Characteristics and pathogenicity of Pythium spp. associated with damping-off of sugar beet in Ireland

Five hundred and eight Pythium isolates were obtained from diseased sugar-beet seedlings in the field from beet field soils in Ireland. Pythium sylvaticum and P. intermedium were the dominant species, together representing 86% of isolates, and P. salpingophorum, P. ultimum, P. mamillatum, P. oligandrum and Pythium‘group HS’were the other species identified. The cultural characteristics of these species corresponded generally with previous descriptions, with the exception of P. sylvaticum and P. mamillatum, which varied in some respects. In glasshouse pathogenicity tests, P. sylvaticum, P. intermedium, P. salpingophorum, P. ultimum, P. mamillatum and one unidentified Pythium isolate caused pre-emergence and early post-emergence damping-off of sugar-beet seedlings. Isolates off. oligandrum and Pythium‘group HS’were weakly pathogenic or not pathogenic to beet seedlings.