| Cotton Verticillium wilt, caused by soilborne pathogen of Verticillium dahliae Kleb. (V. dahliae), is one of the most prevalent diseases, which typically occurs in cotton fields with continuously cropping obstacles. Biological control has become the most important way in control of soil-borne plant diseases, and the use of antagonistic bacteria against Cotton Verticillium wilt is drawing more and more attention. In this study, two antagonistic strains (HJ5 and DF14) were isolated from the rhizosphere soil of health cotton plants in the field severely diseased by cotton Verticillium wilt. The two strains were conserved in the China General Microbiology Culture Collection Center (CGMCC) and their registration numbers were given as CGMCC 3301 and CGMCC 3302, to strain HJ5 and strain DF14, respectively. To provide proper organic carrier and nutrients to the functional antagonists and subsequently to facilitate conlonization of soil and plant roots by the antagonists, a new bio-organic fertilizer (BIO) enriched with the antagonists was produced by secondary fermentation of organic fertilizers (OF).The present study validated that application of BIO in both nursery and transplanted soils could effectively control the incidence of Verticillium wilt of cotton and regulate the composition of microbial flora in rhizosphere soil. BIO application significantly increased the number of bacteria, and decreased the amounts of fungi. Results from three seasons of repeated greenhouse experiments showed that when the nursery soil was amended with 1% of BIO and the transplanted soil with 0.5% of BIO (treatment NBIOo+TBIO), high than 95% of control efficiency against the wilt were obtained in the third season, and the cotton yields were increased by 3 times of the control. While only application of BIO in nursery soil (treatment NBIO+TCK) or only application of BIO in growing pot soil (treatment NCK+TBIO) also increased the control efficiency, application of BIO in both nursery and transplanted soil (treatment NBIO+TBIO) had the highest control efficiency. Molecular PCR-DGGE results from the samples of three growing seasons showed that application of BIO changed the bacterial community structure of soil and decreased fungal community diversity by sharp reduction of band numbers. The analysis of Real-time PCR showed that the application of BIO could effectively prevent Cotton Verticillium wilt disease by reducing the amounts of V. dahliae in rhizosphere soil.In conclusion, the present paper revealed the microbiological and molecular biological characteristics of bio-organic fertilizers applied on the control of Verticillium wilt of cotton and provided theoretic proofs for research and development as well as use of bio-organic fertilizers. Further researches should be given to the molecular microbilogical aspects of the functions performed by bio-organic fertilizers in remediation of continuously cropping obstacles and in the promotion of plant growth and health exerted by soil functional microbes. |
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