Interactions between Sclerotinia sclerotiorum and other fungi on the phylloplane of lettuce

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Abstract
Selected fungi recovered from the phylloplane of lettuce were assayed, using in vitro and in vivo techniques, to determine their effectiveness as antagonists of ascospores of the lettuce drop pathogen, Sclerotinia sclerotiorum. On leaf discs, Trichoderma viride, Alternaria alternata, and Epicoccum purpurascens significantly reduced ascospore germ-tube elongation by 34.2, 60.6, and 38.3%, respectively. On whole plants, these three fungi significantly reduced infection by 40-93.3%. Isolates of Cladosporium cladosporioides and a red yeast inhibited ascospore elongation significantly in the in vitro leaf disc assay but failed to provide significant protection against infection by S. sclerotiorum in the in vivo whole-plant assay. Observations with the scanning electron microscope indicated that hyphae of T. viride and A. alternata came into close contact with ascospores on the leaf surface, suggesting parasitic relationships. Hyphae of E. purpurascens did not come into direct contact with ascospores and inhibtion may have been due to production of antifungal compounds.