Phytoelicitor activity of Sargassum vulgare and Acanthophora spicifera extracts and their prospects for use in vegetable crops for sustainable crop production

The phytoelicitor and phytostimulatory properties of alkaline extracts of two tropical seaweeds, Sargassum vulgare C. Agardh and Acanthophora spicifera (M.Vahl) Borgesen, collected from the coasts of Trinidad were investigated in tomato and sweet pepper crops. Foliar applications of seaweed extracts (SWE), at 0.5% concentration, resulted in substantial reductions in disease severity by the pathogens, Xanthomonas campestris pv. vesicatoria and Alternaria solani under greenhouse and field conditions. The effects of SWE on disease suppression were significantly improved when integrated with a minimum dose of fungicide. SWE-treated plants also showed enhanced plant growth and yield parameters. Investigations into the modes of action for disease suppressive effects revealed that SWE-treated plants had sustainably augmented defense enzyme activities and phenolic levels. The activation of defense pathways was validated by confirming the upregulation of marker gene transcripts (PR-1a, PinII, and ETR-1) which are involved in defense signalling pathways. The SWE-treated plants also showed significant upregulation of genes involved in auxin (IAA), gibberellin (Ga2Ox), and cytokinin (IPT) biosynthesis. Multiple applications of SWE in crop plants have minimized the need for chemical fungicide sprays. The current study demonstrates the applicability of tropical SWE for use in vegetable plants for achieving environmental-friendly and sustainable crop production.