RFLP analysis of rDNA-ITS regions of native non-pathogenic Fusarium oxysporum isolates and their field evaluation for the suppression of Fusarium wilt disease of banana

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense is the most devastating disease of banana affecting commercial cultivars grown worldwide. An attempt has been made to identify antagonistic, non-pathogenic Fusarium oxysporum (np Fo ) isolates from banana soil. A total of 200 rhizosphere soil samples were collected from different commercial cultivars, as well as wild bananas. Forty Fusarium isolates were recovered, of which 33 were identified as Fo based on mycelial and spore characters. The identity of Fo isolates was confirmed by specific primers FOF1 and FOR1 in PCR reactions. The 33 isolates were confirmed as non-pathogenic following inoculation studies. Molecular characterisation of the np Fo isolates was determined by ribosomal internally transcribed spacer (ITS) restriction fragment length polymorphism. Pathogenic isolates were also included for comparison. Among the np Fo isolates, 14 ITS haplotypes were observed of which groups 6 and 10 were major groups consisting of 6 and 5 np Fo isolates, respectively. The in vitro evaluation of these np Fo isolates by dual culture plate and spore germination technique against the Fusarium wilt pathogen revealed the most inhibiting isolates were Ro-3 and Ra-1. Under pot culture studies, these np Fo isolates were evaluated by application: (i) at planting; (ii) at planting + 2 months after planting; and (iii) at planting + 2 months after planting + 4 months after planting, in both tissue-cultured as well as sucker-derived plants of the cultivar Rasthali. The Fusarium wilt severity score observed after 6 months demonstrated that the application of Ro-3 three times resulted in the reduction of Fusarium wilt severity by up to 89% as well as increasing the plant growth parameters significantly when compared with the pathogen-inoculated control plants. Field application of these np Fo isolates also reduced Fusarium wilt disease by 80%. The results of this study suggest that np Fo strain Ro-3 could be used for the management of Fusarium wilt disease of banana to sustain banana production.