Effects of heat events on Shiraz berry composition

by | Jul 31, 2019 | Winetech Scan

In this project researchers wanted to determine what the effects of a single heat event, as well as cumulative effects of a number of heat events are on Shiraz berry composition and tannins.

PROJECT LAYOUT:
In order to control the environment, the experiment was done in a greenhouse on potted Shiraz vines.

To simulate a heat event, temperatures were increased by 6°C while fruit and canopy light exposure remained unchanged.

The following treatments were applied:

  • Control (C )
  • Heat event at the end of fruit set (HE1)
  • Heat event prior to veraison (HE2)
  • Heat events at both end of fruit set and veraison (HE1&2)

Temperatures inside the greenhouse was affected by outdoor temperatures. During HE1, maximum temperatures inside the greenhouse reached 45°C while reaching 40°C at HE2.

Berries were regularly sampled from fruit set to maturity, where primary and secondary metabolites as well as tannins were analysed.

RESULTS:
Photosynthesis was significantly decreased for the heated vines during HE1 where maximum temperature reached 45 °C, affecting both berry weight and titratable acidity.

  • Shiraz showed an elastic response to HE1. Skin tannin was mostly affected short after the heat event, along with seed tannin, but by maturity these differences were no longer evident.
  • HE2 had no effect on photosynthesis and less direct impact on berry composition, metabolites or tannins.
  • Some primary metabolites were affected by either HE1 or HE2 such as valine, leucine, pyruvic and lactic acids.
  • Two heat events (HE1&2) showed increased malic acid by harvest, and delayed the onset of veraison. However the phenolic profile and sugar at harvest were similair to controls.

SIGNIFICANCE OF THE STUDY:
The reality of climate change means that more frequent, extreme events such as heatwaves can occur. This research indicated that well-irrigated Shiraz grapevines showed that they could adapt to a short-term heat stress of 45 °C during berry development and remain unaffected at a temperature just above 40 °C.

Reference: https://oeno-one.eu/article/view/2392

Image: Shutterstock

Generic selectors
Exact matches only
Search in title
Search in content