Exploration of New Oxidative Stress Nematicidal Compounds and Valorization of Satureja montana L. Essential Oils and Hydrolates as Plant Biopesticides

Plant diseases cause economic challenges because they are responsible for estimated pre- and postharvest losses of 16–28% of crops yearly. Control is aimed at the use of chemical protectants, which reduce or retard the growth of the pathogen population. Another option is the use of resistant varieties, which reduce the pest population or increase recovery from injury caused by the enemies. However, resistant varieties become susceptible after few years of cultivation due to pathogen adaptation and evolution to cultivated varieties. Research of new environmentally benign products active against pests and diseases are required that control target organisms without harming the environment. In this thesis, I evaluated for the first time the nematicidal activity of new synthesized maleimide derivatives by structure-activity relationship (SAR), some selected haloacetophenones and transition metal ions. I also developed a new method to assess the metabolome alteration induced by these products on nematodes. Finally, I valorized a carvacrol chemotype domesticated plant of S. montana by evaluating its activity on insects, Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi; and on the root-knot nematode Meloidogyne javanica. The maleimide derivatives were easily synthesized in a one pot reaction; haloacetophenones were commercially available and metal ions present as sulphate or nitrate salts. The tested compounds showed strong nematicidal activity against Meloidogyne incognita, X. index and G. pallida with EC50 values lower than 5 mg/L. I also found a synergism action between maleimide and copper ion on one hand and between copper ions and tannins on the other hand. A GC-MS metabolomics analysis showed that these compounds might induce oxidative stress in nematodes by modifying the levels of fatty acids and acylglycerols. After a field experiment and phytotoxicity assays, these first reported nematicidal compounds could be used in crop protection against nematodes. S. montana essential oil (EO) chemical composition was influenced by the fertilizers applied and the EO extraction method. Hence, the conventional agriculture plants showed a lower level of p-cymene with a higher level of carvacrol while more than 20 compounds showed significantly difference levels according to the method of extraction, laboratory or semiindustrial. The EOs and the organic phase of hydrolates with LC50 values of 20-65 µg/cm2 modified the feeding behavior of Spodoptera. littoralis. S. montana EOs repel Rhopalosiphon. padi and Myzus. persicae with settlement inhibition LC50 values estimated at 25-60 µg/cm2. The plant also inhibited the germination and growth of Lolium perenne at 10 mg/mL. Furthermore, ethanol extracts of S. montana did not show any activity on the pests. However, we successfully valorized the EO by product hydrolates on the insects and nematode.