The phytohormone methyl jasmonate as an activator of induced resistance against the necrotroph Alternaria porri f. sp solani in tomato plants

Exogenous application of 0.1 mM methyl jasmonate (MeJA) throughout seed soaking or fumigation of seedlings could induce resistance against the necrotrophic fungus Alternaria porri f. sp. solani in tomato. MeJA applied at 0.01, 0.1, and 1 mM was found to reduce spore germination and mycelial growth in vitro. This compound at 0.01 and 0.1 mM did not cause toxic responses in the tomato plants; however, ethylene production by seedlings was observed to increase after using of all concentrations. A significant increase in the levels of defense markers such as total phenolics, anthocyanins, and phenylalanine ammonia-lyase activity, in response to exogenous MeJA, was observed. Pretreatment of tomato by soaking the seeds in MeJA or treating them with gaseous MeJA efficiently reduced the development of disease caused by Alternaria only when MeJA was applied at 0.1 mM concentration. Seed priming is an easier method of resistance induction than exposure to gaseous MeJA.