The Heat is on: Consequences and Mitigation of Heat and Drought Stress - 9th International Table Grape Symposium
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3/3/2020
9th International Table Grape Symposium
Santiago, Chile
February 16-21, 2020
The Heat is on:
Consequences
and Mitigation
of Heat and
Drought Stress
Markus Keller
1
Climate change: Temperature on the rise
Worldwide mean annual temperature anomalies since 1880
…so is CO2 NASA (2020)
2
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3/3/2020
Latitude: 39.7 °N
Altitude: 1000 m
Rainfall: 300 mm
wikipedia.org
Areni, Armenia: World’s oldest winery (4100 BC)
3
Lessons from history: Early heat & drought
Areni
• Grapes among earliest domesticated fruit crops (with olives, figs, dates)
• Cultivation from 8000 to 7000 years ago in Caucasus, later Fertile Crescent
• Southward wine trade raised price → Local grape production in Sumer,
later Persia and Egypt
• Growth of wine, raisin, table grapes aided by invention of irrigation
• Irrigation contributed to downfall of early civilizations due to soil salinization
4
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Cool Intermediate Warm Hot
Matchmaking Average growing season temperature (NH Apr–Oct, SH Oct–Apr)
13–15°C 15–17°C 17–19°C 19–24°C
• Climates with 17–24°C
average growing season 17–24°C
temperature: Warm–hot
• Most table grapes are
adapted to warm climates
(Negrul’s Proles orientalis)
• Increase in area for table
grape and raisin
production?
• But: +1°C in average
temperature → +214 GDD
across growing season
→ Earlier phenology Table grapes
• Vineyards planted in 2020
may experience warmer
climate in 2050
Jones (2006) Dried grapes
5
Grape production: Table grapes on the rise
Wine Table Dried grapes
Production Kyoho
Country MT
China 14.8 Equator
Italy 8.2
USA 7.1
France 6.2
Spain 5.9
Turkey 4.0 • 47% wine, brandy (down from >70%)
India 2.6 • 36% table grapes
Uses • 8% dried fruit (raisins)
Chile 2.5
• 9% grape juice, vinegar, jelly
Iran 2.5
South Africa 2.0 MT = Million tons http://www.oiv.int (2017)
6
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Lessons from botany: Tolerance & genes
Utah, USA
37°N – 1200 m
• Grapes are heat and drought tolerant
• But: Narrow genetic basis in current varieties
• Most seedless varieties descended from ancient Middle
Eastern Sultanina (syn. Sultana, Kishmish, Thompson
Seedless)
• Most “muscat” varieties descended from ancient Greek
Muscat blanc or its offspring Muscat of Alexandria
7
Drought stress: A varietal continuum
Seasonal minimum midday Ψl at v ≈ 10%
Petit Muscat blanc
Sauvignon blanc Grenache Riesling Pinot noir
Verdot
Chardonnay Nebbiolo Auxerrois Albariño
Ψl = Leaf water potential; v = Soil moisture Silt loam v: FC 29%, PWP 8%
• Response to drought stress varies by grape variety Ψl
• All varieties have sensitive stomata, but… v
• Continuum from near-isohydric to strict anisohydric
Ψl
behavior with varying slopes and variability
v
• More anisohydric (optimistic, risky) → More carbon
assimilation under mild–moderate water stress, but Ψl
greater risk of hydraulic failure (canopy collapse) v
under severe stress
Martinez (2019)
8
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Heat & drought stress: How vines cope
0.6
● No
gsstress:
for l
the -0.3 MPafit
exponnetial
0.5 ● Stress: Predawn
