Diversity and Biocontrol Potential of Culturable Endophytic Fungi in Cotton

Healthy cotton samples were collected and 93 endophytic fungal strains were isolated: 23 strains from the roots and 70 strains from the stems. Morphological characterization and ITS sequence analysis were used for the identification of these isolates. The results showed that the 93 strains including 20 species were highly diverse in terms of their taxonomy. Simpson’s and Shannon’s diversity indices were 0.915 and 3.848, respectively. Fusarium and Alternaria were the two dominant genera, constituting 19.4% of the total strains. Then, 72 spore-producing strains were tested for the suppression of cotton Verticillium wilt (CVW) caused by Verticillium dahliae in a greenhouse. Five strains exhibited effective suppression of CVW with average efficacy values higher than 50%. One of the effective strains, namely, Fusarium proliferatum 10R-7, was selected for the investigation of the role of fusaric acid, a secondary metabolite of strain 10R-7, in the suppression of V. dahliae and CVW. The results showed that F. proliferatum 10R-7 could produce fusaric acid, and this metabolite exhibited 100% inhibition of mycelial growth of V. dahliae at concentrations higher than 20 μg/ml. However, fusaric acid at 2.5 to 80 μg/ml was not effective in the suppression of CVW, compared with the control treatment with V. dahliae alone. F. proliferatum 10R-7 was labeled with green fluorescent protein (GFP), and the GFP-tagged strain was found to be able to colonize inside the taproots of cotton, suggesting that F. proliferatum 10R-7 is a true endophyte of cotton and endophytic colonization may play a role in the suppression of infection of cotton by V. dahliae.