Fungistatic Intensity of Agricultural Soil Against Fungal Agents and Phylogenetic Analysis on the Actinobacteria Involved

A total of 287 agricultural soil samples collected from 26 provinces or autonomous regions of China were tested on their ability to suppress the conidial germination of nine biocontrol fungal agents. These soil samples showed great differences in the degree to inhibit the germination of conidia (22.8% < mean inhibition rate < 97.5%), but all exhibited fungistatic activities above the moderate levels (mean inhibition rate > 50%) to most of tested fungi. Ten soil samples that have stronger fungistatic intensity (germination inhibition rate > 68.3%) to the target fungi, Trichoderma viride and Paecilomyces lilacinus, were selected to evaluate their soil actinobacteria involved fungistasis in soil. Of the 1,000 isolates from those soil samples, 345 actinobacteria exhibited fungistatic activity to conidial germination of T. viride and P. lilacinus with germination inhibition rates higher than 10%. Sequences encoding 16S rRNA gene of the 345 actinobacteria were analyzed by ARDRA and resulted 44 different ARDRA types. Fifty-six isolates, at least one from each unique ARDRA type, were selected for 16S rDNA sequencing and phylogenetic analysis. Results indicated that the actinobacteria involved in the soil fungistasis had close phylogenetic relationship with the members of Sterptomycetaceae, Microbacteriaceae, Micrococcaceae, and Nocardiacea.