Methyl jasmonate induced defense responses increase resistance to Fusarium oxysporum f. sp. cubense race 4 in banana

Abstract

Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum, is a severe banana (Musa spp.) root disease, currently threatening banana production worldwide. Methyl jasmonate (MeJA) has been recognized for its ability to induce systemic defense against various pathogens. In this study, we treated banana plantlets with 1.5mM exogenous MeJA. The effects of treatment on the level of chitinase, β-1,3-glucanase, total phenols (TP), hydrogen peroxide (H2O2), superoxide radicals (O2−), malondialdehyde (MDA), as well as the activities of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), catalase (CAT) and phenylalanine ammonia-lyase (PAL), plus disease incidence (DI) and disease severity (DS) were investigated. The results demonstrated that MeJA regulated the contents of H2O2 and O2−, and decreased MDA in banana roots. Meanwhile, plantlets treated with MeJA exhibited considerably higher chitinase, β-1,3-glucanase and TP contents, and higher activities of SOD, POD, PPO, CAT and PAL. In addition, MeJA treatment dramatically reduced disease incidence (DI) and disease severity (DS) of banana plants compared to control. The higher activities of scavenger antioxidant enzymes account for the reduction of cellular levels of reactive oxygen species (ROS), which is of vital importance for maintaining cell membrane integrity. The accumulation of pathogenesis-related proteins, chitinases and β-1,3-glucanase, as well as total phenols and PAL activity in the treated roots also indicated that MeJA triggered key enzymes of secondary metabolite biosynthetic pathways, suggesting that MeJA was involved in the activation of a disease-related defense system.