Dr. Kenneth Wells of the University of California at Davis is studying fungi of the group Heterobasidiomycetes, primarily wood-decaying fungi found in temperate regions of North America and western Europe. The fruiting bodies, or basidiocarps, have traditionally been used as the sole basis for the classification of these species, especially microscopic characters of the sexual reproductive structures. Dr. Wells and others have shown over the past ten years that basidiocarp morphology does not accurately reflect genetic differences between species. Gene differences at several loci, termed mating-type loci and sterility/fertility loci, are more important in determining whether strains can cross and form viable progeny. Interbreeding groups in turn form discrete species, usually with distinct habitat preferences. Not all interbreeding populations are sharply defined, however. Isolates from some populations are only partially interfertile with other populations. Careful laboratory studies of the genetic controls of such partial fertility will help determine how genetic and environmental factors interact to limit sexual reproduction in these fungi. Comparative morphological data generated by microscopy, results of pairing tests, and isozyme analyses of proteins are being used to examine species of Exidia, Tremella, Exidiopsis, and Auricularia and to begin to assess the amount of genetic variability in natural populations of these saprophytes.
