Characterisation of systemic resistance in sugar beet elicited by a non-pathogenic, phyllosphere-colonizing Bacillus mycoides, biological control agent

Bacillus mycoides isolate Bac J, a non-pathogenic, phyllosphere-inhabiting bacterium, reduces Cercospora leaf spot (Cercospora beticola Sacc.) of sugar beet by 38-91 % in both glasshouse and field experiments. Disease control is attributed to the bacterium's ability to induce systemic resistance, which was demonstrated through classical induced resistance challenge experiments, western analysis and enzyme activity assays. Enzyme assays following B. mycoides and acibenzolar-S-methyl treatment demonstrated increased activity of chitinase, beta-1,3-glucanase, and peroxidase, all pathogenesis-related proteins and accepted indicators of systemic resistance. Western analysis detected numerous chitinase isoforms in B. mycoides and acibenzolar-S-methyl-treated plants that were not detected in the water controls. The active chitinase isoforms were identified using in-gel activity assays. beta-1,3-glucanase activity assays following native polyacrylamide gel electrophoresis revealed two unique isoforms produced following B. mycoides treatment, one of which was also found with acibenzolar-S-methyl treatment. The increase in peroxidase specific activity following acibenzolar-S-methyl and B. mycoides treatment was due to production of two unique isoforms not found in the water-treated plants as shown by activity assays following native polyacrylamide gel electrophoresis. (C) 2003 Elsevier Science Ltd. All rights reserved.