PATHOGENICITY OF PYTHIUM SPECIES ON CUCUMBER IN PEAT-SAND, ROCKWOOL AND HYDROPONICS

Pythium spp. that cause damping-off of seedlings also can cause root r ot of older plants and lead to yield reductions. This can be especiall y severe in soilless cultures where the fungus can spread easily with the nutrient solution. 39 Pythium isolates obtained from discolored ro ots were assayed for their ability to cause damping-off on cucumber se edlings in sand-peat and for their pathogenicity in soilless culture o f cucumber in rockwool or hydroponic solution. Isolates of Pythium aph anidermatum, P. irregulare, P. sylvaticum and P. ultimum were highly p athogenic in sand-peat, but only P. aphanidermatum strains were pathog enic in soilless conditions and led to root decay, plant death in rock wool culture and growth reduction in hydroponic culture. One strain of P. aphanidermatum significantly reduced the yield of cucumber grown i n rockwool under conditions similar to those of commercial cultures.