Identification of a new Bacillus sonorensis strain KLBC GS-3 as a biocontrol agent for postharvest green mould in grapefruit

•Bacillus sonorensis KLBC GS-3 treatment was effective in controlling green mold.•The preventive treatment displayed higher efficacy than the curative treatment in vivo.•The strain KLBC GS-3 induced disease resistance on grapefruit fruit.•Application of strain KLBC GS-3 maintained the postharvest fruit quality. The strain Bacillus sonorensis KLBC GS-3 was isolated from grapefruit rhizosphere soil to assess its potential as a biocontrol agent. Its efficacy in the control of green mould caused by Penicillium digitatum in postharvest grapefruit, together with its underlying mechanism, was explored. Our findings indicated that treatment with B. sonorensis KLBC GS-3 could inhibit the growth of mycelia, as well as P. digitatum conidial germination in vitro. In addition, the incidence of green mould in grapefruit decreased after inoculation with P. digitatum, compared to the control fruit after 4 d incubation, under both preventive and curative treatments. The preventive treatment displayed a greater efficacy than the curative treatment at controlling the decay caused by green mould. B. sonorensis KLBC GS-3-treated grapefruit also displayed a significant activity of enzymes associated with disease resistance (polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase). Moreover, compared to control fruit, a higher ascorbic acid content, titratable acidity level, and the total amount of soluble solids were maintained in fruit treated with B. sonorensis KLBC GS-3. Therefore, it was concluded that B. sonorensis KLBC GS-3 is a highly suitable biocontrol agent for the prolongation of postharvest grapefruit shelf-life.