Studies on the physiology of the three soft rot fungi Allescheria terrestris, Phialophora (Margarinomyces) luteovirdis and Phialophora richardsiae
A study was made of the general physiological aspects of three soft rot fungi commonly occurring in stored soft wood chips, namely: Allescheria terrestris Apinis (strain Apinis and strain H63 - 1 ), Phialophora (Margarinomyces) luteo-viridis (van Beyma) Schol- Schwarz (strain Beyma 206.38 and strain M 74 - IV) and Phialophora richardsiae (Nannf.) Conant (strain BB40-V). A. terrestris is a so-called thermophilic fungus with a temperature growth range of approximately 20°C to 55°C. Both of the Allescheria terrestris strains grew on malt agar within the entire temperature range of 20°C to 50°C. If the fungus was permitted to grow out from birchwood, the maximum growth temperature increased to 55°C. The optimum temperature for radial growth of strain H63-1 was 45°C, while strain Apinis achieved optimum growth at 40°C. The production of mycelium measured as dry weight largely coincided with the respective increase or reduction in length of growth at the different temperatures. However, both strains showed optimum mycelium production at 40°C. None of the Allescheria terrestris strains survived one hour at a temperature of 75° on malt agar but survived 14 days at 55°C if the temperature was again reduced to 45°C. The two Phialophora luteo-viridis strains grew on malt agar at temperatures between 5°C and 35°C, with an optimum growth for both strains at 30°C. No increase in the maximum temperature for growth was achieved by permitting the mycelium to grow out from birchwood. The fungi did not survive storage at 70°C for an hour on malt agar but, on the other hand, survived 40°C for 14 days if the cultivation temperature was again reduced to 30°C. Phialophop richardsiae grew on malt agar between 5°C and 30°C. The maximum growth temperature was not raised if the mycelium was permitted to grow out from the birchwood. The fungi did not survive storage for one hour on malt agar at 60°C but did survive seven days at a temperature of 35°C if the cultivation temperature was again reduced to the optimum growth temperature of 25°C. Allescheria terrestris grew within the entire pH range tested, 2.4 to 7.3 at 30°C and 45°C. An initial pH of between 5 and 6 gave the greatest mycelium production. Both strains of Allescheria terrestris have been well able to utilize nitrogen from both inorganic and organic nitrogen sources; even nitrate nitrogen which is difficult of access for certain groups of fungi. All of the carbohydrate sources employed were well utilized by Allescheria terrestris with the exception of D-arabinose. D-arabinose has earlier been reported to afford difficult access for certain fungi. The tests employed to determine the vitamin requirements showed that Allescheria terrestris was auxoautotrophic for thiamine and biotin. All of the three soft rot fungi studied displayed a positive reaction to a-naphthol as registered by means of a drop-test.
soft rot fungi; Phialophora (Margarinomyces) luteovirdis; Allescheria terrestris; Phialophora richardsiae
Studia Forestalia Suecica
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