Contribution à l’étude des effets biocides des extraits végétaux d’espèces spontanées sur des bioagresseurs des cultures en milieu saharien

Abstract

In the context of enhancing and valorizing natural resources, methanolic extracts from two parts of three spontaneous plant species collected in the Algerian Sahara Cotula cinerea Del. (inflorescences and leaves), Peganum harmala L. (seeds and leaves), and Pergularia tomentosa L. (seeds and leaves) were tested for their antifungal activity. Extraction yields ranged from 11% to 24%. The highest yield was obtained from the leaf extract of C. cinerea (24%), followed by the leaf extract of P. harmala (22%) and P. tomentosa (21%). The seed extract of P. harmala showed a yield of 20.1%, while the inflorescence extract of C. cinerea yielded 18%. The lowest extraction yield (11%) was obtained from P. tomentosa seeds. Phytochemical screening of the hydro-methanolic extracts obtained by reflux extraction revealed a rich and diverse composition of secondary metabolites. Tannins were present in all crude extracts except the leaf extract of P. harmala Alkaloids were characteristic of C. cinerea and P. harmala, but absent in P. tomentosa. Flavonoids were detected in all extracts except those of P. harmala. Reducing compounds, free quinones, saponins, and steroids were completely absent in C. cinerea, while P. harmala lacked flavonoids and free quinones, and P. tomentosa was devoid of coumarins and alkaloids. Terpenoids were found in all crude extracts except the seed extract of P. harmala. In vitro evaluation of antifungal activity against the mycelial growth of two pathogenic fungi Mauginiella scaettae Cav. and Fusarium oxysporum f.sp. albedinis using a direct contact test, revealed variable inhibitory effects among the tested extracts. Methanolic extracts of C. cinerea and P. harmala exhibited significant antifungal activity at all tested concentrations against both fungal species, with markedly reduced mycelial growth compared to the control. Notably, the seed extract of P. harmala at 20% concentration completely inhibited the mycelial growth of M. scaettae Cav. For F. oxysporum f.sp. albedinis, inhibition rates of 61.29%, 72.89%, and 83.94% were observed at 40%, 50%, and pure extract concentrations, respectively. Abstract The seed extract of P. tomentosa showed moderate antifungal activity against M. scaettae at lower concentrations, while the inflorescence and leaf extracts of C. cinerea at 40% concentration inhibited F. oxysporum f.sp. albedinis growth by more than 50%. These findings suggest that it would be of particular interest to further investigate the potential synergistic effects of aqueous extracts from the studied plants.