GLOBAL GENETIC-RESOURCES FOR AGARICUS BREEDING AND CULTIVATION

Until recently the natural history and resource status of the button mushroom Agaricus bisporus has been but poorly known. At present, five and perhaps six genetically distinctive, reproductively isolated populations of this species from western North America, Europe, and western Asia have been located, sampled, and partially characterized. Morphology, diversity, reproductive syndrome, and other economically important traits vary among these populations. Other populations may exist in northern and central Africa and in Australia. Available evidence suggests that the studied populations are ancient. However, probably through cultivation, European germ plasm has invaded the three known North American populations and has already displaced a large portion of the indigenous coastal Californian population; the trend is less advanced in Alberta and the California desert. The recovery of diverse wild germ plasm of this mushroom, still in its infancy, is likely to become increasingly difficult. The value of these genetic resources, the threats that confront them, and appropriate responses by the mushroom industry are discussed. Hypotheses about the outcomes of heterokaryon somatogamy and the concept of the individual in this species are presented. The term metagenotype is coined to describe the ancestral or consensus genotype of a multigenerational intramictic lineage group.