A Study of Certain Species of the Genus Sclerotinia

SUMMARY Investigations were carried out on Schrotinia serica, two strains of S. Sclerotiorum de Bary, five strains of S. Trifoliorum Eriks., two forms of S. minor Jagger, four isolations of a Sclerotinia from Vicia Faba considered to be a variety of Sclerotinia Trifoliorum, and a variant which arose from one of these isolations. Their pathogenicity to several different plants was tested and the fungi were found to fall into three groups: (1) S. Sclerotiorum and S. minor, (2) S. Trifoliorum and its variety Fabae, and (3) S. serica. A variant with light brown sclerotia which arose from S. Trifoliorum var. Fabae differed from the parent form in pathogenicity. Ascospores of S. Sclerotiorum, S. minor and S. Trifoliorum did not infect healthy leaves. The production of mycelium by sclerotia in the soil was not observed. S. serica differed from the other fungi in that it produced numerous apothecial stipes and several apothecia in test‐tube cultures. Exposing sclerotia to different conditions of temperature and moisture after their removal from culture and before their burial in damp sand did not hasten apothecial production. Sclerotia formed in cultures grown over a wide temperature range produced apothecia when subsequently buried in damp sand. Single‐spore lines of S. serica, S. Sclerotiorum, S. minor and S. Trifoliorum produced apothecia. Apothecial production took place over a wide temperature range. Apothecia of one form of S. minor arising from sclerotia formed on sterilized vegetables were larger than those from sclerotia formed on malt‐extract. The dimensions of the apothecia are given and a description of the apothecia of S. Sclerotiorum, S. minor, S. Trifoliorum and S. Trifoliorum var. Fabae. Measurements are given of asci and ascospores. The minimum, maximum and optimum temperatures fpr linear spread of mycelium are given: also the time taken by cultures to reach a diameter of 6 cm. at 207deg;C. The view is expressed that such data should not be used for differentiating species. S. serica spread more slowly than the other species. The variant of S. Trifoliorum var. Fabae had different temperature relations from the parent form. A brief description is given of the cultural appearance of S. Sclerotiorum, S. Trifoliorum, S. minor, S. Trifoliorum var. Fabae and its variant. The classification of the fungi is discussed.