Screening of effective biocontrol agents against postharvest litchi downy blight caused by Peronophythora litchii

Biocontrol agents (BCAs) could be used for the control of postharvest decay of fruit. In this study, biocontrol bacteria were isolated from litchi soil, leaves and fruit tissues, and their efficacy on the control of postharvest litchi downy blight, caused by Peronophythora litchii, were determined. After evaluating the ability of 188 bacterial isolates to produce certain enzymes and metabolites, and their antagonistic activity in vitro against P. litchii, as well as preliminary identification of 82 representative isolates based on 16 S rDNA sequencing, five isolates including Bacillus amyloliquefaciens PP19 and LI24, Exiguobacterium acetylicum SI17, B. pumilus PI26, and B. licheniformis HS10 were selected for further assessments in several trials in 2016 and 2017. In comparison with control treatment, isolates PP19, SI17 and PI26 could delay the disease development of postharvest litchi downy blight. Furthermore, isolates PP19 and SI17 were able to colonize fruit pericarp without affecting fruit quality. Additionally, the colonization of PP19 changed the microbial community composition on litchi pericarp as demonstrated by pericarp microbiome sequencing. This is the first report of an E. acetylicum acted as a BCA against a phytopathogenic oomycete P. litchii. We conclude that PP19 and SI17 can be used as effective BCAs against postharvest litchi downy blight, especially applied during preharvest stage.