Pathogenesis ofSynchytrium endobioticum

Summary Field plots infested withSynchytrium endobioticum pathotype 2 were amended with agricultural lime, NH₄NO₃ and/or urea and planted with cv. Arran Victory. A weekly survey of changes in pH from planting to harvest revealed constant pH in absence of the chemicals, fluctuating pH with lime, very large increase then falling off with urea, and depressed below normal pH with NH₄NO₃. Best disease control occurred in urea-treated plotsvs NH₄NO₃-treated plots. Addition of lime, although it elevated pH, did not suppress the disease with urea or NH₄NO₃ added. Mechanisms for suppression by urea are related to its role as an ammonia producer and microbial stimulator, and their implication for infection byS. endobioticum.Contribution No. 81, Research Station, Agriculture Canada, P.O. Box 7098 St. John's, Newfoundland, A1E 3Y3