Culture Studies in the Genera Pleospora, Clathrospora, and Leptosphaeria

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Abstract
SUMMARY Isolations were attempted with ascospores from perithecia of 43 collections of species of Pleospora, Clathrospora, and Leptosphaeria. Three of 12 isolates which became established in culture (in addition to cultures of Pleospora infectoria received from another source) produced conidial stages in culture. These were Clathrospora diplospora, C. Elynae, and Leptosphaeria heterospora. Six other isolates of the 12 established in culture produced mature perithecia. These were Pleospora ambigua, P. njegusensis, P. trichostoma, Clathrospora diplospora, an isolate of a species identified as a “large-spored variety” of C. diplospora, and P. rainierensis. In no case was it observed that a conidial strain also produced perithecia or that a perithecial strain also produced a conidial stage in culture. The characters of the different isolates in culture were sufficiently distinct to permit the recognition of the individual species insofar as the isolates used were concerned. Identification of the conidial stages of Clathrospora diplospora, of C. Elynae, and of Leptosphaeria heterospora by means of commonly accepted descriptions necessitated their placement in the form-species Alternaria tenuis. Statistical analyses of conidial lengths observed in strains of Clathrospora diplospora, of C. Elynae, and of Leptosphaeria heterospora indicated that, under certain environmental conditions, the strains studied of each of the species could be differentiated from each of the other two. Nutrient differences in media upon which the Alternaria strains were grown resulted in a greater percentage of statistical differences in comparisons among the strains than did pH or age differences.