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Journal of Biological Sciences

Year: 2010 | Volume: 10 | Issue: 4 | Page No.: 306-315
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Authors

H. Al-Sheikh

Hani M.A. Abdelzaher

Keywords

Research Article

Differentiation Between Two Isolates of Pythium ultimum var. ultimum Isolated from Diseased Plants in Two Different Continents

H. Al-Sheikh and Hani M.A. Abdelzaher
This study was undertaken to investigate the differences between two distinct isolates of Pythium ultimum var. ultimum, the diseased organisms of wheat and lettuce in agricultural fields in each of Egypt and Germany, respectively. Morphological study indicated that the Egyptian and German isolates comprised a single taxon, P. ultimum var. ultimum, by the current taxonomical keys. The isolates were morphologically distinguished as having smaller or larger sexual organs by the sizes of their antheridia and oogonia. The German isolate grew faster in the lower temperature range of 4-15°C whereas the Egyptian isolate grew faster in the higher temperature range of 25-37°C. Similarities in the sequence of the r-DNA-ITS including the 5.8S rDNA demonstrated evident genetic similarity at the species level between the two isolates and should be used for confirmation of identification of species of Pythium. The two isolates were not distinguishable by their pathogenicity to cucumber seedlings. The effect of temperature, hydrogen ion concentration and osmotic potential on oospores production and germination were studied. Oospores production and germination showed a similar manner, however, the Egyptian isolate produced more oospores than the German isolate. Identification of the Egyptian and German isolates of Pythium ultimum var. ultimum to the species level can be done using sequencing of r-DNA-ITS including the 5.8S rDNA, however, some morphological and physiological differences might present within the same species. This might be attributed to the effect of environmental factors and cultural conditions.
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