Bacterial biocontrol of diseases caused bySclerotiniain Australia

Abstract

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.