gs in the Ψl < of
plateau portion -0.6
the MPa
exponential fit
m-2.s s) -1 )
0.4
-1
0.3
-2
gs (mol.m
gs (mol
0.2
H2O
0.1
0.0
-0.1
he
c
y
o
t
er
g
nc
llon
er
c
n
rlo
lbe
na
arin
an
slin
no
erg
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bla
ac
Me
mil
on
t fr
ram
Ma
vig
Rie
en
Alb
mb
at
ard
rne
Se
au
Gr
rzt
sc
Le
ch
tS
be
wu
Mu
Ca
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Ge
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Ca
• Transpiration (evaporative cooling) prevents leaf overheating
• High temperature → High vapor pressure deficit (VPD)
• Stomata close under water stress in the soil or in the
atmosphere, but cannot close more under combination stress
• Heat stress (high VPD) → More water loss → Dehydration at
low soil moisture → Leaf wilting, canopy collapse
9
Stress interaction: Heat versus drought
0.35 18
█ Cabernet Sauvignon Light: ≤1000 µmol/m2s
CS 16
0.30 R
█ Riesling 14
An (umolCO2.m .s )
-1
0.25
gs (mol.m .s )
12
-1
-2
0.20
-2
10
0.15 8
6
0.10
4
0.05
2
0.00 0
s t s t s t ss t
es gh es ea es gh tre ea
Str Dr
ou Str t+H Str Dr
ou S t+H
No at gh No at gh
He
Drou He
Drou ET = Evapotranspiration
Treatments Treatments
• Growth chambers: Control: 2006–16 average max/min temperatures
(30/14°C), water to replace ET; Heat: +10°C; Drought: -50% water
• Leaf physiology: Response mostly to drought stress but exacerbated
by heat stress, depending on phenology, leaf age – recovery in 2–4 d
• Shoot growth: Response dominated by drought stress
✓ Less water → Less growth
• Fruit composition: Response dominated by heat stress
✓ Heat → Higher TSS (+1°Brix) and pH (+0.25), lower TA (-2 g/L)
10
5
3/3/2020
Heat stress compromises yield
Day/night Fruit set Berry wt
24/10°C 20%, 24 d 0.8 g
32/14°C 31%, 10 d 1.0 g 32/14°C 24/10°C
• Some grapes (Thompson Seedless, Muscat of Alexandria)
require >20°C for cluster initiation/differentiation, but…
• Bud fruitfulness is compromised above 35°C
• Time from pollination to fertilization decreases as temperature
increases from 10°C (48 h) to 30°C (12 h), but…
• Low fertilization above 35°C → LGO, inflorescence necrosis
11
Drought stress compromises yield
1.8
1.6
1.4
Shoot vigor (cm/d)
1.2
1.0
0.8
0.6
0.4
Sand: r = 0.89**
0.2 Loam: r = 0.85***
0.0
6 8 10 12 14 16 18 20 22 24
Soil moisture (%)
• Water for cell expansion → Drought stress during budbreak →
Erratic budbreak, low vigor, cluster abortion, poor fruit set
• Shoot growth, yield maximized at 3–4% below field capacity
• No sap flow (bleeding) in spring → Irrigate!
12
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Drought stress exacerbates nutrient stress
Yes Water deficit? Yes
Yes N deficit? No
• Drought stress during bloom → Poor fruit set
• Drought stress exacerbates effect of nutrient deficit
13
Drought stress: Less carbon for berries
18
16
14 More berries
Cfruit (g shoot-1)
12 Bigger berries
10
8
6
4 r = 0.77
2 P < 0.001
Keller et al. (2015)
0
100 150 200 250 300
-2 -1
gmax (mmol H2O m s )
• Drought stress → Stomata close → Photosynthesis declines
→ Less sugar available for export to fruit → Lower Cfruit
• Drought stress before veraison → Smaller berries
• Drought stress after veraison → Lower TSS, berry shrivel
14
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Drought and heat stress: Berry dehydration
140 2.7
Berry size (% starting diam.)
