Biological control of Sclerotinia pseudotuberosa and other fungi during moist storage of Quercus robur seeds

The fungal pathogen Sclerotinia pseudotuberosa is a major cause of deterioration during storage of Quercus robur seeds (acorns) and along with other, mainly saprotrophic fungi, contributes to the decline of viability and vigour in the acorn population. Hot-water thermotherapy (HWT; 41 degreesC for 2.5 h) killed the fungal pathogen S. pseudotuberosa and prolonged the storage life of acorns. The addition of the systemic fungicide benomyl to the HWT and/or the broad-spectrum fungicide thiram as a seed dressing further enhanced the storage life of acorns. Three fungal antagonists, Coniothyrium minitans, Trichoderma sp. (KW3) and Trichoderma virens (G20), were also applied as a film-coating to acorns using a polyvinyl acetate sticker achieving ca. 10(7)-10(8) viable conidia per acorn. The biological treatments provided protection against infection and the spread of infection of S. pseudotuberosa and other fungi on the acorns during storage over several months. All treated and stored acorns grew normally following sowing in seedbeds. The Trichoderma species were more effective than C. minitans, with T virens being the most effective. T virens reduced pathogen spread from acorns infected with S. pseudotuberosa to 'clean' acorns when T virens coated infected and 'clean' acorns were mixed together. However, T virens was less effective than HWT at preventing the proliferation of this pathogen within individual acorns that were infected before coating. A combination of HWT and subsequent coating with T virens provided a more effective control against both S. pseudotuberosa and saprotrophic fungi than when either treatment was applied alone.