It has been one month since I arrived in Australia! I enjoyed a few weeks of travel before I began research (Taiwan → Sydney → Tasmania → Melbourne → Great Ocean Road → Adelaide) and now we are in a frenzy of data collection.
First, I’ll give a little background as to why I’m here and what I’m doing: I am one of the lucky recipients of the Fredrick Dreer Award, an incredible opportunity granted to me by the Horticulture Section at Cornell. I am working with Dr. Vinay Pagay at the University of Adelaide, Waite Campus. His lab is on the cutting edge of vineyard technologies that will allow us to better understand and manage the effects of climate change on vines and wine quality.
Some of the projects Vinay’s lab is working on include:
- Detection of biotic and abiotic stresses in grapevines using proximal and remote sensing techniques
- The effect of heatwaves on aroma compounds in Sauvignon blanc
- The effect of heatwaves on phenolic compounds in Cabernet sauvignon
- Continuous in situ measurements of plant water status using a micro-tensiometer
I’ve had the opportunity to help with most of the experiments already. I’ll explain a few of them to the best of my understanding so far. It is also worth noting that this has been an incredibly wet year for South Australia and so while the vines are experiencing some degree of heat stress, this is by no means the normal amount of precipitation received during the summer months. Growers are hedging vines multiple times this season and battling outbreaks of powdery mildew and downy mildew (the latter is rarely encountered here). The climate is becoming predictably unpredictable, that is for sure.
The Sauvignon blanc trial is located at a commercial site in the Riverland, a region 2 hours north of Adelaide and mostly known for bulk production. Wen-Ching Huang, one of Vinay’s masters students, is leading this trial. The experiment uses in-canopy misters to cool the leaves and bunches during high temperatures. The misters turn on for 15 seconds every 10 minutes when ambient temperature is above 35°C. We installed thermocouples (temperature sensors) on the leaf blades and inside bunches to monitor changes in temperature that occur when the misters turn on and off. Basically, the thought is that the water from the mist will create an evaporative cooling effect in the canopy during high temperature events. We know that temperature indirectly affects the production of secondary metabolites (C-6 alcohols, pyrazines, thiol precursors, etc, all important to the varietal character of quality Sauvignon blanc wine) by directly affecting primary metabolites. So far, data is showing an 8-10 °C temperature drop on leaves and bunches immediately after misting! The next step to see if these desired compounds are present will be berry and juice analysis with gas chromatography. We also collect data on midday stem water potential, predawn leaf water potential, and leaf gas exchange with an Infrared Gas Analyzer (IRGA). The IRGA data gives us a measure of the stomatal conductance – this is important to consider alongside water potential measurements because it can indicate if the vine is actually respiring or not, providing a realistic assessment of stress.
Phew! That was just the description of one experiment! I guess I’ll save the others for future blog posts – there is no shortage of information to share. I’ll briefly discuss a protocol I learned to assess berry cell death (because I have a cool picture of that), then save the rest for next time.
Berry cell death is being looked at intensively by one of the other labs here, the Tyerman lab. It results in decreased fruit quality and yield loss (up to 30% in some cases). Ideally, it can be mitigated by increasing irrigation during times of vine stress. There are two ways to measure berry cell death (or berry cell viability, if you want to look at it glass half full!). You can use electrical impedence and/or cell staining with a fluorescent dye. I learned how to do both, and hopefully we will incorporate this data into the findings of the Sauvignon blanc and Cabernet sauvignon experiments. Impedance works by measuring electrical current through a berry – low impedance indicates high cell death, while relatively high impedance indicates low cell death. Staining the mesocarp with FDA (fluorescent diacetate) and putting it under UV light gives a visual of berry cell death. We can input this image into a computer program that will measure the area of green (live cells) vs black (dead cells). It is important to exclude the seeds from the measured area (they show up as the large kidney-bean shaped black masses). It’s kind of like doing a berry xray!