Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2009
Publication Date: 7/1/2009
Citation: Polashock, J.J., Ehlenfeldt, M.K., Crouch, J.A. 2009. Molecular detection and discrimination of blueberry red ringspot virus strains causing disease in cultivated blueberry and cranberry. Plant Disease. 23:720-726. Interpretive Summary: Viruses, such as blueberry red ringspot virus (BRRV) can cause significant crop loss as well as a reduction in fruit quality. As with most plant viruses, the plants can not be cured. Symptoms appear only in the late summer and fall and can vary in different varieties, so symptoms can not be relied upon for diagnosis. Since blueberry is perennial, with plants in production often for decades, a reliable detection method is required, and previous methods have not been satisfactory. Here we report a simple DNA-based technique for rapid detection of the virus from plant extracts. This virus has previously been known only in highbush blueberry. Other species of blueberry are cultivated in the U.S. and by using our new detection method we have confirmed natural infection of BRRV in rabbiteye blueberry cultivars grown in the southern U.S. as well as in the hybrid variety ‘Little Giant’. This new information is important since the impact of the virus in these species is unknown. A disease with similar symptoms occurs in cranberry, but the causal agent was unknown. Cranberry plants are closely related to blueberries, and so the cranberry disease could be caused by the same virus. We have identified a virus in these plants and determined that the virus in cranberry is related to the blueberry virus. It is unlikely that the cranberry virus can be transmitted from cranberry to blueberry. This information will be useful in controlling these diseases and so will be useful to growers, extension agents and other research scientists.
Technical Abstract: Blueberry red ringspot virus (BRRV) causes red ringspots to appear on blueberry stems, leaves and ripening fruit. Published reports of the virus in cultivated blueberry have thus far been limited to highbush (V. corymbosum). A disease with similar symptoms occurs in cranberry (V. macrocarpon), but it has never been confirmed that BRRV is the causal agent in cranberry. Impact of the virus includes up to 25% yield loss, smaller fruit and a general weakening of the plant. Detection of the virus in infected plants serologically has been unsatisfactory. Here, we report a simple PCR technique for detection of BRRV from leaf and stem tissue. A primer set (RRSV3/RRSV4) is recommended for routine detection of this virus, even before symptom development. Using the recommended virus set for detection, we confirmed natural infection of BRRV in rabbiteye (V. virgatum) blueberry cultivars and the rabbiteye × V. constablaei hybrid cultivar Little Giant. Viral fragments were cloned from cranberry plants exhibiting red ringspot symptoms. These clones were found to be similar to BRRV, but exhibited some sequence divergence.