Potential bio-control substances produced by fungi and plants of different Mediterranean Basin ecosystems.

Abstract

The main objective of this thesis is the study of metabolites with a potential herbicidal and fungicidal activity, produced by fungi and plants of the Mediterranean basin. These bioactive metabolites have been characterized chemically and biologically using bio-guided chromatographic methods. Indeed, the macro-fungus Agaricus litoralis, collected in the forest of Jebel el Ouahch in the Constantine region in eastern Algeria, was identified using morphological and molecular data. As a result, a high phytotoxicity of its EtOAc extract on the leaves of Lycopersicon esculentum L., test plant, has been revealed from which a well-known phytotoxic metabolite, tyrosol, was isolated and identified by spectroscopic methods. The phytotoxic activity of this latter molecule, tyrosol, was tested on seven agrarian plants and two wild plants using the leaf puncture test. The obtained results revealed that the highest toxic effect was observed on Vitis vinifera L., Prunus armeniaca L., Prunus persica L. Batsch, Cucurbita L., and Rubus fruticosus L. at 1 mg / mL; while moderate toxic effects were observed on Solanum melongena L. leaves and less phytotoxicity on both Ficus carica L. and Citrus limon L. Osbeck leaves. Besides, a new sesquiterpenoid belonging to the seco eudesmanolides subgroup, called inuloxin E, has been isolated from Dittrichia viscosa, as well as the already known sesquiterpenoids inuloxins A-D, and α-costic acid. Inuloxin E was characterized by spectroscopic data, mainly NMR and ESIMS. Both inuloxins D and E inhibited the seed germination of the parasitic weed Orobanche Cumana, but they were inactive on the seeds of Orobanche minor and Phelipanche ramosa. Moreover, the germination activity of certain semisynthetic esters of inuloxin D has also been studied, revealing their antigerminating effects on O. minor and P. ramosa. On another aspect, two new bioactive ophiobolan sestertepenoids ; drophiobiolins A and B, characterized by NMR and HRESIMS, were obtained from Drechslera gigantea, a fungus known as a mycoherbicide in the biological control of Digitaria sanguinalis. In addition, other metabolites characteristic of this same fungus were likewise obtained; ophiobolin A as the main metabolite, 6-epi-ophioboline A, 3-anhydro-6-epi-ophioboline A, and ophioboline I. In fact, the phytotoxic activity of drophiobiolins A and B was sought by a leaf perforation test on plants; cultivated weed (Lycopersicon esculentum L.), host weed (Digitaria sanguinalis L.), and non-host one (Chenopodium album L.) , where, these two newly identified ophiobolins showed significant phytotoxicity, at the highest concentration of 10-3 M, in comparison with that of ophiobolin A. The antiproliferative activity of drophiobolins A and B was also evaluated revealing that the two molecules exhibited a remarkable cytotoxicity against Hela B cells with an IC50 value equal to 10 M. However, they had less effect against Hacat, H1299 and A431 cells, compared to ophiobolin A. In another axis, two new penta- and tetra-substituted cyclopentenones; named phaseocyclopentenones A and B, as well as guignardone A were purified from Macrophonina phaseolina. This phytopathogenic fungus was isolated from infected soybean tissues showing symptoms of anthrax in Argentina. The two phaseocyclopentenones A and B were identified by spectroscopic methods (essentially 1D NMR “1H and 13C”, 2D NMR, and HR-ESIMS). During a phytotoxicity test on a non-host plant (Solanum lycopersicum L.) by leaf puncture, phaseocyclopentenones A and B, as well as guignardone A displayed interesting phytotoxic activity. These new compounds are also active in a cuttings trial on the same plant. In contrast, no phytotoxicity of the three compounds was detected on the soybean host plant (Glycine max L.). Besides, no antifungal activity was developed by the same molecules against certain phytopathogenic molds, namely Cercospora nicotiane and Colletotrichum truncatum, which were similarly isolated from infected soybean plants in Argentina.