الفهرس 
Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
P. aphanidermatum, P. catenulatum, P. diclinum, P. oligandrum, P. periilum, P. spinosum var. spinosum, P. ultimum var. ultimum, Pythium ”group F”, Pythium ”group G”, Pythium ”group P”, Pythium ”group T” and a new species of Pythium were isolated and identified using morphological and molecular criteria. Sequencing of rDNA-ITS including the 5.8Sr DNA were analyzed for the Pythium species tested to confirm the species identification. Two hundred and thirty-nine isolates of Pythium spp. were obtained from the studied area in Egypt. Of these, a total of 8 species and 4 groups of pythia could be identified on the basis of morphological and molecular criteria. Sequencing of rDNA-ITS including the 5.8SrDNA were analyzed for the Pythium species tested by the method of to confirm the species identification. The sequence of (EgH108) was closely related with that of P. aphanidermatum (Genbank accession number, AB160845.1) with 100% similarity. The sequence of (EgH 104) was closely related with that of P. catenulatum (Genbank accession number, AY598675.1) with 99% similarity. The sequence of (EgH73) was closely related with that of P. diclinum (Genbank accession number, AY598690.1) with 99% similarity. The sequence of (EgH105) was closely related with that of P. oligandrum (Genbank accession number, AB355600.1) with 99% similarity. The sequence of (EgH103) was closely related with that of P. periilum (Genbank accession number, AJ233454.1) with 97% similarity. The sequence of (EgH102) was closely related with that of P. spinosum var. spinosum (Genbank accession number, EF21021301) with 100% similarity. The sequence of (EgH25) was closely related with that of P. ultmium var. ultmium (Genbank accession number, AB355596.1) with 99% similarity. Sequence of this species revealed that it is a new species. Steps were taken to publish it as a new species in the near future.
A key for morphological identification was designed to help in morphological identification. Seven species and 4 groups of Pythium, as well as, a new species were isolated. The number of species isolated from each season was fluctuated. The maximum was observed in winter (10 species and groups) followed by spring (9 species and groups) and then autumn (8 species and groups), and the minimum were detected in summer (6 species and groups).
P. aphanidermatum has not been obtained in winter while P. catenulatum, P. diclinum, P. oligandrum, P. ultimum var. ultimum and P. spinosum were not detected in summer. The new species of Pythium isolated in this study was only isolated in summer and could not detected in the other seasons. P. spinosum isolated only in winter and could not be obtained thereafter.
Pathogenicity (pre-emergence damping-off) of Pythia in agar bottles was tested on cucumber seeds and maize grains. P. aphanidermatum and P. ultimum var. ultimum were highly pathogenic to cucumber seeds and maize grains causing 100% damping-off. P. spinosum was highly pathogenic to cucumber (100%) damping off and moderately pathogenic to maize (67%) damping-off. P. diclinum was moderately pathogenic to both cucumber and maize (67%) damping off, P. catenulatum and Pythium new species were weakly pathogenic producing 33% damping-off in case of both cucumber and maize germinating grains. P. oligandrum, Pythium ”group F”, Pythium ”group G”, Pythium ”group P” and Pythium ”group T” were non-pathogenic to both cucumber and maize. Pathogenicity tests (pre-emergence damping-off) in the pot experiment were performed also in pots using 2.5% inoculum concentration of the tested Pythia added to soil and incubated for 2-3 weeks before cultivated cucumber seeds and maize grains. P. aphanidermatum was highly pathogenic to cucumber seeds and maize grains causing 100% damping-off. P. ultimum was highly pathogenic to cucumber germinating seeds and maize grains causing 100% and 80%, respectively. P. spinosum was highly pathogenic to cucumber germinating seeds causing 80% damping-off. In case of maize germinating grains, P. spinosum were moderately pathogenic causing 60%. P. diclinum, Pythium new species and P. catenulatum, were weakly pathogenic causing 40%. In case of cucumber seed P. diclinum was moderately pathogenic producing 60% while P. catenulatum and Pythium new species were weakly pathogenic causing 40% and 20% damping –off, respectively. P. periilum, P. oligandrum, Pythium ”group F”, Pythium ”group G”, Pythium ”group P” and Pythium ”group T” were non-pathogenic to both cucumber and maize.