April 2020 - 22

Simulated heat waves help vineyards mitigate stress
By Brandon Schrand
Washington State University
By creating " heat waves " in
environment-controlled growth
chambers, Washington State University
(WSU) post-doctoral research associate
Esther Hernández-Montes aims to help
growers better mitigate the effects of heatstress
on wine grapes.
Because heat-stress and drought are
becoming common concerns in arid
grape-growing regions like Washington
state, growers are looking for tools and
methods to help protect their crops from
these often-unpredictable conditions while
simultaneously improving grape quality.
Hernández-Montes' current project
stems from previous work in which her
team focused on the effects of heat waves on
physiological processes like photosynthesis,
plant growth and grape quality.
" In the previous study, we found that
acidity and pH were affected by heat
waves, " Hernández-Montes said.
This finding is important because
both acidity and pH are key parameters
that affect wine quality, along with
chemical and microbial stability and
sensory properties.
It now appears that temperature is the
main driver affecting these parameters.
" We learned that excessive heat during
grape ripening decreased acidity and
increased pH, " she added.
Now they are focusing solely on
grape acidity, studying the relationship
between organic acids, pH and potassium,
specifically in grapes grown for white wines.
" Consumers usually want a refreshing
white wine, " she said, " and acidity is an
important factor in white wines. "
Significantly, the team found that heat
waves actually accelerate the degradation
of the malic acid in the grapes, potentially
affecting that acidic trait so sought after in
white wines.
" We are studying in detail the effect
of irrigation, different intensities of light
exposure of the grape clusters and the
temperature in the clusters on acidity,
pH and potassium, looking for variations
during the developmental stages, "
Hernández-Montes said.
Identifying any variations or changes
in acidity, pH, and sugar content during
different growth periods of heatstressed
grapes is vital when it comes to
recommending best irrigation and canopy
management practices for growers in
drought-prone climates.
The team, led by Markus Keller, found
that plants will recover after one or two
days of a heat wave, but prolonged periods
may require a much more methodical and
sustainable approach.
For their experiment, the team
used the growth chambers to simulate
temperature conditions that have
occurred historically in the field. They
then identified three stages to focus on:
bloom, veraison (i.e. when grapes change
color), and post-veraison.
" First, we download the temperature
data from different meteorological
stations in our area from the last 10 years, "
Hernandez-Montes said.
Then the team sets the growth chamber
temperatures to mimic the 10-year hourly
averages for each phenological stage.
" For instance, in the bloom-stage
experiment, we averaged the temperatures
from the month when bloom occurs in the
field and simulated those in the chamber.
Then we did the same for the veraison and
post-veraison stages, " she said.
From there, the team can adjust the
chambers by both temperature and light
intensity.
" Each growth chamber has a computer
that allows us to change the conditions
hour by hour. We also adjusted them
for day and night, to simulate the real
conditions in the field. "
Learning how the vines, fruit, and the
acids in particular respond to simulated
heat stress using different soil water
contents will help give growers a nimbler
set of management skills, especially when it
comes to irrigation.
" In a heat wave or drought conditions,
we want to know what the best irrigation
practices are for each phenological stage of
the grape's maturity, " she added.
Although the team is currently focusing
on grapes for white wines, the same studies
can be applied to grapes for red wines as
well, potentially helping all wine-grape
growers across the state.
By utilizing the four growth chambers
in Markus Keller's laboratory, HernándezMontes
isn't limited by seasons or
environmental conditions to conduct her
research, allowing the team to monitor
their subjects year-round.
" Using this technology, we can simulate
heat waves whenever we want and at
Esther Hernández-Montes can closely
monitor changes to grapes and grape
vines in specialized growth chambers.
Photo: Washington State University
whatever phenological state we want, "
she said.
Hernández-Montes and the team hope
their research will provide yet another
critical tool growers can utilize not just for
mitigating heat stress, but for unlocking
new and innovative ways to think about
growing high-quality wine grapes in the
state of Washington and beyond.
This research was funded by the
Washington Specialty Crop Block Grant
Program and the Washington State Grape
and Wine Research Program. FGN
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April 2020

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