Dr. Elina Coneva, Fruit Crops Extension Specialist and W. A. Jr. & C. Dozier Endowed Professor, Department of Horticulture, Auburn University
Studies to establish the feasibility of growing Pierce’s Disease (PD) resistant, predominantly European grape hybrids are ongoing at Auburn University, Alabama since 2010 https://www.asevcatalyst.org/content/early/2020/07/06/catalyst.2020.19008. We have evaluated advanced selections with early-, mid-, and late season of ripening trained to the traditional vertical shoot positioning system (VSP) recommended for European grapes. The location selected for this experiment is at the Chilton Research and Extension Center (CREC) near Clanton in central Alabama. It was found that all of the evaluated selections grew vigorously under humid southeastern conditions. The late season hybrid ‘U0501-12’ produced the highest dormant pruning weight, while early ripening ‘U0502-10’ was the most productive selection as measured by total yield per vine, and it also had the largest cluster size. Until this day, the experimental vines neither exhibited symptoms nor did they test positive for PD. Under regional commercial management practices, no vine losses were observed from other pathogens. These results indicate PD resistant predominantly European (Vitis vinifera) hybrid grapevines can survive and consistently produce a good quality crop under humid conditions in central Alabama.
The outcomes of this initial study had encouraged us to expand the experiment in 2017 and test another UC Davis developed advanced PD resistant European grape hybrid, namely ‘U0502-20’. The major goal of the new study is to evaluate the vine production potential when plants are trained to a highly efficient ‘Watson’ trellis system. ‘Watson’ system is a relatively new trellising structure that continues to gain popularity in southeastern viticulture. It features divided canopy training for better air movement and reduced risk of foliar disease development. Also, we aimed to determine the optimal planting distance for ‘U0502-20’ based on the vine vigor, productivity, and fruit quality evaluations when vines are planted at in-row distance of 6’, 7’, or 8’, and the between-row distance is 12’.
Data is being collected to determine vine phenology, total yield, fruit quality and vigor of ‘U0502-20’ grape at each planting distance. Fruit cluster production was observed during the second growing season, when clusters were removed before flowering in order to encourage root system establishment of the young vines. Annually, the experimental vines are dormant pruned to 12 spurs per vine (6 spurs/cordon) with two buds per spur retained for a total number of 24 buds per vine. Shoot thinning is conducted during spring to maintain the desirable shoot number. Additionally, cluster thinning is applied to adjust the crop load to one cluster per shoot.
The ‘U0502-20’ vines produced the first commercial crop during the 2019 season. Current season results for total yield per vine (Fig.12) suggest similar cropping level regardless of planting distances with the 6’ in-row treatment producing 18.7 lb/vine, and the 7’ and 8’ in-row distance treatments producing 19.4 lb/vine. No statistical differences were found in cumulative yield per vine during 2019-2020, when the plants produced between 36.2 and 36.8 lb/vine. Mean cluster weight varied between 367.2 g for vines planted at 6’ X 12’ to 394.3 g for vines planted at 7’ X 12’ during the current season, when the number of clusters harvested per vine ranged from 27.7 for plants at 7’ X 12’ to 31.6 for vines at 8’ X 12’. Mean berry weight for all planting distances was slightly above 2.0 g with soluble solids content of 18.4-18.7
Research will continue to more fully assess the vegetative and productive responses of PD resistant predominantly European grape ‘U0502-20’ and determine the optimal planting distance in Alabama conditions.