Bacterial biocontrol of diseases caused by Sclerotinia

Among the diseases caused by Sclerotinia in Australia, lettuce drop, caused by the fungal pathogens Sclerotinia minor and Sclerotinia sclerotiorum, was considered as a model in this study as it poses a major threat to lettuce production in Australia. The management of this disease with synthetic fungicides is strategic and the presence of fungicide residues in the consumable parts of lettuce is a continuing concern to human health. To address this challenge, Bacillus cereus SC-1 was chosen from a previous study, for biological control of S. sclerotiorum induced lettuce drop. Soil drenching with B. cereus SC-1 applied at 1×108 cfu mL-1 in a glasshouse trial completely restricted the pathogen, and no disease incidence was observed (P=0.05). Sclerotial colonization was tested and it was found that 6-8 log cfu per sclerotium of B.cereus resulted in a reduction of sclerotial viability to 1.58% compared to the control(P=0.05). Volatile organic compounds (VOC) produced by the bacteria increased root length, shoot length, and seedling fresh weight of the lettuce seedlings by 46.6, 35.4,and 32% respectively when compared with the control (P=0.05). In addition to VOC induced growth promotion, B. cereus SC-1 enhanced lettuce growth, resulting in increased root length, shoot length, head weight, and biomass weight by 34.8, 21.5,19.4, and 24.8%, respectively when compared with untreated control plants (P=0.05).The bacteria were able to survive in the rhizosphere of lettuce plants for up to 30 days reaching populations of 7 log cfu g-1 of root-adhering soil. These results indicate that biological control of lettuce drop with B. cereus SC-1 could be feasible when used either alone or integrated into IPM and best management practice programs for sustainable management of lettuce drop and other Sclerotinia diseases.