Diversity of cultivable endophytic bacteria in mulberry and their potential for antimicrobial and plant growth-promoting activities

Endophytic bacteria-based biocontrol is regarded as a potential plant disease management strategy. Present study analyzed the diversity of mulberry endophytic bacteria basing on a culture-dependent approach and further evaluated their antimicrobial and plant growth-promoting (PGP) activities. A total of 608 cultivable endophytic bacteria, belonging to 4 phyla and 36 genera, were isolated from four mulberry cultivars having different resistance to sclerotiniosis in three seasons. Taxonomic compositional analysis results showed that Proteobacteria, Firmicutes, and Actinobacteria were the three dominant bacterial phyla in all communities, with the representative genera Pantoea, Bacillus, Pseudomonas, Curtobacterium, and Sphingomonas. Diversity analysis results indicated that the diversity of winter community was higher than that of spring or autumn, and higher diversities were detected in the resistant cultivar communities compared with the susceptible cultivar. Antagonism assays results showed that 33 isolates exhibited strong and stable activity against three phytopathogens which are Sclerotinia sclerotiorum, Botrytis cinerea, and Colletotrichum gloeosporioide. Eight endophytic bacteria were selected out from 33 antagonists based on the evaluation of antagonistic and PGP activities. Furthermore, pot experiment results revealed that all the 8 tested endophytes stimulated the growth of mulberry seedlings at different levels, and Bacillus sp. CW16-5 exhibited the highest promotion capacity, which the shoot length and the root fresh weight were increased by 83.37% and 217.70%, respectively. Altogether, present study revealed that mulberry harbors a large amount of diverse cultivable endophytic bacteria and they also serve as novel sources of beneficial bacteria and bioactive metabolites.