Carbon source dependent-anaerobic soil disinfestation (ASD) mitigates the sclerotial germination of Sclerotinia sclerotiorum

Though Sclerotinia sclerotiorum is a well-studied plant pathogen that causes significant economic damage worldwide, sustainable and environmental friendly control methods are difficult to establish due to it wide host range, cosmopolitan distribution and production of recalcitrant structures that can survive in soil for a long time. The pathogen was found causing a severe disease incidence on cabbage in 2016 in Sri Lanka. It was hypothesized that a) isolates of the recent disease outbreak display cross resistance to commonly applied fungicides and b) carbon (C) source supplemented Anaerobic Soil Disinfestation (ASD) is effective in mitigating the germination of sclerotia. In vitro fungicide sensitivity assays showed large variation in mycelial growth inhibition indicating high adaptability of the population towards environmental fluctuations and management practices. Signatures of cross resistance were evident. ASD was carried out using cabbage (Brassica oleracea) and leek (Allium ampeloprasum) cull piles, durian (Durio zibethinus) peels and grass cuttings (Axonopus compressus) as C sources and determined the sclerotial viability. Cabbage and leek cull piles at rates of 60–100 mg/g soil completely inhibited sclerotial germination. Maintaining anaerobic condition along with C source amendments was found to be a critical step in mitigating the sclerotial germination. GC-MS analysis of the volatiles of cabbage leaves, leeks and durian further confirmed the presence of various bioactive compounds with potential antifungal activity. Therefore, in addition to elevated microbial activity in treatments, the volatiles of C sources may have helped mitigating sclerotial germination.