Abstract

MOHAMED khouloud

In this study, potential allelopathic of a brown alga Padina pavonica (L) was evaluated. Aqueous extracts of the alga obtained at room temperature / 24 h (E1), 50°C / 4 h (E2) and 100°C / 2 h (E3) were tested on the germination and early growth of crop plants and growth of three fungal strains: Fusarium graminearum, Penicillium expansum and Alternaria alternata. Also, a fractional, of the alga in three organic solvents with increasing polarity: hexane, chloroform and acetone, was carried out and estimated as well as that the seedling growth soil composition was estimated. Results revealed a perceptible allelopathic capacity of P. pavonica. Although the percentage of germination of seeds was not influenced or slightly stimulated compared to the control in the presence of the three kind extracts and the dry powder, root and shoot growth was clearly improved. Results varied according to extracts and the vegetable material dose. Extract prepared at room temperature (E1) was most favorable. Stimulation percentage varied between 15 and 78% for roots and between 1 and 67% for shoots. Fungal growth was strongly inhibited in the presence of extract E3 compared with E1. Thus, growth inhibition percentages were 95.83, 80.76 and 63.33% for F. graminearum, P. expansum and A. alternata respectively, in presence of E1, against 41.66, 72.30 and 51.66% in presence of E3. For organic extracts, the most spectacular seedling growth stimulations were recorded in the presence of the chloroform extract. This indicated that the active molecules had an average polarity. The incorporation of algal powder in the soil was shown very beneficial for the target species in particular with low dose (50 g/Kg). Moreover, the effect of the algal powder was similar to that obtained by the addition of chemical fertilizers. Finally, algal powder allowed a clear improvement of the chemical composition of the soil concerning its richness on calcium, magnesium and organic matter and did not affect its pH. Results might be considered very interesting, since molecules of this species could have a double effect in the crops: a fertilizing effect and an antifungal effect without deteriorating the physico-chemical properties of the soil.