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Detection and Diagnosis of Red Leaf Diseases of Grapes (Vitis spp) in Oklahoma

Wallace, Sara Elizabeth
The grape industry in Oklahoma was valued at $98 million in 2010. In 2015, symptoms resembling Grapevine Leafroll disease were observed, but Grapevine Leafroll-associated Viruses were not detected using enzyme-linked immunosorbent assay (ELISA). A 2-year Cooperative Agricultural Pest Survey was initiated to determine the etiology of the red leaf symptoms in Oklahoma vineyards. In 2016, a total of 121 symptomatic grapevines from 13 counties were sampled and 96 symptomatic grapevines from 14 counties were sampled in 2017. Each sample was tested for Grapevine Red Blotch Virus (GRBV), Xylella fastidiosa (Pierce's Disease), and "Candidatus Phytoplasma spp," by polymerase chain reaction (PCR). ELISA was used to test for Grapevine Leafroll associated Virus (GLRaV) strains 1,3 and 4 strains. Rotbrenner, caused by Pseudopezicula traceiphila, (2017 only), can be found in xylem from petioles and the xylem was examined morphologically for signs of fungal structures. In 2016, GRBV was detected in 38% of 121 symptomatic samples, GLRaV-1 and -3 were detected in 16%, GLRaV 4 strains were detected in 2%, and X. fastidiosa was detected in 2%. There were no detections of"Ca Phytoplasma spp" in 2016 or 2017. In 2017, GRBV was detected in 34% of the 96 samples, GLRaV-1 and -3 were detected in 17%, GLRaV 4 strains were detected in 3%, and X. fastidiosa was detected in 3%. Rotbrenner was not detected in any of the samples in 2017. The findings of this survey provide information to Oklahoma grape growers and extension personnel about the cause of red leaf diseases affecting grapevines so that appropriate management strategies can be implemented in the near future.