Volatiles From Soil Influencing Activities of Soil Fungi

PAVLICA, D. A. , T. S. HORA, J. J. BRADSHAW, R. K. SKOGERBOE, and R. BAKER. 1978. Volatiles from soil influencing activities of soil fungi. Phytopathology 68: 758-765. Volatile compounds were detected in natural soils. Among below 1 big ammonia/g air. Reduced germination due to these, dosage-response curves for acetone, ethylene, volatiles from five soils, limed and not limed, was correlated ammonia, and formaldehyde were developed, directly with concentrations of volatile ammonia Concentrations of ethylene and acetone considerably above accumulated for 24 hr above these same soils. At certain those detected in soil were necessary to inhibit germination of concentrations, ammonia, ethylene, and acetone stimulated conidia of test soil fungi. Formaldehyde was detected in some growth and/or germination of some of the test organisms. soils at concentrations high enough to inhibit spore Ammonia must be considered a prime candidate for a volatile germination. Inhibition of conidium germination of inhibitor in soil. Formaldehyde may inhibit some fungi in Aspergillus flavus by formaldehyde was nullified by certain soils. Bioassays, however, provided evidence for exogenous nitrogen and carbon, but the same phenomenon another volatile component present in the atmospheres of was not observed for conidia of Fusarium solani f. sp. acid soils. So far, it has not been identified by chemical phaseoli. The ED50 values for conidium germination of analysis. Penicillium chrysogenum and Gonatobotrys simplex were Additional key words: spore germination, soil fungistasis. A volatile fungistatic factor in soil has been implicated identification. Despite this problem, a number of in the inhibition of germination of fungal propagules in compounds have been suggested as inhibitory volatiles in soil (7, 21). Lockwood (15) recently reviewed literature in soil. Smith (24) found emanations of ethylene from soils this and other areas of research on soil fungistasis. fungistatic to propagule germination. Balis (1) was unable Certain properties and characteristics can be assigned to confirm the inhibitory properties of ethylene, but to the inhibitory volatile on the basis of literature reports: suggested it might induce formation of a fungistatic (i) it is volatile at ambient temperatures and is water compound tentatively identified as allyl alcohoL. Ko and extractable (8); (ii) emanations from soils may occur over Hora (14) implicated ammonia as an inhibitor of spores in extended periods, but their effects may be nullified by certain alkaline soils. Few of these reports, however, small quantities of nutrients (6, 21); (iii) the factor is relate quantitative data on volatiles originating from typically adsorbed on activated charcoal; (iv) inhibition aerobic raw soil to dosage-response measurements for the of spore germination by the volatile(s) decreases with suspected volatile inhibitors. We present in this paper increasing depth of soil (20); (v) increasing alkalinity of qualitative and quantitative studies of volatiles in soil and soil increases inhibition of germination (10, 11) and may their dosage-response relationships for inhibition of indicate increases in release of at least one of several germination of spores of several soil fungi. possible fungistatic chemicals; and (vi) inhibitory volatiles may be produced by soil microorganisms (9). In MATERIALS AND METHODS general, these observations suggest that the factor might be one or more low-molecular-weight compounds. Trapping methods. --Because of the generally low Although there appear to be sufficient data in the emanation rates of the fungistatic factor(s) in soils, the literature supporting the participation of inhibitory experimental approach devised for their identification chemicals in the phenomenon of soil fungistasis (2, 7, 12, included means for nondestructive isolation and 13, 21, 24), the emanation rates from soils are generally preconcentration under fairly representative soil very low. Thus, the identification of the factor requires conditions. To accomplish this, soil samples (see Table 1) collecting sufficient quantities nondestructively to permit were purged under conditions to be described while using 00032-949X/78/000 128$03.00/0 the following collection/ preconcentration systems. The Copyright © 1978 The American Phytopathological Society, 3340 first was a cryosorption trap of activated charcoal Pilot Knob Road, St. Paul, MN 55121. All rights reserved. [Nuchor WV-G, 1.85-0.50 mm particle size range (12-40