شناسايي و بيماريزايي آرايه هاي PYTHIUM جداشده از ريشه و طوقه گندم در فارس

To study the role of Pythium species associated with wheat root and crown rot during two growing seasons 1995-1996 diseased samples were collected from different irrigated wheat fields in Fars province including Maharloo, Marvdasht, Firoozabad, Kavar, Estahban, Neiriz, Fassa, Darab, Borazjan, Kazeroon and Badjgah. Decaying root and crown segments (5mm) were washed and plated on CMA containing Delvocid (50% pimaricin), ampicillin, rifampicin, benomyl and PCNB. Of 17 isolates recoverd from various parts of the province, based on morphological characters, the following Pythium species were identifield: P. aristosponum, P. ultirnum var. ultium P. ultirnum var. ultimurn, P. periplocum, P. heterothallicurn, Pythium G. "Fʹ. Pathogenicity tests were carried out under greenhouse conditions using sterlized soil artificially infested with corn seed inoculum. Pre-and post-emergence damping-off and root and crown rot were evaluated. None of the isolates caused mortality of wheat seedlings and seed dacay was low in some isolates of Pythium G. "F. P. aristosporum and P. ultimum var. ultimum caused root and crown dacay. Isolates which caused root and crown rot in ascending order of pathogenicity were: Pythium G. "F", P. aristosporum and P. u. var. ultimum.