[Pathogenic Diversity Among Alternaria solani Isolates (The Agent of Early Blight Disease), Testing The Sensitivity of Some Tomato Varieties, and The Effect of Sodium Bicarbonate in Fungal growth in vitro]

The study was conducted in the southern region of Syria (Daraa, Damascus countryside , Al Qunytira) in order to determinate the casual agent of spot and leaf blight of tomato , testing the pathogenicity of the pathogen Isolates . The results showed that the main agent of this disease is the fungus Alernaria alternata Kiessler in frequency (93.2%) and the fungus Stemphylium in frequency (6.8%). The pathogen Isolates showed a variation of pathogenicity, some of them was virulence (18.75 %), but the rest ranged from medium (31.25%) to low (6.25 %) in virulence, in addition some of the Isolates was nonpathogenic (43.75 %) .There was a clearly different between regions in frequency of Stemphylium and the results showed that the highest one was in Daraa (85%) and in Al Qunytira (15%) ,while the Stemphylium was absent in Damascus countryside . The sensitivity of some tomato varieties (KAMARNo.4.F1, VT60788.F1, Orient. F1, Super red , Alegro and Yarmok) -inputted and cultivated - in southern region of Syria to infection by local isolates of the pathogen Alternaria alteranta ( D 2.3- R6.1a _ Q12.4), the major agent of blight and leaf spot of tomato was detrminated. The results showed that the severity of infection ranged between 20.03% to 74%. The cultivars ranged from sensitive to high resistance , there is no significant differences between inputted varieties with each other for the isolates Q12.4, R6.1a and D2.3(with probability level 1%) , and there is a significant differences with the rest of varieties . on the other hand , the cultivated varieties did not show a significant differences between the isolate R6.1a , but the significant differences existed for the isolate Q12.4 and D2.3 . the inhibitory effect of sodium bicarbonate (NaHCo3) on fungal linear growth was studied by using a local isolate Q12.4 with four concentrations of NaHCo3 (0.25 % , 0.50 % , 1 % and 2 % ) W/V in addition to the control . The results showed that concentrations ( 0.25% , 0.50% ) had a catalytic effect on fungal growth by 68.97 % and 44.87 % respectively , while ,highest concentrations ( 1% , 2%) had an inhibitory effect on the growth ( 18.17% and 100% respectively), with the presence of significant differences between themselves ,and with the control at the level of probability 1% .