CHARACTERIZATION OF ANTIFUNGAL VOLATILE COMPOUNDS EVOLVED FROM SOLARIZED SOIL AMENDED WITH CABBAGE RESIDUES

The objectives of this study were to characterize volatile compounds evolved from solarized soil amended with cabbage residues and to assess the effect of these volatile compounds on soilborne fungi. Quantitative and qualitative differences in volatile compounds from heated and nonheated cabbage-amended soil were found. Heated cabbage-amended soil generated a wide range of volatile compounds, including alcohols, aldehydes, sulfides, and isothiocyanates. The levels of isothiocyanates and aldehydes generated in heated soil were significantly correlated with reduced propagule numbers of Pythium ultimum and Sclerotium rolfsii during exposure. Viability of P. ultimum and S. rolfsii was reduced in soil amended with dried, ground cabbage residues when the soil was heated in a controlled-environment system simulating a diurnal solarization temperature curve at a sublethal maximum of 38 C. The propagule numbers of the two fungi were reduced by more than 95% when they were exposed for 14 days to volatile compounds generated from heated cabbage-amended soil but were not reduced to this extent when exposed to compounds generated from nonheated cabbage-amended soil. Total microbial activity in heated cabbage-amended soil rapidly decreased during direct exposure to the heat treatment. The microbial activity of soil exposed only to volatile compounds from heated cabbage-amended soil increased, however, suggesting selective toxicity of the volatile compounds to soil microbiota, additional biocidal activity of compounds in the soil's liquid and/or solid phases, and contribution of microbial antagonism to pathogen control.