Trichoderma communities in soils from organic, sustainable, and conventional farms, and their relation with Southern blight of tomato

The objectives of this research were to investigate the relationship between propagule numbers and genetic diversity of Trichoderma species and Southern blight of tomato caused by soilborne plant pathogen Sclerotium rolfsii in soils with long-term organic, sustainable, and conventional farms. Dilution plating was use to quantify the propagule numbers of Trichoderma, denaturing gradient gel electrophoresis (DGGE) and DNA sequence analysis were used to identify Trichoderma species, and greenhouse assay were conducted for soil suppressiveness to Southern blight. The propagule numbers of Trichoderma tend to be higher in soils from conventional farms. There was no clear separation for the propagule numbers of Trichoderma based on different management systems using canonical correspondence analysis (CCA). However, there was general separation for total microbial communities based on organic and conventional management systems using CCA. That suggests that the difference of soil suppressiveness to disease from organic, sustainable, and conventional farms is due to the difference of the total microbial diversity but not directly due to the Trichoderma populations in each farming system. The propagule numbers of soil Trichoderma did not significantly correlate with the diseases suppressiveness, although individual species of Trichoderma harzianum was shown to be related to disease suppressiveness. Moreover, several Trichoderma species were found in the soil tested based on DGGE and DNA sequence analysis. Trichoderma hamatum, T. harzianum, Trichoderma virens, and Trichoderma erinaecem were the most abundant species in tested soil.