Stimulatory as well as inhibitory effects of volatile metabolites on the growth and development of fungi have been observed and studied by numerous investigators. As early as in 1902 FE~GVSON found that the germination of spores of the edible mushroom, Psalliota campestris, was stimulated by a myeclium of the same species growing close to the spores (Fngavso~, 1902). Later investigators found that the effect was due to volatile mctabolites emitted by the mycelium (McTEAGU~ et al., 1959; STAX~K, 1959). Some other fungi, including yeast, in the same way affected the mushroom spore germination (L6sEL, 1964). A stimulation of the germination was also produced by certain organic substances, viz. 2,3-dimethyl-l-pentene, iso-amyl alcohol and iso-valeric acid, acting through the gas phase.
The mycelinm of Psalliota campestris has been shown to produce a volatile factor, so far unidentified, which inhibits the sporophore formation in this species (MAn~R, 1943; EGnn, 1961). In Rhizopus sexualis the zygospore formation is stimulated by a volatile emission from cultures of the same species (tIEPDEN and I-IAWKEn, 1961).
Furthermore it may be mentioned that n-nonanal, a volatile metabolite of wheat rust, induces uredospore germination in this fungus (Fgxxc~ and WEIXTt~AVB, 1957) and stimulates the growth of several other fungi (F~IES, 1960(F~IES, , 1961;; NYMAN, 1966).
In the present investigation a comparison was made between the growth of Pestalotia rhododendri in a still atmosphere, where volatile metabolites could be supposed to accumulate, and the growth of this fungus in a streaming atmosphere, where such metabolites were removed.
Material and Methods
The genus Pe~talotia belongs to .Fungi Imper]ecti and is spread all over the world. Most species are common in the warmer regions. According to Gu~A (1961) there are more than two hundred and sixty species. A few of them are parasites on woody plants but most are saprophytes. Pestalotia rhododendri Guba is found on diseased specimens of Rhododendron spp. and LI~LL (1943) thought Pestalotia rhododendri to be a secondary infection on azaleas already attacked by other fungi.