Defense-related gene expression in susceptible and tolerant bananas ( Musa spp.) following inoculation with non-pathogenic Fusarium oxysporum endophytes and challenge with Radopholus similis

Radopholus similis is a major pest of East African highland cooking bananas ( Musa spp.) in Uganda. Non-pathogenic Fusarium oxysporum endophytes, isolated from bananas in farmers’ fields, have shown potential to reduce R. similis numbers in tissue culture banana. The mechanism through which endophytes confer resistance to nematodes has previously been demonstrated to involve induced resistance. In this study, the expression of eight defense-related genes in banana was investigated using quantitative real-time reverse transcription PCR. Plants of susceptible (cv. Nabusa, genomic group AAA-EA) and tolerant (cv. Kayinja, genomic group ABB) banana cultivars were inoculated with endophytic F. oxysporum strain V5w2. Gene expression levels were analysed following endophyte inoculation and nematode challenge. Endophyte colonization of roots of the tolerant cultivar induced transient expression of POX and suppressed expression of PR-3, lectin, PAE, PAL and PIR7A. Catalase and PR-1 activities were up-regulated in the tolerant cultivar 33 days after endophyte colonization of roots, but their expressions were further up-regulated following nematode challenge. Apart from POX and lectin, the other genes analysed were not responsive to endophyte colonization or R. similis challenge in the susceptible cv. Nabusa. This is the first report of endophyte-induced defense-related gene expression in banana.