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Abstract: Breeding of the commonly cultivated mushroom, Agaricus bisporus, has become possible from our knowledge of its life cycle (Raper et al., 1972), but the nature of the life cycle is such as to make a breeding program tedious and difficult (Raper and Raper, 1972). The characteristic self-fertility of single-spore isolates due to a type of sexuality known as secondary homothallism renders the genetic manipulation to improve strains far more cumbersome than would be the case if the species were heterothallic with self-sterile, cross-fertile progeny. Several species of Agaricus found in nature are edible and a few have been cultivated (Singer, 1961; see also Poppe, 1972). The possibility that some of the edible, cultivatable, wild forms are also heterothallic and therefore more easily managed in breeding programs than is the currently cultivated A. bisporus is worthy of investigation. Heterothallism in wild species of Agaricus seems plausible in view of the facts that the basidia of most wild forms are predominantly four-spored rather than two-spored (Singer, 1975) and the primordial spores are uninucleate rather than binucleate (Colson, 1935; Jiri, 1965). A study of collections of Agaricus from nature has led to the identification of Agaricus bitorquis as an edible and a cultivatable heterothallic species with high breeding potential. Its biology is outlined in this paper and its suitability to the development of commercially desirable strains through a relatively simple breeding program is discussed. A detailed account of the genetic analysis of the life cycle of A. bitorquis is in press (Raper, C.A., J. Gen. Microbiol.).
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