GENETICS OF SORDARIA FIMICOLA. III. CROSS‐COMPATIBILITY AMONG SELF‐FERTILE AND SELF‐STERILE CULTURES

Abstract

Carr, A. J. H. (Univ. Coll. Wales, Aberystwyth), and Lindsay S. Olive. Genetics of Sordaria fimicola. III. Cross compatibility among self‐fertile and self‐sterile cultures. Amer. Jour. Bot. 46(2) : 81‐91. Illis. 1959.—Cross‐compatibility in Sordaria fimicola is shown to be dependent upon a number of factors controlling the sexual process, from hyphal anastomosis and nuclear migration on through to perithecial formation and nuclear compatibility. Fertile cultures which were incompatible through inability to anastomose were induced to cross by the use of a third culture which would anastomose with both. Certain spontaneous or irradiation‐produced sterility mutants were found to be compatible if the sterility genes were at different loci, through complementation by the wild‐type alleles. In some pairings, cross‐karyogamy was preferential, and in one case, only hybrid perithecia were produced. Fully fertile recombinants segregated from these crosses in frequencies which indicated that the sterility loci were unlinked. Certain sterility genes were found to influence hyphal anastomosis, nuclear migration, and the development of fertile sector heterokaryons from the zone of anastomosis. Mutant factors at two loci in a U.V. mutant causing self‐sterility were found also to be responsible for lethality in ascospore germination. Factors in one sterility mutant controlled the production of a sterility‐inducing substance which diffused into the medium. In some crosses, complementation of two sterile cultures towards fertility is shown to require a balanced nuclear ratio. Factors are described which increase the inhibitory effect of one sterility gene, while another factor was found to suppress its effect and thereby make the culture self‐fertile. It is concluded that, since there is recombination between the sterility loci, these results do not represent the derivation of balanced heterothallism from a normally homothallic system, although it may lead by evolutionary progression to such a life cycle. The possible physiologic action of the sterility genes is discussed.