Investigating the resistance responses to Alternaria brassicicola in 'Korla' fragrant pear fruit induced by a biocontrol strain Bacillus subtilis Y2

Bacillus, as important biocontrol microbes, have been proposed to be eco-friendly and effective candidates to reduce the occurrence of fruit postharvest diseases. In this study, the inductive disease resistance response of pear fruit primed by Bacillus subtilis Y2, which can suppress black spot disease of ‘Korla’ fragrant pear fruit caused by the fungal pathogen Alternaria brassicicola, was investigated. Comparative transcriptome analysis revealed that 216 genes were up-regulated and 91 genes were down-regulated upon treatment with B. subtilis Y2, and the five most enriched pathways associating with the differentially expressed genes were related to flavonoid biosynthesis; antenna protein production; cutin, suberine, and wax biosynthesis; carotenoid biosynthesis; and plant-pathogen interactions. The increased flavonoid content, the enhanced antioxidant enzyme activities, including peroxidase, catalase, and superoxide dismutase, the higher cuticular wax content, and the changes in the micro-morphology of epicuticular wax were further investigated as the induced resistance response of pear fruit by B. subtilis Y2. These results provide new insights into the biocontrol mechanism of antagonistic B. subtilis Y2 in ‘Korla’ fragrant pears against A. brassicicola.