Abstract

Seventy-eight Pythium isolates were obtained from diseased sugarbeet seedlings that were planted in soil samples collected from different sugarbeet fields in northwest Iran. P. ultimum var. ultimum was the dominant species, representing 52.6% of isolates, and P. aphanidermatum, P. deliens, P. oligandrum, P. ostracodes, Pythium group HS and Pythium group T were the other species identified. Five other isolates could not be identified and were designated as Pythium sp. In the greenhouse pathogenicity test, P. ostracodes and two isolates of P. oligandrum and Pythium sp. were non-pathogenic and four isolates belonging to P. aphanidermatum, P. ultimum var. ultinmum and Pythium group HS were very highly pathogenic. The remaining 24 isolates were weakly, moderately or highly pathogenic. This is the first report of isolation of Pythium group T and P. ostracodes from sugarbeet and the pathogenicity of the Pythium group T on sugarbeet. It is also the first report of P. paroecandrum and Pythium group HS being isolated from sugarbeet and their pathogenicity on sugarbeet in Iran. Pythium group T is a new record for Iran.