Application of Bio-Organic Fertilizer Significantly Affected Fungal Diversity of Soils

Cotton verticillium wilt (Verticillium dahliae Kleb.) is a very destructive disease. In this study, we evaluated a Bacillus subtilis enhanced bio-organic fertilizer (BOF) for control of the disease and for its effect on rhizosphere microbiota. Greenhouse pot experiments were conducted during three cotton (Gossypium hirsutum L.) growing seasons with serial treatments of BOF or unenhanced organic fertilizer (OF). Consistent control of cotton verticillium wilt was obtained in the three trials. The complete BOF treatment, in which both nursery cups with healthy soils and transplanted pots with diseased soils were amended with BOF, was the most effective in reducing the counts of pathogenic V dahliae and of total fungi in the cotton rhizosphere. The complete BOF treatment was also the most effective in reducing disease incidence. Rhizosphere soil DNA was extracted at harvest and the 5' end (370 base pairs) of the fungal 18S rRNA gene was amplified by using the primer pair NS1 and GCFung (fungus specific). Seventy-one bands were recognized in denaturing gradient gel electrophoresis (DGGE) gels and excised for sequencing, but only 35 bands were successfully sequenced during the study. Nonmetric multidimensional scaling analysis of DGGE patterns showed that the complete BOF treatments were not close to any other treatment. Ribotypes related to four Ascomycota and two Basidiomycota fungi were detected in the untreated but not in the BOF-amended soil. The results suggest that the complete B 0 F treatment could effectively control cotton verticillium wilt by significantly improving fungal structure in rhizosphere soils.