Identification and characterization of the Rose Rosette disease causal agent

Rose rosette disease is lethal to multiflora rose, a noxious weed occurring in pastureland in most of Iowa. The potential use of rose rosette disease as a biocontrol agent can be enhanced by grafting infected shoots onto plants in established stands (i.e., augmentation). However, questions arose about whether the disease could be spread to ornamental roses. This study probes the identity of the causal agent for the disease in hopes of determining whether fears of transmission to ornamental roses were valid. Background to infect or infest multiflora rose in the United States. The seed chalcid (insect) attacks and Multiflora rose is a vigorous, thorny shrub destroys the embryo of the seed but requires native to Japan that has been widely planted as too much time (20 years) to be effective. The an aid to soil conservation, wildlife cover, and rose rosette disease (RRD) has proved fatal to as a “living fence.” The plant has been more infected multiflora rose within two to four aggressive than first recognized and has beyears after first observation, depending on the come particularly troublesome in the southern size and complexity of the bush. Electron half of the U.S. Corn Belt on non-cultivated microscopy of thin sections from the diseased sites such as pastureland, woodlands, conserleaf tissue has not presented convincing evi­ vation reserve acres, recreational areas, utility dence for the identity of the causal agent, rights of way, and wildlife areas. In several which remains unidentified. states, multiflora rose has been designated as a noxious weed. In Iowa, it is estimated that Graft transmission of RRD has been successmore than one million acres of pastureland and ful in the greenhouse and in the field. Tests for wildlife areas have sustained significant degsoil and seed transmission of the causal agent radation as a result of colonization by the of RRD have been negative. In the field, the multiflora rose. The principal areas of infestaRRD agent can be transmitted to multiflora tion are 61 counties (nearly two-thirds of the rose by the eriophyid mite. Populations of the counties in Iowa). mite are generally higher (by a factor as great as 17) on diseased multiflora rose plants than Costs of conventional control methods are on nonsymptomatic plants. high ($50 to $200 an acre) and there are con­ cerns about water contamination effects of repeated application of herbicides to pasturelands. Biological control methods would be less environmentally costly because they are better targeted and run no risk of added pollution to groundwater. The diffi­ culty with biological control lies in identifying pathogens and pests with minimal or no risk to non-target organisms. Earliest symptoms of RRD: purple blotches Several pathogens and insects that might be on bottom side of leaf potential biocontrol agents have been reported blades and veins Principal Investigator: John H. Hill