Inhibition of fungal colonization on the rhizoplane of the CS2 - producing plant, Mimosa pudica L.
Carbon disulfide (CS2) is a colorless, volatile, foul-smelling, fungicidal liquid that is produced by some plants. The authors determined the ability of a model CS2-producing plant, Mimosa pudica, to affect the rhizoplane colonization of six species of soil fungi. Tomato (Lycopersicon esculentum), a plant which does not produce CS2, was the control. In plate assays, the mycelia of Fusarium moniliforme, Pythium aphanidermatum, Phytophthora sp., Rhizoctonia solani, Sclerotium rolfsii, and Trichoderma viride showed variable responses to CS2, but all mycelia were inhibited by 4 mg CS2 ml-1. Inhibition of spore germination of F. moniliforme, P. aphanidermatum, and T. viride was similar to mycelial inhibition. When gnotobiotic tomato or M. pudica plants were inoculated with F. moniliforme or T. viride, spore counts were similar in the nonrhizosphere, but 10- to 100-fold lower on the rhizoplane of M. pudica than those of tomato. When the roots of 11-d-old gnotobiotic tomato or M. pudica plants were each inoculated separately with one of the six fungal species, abundant hyphae of all six fungal species were observed on the roots of tomato after 7 days. In contrast, roots of M. pudica showed many or abundant hyphae of R. solani and S. rolfsii but no or few hyphae of the remaining species. These observations were confirmed by ergosterol analysis. Plant-generated CS2 may account for this decreased fungal colonization, although other compounds may also be responsible.