Identification of Metalaxyl- and Ethaboxam-Insensitive Pythium sylvaticum Pathogenic to Pulse Crops in Montana, U.S.A.

Abstract

Pythium root rot and damping-off caused by Pythium spp. are important diseases of pulse crops. In a 2016 pathogen survey from dry pea growing fields in Montana, along with commonly known causal agents P. ultimum and P. irregulare, an isolate identified as P. sylvaticum (LPPY17) was isolated from the rhizosphere of a diseased pea plant collected from Valley County, MT. Root rots and damping-off caused by P. sylvaticum have not previously been reported for chickpea, pea, and lentil crops. The isolate LPPY17 was tested for fungicide resistance in vitro, and results indicated a reduced sensitivity to metalaxyl- and ethaboxam-containing fungicides. LPPY17 was also tested for pathogenicity on chickpea, pea, and lentil seedlings in the greenhouse, and the results from the study revealed LPPY17 is capable of causing both root rots and damping-off. Due to the potential pathogenicity and reduced fungicide sensitivity of this species, in the future it will be important to monitor for P. sylvaticum in pulse root rot surveys and diagnostics, because management options may be different from other common Pythium spp.