Read the new publication in the American Journal of Enology and Viticulture here!
Background and goals Grapevine red blotch virus (GRBV) causes red blotch disease and is a threat to vineyard sustainability in some areas. Advances in disease epidemiology have been made, but information on the latency period of GRBV is lacking. This work aimed to estimate red blotch disease latency (the time between a vine first testing positive for GRBV and the onset of disease symptoms).
Methods and key findings Sentinel vines consisting of GRBV-negative Cabernet franc buds grafted onto GRBV-negative 3309 Couderc cuttings were planted in June 2015 in a red blotch-diseased Cabernet franc vineyard experiencing secondary spread of GRBV. Sentinel vines were monitored for disease symptoms from October 2015 to 2023, and were sampled annually for GRBV testing from October 2015 to 2023 and from June 2021 to 2022. The first sentinel vine tested positive for GRBV by polymerase chain reaction (PCR) in October 2018; this vine became symptomatic the following October. An increasing number of sentinel vines tested positive for GRBV by PCR and exhibited foliar disease symptoms either when the virus was detected, or four to 12 months later.
Conclusions and significance Of those sentinel vines that became infected (69%, 25/36), three distinct patterns of initial GRBV detection and disease symptom onset were observed. The first applied to sentinel vines (20%, 5/25) that were both GRBV positive by PCR and symptomatic for the first time in October. The second pattern applied to sentinel vines (56%, 14/25) that were GRBV positive by PCR for the first time in June and symptomatic the following October. The third pattern applied to sentinel vines (24%, 6/25) that were GRBV positive in PCR for the first time in October and not symptomatic until the following October. Estimating a four-to-12-month latency period enables a better understanding of red blotch disease trajectories in vineyards showing signs of secondary spread.