Arran Rumbaugh, Monica L. Cooper, Rhonda J. Smith, Charles Brenneman, Anji Perry, Raul C. Girardello, Cassandra Plank, Kaan Kurtural, Hildegarde Heymann and Anita Oberholster**Department of Viticulture & Enology, University of California Davis, One Shields Avenue Davis, CA 95616 (email: aoberholster@ucdavis.edu)

Since its identification in 2011, grapevine red blotch disease has been widespread in the United States. This disease is caused by grapevine red blotch virus (GRBV) infection of grapevines. Over the past four years, we investigated the effects of GRBV on grape development and at harvest across multiple vineyards and varieties. In 2017, we completed a multi-year study evaluating the effects on Merlot (ME) and Cabernet Sauvignon (CS) at two locations. In addition, the CS grapevines were grafted on to two different rootstocks, 110R and 420A, allowing evaluation of rootstock effects.  In previous years of the study, it was found that there were considerable differences in sugar accumulation at harvest; thus, sequential harvesting of the diseased grapes was implemented since 2016, meaning that the grapes were harvested at a later date when the sugar content had reached a similar value to the healthy grapes. Basic chemical data and total anthocyanin content were collected from veraison to harvest. Additionally, phenolic profiles of the diseased (at both harvest times) and healthy grapes at harvest were determined using a protein precipitation assay and RP-HPLC, and volatile profiles were analyzed using HS-SPME-GC-MS. Diseased grapes consistently had slower sugar accumulation, higher titratable acidity, and lower pH. The diseased grapes from CS 420A and ME were lower in total phenolics, anthocyanins, and tannins than healthy grapes. The second harvest berries had increased levels of all three when compared to the first harvest diseased berries. On the other hand, for CS 110R, the healthy fruit was lower in total phenolics, anthocyanins and tannins than the diseased berries at both harvest dates, showing variable influences the virus may have on various rootstocks.  

Funding Support: CAPES, WINE X-RAY, AVF, JASTRO, J. LOHR, AGRI ANALYSIS, Agriculture and Environmental Chemistry Graduate Group