GENETIC-STRUCTURE OF A NATURAL-POPULATION OF THE ECTOMYCORRHIZAL FUNGUS SUILLUS PUNGENS

Sequence-based markers were developed to study the genetic structure a nd reproductive biology of the ectomycorrhizal fungus Suillus pungens Thiers & Smith in a Bishop pine (Pinus muricata D. Don) forest. Six di fferent basidiome genotypes were found in a 1200 m(2) area. Five of th e six genotypes were represented by single basidiomes. The remaining g enotype comprised 13 basidiomes and covered an area of at least 300 m( 2), with maximum measured dimensions of 40 m and 14 m. This is the lar gest genet of an ectomycorrhizal fungus described to date, and is like ly the result of vegetative growth, because analysis of single spore i solates eliminates the possibility of genetic identity resulting from either apomixis or fortuitously indistinguishable recombinant genotype s. Genetic analysis also shows that although out-crossing appears to p redominate in the population, at least a low percentage (1.4%) of spor es are secondarily homothallic. The combination of extensive vegetativ e growth and abundant fruiting suggests S. pungens utilizes more carbo n than might be expected for a species which accounts for < 3% of the total ectomycorrhizal abundance at the site. Additional carbon might c ome from either more efficient host-fungus transfer, pooling of carbon from the roots of different host plants, or saprophytism.