Abstract

Banana plants derived from a tissue culture process possess a high rate of random variations that were widely used as popular cultivars due to the new desired traits. In this study, two near-isogenic lines, one susceptible (parental Williams-8818) and the other resistant (somaclonal variation progeny Williams-8818-1 from Williams-8818) to Fusarium oxysporum f. sp. Cubense (Foc4), were inoculated with race 4 of F. oxysporum (Fox). Production of O₂^•− , H₂O₂ and MDA, as well as changes in enzyme activities, and transcript levels of SOD and CAT in root extracts were monitored every 24 h over 4 days. The histochemical location of H₂O₂ was also detected. In the resistant iso-line, the accumulation of O₂^•− and H₂O₂, and the activation of SOD occurred in the first 24 h, but activation of CAT reached its maximum only after 48 h. All changes were generally lower in the susceptible iso-line when compared to the resistant iso-line. SOD transcripts were further up-regulated until 72 h in the resistant iso-line, but not in the susceptible iso-line. CAT expression was not affected in any of the two iso-lines. This suggests that expressions of the two key genes in the antioxidant system are less suitable indicators for Foc resistance in banana. In contrast, the first “oxidative burst” is a better indicator for different susceptibility of banana to Foc.

Key words: Banana, Fusarium oxysporum, catalase, reactive oxygen species, somaclonal variation, disease resistance.