Epidemiological studies on blackberry yellow vein associated virus and blackberry chlorotic ringspot virus

Blackberry yellow vein disease (BYVD), a disorder caused by virus complexes is the most important blackberry disease in the southern United States. Blackberry yellow vein associated virus (BYVaV) is the most prevalent virus in BYVD plants being detected in about 50% of the samples exhibiting BYVD symptoms. Blackberry chlorotic ringspot virus (BCRV) is another virus frequently found in BYVD plants, and in addition to blackberry, it can also infect rose and raspberry. Despite the importance on the viruses as major components of BYVD little was known about their epidemiology. In this study population diversity, transmission modes and potential alternate hosts of both viruses were studied. The variability among BYVaV isolates was determined after sequencing four different genomic regions of 34 isolates. The complete RNA 3 of 30 BCRV isolates from three different hosts was evaluated in the diversity study of this ilarvirus. Two whitefly species were tested for their ability to transmit BYVaV and seed transmission assays for BCRV were performed using two hosts. Over 25 species of plants were tested as potential alternative hosts of the viruses. BYVaV populations are fairly diverse, unlike BCRV US-isolates. The greenhouse and banded-winged whiteflies were identified as efficient vectors of BYVaV. BYVaV was graft-transmissible to rose; and if natural infection of rose is confirmed this can be of great concern to the ornamental industry. BCRV is seed transmissible to the two host tested and was found to naturally infect apple. After obtaining sequence information from over 30 isolates better, more reliable, detection protocols were developed which minimize the possibility of false negatives.