Bioactive substances extracted from seaweeds as a biocontrol agents, effects and identification [electronic resource].

Includes references.

Marine bioactive substances extracted from marine algae as a biocontrol agents are used in agricultural and horticultural crops as a biofertilizers to improve their yield and quality and mOreoVer 10 reduce the negative environmental impact. This study was planned to estimate the allelopathic effect of three seaweeds from different algae classes commonly dispersed in Alexandria beaches on certain (narrow and broad leaves) weeds and crops which grown in both summer and winter seasons as pre-emergence application. In addition qualitative and quantitative determined of the allelochemicals, phenol derivatives in algae using HPLC. The OXidative enzymes and total phenols were also detected. Moreover, to asses its effects as a foliar application on these plants as a post-emergence application by determined the algae phytotoxicity on chlorophyll a, b, carotinoids and total protein. The tested plants and weeds showed different response to the allelopathic effects of the water soluble extract of the tested algae. Ulva laetuea, the green alga was the most effective one followed by Pterocladia pinnate, the red alga. The seaweed Lesthesia difformis, the brown alga came at the last on this manner. Concerning summer plants, tomato was the most affected plant. Leathesia difforrnis by all concentration had no inhibitory effect on the winter weeds and crops germination. Ulva laetuea, had no effect on plant germination only on lower two concentrations but the higher concentrations gave significant reduction to the germination reach to 100% at lettuce, canary grass and black mustered when treated with 100% from this alga. Pterae/adia pinnat had no effect on the germination of barley and bean but this alga not only prevent completely shoot growth but also significantly reduce root growth in these two plants, also the lowest concentrations had the same effect on the rest of the plants. Concerning the acetone extracts of the seaweeds, Pterocladia pinnate had no effect on all plants germination. Tomato plants were the most affected one followed by lettuce, whereas, the highest concentrations of Ulva lactuca and Leathesia difformis prevent tomato germination The aqueous extracts of the three algae when applied as postemergence Canary-grass, lettuce, and common perslane were caused died after 10 days from the treatment. The algae reduced the soluble protein contents, total chlorophyll and carotienoids. On the other hand all algae treatments gave significant increase in these parameters especially in the important crops, bean, barley and tomato. HPLC analysis reflected that, Vanillin and p-coumaric acid were highly concentration in Ulva lactuca, Pterocladia pinnate and Leathesia difformis and the corresponding concentration in water extract were (189.64, 186.61 and 98.81 micro g -1 Dry weight) and (153.57, 173.34· and 76.53) respectively whereas from acetone extract were (227.1,88.91 arid 91.30 micro g -1 Dry weight) and (196.63, 72.81 and 77.22) respectively, followed by Pyrogallol in Ulva lactuca, Chlorogenic acid in· Pterocladia pinnate and Resorcinol in Leathesia diffo"nis in all extracts. Contrary, Salicylic acid and Ferulic acid had the lowest concentration in all tested seaweed.

Summary in Arabic.

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