Efficacy of Different Forms of Green Manure Crops to Reduce Verticillium dahliae in Different Soils

Abstract

The efficacy of green manure crops to reduce the number of Verticillium dahliae microsclerotia in different soils was investigated. Green manures tested were Indian mustard with a high glucosinolate content and sorghum-sudangrass as biocidal plants, and Indian mustard with a low glucosinolate content and rye as non-biocidal plants. The green manure plants were applied in fresh, dried, and ensilaged form. When applied as fresh plants, the glucosinolate content determining the biocidal activity of Indian mustard was only important in loam soil but not in sandy loam soil. In the latter soil, the non-biocidal rye had significantly higher efficacy than the Indian mustard. Volatiles released by fresh and dried, but not ensilaged, Indian mustard with a high glucosinolate content strongly decreased the number of living V. dahliae microsclerotia. When the same green manure crops were added to sandy loam and clay loam soil, the effect of the high glucosinolate content Indian mustard in fresh and dried form disappeared, whereas the ensilaged green manure crops had the highest efficacy. This effect was based on the increase of the soil microbial activity and the Streptomyces population size, which were negatively correlated with the number of living V. dahliae microsclerotia in the soil.