Volume 10 Part 1 Article 7: Occurrence of Slow Septation in the Mycelium of Agaricus bisporus Grown on Extreme Conditions

Volume 10 Part 1 Article 7
Year 1979
Title: Occurrence of Slow Septation in the Mycelium of Agaricus bisporus Grown on Extreme Conditions
Authors: Hsi-Hua Wang, Yung-Long Lee and P.G. Miles


Since the phenomenon of secondary homothallism of the mycelium of the cultivated mushroom Agaricus bisporus, has been confirmed (Miller, 1971; Raper and Raper, 1971; Raper, Raper and Miller, 1972), the writers have worked on nuclear selection of the mycelium under various culture conditions (Wang, 1971; Wang et al., 1976). The homocaryotic cultures of the mushroom were isolated from abnormally formed four-spore basidia and by nuclear selection with mutagens (Wang, 1971). In these works, the mycelium of Agaricus bisporus, which had not been treated with any mutagen, was macerated by a Waring blender to form a suspension of hyphal fragments, an average of five cells per fragment, and then was spread on plates of complete or selective media. It was found that there were always some hyphal fragments which did not grow on the minimum medium but grew well on complete media (Wang, 1971). Raper concluded from his work in trying to isolate homocaryons that the heterocaryotic parental strains contained two types of nuclei, one nutritionally deficient, and the other nutritionally competent (Raper and Raper, 1972). The previous work in this laboratory in obtaining unstable auxotrophs from non-irradiated mycelial fragments also indicated the existence of at least one sort of auxotrophic nucleus in the untreated mycelium (Wang, 1971; Wang et al., 1976). If the primarily auxotrophic mycelium were subcultured on complete medium successively several times, the auxotrophic hyphal fragments would turn into the wild type and become prototrophs. It appears that the two kinds of nuclei in the mycelium may have different division rates, or asynchronized division.

Therefore the distribution of the two kinds of nuclei or the nuclear ratio may be indefinite and can be considered as unbalanced. When the cells are very unbalanced in the sense of nuclear ratio, the hyphal fragments may show auxotrophy. The temporarily auxotrophic fragments were obtained in this way. In the present work we designed to enhance the aberration of the rate of nuclear division by successively subculturing on selective media. The reason is deducible from the following assumption. If we add the nutrient, required by one type of nucleus, to the minimum medium, as selective pressure, we may expect that the nuclei, which require the nutrient, may divide more rapidly than the other type of nucleus. After subculturing hyphal tip cells on the same selective medium several times, the nuclei in the tip cells may consist of one type of nucleus. Finally the auxotrophic homocaryons may be obtained, if the number of hyphal fragments examined is sufficiently great.

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