Analysis Of The Community Structures Of Endophytic Bacteria And Fungus In The Roots Of Verticillium-Infected Cotton In Xinjiang

Cotton Verticillium wilt, a world-wide-spread soil-borne disease, has caused huge economic losses of cotton industry in Xianjiang Province by reducing the cotton yield. It has been proved that cotton Verticillium wilt could affect the community structures of rhizobacteria, however, the correlation between cotton Verticillium wilt and the community structures of endophytic bacteria and fungi in cotton roots has not been reported. In this study, we combined the normal isolation of microorganisms with Denaturing Gradient Gel Electrophoresis (PCR-DGGE) to analyze the community structures of endophytic bacteria and fungi of cotton roots that are either healthy or infected with Verticillium wilt. The main details and results are as follows:1. Research of endophytic bacteria of cotton roots(1) Research of culturable endophytic bacteria of cotton roots:A total of 549 endophytic bacteria, including 17 species belonged to 7 genera of Proteobacteria, Actinobacteria and Firmicutes, were isolated from all healthy and infected cotton roots, The dominant endophytic bacterial populations in healthy cotton roots were Pseudomonas sp., Bacillus sp., and Serratia sp., while Pseudomonas sp., Pantoea sp., and Bacillus sp. in the infected cotton roots. The number of endophytic bacteria in both healthy and infected cotton roots rised at the first growth period and then declined. And the number of endophytic bacteria in the healthy cotton roots was higher than that of the infected ones at the same period.(2) The study on community structure of endophytic bacteria based on PCR-DGGE. According to the clustering analysis and principal component analysis (PCA) of PCR-DGGE of the endophytic bacteria, the community structure of endophytic bacteria closely correlated to the cotton growth. Diversity index of endophytic bacteria in healthy cotton roots was higher than that of infected ones at the same period. The 21 bands were identified based on the different nucleotide sequences and most of them belonged to Proteobacteria. Among those 21 bands, some were shared between the healthy cotton roots and infected ones, while the others were special to the effected cotton roots.In conclusion, the above results showed that the most of endophytic bacteria in the both healthy and infected cotton roots belonged to Proteobacteria. The diversity of endophytic bacterial community structure closely correlated to the cotton growth and endophytic bacteria in healthy cottons were more abundant than those in infected ones, indicating that V. dahlia could influence the endophytic bacterial community structure.2. Research of endophytic fungi of cotton roots(1) Research of culturable endophytic fungi of cotton roots:A total 702 endophytic fungi, which were isolated from both healthy and Verticillium infected cottons roots, belonged to 13 genera of 6 orders in 3 classes in Fungi Imperficti and Ascomycota. The dominant endophytic fungal populations in healthy cotton roots belonged to Alternaria sp., Thielaviopsis sp., and Aspergillus sp., whereas Alternaria sp., Fusarium sp., and Penicillium sp. in the infected cotton roots. The isolation frequency of Verticillium sp. was 33.8% at the late growth stage of Verticillium infected cotton roots, while isolation frequency of other endophytic fungi was very low.(2) The study on community structure of endophytic fungi based on PCR-DGGE. According to the clustering analysis and principal component analysis (PCA) of PCR-DGGE of the endophytic fungui, the endophytic fungal community structure of the cotton roots closely correlated to the infection of V. dahliae. The diversity index of endophytic fungi of infected cotton roots was higher than that of the healthy ones at the late growth stage. The 17 bands were identified based on the different nucleotide sequences and most of them belonged to Fungi Imperficti and Ascomycota. Verticillium sp. were the specific fungal populations at the middle-late growth stage of the infected cotton roots.To sum up, the above results demonstrated that the most of endophytic fungi in the both healthy and Verticillium infected cotton roots belonged to Fungi Imperficti and Ascomycota. The number of Verticillium sp. increased at the middle-late growth stage of the infected cotton roots, suggesting that the endophytic fungual community structures were apparently influenced by V. dahlia at the middle-late growth stage of the infected cotton roots.