The Detection and Characterization of Some Viruses Infecting Blackberry and Cherry in South Carolina

Three separate virus research projects were conducted. Blackberry yellow vein disease (BYVD), a disorder caused by virus complexes, has become a major threat to blackberry production in the United States, especially in the southeastern part of the country where blackberries are grown for the fresh market. More than 30 viruses have been found to be associated with the disease. Most of these induce no symptoms when infecting the plant alone. However, when more than a single virus is present in the host visible symptoms are displayed. The incidence of 6 different viruses (Blackberry yellow vein-associated virus, Blackberry virus Y, Blackberry chlorotic ringspot virus, Blackberry virus E, Blackberry virus Ω, and Tobacco ringspot virus) that have been commonly found in BYVD-infected plants was studied using sentinel plants dispersed in plantings of blackberry in the field. Experiments were completed at the two largest commercial blackberry farms in South Carolina using more than 1200 sentinel plants over the course of three years. The sentinel plants were tested for the presence of the 6 viruses before they were exposed in the field and were again tested for the presence of the 6 viruses after the plants had been recovered from the field and allowed to overwinter in the greenhouse. Both Blackberry virus E, and Blackberry virus Ω were found infecting blackberry in South Carolina for the first time. A potential new ilarvirus was identified in blackberry and veronica. Partial sequence information for the 3 genomic molecules has been obtained. The virus shows closest homology to the members of subgroup 1 of the genus Ilarvirus, but is unique. This subgroup includes BCRV, one of the viruses previously associated with the BYVD complex. Symptoms typical of virus infection were observed in the suckers/watersprouts growing from the 'Mazzard' rootstock of a flowering cherry tree growing at Musser Farm, Clemson University in 2011. However, the III scion of the tree, Prunus serrulata cv. Shirofugen, displayed no symptoms. Double-stranded RNA was isolated from the symptomatic tissues of the rootstock and used to provide templates for cDNA cloning and for nucleotide sequencing. Sequence data showed the virus to be most closely related to Cherry rusty mottle-associated virus. IV DEDICATION This dissertation is dedicated to my parents, Hem and Usha for not hesitating to use all their means and resources to bring me where I am today; to my husband, Sanjay, for being there in every moment; to my little love …