Can glucosinolates act as plant elicitors? The use of kale (Brassica oleracea var. acephala) green manure for the activation of systemic plant defenses in bell pepper

In the search for new alternatives to avoid problems associated with the use of chemical fungicides in agriculture, the use of green manure (GM) could help combat fungal diseases of crops, such as those produced by the necrotrophic pathogen Rhizoctonia solani. In the case of brassica tissues used as GM, this could have an elicitor capacity of systemic plant resistance related to the presence in these tissues of defense metabolites called glucosinolates (GSLs), as a form of damage-associated molecular patterns (DAMPs). Kale (Brassica oleracea var. acephala) leaves were used as GM and their GSL content was removed by autoclaving and applied to pepper plants infected with R. solani. Autoclaving removed part of the GSL glucobrassicin (GBS) (85%) and sinigrin (19%) content of the kale tissues. The application of intact kale tissues to roots of pepper plants produced a systemic activation of foliar defenses via the salicylic acid (SA) and ethylene (ET) pathways, significantly reducing pathogen damage. In addition, this systemic response led to the accumulation of secondary defense metabolites in leaves, such as pipecolinic acid and hydroxycoumarin or gluconic acid, among others. Therefore, GBS-rich GM kale tissues were able to activate systemic defenses in bell pepper against foliar pathogens via the SA/ET hormonal pathways, accumulating secondary defense metabolites.