Essential oil of Noni, Morinda citrifolia L., fruits controls the rice stem-rot disease without detrimentally affect beneficial fungi and ladybeetles

The use of botanical fungicides has been presented as a promising tool to replace the use of synthetic compounds, as the former seems to offer reduced risks to the environment and human health. Here, we characterized the major constituents and evaluated the potential of essential oils of Noni, Morinda citrifolia L. plants for controlling stem-rot disease caused by the fungus Sclerotium rolfsii Catt in Neotropical rice, Oryza sativa L., fields. Using in silico molecular predictions and toxicological approaches, we further assessed the essential oil selectivity against beneficial organisms such as the fungi Trichoderma asperellum Samuels, Lieckfeldt & Nirenbeand the ladybeetles Eriopis connexa Germar and Coleomegilla maculata DeGeer. Our results revealed that octanoic acid (64.0 %), butanoic acid (10.2 %), and hexanoic acid (8.6 %) were the major oil components. When applied at 30 mg/mL, the essential oil inhibited mycelial growth, whereas at 10 mg/mL, it inhibited the germination of all S. rolfsii sclerotia. The essential oil application at 25 mg/mL reduced disease severity in both curative (56.4 %) and preventive (71.2 %) methods. Essential oil applications (30 mg/mL) did not affect the beneficial fungus T. asperellum nor did it kill any ladybeetle. Our molecular docking analyses reinforced the essential oil selectivity actions predicting higher potential interactions between its major components and the tyrosine-tRNA ligase of S. rolfsii compared to those of T. asperellum. Collectively, our findings demonstrated that Noni essential oil could control S. rolfsii infestations without causing any detrimental effects on relevant beneficial organisms, highlighting its potential as an alternative fungicide.