Application of plant-derived bioactive compounds as seed treatments to manage the rice pathogen Fusarium fujikuroi

Plant essential oils (EO) possess antifungal properties due to the presence of terpenoids and phenolics capable of damaging microbial cell membranes. The compounds present in EO could represent a valid alternative to synthetic fungicides in rice crop protection, especially in Europe, where the available plant protection products are increasingly scarce, particularly for managing seed-borne fungal pathogens like Fusarium fujikuroi Nirenberg, the causal agent of bakanae disease. Bakanae is a major concern in Europe for seed producers, which often fail to comply with the strict regulatory limits on the presence of the pathogen in the field, resulting in the rejection of the seed crop from marketing and economic losses. The present work was aimed at studying 1) the in vitro effect of EO derived compounds against F. fujikuroi and 2) their efficacy in disease management under field conditions applied as seed treatments. Results confirmed the in vitro antifungal activity of tested compounds: specifically, thymol (0.025% vol/vol), terpinen-4-ol (0.1%), and eugenol (0.05%) showed strong antifungal activity against all the tested F. fujikuroi strains. Two-years, two-locations open field trials showed that seeds treated with thymol (20%) and eugenol (5%) significantly reduced bakanae incidence compared to untreated control, without any phytotoxicity effect on rice seed. The efficacy of these two compounds in managing the disease without affecting germination rates was comparable to the commercially available prochloraz and triticonazole formulation, considered as the positive control. Our results suggest that thymol and eugenol could be used as alternative fungicides in innovative formulations for seed dressing, with the advantage of being compliant with the European IPM framework and organic farming legislation.