Methyl Jasmonate Induces Phenylphenalenone Accumulation, Resulting in Black Leaf Streak Disease Resistance In Banana (Musa acuminata cv. Grand Nain)

This study analyzes the effects of methyl jasmonic acid (MeJA) and salicylic acid (SA) on the defensive responses of banana cv. Grand Nain against Black Leaf Streak Disease (BLSD), caused by Mycosphaerella fijiensis. The metabolic responses were analyzed using HPLC and NMR. With the exception of rutin, all compounds were identified as phenylphenalenones. Application of MeJA and SA resulted in an increase in the level of irenolone and hydroxyanigofurone production. Furthermore, MeJA was observed to induce the de novo synthesis of 2-(4′-hydroxyphenyl)-1,8-naphthalic anhydride, 2-(4′-methoxyphenyl)-1,8-naphthalic anhydride, and 7-(4′-hydroxyphenyl) naphthal-8-formyl-1-carboxylic anhydride. Molecular analysis revealed a significant upregulation of some genes implicated in the phenolic compound synthesis and of lipoxygenase but not the ones of PR proteins. MeJA-treated leaves showed improved resistance to BLSD. The results suggest that MeJA may serve as an effective protective strategy against the most damaging banana disease, providing a potential strategy for protecting banana crops.