Submitted to: Phytopathology News
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2005
Publication Date: October 1, 2005
Citation: Polashock, J.J., Vaicunis, J., Oudemans, P. 2005. Identification of a new phytophthora species causing root and runner rot of cranberry in New Jersey. Phytopathology News. 95:1237-1243.
Interpretive Summary: Root rot disease in American cranberry causes vine damage and subsequent crop loses. The organism that commonly causes cranberry root-rot is the fungus Phytophthora cinnamomi. In New Jersey, symptoms unlike typical root rot were noted in some cranberry fields. In addition, traditional fungicides were found to be ineffective in controlling the root rot disease in these fields. Isolations from infected cranberry roots in these areas revealed the disease-causing organism to be similar to P. cinnamomi, but with certain different characteristics. Unlike P. cinnamomi, the newly isolated fungus was found to prefer low temperatures for reproduction. Fungicide sensitivity studies confirmed that the newly isolated fungus was resistant to fungicides normally used to control root-rot. Finally, DNA typing methods suggested the fungus is a new Phytophthora species related to a group that has not been described in North America. This study underscores the need for accurate diagnoses when developing a Phytophthora root-rot management program and definitively documents the isolation of a new species of this fungus infecting cranberry. This information will be useful to plant pathologists as well as cranberry growers interested in developing methods for controlling this disease.
In New Jersey, Phytophthora cinnamomi is the most common pathogen isolated from diseased roots and runners of the cultivated cranberry (Vaccinium macrocarpon Ait.). A second distinct species of Phytophthora has been isolated from dying cranberry plants and surface irrigation water. This species is homothallic with paragynous antheridia and ellipsoid ' limoniform, nonpapillate sporangia. It was tentatively identified as P. megasperma in an earlier report. Laboratory experiments demonstrate that the cardinal temperatures for vegetative growth are between 5 and 30 ºC with an optimum near 25 ºC. Sporangia are produced at temperatures between 10 and 20 ºC with the majority of sporangia produced at 10 and 15 ºC. In pathogenicity tests, no growth effect was observed on cranberry plants (cv. Early Black) when tests were conducted at 25 ºC, however, significant reductions in plant growth occurred when tests were conducted at 15 ºC. This species was insensitive to metalaxyl but was sensitive to buffered phosphorous acid. Sequence analysis of the ITS-1, 5.8S rDNA, and ITS-2 regions place these isolates in Phytophthora clade 6 with greatest similarity to Phytophthora taxon raspberry. This is a first report of isolates of this affiliation in North America. However, the observation of low temperature preferences makes this species unique in an otherwise high temperature clade.