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Ecology and Epidemiology

Volatiles From Soil Influencing Activities of Soil Fungi. Daniel A. Pavlica, Department of Chemistry, Colorado State University, Fort Collins, CO 80523; T. S. Hora(2), J. J. Bradshaw(3), R. K. Skogerboe(4), and Ralph Baker(5). (2)(3)(5)Department of Botany and Plant Pathology, Colorado State University, Fort Collins, CO 80523; (4)Department of Chemistry, Colorado State University, Fort Collins, CO 80523. Phytopathology 68:758-765. Accepted for publication 24 October 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-758.

Volatile compounds were detected in natural soils. Among these, dosage-response curves for acetone, ethylene, ammonia, and formaldehyde were developed. Concentrations of ethylene and acetone considerably above those detected in soil were necessary to inhibit germination of conidia of test soil fungi. Formaldehyde was detected in some soils at concentrations high enough to inhibit spore germination. Inhibition of conidium germination of Aspergillus flavus by formaldehyde was nullified by exogenous nitrogen and carbon, but the same phenomenon was not observed for conidia of Fusarium solani f. sp. phaseoli. The ED₅₀ values for conidium germination of Penicillium chrysogenum and Gonatobotrys simplex were below 1 μg ammonia/g air. Reduced germination due to volatiles from five soils, limed and not limed, was correlated directly with concentrations of volatile ammonia accumulated for 24 hr above these same soils. At certain concentrations, ammonia, ethylene, and acetone stimulated growth and/or germination of some of the test organisms. Ammonia must be considered a prime candidate for a volatile inhibitor in soil. Formaldehyde may inhibit some fungi in certain soils. Bioassays, however, provided evidence for another volatile component present in the atmospheres of acid soils. So far, it has not been identified by chemical analysis.