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The research was carried out in the Biodiversity Laboratory of National Commission for Biotechnology and Plant Diseases Laboratory,Faculty of agriculture, Damascus University during 2020-2024 for isolating and identifying some of the causes of cucurbit wilt and bacterial isolates from the rhizosphere of cucurbits and testing their antagonistic ability against the cause of Fusarium vascular wilt. 30 samples were collected from different squash families; Cucumber, zucchini, Sweetmelon, and watermelon from four governorates; Damascus, Damascus countryside, Daraa,and Deir ez-Zor. The fungal pathogens were isolated, described morphologically, their pathogenicity was studied, and the percentage of infection and its severity of each isolate on its host were calculated. It was found that 10 fungal isolates belong to the species Fusarium oxysoporum, then their host specialization and formae specials were determined.Both the isolates FO1 and FO2 belonged to the form Fusarium oxysporum f.sp. cucumerinum and isolates FO5 and FO6 belong to the form Fusarium oxysporum f.sp. melonis while isolates FO7, FO8, FO9 and FO10 were of the form Fusarium oxysporum f.sp. niveum, and the diameter of the fungal culture ranged between 3.8 cm and 6.8 cm after seven days of incubation in PDA medium at 27±3 C°, while the infection severity ranged between 12% and 69.3%, with isolate FO7 taken from watermelon in Daraa being the highest. In terms of infection rate and disease severity, it is followed by isolate FO5, from Sweetmelon from the Deir ez-Zor region, according to the infection scale. 40 bacterial isolates showed an antagonistic ability towards its pathogenic forms; FO7 and FO5 but the 4 bacterial isolates B20, B2, B10, and B25 were chosen that showed superiority in inhibiting the two pathogenic forms FO7 and FO5 in the laboratory. The biochemical identification of the bacterial isolates showed that, the two isolates B2 and B10 belonged to the species Pseudomonas fluorescens, and the two isolates B20 and B25 belonged to Bacillus subtilis. in the pot experiment, Watermelon and Sweetmelon compared to the control infected with the fungus not treated with bacteria. Isolate B20 had the best inhibition rat of both pathogenic fungi FO5 and FO7, as the infection rate on Sweetmelon and Watermelon decreased by 40% and 30%, respectively, and the severity of the disease was 10% and 11%, respectively, compared to the rest. isolates, while the control infection with the pathogenic fungus had an infection rate of 80% on Watermelon and 96% on Sweetmelon. also The results showed the effect of bacterial isolates on some growth indicators of watermelon plants in pots. The significant superiority of isolate B20 was demonstrated in all the studied growth indicators of Watermelon plants compared to the rest of the bacterial isolates. Plant treated with bacterial isolate B20 only recorded the highest of stem height, wet and dry weight of the shoot, length. the root wet and dry weight of the root system, compared to the rest of the treatments and the healthy control (85.60 cm, 52.13 g, 8.43 cm, 32.53 cm, 6.39 g, 3.27 g, respectively). For Sweetmelon, treatment with bacterial isolate B20 only recorded the highest plant height, weight. Wet and dry weight of the shoot, root length, wet weight and dry weight of the root, compared to the rest treatments with the healthy control (76.00 cm, 48.66 g, 7.43 g, 32.83 cm, 5.52 g, 3.51 g, respectively). The ability of the isolates to degrade phosphate and potassium to produce the hormone indole acetic acid was also tested, as isolate B20 ability to decompose phosphate and potassium and had a remarkable efficiency in producing the hormone indole acetic acid. These results open the way for further testing of the selected bacterial isolates in inhibiting the causes of Fusarium vascular wilt disease for later use in the production of biofertilizers.
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