Inhibition of fungal colonization on the rhizoplane of the CS₂-producing plant, Mimosa pudica L.

Abstract

Carbon disulfide (CS₂) is a colourless, volatile, foul-smelling, fungicidal liquid that is produced by some plants. We determined the ability of a model CS₂-producing plant, Mimosa pudica, to affect the rhizoplane colonisation 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 µg 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 colonisation, although other compounds may also be responsible.