Heterothallism in Chætomium

DURING the course of an investigation of the fungus flora of seed oats being carried out by Malone 1 , evidence was obtained which suggested that Chætomium elatum Kunze and Schmidt might be heterothallic in spite of the fact that Marchal and Marchal 2 and Ames 3 had reported fruiting from single ascospore cultures of this species. To investigate this point, eight single ascospore isolations obtained from a perithecium produced on an oat seed were grown on a wide range of media, where they failed to produce fertile perithecia although perithecial primordia were formed abundantly. Fertile perithecia were obtained, however, in some cases when these isolates were plated in pairs in all combinations and the isolates were therefore numbered 1–8 with 1 arbitrarily designated as (+). Of the eight strains, 1, 5 and 6 were (+) and fruiting occurred when these were plated with the (−) strains 2, 3, 4, 7 and 8. A further 114 single ascospore isolations were made and cultured in quadruplicate against the original 1 (+) and 2 (−) strains. Of these, 63 fruited in contact with a (−) strain and 51 with a (+) strain, thus giving totals of 66 (+) and 56 (−) for the 122 isolates used. Control cultures of all isolations produced only perithecial primordia.