Suppression of Sclerotinia sclerotiorum apothecial formation by the soil bacterium Serratia plymuthica: identification of a chlorinated macrolide as one of the causal agents

Abstract

A selection of soil bacteria was screened for their ability to interfere with carpogenic germination of Sclerotinia sclerotiorum. Nine out of 300 bacterial isolates were found to significantly suppress apothecial formation. One of these isolates, identified as a strain of Serratia plymuthica, was highly effective in inducing complete suppression of apothecial formation at high concentrations, and also strongly inhibited the germination of ascospores as well as hyphal growth of S. sclerotiorum. A bioassay-guided purification procedure starting with the cell-free supernatant of the bacterial culture led to the identification of a chlorinated macrolide as an active compound able to induce the observed inhibition. Spectroscopic data showed the compound to be identical to haterumalide A. The data presented show the ability of this compound to inhibit apothecial formation and ascospore germination. Other possible mechanisms involved in inhibition of apothecial formation and mycelial and hyphal growth of S. sclerotiorum by the same isolate are discussed. The relevance of our observations to natural systems will be the subject of further research.