Further observations on the growth of flax rust fungus in axenic culture

摘要

Axenic cultures of flax rust (Melampsora lini(Ehrenb.) Leacute;v.) grown from sterile uredospores on a defined liquid medium in 125-mL Erlenmeyer flasks exhibited an incubation period of 12 to 20 days followed by a period of rapid growth and sporulation. A heat shock (31ndash;33 deg;C for 2ndash;2.5ensp;h) administered 3ensp;h after seeding the medium did not induce the formation of infection structures, but doubled the number of vegetative colonies initiated and increased total growth per flask (protein/flask) in 4 weeks by 20-fold. The optimum timing of the heat shock corresponded closely with the maximum rate of germ tube emergence. Ambient CO2was not essential for germination or perception of the heat shock, but was essential, during the first half of the incubation period, for the subsequent development of vegetative colonies. CO2fixation occurred at all stages of growth from 1 day onward,14CO2being incorporated into ethanol-insoluble and ethanol-soluble fractions, including amino acids. Growth rate following the incubation period was not affected by the initial pH of the medium between 5.0 and 6.0, but the incubation period was shorter at pH 6.0.