A Volatile Substance Controlling Early Staǵes of Zygospore Formation in Rhizopus sexualis

SUMMARY: The inhibitory effect of low temperature (c. 10°) on initiation and early development of zygospores of Rhizopus sexualis is less severe in mature cultures (in which numerous zygospores have already been formed before transfer to the low temperature) than in young ones. The severe effect of low temperature on immature cultures is not counteracted by any of a number of known growth substances, by extracts of mature mycelium and zygospores, or by used culture media. The effect of mature cultures in counteracting low temperature inhibition of zygospore production in young ones is able to pass across a gap of 5 mm. between the cultures and must therefore be due to a volatile substance (or substances) produced by the mature mycelium. By the use of small chambers which allow young test cultures to be kept at 10° while a stream of air from mature ones growing at 20° passes over them, it is confirmed that the active factor is volatile. This substance is not carbon dioxide or ammonia and is basic in nature. Its probable identity is discussed and comparison is made with some other volatile substances reported to influence growth and development of fungi.