الفهرس 
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Abstract
Watermelon (Citrullus lanatus (Trunb.) Matsum and Nakai) is a widely cultivated vegetable crop that is consumed globally as fruit. However, the growth of this plant is often threatened by Fusarium wilt in soils where watermelon is continuously mono-cropped. Watermelon wilt disease is caused by Fusarium oxysporum f. sp. niveum . The fungus is found worldwide in soils in temperate, subtropical and tropical regions and causes wilt disease of watermelon seedlings and older plants. Results could be summarized as follow :- 1-Survey of watermelon wilt disease was carried out three times during each growing seasons at three governorates, i.e. Kafr El-Shikh (Baltem, Kafr El-Shikh), Ismailyia (Abo-Soyer, Salhiya) and Behira (Noubariya, Badr City). Results indicated that a high percentages of infection were recorded in all surveyed locations especially with Gorma cv. 2--Frequency of isolated fungi from diseased watermelon plants(cvs. Giza 1, Gorma and Aswan hybrid ) showing wilt disease symptoms were recorded . Results illustrated that FON was the most frequent isolated fungus from diseased watermelon roots . It occupied the first order ( 86.4 to 94.3 %). Meanwhile, F. solani , R. solani and Penicillium sp. were least frequency . 3- Three purified isolates of FON which were isolated from wilted watermelon plants of different cultivars i.e. Giza1, Aswan hybrid and Gorma collected from different locations i.e. Kafr El-Shikh (Baltem & Kafr El-Shikh), Ismailiya (Abo-Soyer & Salhiya) and Behira (Noubariya & Badr City) were tested for their pathogenic ability on watermelon plants under greenhouse conditions. Results indicated that all isolates of FON were able to attack watermelon plants causing wilt symptoms. The most aggressive isolate was Nobariya ( Giza 1 cv ) it caused disease infection by 71.9, 56.3 and 53.1 % for Gorma , Giza1 cvs and Aswan hybrid respectively after 30 days of sowing. 4- Three isolates of FON, F. solani , R. solani and Penicillium sp. were screened depending on their pathogenic ability were tested for their pathogenic ability on watermelon plants under greenhouse conditions. Results indicated that all isolates of FON were able to attack watermelon plants causing damping off symptoms. The most aggressive isolate was isolated from Giza 1 cv. it caused disease infection by it caused disease infection by 70.3, 57.7 and 54.7 % for Gorma , Giza1 cvs and Aswan hybrid respectively after 30 days of sowing. Other isolates of F. solani and R. solani caused the disease infection ranged between 7.8 to 9.4 and 13 to 16.0 % after 15 and 30 days of sowing respectively . 5- Three watermelon cultivars, namely Giza 1 , Gorma and Aswan hybrid in addition to Beita Alpha (cucumber) , Honeydew (Muskmelon ), Eskandarany (Squash ), Castel Rock ( tomato) , California ( pepper) , Giza 3 ( bean) and master ( pea ) were evaluated against FON infection. Results showed that among the tested host plants, watermelon cultivars only were susceptible to infection . 6- Five watermelon cultivars, namely Giza 1 , Giza 21, Gorma ( for seed production ) ,Aswan hybrid and Sugar baby against FON infection were evaluated. Results illustrated that all tested watermelon cultivars are susceptible to infection with FON. The highest infection was recorded with cvs. Gorma and Sugar Baby they recorded the disease infection by 75.0 and 71.9 after 30 days of sowing respectively, followed by Giza1, Giza 21 and Aswan hybrid. 7-All isolates of pathogenic fungus ( 6 isolates ) differed in protein pattern . It is apparent that isolates are separated into three groups , the first group included 3 isolates (4, 5, and 6 ) which were isolated from Salhiya , Noubariya and Badr City respectively. The second group included 2 isolate ( 1 and 3 ) which were isolated from Baltem and Abo-Soyer, while the third group included one isolate ( 2) isolated from Kafr El-Shikh. It is noticed that no relationship between isolates , level of virulence or geographic origin. Laboratory experiments8- Five antagonistic isolates of Trichoderma harzianum, T. viride ,Chaetomium sp., Aspergillus niger and Penicillium sp. were tested to study their inhibitory effect against FON in vitro. Results showed that all isolates of tested fungi significantly reduced the growth area of FON. The highest reduction in fungal growth area was obtained with T. harzianum ( 2) , T. viride ( 3) and Chetomium sp. (4) which reduced the fungal growth area by 84.3 , 84.3 and 81.1 % respectively . Meanwhile, other isolates showed moderate effect. 