Effects of Ultraviolet a Radiation and Inhibitory Volatile Substances on the Discomycete, Pyronema Domesticum

ABSTRACT

Pyronema domesticum forms apothecia in white light but not in darkness in a closed Petri dish and in the absence of circulating air in the incubator. Ultraviolet A radiation (320-400 nm) at an intensity of 104 microwatts cm^-2 induces large numbers of apothecia in sealed flask cultures. These apothecia have impaired development of the ascogenous system but development is normal in a closed Petri dish in which some diffusion of air can occur between the interior and exterior environments. The numbers of apothecia decrease sharply at either higher or lower irradiances of ultraviolet A. Exposure to an irradiance greater than 3.8 microwatts cm^-2 inhibits mycelial growth which is prevented at 4030 microwatts cm^-2. At the intensity inducing large numbers of apothecia, mycelial growth is less than that of the dark control. Exposure to intense ultraviolet A radiation is damaging and results in the death of some of the cultures. Apothecia can be induced to form in darkness in stagnant air in the presence of activated charcoal because unknown volatile substances released by the fungus and inhibitory to apothecia formation are adsorbed.

Key Words:

• ultraviolet
• apothecia
• Pyronema
• Discomycetes