Below is a brief description of the research we are working on to answer questions related to Armillaria's great longevity and ecological versatility.

     Species of Armillaria are economically important white-rot fungi that attack woody plants in many of the world's boreal and temperate forests (Kile et al., 1991). Armillaria spp. are unique among higher fungi in that they have a diploid vegetative stage that is the persistent stage found in nature (Guillaumin et al.,1991). The fruiting stage (mushroom) forms from the vegetative stage that grows beneath the soil surface. 

     We have collected Armillaria gallica in Bridgewater, MA and Raynham, MA for over twenty years. We have found that the fruiting stage of A. gallica's life cycle is a genetic mosaic in that cells of the mushroom stipe differ genetically from one another (Peabody et al., 2000). The presence of genetic mosaicism in the mushroom means that, unlike most sexually reproducing organisms, A. gallica has a life cycle that includes two diploidizations and two haploidizations. The first diploidization/haploidization precedes mushroom formation. The second diploidization/haploidization takes places in cells (basidia) that line gills under the mushroom cap. Based on this work, the primary objective of our research is to investigate the hypothesis that:

Because of genetic mosaicism, both mushroom stipe cells and spores are genetically more variable than they would be without it; and that among-cell genetic variation produced by mosaicism increases the probability that both stipe cells and spores will survive and spread vegetatively within forest soil habitats. 

     Our present research is designed to test the idea that among-stipe-cell genetic variation (genetic mosaicism) increases the probability that at least some cells of the mushroom will successfully spread through the environment either by direct growth from the point where mushrooms develop or by the action of soil organisms transporting mushroom cells to more distant points. We would consider either of these outcomes to be an advantage of the first diploidization/ haploidization event that characterizes the life cycle of A. gallica. The obvious function of fertile portions (gills) of mushrooms is that they produce haploid, genetically variable spores capable of aerial dispersal. Our study is also designed to test the idea that because A. gallica's life cycle includes two diploidization / haploidization cycles, A. gallica spores are genetically more variable than they would be if the species had only one diploidization / haploidization cycle. 

     Growth studies and assays of molecular marker traits will be used to distinguish among cells isolated from A. gallica mushrooms collected in Bridgewater, MA and Raynham, MA during the falls of 1999 and 2000. We will test hypotheses that spores, stipe cells, and rhizomorph cells isolated from single mushrooms possess: (1) among-cell genetic variation for rates of hyphal extension, (2) differing responses to environmental variables such as pH, temperature, and water potential, and (3) among-cell genetic variation for these differential responses to environmental variables. 

     The quantitative traits we will use to distinguish among cells are (1)hyphal extension rate, (2) extracellular enzyme production, (3) germination rate (spores only), (4) phenotypic plasticity, (5) fragmentation dispersal. The design of our experiments will also allow us to estimate "heritability" (for quantitative traits 1-3). (Heritability is the proportion of total trait variation caused by genetic differences among individuals.) 

     The molecular markers (genetic traits) we will use to distinguish among cells of the mushroom include (1) isocitrate dehydrogenase (IDH), (2) malate dehydrogenase (MDH), (3) phosphoglucomutase (PGM), (4) intergenic spacer region-1 (IGS-1), (5) IGS-2, (6) mating type locus A, (7) mating type locus B. 

     By comparing genetic variation for these quantitative and molecular traits in two different geographic locations (Bridgewater, MA and Raynham, MA) in each of three successive years, we will be able to determine whether these local populations are genetically variable. If they are variable, we should be able to predict these populations' evolutionary response to natural selection.