Control of cotton Verticillium wilt and fungal diversity of rhizosphere soils by bio-organic fertilizer

Cotton Verticillium wilt is a destructive soilborne disease affecting cotton production. In this study, application of bio-organic fertilizer (BIO) at the beginning of nursery growth and/or at the beginning of transplanting was evaluated for its ability to control Verticillium dahliae Kleb. The most efficient control of cotton Verticillium wilt was achieved when the nursery application of BIO was combined with a second application in transplanted soil, resulting in a wilt disease incidence of only 4.4%, compared with 90.0% in the control. Denaturing gradient gel electrophoresis patterns showed that the consecutive applications of BIO at nursery and transplanting stage resulted in the presence of a unique group of fungi not found in any other treatments. Humicola sp., Metarhizium anisopliae, and Chaetomium sp., which were considered to be beneficial fungi, were found in the BIO treatment, whereas some harmful fungi, such as Alternaria alternate, Coniochaeta velutina, and Chaetothyriales sp. were detected in the control. After the consecutive applications of BIO at nursery and transplanting stage, the V. dahliae population in the rhizosphere soil in the budding period, flowering and boll-forming stage, boll-opening stage, and at harvest time were 8.5 x 10(2), 3.1 x 10(2), 4.6 x 10(2), and 1.7 x 10(2) colony-forming units per gram of soil (cfu g(-1)), respectively, which were significantly lower than in the control (6.1 x 10(3), 3.4 x 10(3), 5.2 x 10(3), and 7.0 x 10(3) cfu g(-1), respectively). These results indicate that the suggested application mode of BIO could effectively control cotton Verticillium wilt by significantly changing the fungal community structure and reducing the V. dahliae population in the rhizosphere soil.