Relationship among Lepista species determined by CAPS and RAPD.

To determine the relationship of Australian members of the genus Lepista with those from other parts of the world, genetic variation of isolates representing 27 accessions was assayed by cleaved amplified polymorphic sequences (CAPS) and random amplified polymorphic DNA (RAPD). CAPS and RAPD identified eight and seven groups, respectively. CAPS Groups 1 and 2 and RAPD Group 1 consisted of French and Australian accessions classified as morphospecies L. nuda. CAPS Group 3 and RAPD Groups 2 and 2A consisted of mostly Australian isolates identified as L. sordida var. sordida or L. sordida var. umbonata. Isolates earlier identified as morphospecies L. sp. were also placed in CAPS Group 3 and RAPD Group 2A indicating that these isolates are L. sordida var. sordida. In addition, three smaller groups were distinguished. A French isolate of L. sordida var. sordida was placed in distinctly separate CAPS and RAPD groups to Australian L. sordida var. sordida Groups 4,4 respectively. A French isolate of L. sordida var. aianthina was placed in CAPS and RAPD Groups 3,3. An accession of L. saeva was placed in CAPS Group 6 and RAPD Group 5, separate from other isolates. RAPD Groups 6 and 7 consist, respectively, of Greek and American accessions of L. nuda that were only distantly related to the Australian and French accessions of this morphospecies: CAPS also separated these isolates from each other and from all other isolates. The data suggest that the classification of morphospecies and varieties within Lepista cannot be determined on the basis of morphology alone. The Greek and American accessions of L. nuda are separated from the French and Australian accessions and may not be L. nuda. Similarly, the Australian accessions currently classified as L. sordida var. sordida together with the accessions of L. sordida var. umbonata are distinct from the French accessions of L. sordida var. sordida suggesting that Australian isolates may represent a new species or variety. Further studies using a combination of morphological and genetic characterization are required to provide a more accurate understanding of Lepista species.

A novel homothallic variety of Agaricus bisporus comprises rare tetrasporic isolates from Europe.

Among 400 wild specimens of A. bisporus collected in Europe, only three were tetrasporic. In the case of two of them from France, a previous study showed that one was homokaryotic and hypothetically belonged to a homothallic entity while the other was heterokaryotic and possibly resulted from hybridization between a member of this entity and a classical bisporic strain. A third tetrasporic specimen recently was discovered in Greece. Morphological and genetic comparisons, using alloenzymatic markers, molecular markers and ITS polymorphisms, reveal that this third specimen is homokaryotic and belongs, with the homokaryotic specimen from France, to the same entity. Dissimilarity analysis confirms the hybrid origin of the heterokaryotic specimen. Varietal status is proposed for this homothallic, highly homogeneous entity, and A. bisporus var. eurotetrasporus is described. This novel variety clearly differs from var. bisporus by its tetrasporic basidia and from var. burnettii by its longer spores. It has a complex story because it can interbreed with var. bisporus and shares the same habitat; however, because of its homothallic life cycle and its partial intersterility, it is probably in the process of speciation.

Fine-scale genetic analyses reveal unexpected spatial-temporal heterogeneity in two natural populations of the commercial mushroom Agaricus bisporus.

This study examined the fine-scale genetic variation of the commercial mushroom, Agaricus bisporus, over 2 years at two sites in France. One site was a meadow fertilized with horse manure and disturbed regularly by humans; the other was a Monterey cypress forest free of human disturbance. Altogether, 50 mushrooms were collected and analysed for mitochondrial and nuclear genetic variation marked by RFLPs and multilocus enzyme electrophoretic polymorphisms. Population samples from these two sites were genetically different and both sites contained high levels of genetic diversity. No identical genotypes were found at either site between the 2 years and there was little evidence for extensive vegetative clonality for this species. Contrary to expectations, very limited evidence of pseudohomothallic reproduction was found. Results from tests of Hardy-Weinberg equilibrium and genotypic equilibrium showed that outcrossing and recombination have played significant roles in both populations. The results demonstrated spatial-temporal genetic heterogeneity of A. bisporus in natural populations.