Effect of Methyl Jasmonate on Phytoalexins Biosynthesis and Induced Disease Resistance to Fusarium oxysporum f. sp. Vasinfectum in Cotton (Gossypium hirsutum L.)

The effect of methyl jasmonate (MeJA) sprayed on cotton healthy leaves was evaluated in terms of inherent bioactive chemicals induction. The total phenolic content significantly increased after MeJA 5.0mM treatments compared to the other tested concentrations (0; 2.5; 10; 15; 20mM). Among the eleven phenolic compounds which were found except for ferulic acid, gossypetin, gossypol, 3-p-coumaroylquinic acid, and piceatannol were identified as major phenolic constituents of cotton. Their content also significantly increased after the MeJA treatment. In addition, gossypol increased 64 times compared to the control, in the 5.0mM MeJA treatment. Furthermore, cichoric acid, chlorogenic acid, and pterostilbene are synthesized de novo in leaves of MeJA-treated plant. Treatment of cotton leaves with MeJA5.0mM followed 72h of incubation hampered the expression of Fusarium wilt caused by Fusarium oxysporium f. sp. vasinfectum (FOV). MeJA efficiency was concentration and incubation time dependent. Disease severity onMeJA-treated leaves was significantly lower as compared to the control. Therefore, the high content of gossypetin, gossypol, 3-pcoumaroylquinic acid, ferulic acid, and piceatannol and the presence of cichoric acid, chlorogenic acid, and pterostilbene in plants treated with MeJA, contrary to the control, are essential to equip the cotton compounds with defences or phytoalexins against FOV.