The aim of this study was to determine how elevated CO2 levels affect bud fertility and yield of field-grown Riesling and Cabernet Sauvignon in the Rheingau area in Germany.
It has been shown that yields increase under elevated CO2 (eCO2) levels but the effect of bud fertility under eCO2 and its relation to yield has not been researched. In this trial, conducted over two years, 2016-2017, both Riesling and Cabernet Sauvignon vines were investigated. The following was recorded under conditions of ambient CO2 concentration (aCO2) and eCO2:
- Number of inflorescence primordia (IP) per node,
- The cross-sectional area of the IP,
- The incidence of primary bud necrosis (PBN), in grapevine compound buds.
- Yield parameters at harvest was then related to the data.
- No differences were found with regard to IP number per node or subsequent number of bunches per shoot in either of the treatments.
- In the eCO2 treatment, compound buds of Riesling had larger IP cross-sectional area, however, this did not result in higher bunch weight or yield over the two years.
- IP number per node was higher in plants grown under eCO2 but no changes in bunch number per shoot were found in either season.
- Contrary to the results in Riesling, in the eCO2 treatment, the Cabernet Sauvignon also had larger IP cross-sectional area, however, it translated into higher bunch weight and yield in both seasons.
PBN incidence of both cultivars was highest at basal node positions along the fruiting cane, except for Cabernet-Sauvignon in 2017, where both treatments showed higher incidence at the distal ends.
In both cultivars, average PBN incidence along the cane was not affected by eCO2.
SIGNIFICANCE OF THE STUDY:
The study showed that cultivars respond differently to eCO2 levels with regard to bud fruitfulness. As climatic conditions change over time, it is important to understand how the grapevine is affected in order to adapt viticultural practices in future.
Image: Kevin Crause