ِidentification of pythium spp. and their pathogenicity on cucurbits in khorasan-razavi province

abstract the pythium spp. are known as the principle agents of seedling blight, damping-off and root rot of cucurbits. this study was performed for determination of pythium species involved in this diseases as well study their pathogenecity on different cucurbits. the numerous samples were taken at cultivation seasons 2006- 2007 from the fields of cucumber, tomato, egg plant, muskmelon, cucurbit, melon, and watermelon, situated in mashhad, chenaran, ghochan, fariman, torbtejam, gonabad, kashmar, khvaf, neishboor, sabzevar, torbateheydarieh, kalat, dargaz, sarakhs, and taibad ( north east of iran). sixty pythium isolates were obtined from the diseased samples in total. they were identified based on morphological and micrometric characteristics. the results showed that 46.44% are belonging to the p. ultimum var. ultimum, 16.66% to the p. aphanidermatum, 13.33% to the p. amasculinum, 10% to the pythium group hs, 16.6.66% to p. oliganderum, 3.33% to the p. paroecondrum, and 3.33% to the p. echinulatum . the p. amasculinu، p. echinulatum and p. paroecondrum are the first report from iran . the pythium group hs and p. oliganderum are also the first report from cucurbits in iran. the pathogenesity test of isolates showed that p. ultimum var ultimum ، pythium group hs، p. paroecondrum ،p. aphanidermatum and p. echinulatum are pathogenic on cucumber, tomato, egg plant, muskmelon, cucurbit, melon, and watermelon, while p. amasculinum was not pathogenic on melon and cucurbit.