Impacts of Rootstocks on Performance and Fruit Quality of Mature ‘Autumn King’ Vines
Tian Tian, UCCE Viticulture Advisor for Kern County
Rootstocks are used in vineyards to protect vines from soil-borne pests, alter the water and nutrient uptake of vines, and improve vine tolerance to drought and salinity. Given the complicated interactions between different vineyard environments, rootstocks, and scions, choosing the appropriate rootstock for a given site remains challenging. It is not uncommon to see the same rootstock has different impacts on yield and berry composition in different vineyards with the same scions. To provide growers with more knowledge on rootstock selection, several studies were conducted in the San Joaquin Valley (SJV) to examine rootstock impacts on popular table grape varieties in the last three decades. Freedom, 1103 Paulsen, and Salt Creek (Ramsey) were identified as the top performers and then used extensively in the industry.
The grape industry is always facing new challenges, with additional restrictions on soil fumigants and the slow development of safe and effective nematicide. Grape growers are more dependent on rootstocks to fight against phylloxera and plant-parasitic nematodes. There are also reports of new nematode isolates overcoming the resistance of rootstocks over time. To address these industry needs, newer rootstocks like 10-17 A, RS-3, and the grapevine rootstocks for nematodes (GRN) were developed by USDA and UC Davis breeders, to offer broader and more durable resistance to soil-borne pests. Field tests provide valuable information on the suitability of these newer stocks for table grapes, particularly for replanting sites with high nematodes and phylloxera pressure.
In addition, concerns over using Freedom rootstock, due to its susceptibility to sudden vine collapse have increased. Sudden vine collapse can cause vines to have stunted growth in the early growing season and then collapse later in the summer. The vine death appears to be associated with a complex of viruses and fungal pathogens that lead to a breakdown of the graft union. Rootstocks like Freedom are sensitive to viruses, leading to it being the most common rootstock involved with sudden vine collapse. In addition, the insect vectors for the viruses involved in sudden vine collapse, mealybugs, are commonly present in vineyards in the Southern San Joaquin Valley. Mealybugs can spread the virus even in a low population. To avoid a potential loss to sudden vine collapse, growers have become more interested in adopting rootstocks other than Freedom.
An additional concern addressed in this study is the complication of time. Given that researchers can only keep rootstock trials for five to seven years, we rarely have the opportunity to evaluate rootstock impact in older vines. Some growers have observed a larger impact of rootstocks as vines age. Luckily, one of the rootstock trials planted by my predecessor Jennifer Maguire was kept by a grower collaborator beyond the typical time frame. With funding from the American Vineyard Foundation and support from grower cooperators and UC colleagues, we were able to collect valuable data before those vines got removed in the spring of 2023.
Experimental vines were planted in 2010 in Ducor, CA with ‘Autumn King’ as the scion. Vines were on an open Gable trellis system. The soil of the vineyard is the San Joaquin series (fine loam). The vineyard was flood-irrigated but switched to drip irrigation around 2016. The original experiment included vines on 14
traditional and newer rootstocks, along with own-rooted vines. Yet, vines on GRN-5 and RS-34 had low survival rates in the first five years after planting. As such, we collected data from vines on 12 rootstocks as well as own-rooted vines in 2021 and 2022 (Table 1).
Pruning mass. Rootstock showed significant influences on pruning mass. Vines on Salt Creek, GRN 2, GRN 3, Teleki 5C, 1103 Paulsen, and 10-17 A had higher pruning mass than others at dormancy, suggesting those stocks convey more vigor to the scion (Figure 1). The pruning mass of vines on Freedom, RS3, Harmony, Crimson, and GRN 4 remained intermediate among all, while vines on GRN 1 and own-rooted vines had the lowest pruning weight.
Yield. Influences of rootstocks on yield followed a similar pattern as on pruning mass. Vines with larger canopies generally had higher yields. The exception is vines on 10-17A (Figure 2). They were as vigorous as the top performers like vines on Salt Creek, yet the total yield remained intermediate. It is possible vines on 10-17A favored vegetative growth more than reproductive growth. Rootstocks had similar impacts on marketable yield as total yield (Figure 3). It is worthwhile to note that vines on GRN-1 and own-rooted vines experienced sunburn and fruit yellowing, and thus the marketable yield of those two treatments was only 20 to 30% of the top performers.
Berry composition at harvest. Vines on GRN 2, Salt Creek, and 10-17A had delayed ripening in one of the two years. Rootstock did not have a consistent effect on the pH and titratable acid of fruit juice at harvest.
Soil-borne pests. We observed an overall increase of dagger nematode (X. americanum) and citrus nematode (T. semipenetrans) populations across all rootstocks as vines age. Yet, vine growth did not show a clear association with nematode population. For example, vines on Salt Creek and own-rooted vines had similar counts for dagger and citrus nematodes, but the former performed way better than own-rooted vines in this trial. It seems vines grew well and would have more tolerance to nematode damage. We did not find phylloxera in this experimental site.
Conclusion. Overall, even though this site had a low population of plant parasitic nematodes in the early years, own-rooted vines experienced a clear decline in growth and yield as vines became older. Rootstocks showed benefits in boosting vine vigor, increasing yield, and extending vineyard longevity. GRN 2, GRN 3, and Teleki 5C could be the alternative options for traditional rootstocks like Freedom, 1103 Paulsen, and Salt Creek, which convey moderate to high vigor to the scion. In cases where scions are already vigorous, rootstocks like GRN 4 and RS-3 can be good options. GRN-1 is unlikely a suitable rootstock for table grape vineyards.
Acknowledgment. I would like to thank our grower cooperators, Leroy Kuntz and Konrad Kuntz, for their generous support. The help and support from Matthew Fidelibus, Don Luvisi, Ashraf El Kereamy, and Andreas Westphal are greatly appreciated. Special thanks go to Minerva Gonzalez, our viticulture technician, for her technical support over the course of this experiment. I also thank Karl Lund and Matthew Fidelibus for reviewing this article.