Viruses Detected in Stone Fruit Germplasm Entering the United States

Abstract

No. accessions Except stone fruit from Canada and cherry seed from all countries, stone fruit germplasm (Prunus spp.) must be sent to the National Plant Quarantine Center on arrival in the United States. Thus, germplasm can be imported only by the U.S. Dept. of Agriculture and must be held in quarantine for 3 to 4 years while it is tested for pathogens (U.S. Dept. of Agriculture, 1992). Prunus spp. is prohibited because it may be infected with submicroscopic pathogens [i.e., viruses, viroids, mycoplasma-like organisms (MLO), or unknown infectious agents]. Compared with other perennial crops, stone fruit seem to be unusually prone to many virus-like disorders. Nemeth (1986) listed and described 161 diseases of the five stone fruit crops that are associated with submicroscopic pathogens. Of these diseases, 40% have been reported only in North America, but another 43% are not known to occur in the United States. Some of these pathogens, such as plum pox (sharka) and tomato ringspot viruses, have been destructive in Europe and the United States, respectively. Other diseases are obscure, do not appear to have economic importance, or may be caused by strains of wellknown pathogens. My objective was to report results of tests completed during the last 3 years for virus and virus-like pathogens in introduced Prunus germplasm. When the Prunus arrived in quarantine, vegetative accessions were budded onto virus-free rootstocks; and accessions of seed were sown after stratification. Resulting plants were closely monitored for symptoms of disease and subjected to a battery of tests for virus and virus-like pathogens. Tests were conducted to detect all known pathogens, whether or not they were already widespread within the United States. The Animal and Plant Health Inspec-