Biostimulants derived from red seaweed stimulate the plant defence mechanism in rice against Magnaporthe oryzae

Seaweed extracts contain many bio-elicitors that can greatly improve natural plant immunity, so stimulating plant immunity with these formulations is a sustainable approach. The red seaweed (Kappaphycus sp. and Eucheuma sp.)–derived biostimulants (LBS6 and LBD1) were tested for their ability to protect rice against fungal blast disease. Compared to non-primed plants, LBD-1 primed and challenged inoculated plants had substantially higher levels of defence-related enzymes such as phenylalanine ammonia lyase, chitinase, peroxidase, polyphenol oxidase and phenolic content. In primed and Magnaporthe oryzae isolate MG-01 challenge–inoculated plants, altered transcript levels of various defence genes such as OsPR-1, PAL-6, PR1-5 and PR-15 were observed. Disease tolerance to the blast pathogen was tested in glasshouse conditions using the foliar application or root dipping with various concentrations of LBD-1. Both approaches significantly decreased disease severity, but the combined spray and root dipping was more effective than either spray or root dipping alone. These findings indicate that priming rice plants with seaweed biostimulant induces resistance to blast fungus, most likely by inducing defence-related genes and enzymes.