Biocontrol potential of two deep-sea microorganisms against gray blight disease of tea

Background Gray blight is among the most destructive diseases that affect tea plants worldwide. In this study, microorganisms from deep-sea sediment samples for those with antagonistic effects were screened against gray blight caused by Pestalotiopsis theae . Results Thirty-two and twenty-eight morphologically different deep-sea bacteria and fungi were isolated, respectively. Isolates B5 and A65 clearly inhibited the pathogens in vitro and were prepared as wettable agent powders for evaluation in micro-plot field trials. Foliar application of the 48-h culture of B5 (1 × 10 8 , 2 × 10 7 , 1 × 10 7 colony-forming units (CFU)/ml) significantly reduced the incidence of gray blight disease. Compared to the untreated control, spraying with B5 inhibited gray blight disease by 78.57%. Isolate B5 was identified as Bacillus subtilis B5 in morphological and 16S rDNA sequence analyses. The foliar application of 7-day cultures of A65 (1 × 10 8 , 2 × 10 7 , 1 × 10 7 CFU/ml) significantly reduced the incidence of gray blight disease. A65 (10 8 CFU/ml) inhibited gray blight disease by 75.46% and was identified as Paecilomyces lilacinus A65 in morphologically and internally transcribed spacer sequence analyses. Conclusions These candidate microbial pesticides may inhibit gray wilt in tea, replace chemical pesticides’ use without causing environmental pollution, and promote the development of green agriculture.