Development Of A Bio-Organic Fertilizer Against Cotton Verticillium Wilt And Their Effect On The Soil-Cotton System

Verticillium dahliae Kleb(Vd), the soil born pathogen, is one of the causative agents of Cotton Verticillium Wilt which has been causing catastrophic damage to cotton. A lot of methods have been carried out to prevent or cure this disease, among which, biocontrol was proved to be very promissing.Here we reported the isolation and screening of antagonistic strains to Verticillium dahliae. By plate confrontation assay, about 50 potential antagonistic strains were selected out of more than 600 strains isolated from rhizosphere soil of healthy cotton plants grown in the field strongly attacked by Verticillium Wilt disease, and 8 of the strains showed promising inhibition activity against Verticillium dahliae, with the inhibition rate more than 70%. Secondary screening found that three of the promising strains, HJ-5, DF-15, DF-14 demonstrated the inhibition rate of more than 30%, and no antagonism was detected between each pair of them by bioassay. Therefore, HJ-5, DF-15 and DF-14 were mixed as antagonistic compound liquid for pot tests.Pot tests showed that dry weight of cotton plants treated with antagonistic compound liquid differed significantly from that treated with organic fertilizer, but dry weight of cotton plants in both treatments were higher than CK. Single application of antagonistic compound liquid or organic fertilizer could significantly increase plant height, stem width and dry weight, compared with CK Mixed application of antagonistic compound liquid with organic fertilizer could promote cotton seedling growth to a greatest extent. Either single application of antagonistic compound liquid or organic fertilizer could protect cotton plants from Verticillium Wilt, and the mixed application of antagonistic compound liquid with organic fertilizer resulted in a control effect as high as 57%, indicating that combination of antagonistic compound liquid with organic fertilizer was the best way to control this disease.The amounts of soil microbe in cotton rhizosphere under different treatments showed that fungi amounts in the three treatments of antagonistic compound liquid, organic fertilizer and the combination were lower than that of CK, but the amounts of actinomycetes increased significantly, and the amount bacteria were increased by 4.94～9.06, 3.56～5.89 and 7.33～13.44 fold in the three treatments, respectively, when compared with CK. Single application of antagonistic compound liquid and single application of organic fertilizer increased actinomycetes by 2.44～4.81 and 3.15～5.89 folds in the two treatments, respectively, in comparison with CK; Sclerotia amounts of V. dahliae in treatment of both antagonistic compound liquid, and organic fertilizer were decreased by 34%, compared with the CK. Denaturing Gradient gel Electrophoresis (DGGE) study of microflora in the rhizosphere of cotton showed that lanes of DGGE were increased after application of antagonistic compound liquid or organic fertilizer, or the combination, indicating that soil microbial diversity was increased by application of antagonistic compound liquid and organic fertilizer. In conclusion, application of bio-organic fertilizer specific to control Cotton Verticillium Wilt could have a good biological control of this disease by helping the formation of characteristic soil microflora and improving the organization of soil microbial community.