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المستخلص: تضمنت الدراسة الحالية عزل وتشخيص طحالب كبيرة من بيئتين مائيتين محليتين مختلفتين. تم عزل ثلاث طحالب كبيرة هي Cladophora glomerata (N) وEnteromorpha rafsii من منطقه بحر النجف في محافظة النجف, في حين عزل Cladophora glomerata (R) من احد مبازل منطقة الراشدية ش | The present study includes isolation and identification of Macro - algae from two different environmental water bodies. Three Macro - algae were isolated, Cladophora glomerata (N) and Enteromorpha ralfsii from Baher Al - Najaf region in Holy Najaf city. In addition, C. glomerata (R) was isolated from Al - Rashdiya, north of Baghdad.Phytopathogenic fungi from soil and some infected fruits were also isolated. They were identified as Pythium ultimum and Rhizoctonia solani.Water and ethanol were used to extract each algae to evaluate their antifungal activity against isolated phytopathogenic fungi. Different concentrations of these algal extracts had been prepared which are (10, 25 and 50) mg/ml and the antagonistic activity against the isolated phytopathogenic fungi were evaluated, the hot and cold water extracts did not show any antagonistic activity against fungi. However, all these extracts were ignored in the future work for this study. Furthermore, the hot ethanolic extract was more efficient than these of cold ethanolic extracts. Results have been shown that there were significant differences when macro - algal ethanolic extract were used.C. glomerata (R), which isolated from Al - Rashdiya, was more efficient against tested fungi than the same alga what isolated from Baher Al - Najaf region. However, E. ralfsii extract was more efficient against tested fungi than C. glomerata (N). Percentage of inhibition against P. ultimum when hot ethanolic extract of E. ralfsii, C. glomerata(R) and C. glomerata(N) were (88.8, 83.3 and 63.3) respectively.However, results for cold ethanolic extract of the same algae were (63.3, 52.2 and 32.2) respectively when 50 mg/ml of algal extracts were used.Percentage of inhibition against R. solani when hot ethanolic extract of E. ralfsii, C.glomerata (R) and C.glomerata(N) were (94.4, 100 and 78.8) respectively.However, results for cold ethanolic extract of the same algae were (66.6, 64.4 and 48.8) respectively when 50 mg/ml was used. According to the difference in biological activities against those phytopathogenic fungi caused by the same species of macro - algae or different genera from different environments. Due to difference in biological activity of the same macro - algae species Physiochemical parameter for each environments obtained such as air and water temperature, Turbidity (NTU), Electrical Conductivity(EC)and Salinity%, Water pH, CA+2 concentration, Mg+2 concentration, Total Hardness and Total Alkalinity. Results indicated that soaked Cucumis sativus and Capsicum annum seeds in cold and hot ethanolic macro - algae extracts of (E. ralfsii, C. glomerata (R) and C.glomerata (N) for 24 hours were able to protect seed germination that have been grown in a Petri dish contaminated with P. ultimum and R. solani comparing with control. In addition, results indicated that spraying C. sativus and C. annum seedling with these algal extracts within two weeks old again protects these seedlings from the same phytopathogenic fungi either before or after 24 hr. However, results indicated that adding the algal extracts within two months age to the C. sativus and C. annum plants again protects these plants from the same phytopathogenic fungi comparing with control and fungicide treatment. Moreover, results indicated that the active chemical compounds in E. ralfsii was Tannins, Saponins and Flavonoids. While C. glomerata was contained Tannins, Saponins, Alkaloid and Phenols. Results indicated that both hot crud methanolic extract of C. glomerata (R) and E. ralfsii have a lot of active chemical compounds against micro - organisms by using the GC - Mass Spectrometry technology.