Zs. P. Komáromy szerk.: Studia Botanica Hungarica 16. 1982 (Budapest, 1982)

Bohus, Gábor: Some results of systematical and ecological research on Agaricales, IX.

The effect of low temperature on Agaricus macrosporoides The examination of the effect of temperature is interesting from an ecological viewpoint in the case of soil-inhabiting and xylophagous fungi. Examples can be found in the researches pres­ented earlier: Mycelium of Flammulina velutipes is still viable after 138 days at -21°C (PEHRSON cf. COCHRANE 1958) and fruit bodies of Schizophyllum commune withstand exposure to -15 to -40°C (BUXTON et al. cf. COCHRANE, 1958). The experiments presented here were carried out with cultures of 320 g culture media in weight. The interlacing of the culture media at 25°C lasted 15-20 days. It was after this that freezing effect was introduced in several varieties. After freezing, incubation was continued again at 25°C, then cultivation followed at 17°C, when - if there was no freeze damage - fruit bodies were formed. The four varieties of experiment were as follows: Variety 1: Freezing effect held on one day, at -8°C. During cultivation, the fruit bodies were formed on the 57th day after inoculation, their weight was 69% of the dry matter weight of the culture medium. This can be taken as identical with the usual quantity observable under normal conditions after a growth of 50-60 days. Consequently, the above freezing effect was practically not harmful, or inhibiting. Variety 2: Freezing effect continued for 1.5 days, at -24°C. There was no visible damage on the mycelia but the fruit body appeared 30-40 days later than usual. The weight of the body appeared 30-40 days later than usual. The weight of the fruit body was 66% of the dry matter weight of the culture medium, measured on the 90th day after inoculation. The influence of freezing is docu­mentated by prolongation of the fruit body formation. Variety 3: Freezing effect continued for one day, at -8 C, then for 2 days cultivation at about 23°C, then again for one day at -8°C. Frost damage could not practically occur because one fruit body started to form on the 40th day after inoculation - that is relatively early - and when it developed (on the 50th day) its weight was 56% of the dry matter weight. Variety 4: Freezing effect lasted for 4 days, at -8°C. In this case the frost damage could already be observed, some part of thalli were damaged and the growth of the other parts were inhibited. Keeping the culture at 25°C, the continuation of the interlacing could not be noticed even after two weeks had passed. After this further interlacing started, presumably from those parts of the thalli that had not been damaged. A fruit body appeared on the 95th day and the observation was finished. Discussion of some phenomena related to freezing effect In the experiments carried out in consequence of relatively slow freezing (at -8°C 1.5-2 cm/h), and the bulk of media, the rate of freezing was different on the surface and inside the culture. In the case of 1st and 3rd experiments extracellular ice-crystals - withdrawing water from the cells - did not form even in the mycelia grown on the surface of the culture, cooling rapidly. It was documented by the practically normal fruit body formation. In the case of 2nd experiment real frost damage could not also been observed but the fructification was extended in consequence of fairly short but low temperature (-24°C for 1.5 days). In the course of 4th experiment the duration (-8°C for 4 days) causes a stronger inhibition in growth. The rate of thawing is another factor in the frost injury induced. In the case of experiments carried out, the thawing was relatively rapid, although it was different in rate on the surface and inside of the culture. Any kind of damage was observed. The extent of frost-resistance depends on the type of the cells, and their physiological condition, too. Since, the cells of mycelia were young (about 20 days old) at the time of freezing, resting cells could not have formed. In the case of species examined, the cells of mycelia them­selves were able to endure the frost effect even repeatedly.

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