Chitosan induces salicylic acid and methyl salicylate in banana plants and reduces colonisation by Fusarium oxysporum f. sp. cubense TR4

Banana ( Musa spp.) cultivation is essential for food security; however, the clonality of commonly used forms renders them highly susceptible to pests and diseases. The wilt fungus Fusarium oxysporum f. sp. cubense Tropical Race 4 (FocTR4) threatens banana production worldwide. Chitosan induces salicylic acid (SA) and methyl salicylate (MeSA) production in banana plants and reduces colonisation by FocTR4. This polymer induces the main SA biosynthetic pathway mediated by isochorismate synthase 1 and phenylalanine ammonia-lyase. Chitosan also induces systemic acquired resistance genes, mainly flavin-dependent monooxygenase 1 ( FMO1 ), in banana roots. The banana genotypes Petit Naine, Gros Michel, Enzirabahima, Yangambi Km5, and Foconah differ in their response to chitosan. In the Foc-resistant Yangambi Km5, chitosan induced an approximately 7-fold increase in FMO1 . Preventive chitosan treatments together with the endophytic biocontrol fungus Pochonia chlamydosporia strain 123 reduced colonisation of banana roots by FocTR4 (approximately 4-fold). Therefore, chitosan and beneficial endophytes can help sustainably manage FocTR4 infection in bananas. We propose a novel method to induce local and systemic defences for biomanagement of banana pests and diseases. • Chitosan depolarizes banana root cell membranes which respond reducing their fluidity. • Chitosan increased root exudation of jasmonic (JA) and salicylic (SA). • Chitosan applied to roots induced SA systemic acquired resistance inducing MeSA biosynthesis in banana leaves. • Chitosan and the biocontrol fungus Pochonia chlamydosporia 123 reduce colonization of banana roots by FocTR4.