[What potentialities does the four-spored mushroom "Agaricus bitorquis (Quél.) Sacc." offer to the breeder?].

A. bitorquis was first taken into cultivation in 1968. It differs from A.bisporus, the only mushroom cultivated previously, in a range of properties. The claims for temperature are about 5° C higher. The fruitbodies (white smooth) are more vigorous than the sporophores of the white, scale-less strains of A.bisporus. Especially valuable characteristics which A. bitorquis brings are virus resistance, resistance to pressure, easy pickability and longer shelflife. The basidia have 4 instead of 2 spores. Consequently monosporecultures are infertile and systematic crossbreeding is a suitable breeding method.Because the hyphae do not form clamp connections, it is not possible to distinguish microscopically monocaryotic and dicaryotic mycelium. As the trials have shown, however, the compatibility of the monospore cultures can be recognized by the manner of mycelium growth on biomalt-agar. Where heterocaryotic mycelium has arisen matted, slow growing mycelium can turn into fluffy, and later on stringy fast-growing mycelium. With enough ventilation condensations of mycelium can be formed. Some combinations of monospore-cultures of different origin showed very significantly higher yields than the parental wild types, whereas other combinations of two monospore cultures were very significantly lower in yield than the parents. The combination of parental wildtypes scarcely differed in yield from the wildtype self. Regarding the course of the yield there were big differences in general.The strains also showed great variability in the shape and colour of the fruitbodies, their distribution on the bed and in other properties, such as the propensity of the mycelium to grow into the casing layer. The results are discussed.