endophytes were promoting the growth of the plants through both direct and indirect mechanisms. They were capable of producing various plant growth-promoting traits, such as indole acetic acid and hydrolytic enzymes like cellulase, amylase, protease, and lipase. They were assessed for additional traits like phosphate solubilization, hydrogen cyanide production, and ammonia production. Further, these endophytes were screened for antagonistic activity against six X. citri pv. viticola isolated from different locations. Eleven out of 50 endophytic bacteria significantly inhibited Xcv, as evident from well-diffusion methods. Three isolates, that is, EB7, EB26, and EB45, manifested the highest inhibition and were further screened for antibacterial activity using the detached leaf assay. The results showed that all three isolates have the highest potential to inhibit the Xcv, causing bacterial leaf spot. The molecular identification on the basis of 16S rRNA sequencing of the isolates EB7, EB26, and EB45 revealed that they were Providencia vermicola, Bacillus australimaris, and Bacillus zhangzhouensis, respectively. B. australimaris and B. zhangzhouensis could be effectively used for the biological control of Xcv as they exhibited effective control in field trials.