Seven isolates of Fusarium graminearum obtained from Seed and Plant Improvement Institute were grown on autoclaved barley grains and toxicity of their cultures to wheat germinating seeds was tested using their semi-purified phytotoxins. The extracts of isolates 167, 169, 173 and 179 did not have considerable inhibitory effects on wheat seed germination, whereas that of 161 (a = 0.05) and two other isolates 131 and 164 displayed a significant inhibitory effect on germination. However, no correlation was found between virulence and toxicity of the isolates examined. Also, the effect of light was studied in relation to wheat germling level of tolerance. Six isolates were investigated for their ability of deoxynivalenol synthesis. Thus, their crude extracts were prepared and partially purified, and subjected to thin layer chromatography with chloroform (acetone and hexane) ethyl acetate solvent systems on fluorescent silica gel plates (60 meshes) using a commercial standard deoxynivalenol (1 mg/ml, Sigma Co., USA) along with the samples. The spots of interest were detected and analyzed under ultraviolet (UV) lights (254 and 365 nm). The isolate 161 produced the most amount of deoxynivalenol compared to others. Also, no correlation was found between virulence and toxigenicity of the isolates.
Key words: Phytotoxicity,usarium head blight,head scab, virulence, deoxynivalenol, mycotoxin, phytotoxin,Fusarium graminearum.
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