Marine weeds against fungal phytopathogens - Current agronomical implications and intriguing perspectives for a sustainable future

Abstract

Controlling plant diseases is essential to the long-term viability of agriculture. As the most significant global agricultural liability, fungal phytopathogens infect a widespread array of host plants and epitomize a substantial menace to plant species. Appropriate solutions are needed in contemporary agriculture to solve the current trend of agricultural and food insecurity challenges. The use of bioproducts, including seaweeds, is one potential lever to encourage this transition. Alginates, laminarins, ulvans, phenols, and carrageneans are seaweed metabolites and chemicals that have been shown to have direct antifungal properties. These substances limit the growth of the fungi by breaking down their cell walls and causing oxidative stress. This provides considerable disease control in plants at an early stage and substantially lowers the incidence of disease. It is believed that by starting a cross-talk between the defense pathway and phytohormone, seaweed oligosaccharides and ulvans stimulate synthesis of plant protective compounds as well as physiological changes that prevent pathogen entry like lignification or accumulate cell wall degrading enzymes (chitinase or glucanase) or antimicrobial compounds (phenols, salicylic acid) at the sites of infection. This activates the ethylene, jasmonic, and salicylic acid pathways, which in turn increases the synthesis of several plant defense chemicals and activates pathogenesis-related genes (PR 1–3). Effective disease management has been facilitated by increased oxidative enzyme production to avoid oxidative stress induced by pathogen entry also. Rather than a single mechanism for disease control, seaweed compounds instigate a cascade of reactions that activate plant defense offering multifold resistance and protection against phytopathogenic fungi. This substantially facilitates a benign environment for plant growth, positively influencing the nutritional status of plant products and yield, in an economic as well as sustainable manner.