VIEW ARTICLE

Influence of Volatile Compounds from Alfalfa Hay on Microbial Activity in Soil in Relation to Growth of Sclerotium rolfsii. R. G. Linderman, Research Plant Pathologist, USDA, ARS, Agricultural Research Center, Beltsville, Maryland 20705; R. G. Gilbert, Research Microbiologist, Water Conservation Laboratory, Phoenix, Arizona 85040. Phytopathology 63:359-362. Accepted for publication 21 September 1972. DOI: 10.1094/Phyto-63-359.

Mycelial growth from sclerotia of Sclerotium rolfsii on natural soil is stimulated when exposed to vapors of alfalfa distillate (AD). This growth was indexed on soils which had been previously exposed to AD or water vapors. Vigor of mycelial growth from sclerotia was markedly decreased in soil previously exposed to vapors from natural or synthetic mixtures of AD. Inhibition of mycelial growth from sclerotia also occurred in soil previously amended with sclerotia or a sclerotial leachate. This self-induced inhibition was further enhanced by simultaneous exposure of the soil to AD vapors. Soil microbial population and respiration studies indicated that growth inhibition of S. rolfsii may be related to the increased activity of soil microbes, primarily bacteria. Respiration rates of soils previously treated with water or AD, when exposed to AD vapors for 4 hr in Warburg flasks, were 12.3 and 22.9 µliters O₂/g per hr, respectively. The same soils exposed only to water vapor in the Warburg flasks respired at only 3.1 and 3.9 µliters O₂/g per hr, respectively. Greater respiratory activity in AD-treated soil over water-treated soil was attributed to the increased bacterial population, which was 3.5 times greater in the AD-treated than the water-treated soil.