Document Type : Research Paper
Authors
University of Alanbar-College of Science
Abstract
The pathogenicity of three isolates of the genus Pythiumthat isolated from infected Okra (P.afertile) ,hay and cress plants for many economical plants such as maize , sesame , cucumber and tomato were studied in artificially infested soils . The pathogenicity was determined according to it's ability to cause pre – and post emergence damping – off of seedlings. The pathogenicity tests showed that the P.afertile isolate recorded the maximum reduction in percentage of pre – emergence damping – off , where it's percent was 39.99% , followed by cress isolate as 32.08 % and hay isolate as 27.08% , whereas the cress isolate gave a significant reduction in percentage of post – emergence damping – off which was 27.35 % , followed by P.afertileand hay isolates which were 21.44 % and 16.35 % respectively .Results indicated that the maize root exudates had more inhibition activity against both Pythium isolates ( P. afertileand cress isolates ) in comparison with sesame root exudates , which project the growth rate about 56.915 millimeters and 60.025 % millimeters for both treatments of maize and sesame root exudates respectively . The maximal inhibitory effect of root exudates was against the P. afertile isolate in comparison to the cress isolate , where the size of the fungal colonies were 35.116 millimeters and 83.7 millimeters for the P. afertile and cress isolates respectively .The study showed that maize root powder extract had positive effect against the growth of the P. afertileisolate ,Where the size of the fungal colony reached to 51.75 millimeter in comparison to the control which was 42.58 millimeters . This positive effect was missing against cress isolate , furthermore the prepared medium from the mixing of Root Maize Extract Agar ( R.M.E.A. ) and Potato Sucrose Agar (P.S.A.) media did remarkable support for the growth of the P. afertileisolate , which was 58.0 millimeters colony diameter in comparison to R.M.E.A and P.S.A. which were 41.0 millimeters and 40.0 millimeters respectively , whereas such differences disappeared to the cress isolate . The study showed the high efficacy of coating sesame seeds with the powders of root maize in reducing infection rates with pre – and post emergence damping – off caused by Pythium sp. in comparison with the effect of the fungicide Beltanol , as 15.18 % and 22.4 % for the treatments of coating sesame seeds with the powders of root maize or the fungicide respectively , which planted in the soils that infested with the P. afertile isolate , and 31.10 % and 23.04% for the same treatments but planted in the soils that infested with cress isolate .
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