Moringa oleifera Seed Cake as a Promising Prototype for Designing Phyto-Protectants Against Fusarium oxysporum f. sp. lycopersici in Tomato

Moringa oleifera seed cake is the byproduct of moringa oil extraction and the most valuable source of 4-(α-L-rhamnosyloxy)benzyl glucosinolate (glucomoringin; GMG), the precursor of 4-(α-L-rhamnosyloxy)benzyl isothiocyanate (moringin; GMG+M). The vascular fungus Fusarium oxysporum f. sp. lycopersici (FOL) is an important soil-borne pathogen of tomato in cultivated areas worldwide. Coating seeds with phytochemicals has been reported to prevent seed transmission and control seedling infection. In this work, GMG was extracted and purified from moringa seed cake on the multigram scale, and GMG+M solutions obtained through controlled hydrolysis of the precursor with commercial myrosinase were evaluated against the pathogen both in vitro and in planta. FOL conidia germination and mycelial growth were significantly inhibited by GMG+M solutions in the range 1–1000 µM, in a dose-dependent manner, compared to GMG and control treatments, which did not differ significantly. Interestingly, the coating of tomato var. crovarese seeds with GMG or GMG+M (100 µM) resulted in equally effective reduction (70%) of the disease severity in post-emergence, suggesting a plant-mediated mechanism underlying the efficacy of the intact glucosinolate. Seed coating with both phytochemicals triggered polyphenol oxidase (PPO) activity in five-day-old tomato sprouted rootlets. This study highlighted the potential biotechnological value of M. oleifera seedcake for the development of a sustainable biopesticide.