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Effect of Sulfur-Containing Volatile Compounds and Vapors from Cabbage Decomposition on Aphanomyces euteiches. J. A. Lewis, Soil Scientist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; G. C. Papavizas, Microbiologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:208-214. Accepted for publication 23 September 1970. DOI: 10.1094/Phyto-61-208.

Vapors from several sulfur-containing compounds adversely affected various processes in the life cycle of Aphanomyces euteiches. Isothiocyanate vapors were more effective than those of sulfides in inhibiting growth, zoospore formation, motility, and zoospore germination. For example, mycelial growth and zoospore formation and germination were prevented by vapors of 0.04, 0.10, and 0.30 parts per million (ppm) of allylisothiocyanate (AIT), respectively, and the same processes were prevented by vapors from 20, 100, and 350 ppm of (CH3)2S2. Sublethal amounts of the volatiles had no effect on oospore formation. Pea root rot was reduced by more than 90% when soils were fumigated with CS2, (CH3)2S2, AIT, methylisothiocyanate (MIT), or CH3SH. Materials not as effective in disease reduction included butylisothiocyanate (BIT), phenethyl-isothiocyanate (PhIT), and (CH3)2S. Vapors from the decomposition of cabbage tissue, an amendment which suppressed disease, adversely affected morphology of the fungus, development of oospores, and mycelial growth. Vapors arising from the decomposition of corn tissue, an amendment which did not suppress disease, had no effect on the fungus.