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USDA Animal and Plant Health Inspection Services (APHIS), along with the California Department of Food and Agriculture (CDFA), are adding wood rose (Rosa gymnocarpa) to the list of nearly 30 confirmed Phytophthora ramorum host plants.  As a host plant, wood rose will fall under Phytophthora ramorum regulations, requiring inspection before being certified for shipment from California nurseries. 

Research conducted by Daniel Huberli in the Garbelotto laboratory at the University of California Berkeley concluded that the pathogen sporulates on the infected leaflets, making it a potential vector for the disease.  Further studies are being conducted to determine if the stem of wood rose is also affected by the pathogen. 

“The genus Rosa is the quintessential ornamental genus, probably one of the most widespread across the globe.  Although no infected roses have been found in commercial nurseries yet, this finding should prompt surveys of roses sold commercially (especially wood rose) to ascertain their infection status,” said Matteo Garbelotto, a professor and forest pathologist extension specialist at UC Berkeley. 

Based on the wood rose findings, hybrid roses, most often found in nurseries, are being laboratory tested by UC Berkeley scientists for their susceptibility to Phytophthora ramorum. 

Wood rose is native to California, and is commonly found in a wide range of habitats.  It is popular in the horticultural industry and is readily available from native plant nurseries in California, Oregon, Washington, and British Columbia.