MERAH Othmane, Jean Michel Nancé, Isabelle Ribera, Johan Zicola, Emmanuel Raffy, Nicolas Urruty, Hélène Bardou, Clémence Beaudoin
The last decade has shown the decrease of chemical inputs use in agriculture. Indeed, REACH recommendations, advised the lowering of numerous chemical molecules which were used in agriculture. The chemical registration conditions have been hardned. This fact allows searching “green” molecules extracted from plants which are environmentally friendly. The botanical family of Brassicaceae is known aspotential source of bioactive molecules with antifungal, bacterial as well as nematicidal effects. All the Brassica species are rich in glucosinolates (GLs), in their seeds as well as in the green parts. The degaradation of GLs is catalysed by Myrosinases allowing to the production of several volatile compounds among them thiocyanates, isothiocyanates and nitriles, which present effective biocidal activities.
The aims of this study were to examine the chemical composition of the several plant parts at different phenological stages of brown mustard (Brassica juncea), and to test the efficacy of their glucosinolates (GLs) as an antifungal potential.
The HPLC analysis determined that two main compounds (Sinigrin and Gluconapin), which represented 99.5% of total GLs, were present in the different plant parts. As expected, the grain (110μmol.g-1DW) is the richer organ in GLs and 10 times higher than the green plant parts, at ripenning stage.
In order to study the effect of glucosinolates and their degradation compounds as antifungal molecules, biofumugation assays were performed against Fusarium solani, Botrytis cinerea and Rhizoctonia solani. Four GLs concentration (1, 3, 5 and 10μmol.g-1DW) were tested against three fungi culture of 10days old. The brown mustard powder, which was activated by adding water, revealed remarkable antifungal effect against the three studied fungi. Indeed, the growth and spore germination inhibition was complet at 10μmol.g-1DW for the all fungi and for rhizoctonia at 5μmol.g-1DW. The GLs and their degradation products had also a strong detrimental effect on spore germination of all the tested plant pathogens along with concentration as well as time-dependent kinetic inhibition of B. cinerea. Thus, the results obtained in this study demonstrate that B. juncea possess a wide range spectrum of fungicidal activity and could become an alternative to synthetic fungicides for controlling certain important plant fungal diseases.