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Soil fumigants constitute a major tool for the control of soil borne fungal plant pathogens in protected crops. Dimethyl disulfide (DMDS) is a novel soil fumigant used either alone or in combination with other fumigants for the control of soil borne pests and diseases. In a commercial greenhouse for tomato production, we evaluated the impact of DMDS, comparatively to the alternative fumigant metam sodium, on the population of the dominant fungal plant pathogens in the study soil via q-PCR. Prior to soil fumigation, estimation of the fungal diversity in the studied soil via clone libraries identified Fusarium oxysporum and Rhizoctonia solani as the most abundant soil borne plant pathogens, while Cladosporium spp., known as opportunistic airborne tomato pathogens, were the most dominant fungi and based on this their dynamics upon fumigation was also studied. DMDS, at two dose rates, induced a drastic reduction in the population of F. oxysporum and R. solani, which lasted for the whole cultivation season. On the contrary, metam sodium exhibited an inhibitory effect on F. oxysporum that was alleviated at 120 d post fumigation. Both DMDS and metam sodium induced only a temporal reduction in the soil population of Cladosporium sp. which recovered by 60 days post fumigation. Our data suggest that DMDS even at the low dose rate (56.4 g m −2 ) could drastically reduce the population of the major soil borne tomato pathogens F. oxysporum and R. solani. Establishment of population thresholds as determined by q-PCR could represent a valuable tool for the estimation of the risk for disease severity and crop yield losses.

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