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Pierce Disease Resistant grapes

Figure 1. Crop load and fruit quality of PD resistant predominantly European grape ‘U0502-20’ trained to a ‘Watson’ trellis system, grown at the CREC, Clanton, Alabama, 2021.

Studies continue to evaluate the Pierce’s Disease (PD) resistant, predominantly European grape ‘U0502-20’ developed by the UC Davis breeding program in central Alabama. The major goal is to assess the vinegrape vegetative and cropping potential when vines are planted at three different planting distances and trained to a highly efficient ‘Watson’ trellis system. ‘Watson’ 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, while providingease in canopy management and crop harvest. Additionally, we aimed to determine the effect of planting distance on ‘U0502-20’ fruit quality characteristics.

Data is being collected to determine vine phenology, total yield, fruit quality and vigor of ‘U0502-20’ grape at each planting distance. 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.

The ‘U0502-20’ vines produced the first commercial crop during the 2019 season. The 2019-2021 yield per vine results (figures 1 and 2) suggest similar cropping levels (between 8.0 and 8.8 kg/vine) occurred during 2019-2020 season, regardless of the planting distance. In 2021, the total yield per vine was similar to previous season’s level for vines planted at 6’ X 12’ and 7’ X 12’, but was significantly higher for vines planted at a distance of 8’ X 12’, which produced 12.6 kg/vine on average.

Our results on cumulative yield per vine (figure 3) for the period of plant establishment (2019-2021) are demonstrating the vines planted at a distance of 8’ within the row were the most productive and produced 29.4 kg/vine. We estimated the average annual yield per acre based on the number of vines at each planting density and found out that the highest crop per acre (5 MT/acre) was produced at distance of 6’ x 12’, followed by vines planted at 8’ X 12’ (4.5 MT/acre), and 7’ X 12’ had 4.4 MT/acre.

Mean cluster weight varied between 320.0 and 621.2 g between seasons, with vines planted at 7’ x 12’ consistently producing the largest clusters each season (table 1). Planting distance had a significant effect on soluble solids content in 2021, when vines planted at 8’ x 12’ produced the sweetest berries.


Effect of planting distance on cluster weight and SSC of '502-20', 2019-2021

Planting distanceMean cluster weight, gramsSSC
6x12'(2019) 320.0 (2020) 367.2 (2021) 569.0(2019) 17.4 (2020) 18.7 (2021) 17.1 ab
7x12'(2019) 332.2 (2020) 394.3 (2021) 621.2(2019) 17.7 (2020) 18.5 (2021) 16.3 b
8x12'(2019) 328.1 (2020) 377.0 (2021) 597.9(2019) 18.6 (2020) 18.4 (2021) 18.1 a
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