Induction of Resistance in Melon Seedlings Against Soil-borne Fungal Pathogens by Gaseous Treatments with Methyl Jasmonate and Ethylene

The plant signalling molecules methyl jasmonate (MeJA) and ethylene, alone and in combination, were tested by seed gaseous treatment for their ability to induce resistance in melon seedlings against gummy stem blight, white mould disease and fusarium wilt caused by the soil-borne fungal pathogens, Didymella bryoniae, Sclerotinia sclerotiorum and Fusarium oxysporum f. sp. melonis, respectively. MeJA and ethylene treatments significantly enhanced the resistance level against the tested fungi, whereas when applied simultaneously their protective effect was less pronounced. Treatments with MeJA and ethylene were also tested in terms of biochemical responses by the measurement of variations of chitinase and peroxidase activities. MeJA treatment increased exochitinase activity in melon seedlings, whereas ethylene induced both exochitinase and peroxidase activities. Conversely, when combined, MeJA and ethylene consistently enhanced the activity of both exo- and endochitinase as well as peroxidase activity. The augmented level of chitinase and peroxidase activity was accompanied by the differential induction of an acidic chitinase isoenzyme and of both basic and acidic peroxidase isoenzymes. Results indicate that some inducible defences and associated resistance are independently enhanced in melon seedlings by the action of MeJA or ethylene, suggesting the coexistence of different resistance mechanisms.