9- Culture filtrates of antagonistic fungi were tested to study their inhibitory effect against FON in vitro. Results indicated that. compete inhibition was obtained with culture filtrates of T. harzianum ( 1, 2) , T. viride ( 2, 3 ) at concentration of 50.0 and 75.0 %, while, Chetomium sp ( 2, 4) at 75.0 %. As for spore germination, complete reduction was obtained with culture filtrates of all isolates of T. harzianum and T. viride at concentration of 50.0 or 75.0 %, and Chetomium sp. at 75.0 %.10- Four pure cultures of antagonistic bacteria i.e. Bacillus subtilis, B. megatherium, P. fluorescens, and P. putida were tested to study their inhibitory effect against F. oxysporum f. sp. niveum in vitro. Results illustrated that complete inhibition was obtained with B. subtilis ( 4, 5) and P. fluorescens ( 1,2 ) . The highest reduction was obtained with B. subtilis ( 1,2 ) and P. fluorescens ( 3 ) which reduced the fungal growth area by 86.6 %11- Culture filtrates of antagonistic bacteria were tested to study their inhibitory effect against linear growth and spore germination of FON. Results revealed that complete inhibition in linear growth was obtained with B. subtilis ( 4) and P. fluorescens ( 1 ) at concentración of 50.0 and 75 .0 % . As for spore germination, complete reduction was obtained with culture filtrates of all isolates of B. subtilis and P. fluorescens at concentration of 50.0 or 75 %, and P. putida at 75.0 %.12- Three antagonistic fungi i.e. T. harzianum, T. viride and Chaetomium sp. in addition to three antagonistic bacteria i.e. B. subtilis, P. fluorescens, and P. putida were tested to study the activity of produced enzymes i.e. chitinase and β,1-3- glucanase . 12-1 - Effect on chitinase activity: Results indicated that the highest increase was obtained with B. subtilis and P. fluorescens which increased the chitinase activity to 0.88 and 0.87 after 14 days of incubation. 12-2- Effect on β- 1,3- glucanase activityResults indicated that the highest increase was obtained with . B. subtilis and P. fluorescens which increased the β- 1,3- glucanase activity to 0.94 after 14 days of incubation. 13- The inhibitory effect of chitosan on the linear growth and spore germination of the FON fungi was evaluated. Results indicated that complete inhibition was obtained with chitosan at concentration of 8 g/ L, followed by concentration of 6 g / L. which reduced the linear growth by 93.3 % . As for spore germination, complete inhibition was obtained with chitosan at concentration of 6 and 8 g/ L . 14- The inhibitory effect of salicylic acid on the linear growth and spore germination of the FON fungi was evaluated . Results illustrated that complete inhibition was obtained with salicylic acid at concentration of 2.0 g / L. As for spore germination, complete inhibition was obtained with salicylic acid at concentration of 1.5 and 2.0 g / L . 15- Water extract of two types of compost i.e. animal and plant at concentrations of 25, 50 and 75 % were tested to study their effect on the linear growth and spore germination of FON. Results showed that the moderate reduction was obtained with plant compost extract at 75.0 % which reduced the linear growth and spore germination by 32.2 and 41.4 % respectively. Pot experiments16- Biological control with antagonistic fungiOne isolate of T. harzianum, T. viride and Chaetomium sp, were tested to study their effects against watermelon damping off disease caused by FON nder greenhouse conditions . 16-1- Applied as seed or soil treatments Results indicated the most effective antagonistic fungi were T. harzianum and T. viride with all tested cultivars when applied as soil treatments. They reduced the percentage of diseased plants more than 69.1 and 64.0 % % respectively for all tested cultivars after 30 days of sowing . 16-2- Applied as soil treatments alone or in combinationResults indicated that the most effective antagonistic fungi were mixture treatments between T. harzianum + T. viride which reduced the disease incidence by 76.8, 78.5 and 75.0 % for Giza1 cv., Aswan hybrid and Gorma cv. respectively after 30 days of sowing. 17- Biological control with antagonistic bacteria One isolate of rhizospheric bacteria i.e. B. subtilis, P.fluorescens, and P. putida were tested to study their effects against watermelon damping off disease caused by FON under greenhouse conditions . 17-1- Applied as seed or soil treatments Results revealed that the most effective rhizospheric bacteria were B. subtilis and P.fluorescens when applied as soil treatments. They reduced the percentage of damping off disease more than 65.0 and 66.6 % respectively after 30 days of sowing for all tested cultivars. 17-2- Applied as soil treatments alone or in combination Results indicated the most effective rhizospheric bacteria were mixture treatments between B. subtilis and P.fluorescens which reduced the percentage of diseased plants by 74.4, 75.7 and 76.9 % for Giza 1 cv., Aswan hybrid and Gorma cv. respectively after 30 days of sowing.