Berry transpiration (μmol m-2 s-1)
Berry transpiration 2.4
120
VPD
2.1
100
VPD (kPa)
1.8
VPD (kPa)
80 1.5
60 1.2
0.9
40
0.6
20
0.3
0 0.0
0:00 16:00 8:00 0:00 16:00 8:00 0:00 16:00
8:00 0:00 16:00 8:00 0:00 16:00 8:00
Time of the day
• Grape berries are designed to minimize transpiration (100-
fold less than leaves); no stomatal control after veraison Dysfunctional
• VPD (temperature!) drives berry transpiration: E gc VPD
• Lower gc above 15°Brix → Lower transpiration rate
• Ripening berries are vulnerable to heat injury → Sunburn
• Drought and/or heat stress → Water loss → Berry shrivel
• Postveraison irrigation may prevent but not reverse berry
shrivel (shrinkage from dehydration)
gc = Cuticular conductance Keller et al. (2015); Zhang & Keller (2015)
15
Water for yield, temperature for quality
50
47°C 15°C above air
temperature!
40
Temperature (°C)
35°C
30 32°C
Anthocyanin,
flavonol window
20 20°C
Monoterpene
10 Fruit exposure window
10°C
25% ETc Exterior Interior
Ambient 100% ETc Exterior Interior
0
245 246 247 248 249 250
Day of year
Day of year
• Water deficit → Small berries and low shoot vigor
→ Open canopy, high cluster sun-exposure
→ High light and high temperature
• Exposed berries are warm berries
• Alters monoterpenes, anthocyanins, flavonols Keller et al. (2016)
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Expect the unexpected: Split happens
600
Concord Excess water:
Splitting resistance (kPa)
500 Merlot
→ Pressure increases
Syrah
400 Zinfandel → Berries swell, may split
300
→ Sugar may leach out
→ Berries may expand or
200
shrink (weather!)
100 → Disease susceptibility
(Botrytis…)
0
0 5 10 15 20 25 30
Soluble solids (Brix)
• Splitting resistance drops during berry softening
• Berry splitting may occur due to rainfall, overhead
sprinkler irrigation, or high relative humidity (low E)
• Preveraison drought stress increases postveraison
splitting susceptibility (+20%)
Chang et al. (2019)
17
Expect the unexpected: Sour shrivel
20
Irrigation water
Cold
Berry shrivel (%)
15
Ambient
10
5
0
No stress Water stress
• Irrigation cut off during lag phase, then irrigation with ambient
or ice-cooled water at veraison
• Cold irrigation water → 4–8ºC lower soil temperature
➢ Control vines → 5% berry shrivel (BS)
➢ Cold water → 9% BS
➢ Water stress during lag phase → 17% BS
• Effect of water stress or rewatering or water/soil temperature?
18
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Mitigating drought stress: Irrigation
50
Merlot (r=-0.45*)
1.4 40
Berry weight loss (%)
Syrah (r=-0.41*)
Chardonnay (ns)
Berry weight (g)
30
1.2
20
1.0 10
0
0.8
Merlot (r=0.53**) -10
Syrah (r=0.43*) -20
0.6
Chardonnay (r=0.51*)
-30
-1.4 -1.2 -1.0 -0.8 -1.2 -1.0 -0.8 -0.6
Preveraison Ψstem (MPa) Postveraison Ψstem (MPa)
2.2
50-100% ET
• Yield, berry size are determined before veraison
Harvest berry weight (g)
2.0 100-100% ET
r = 0.84***
• Compensation after veraison is not possible 1.8
1.6
• Preveraison: Irrigate more to maximize cluster 1.4
number and berry size → Yield 1.2
2010
• Postveraison: Irrigate to limit berry shrivel, but 1.0 2011
2012
irrigate less (-50%) to save water and favor 0.8
ripening → Quality
0.4 0.5 0.6 0.7 0.8 0.9
Lag-phase berry weight (g)
19
Mitigating heat stress
• Heat waves are a recurring issue in grape production
• Very hot days (Tmax > 35°C) are on the rise
• Conflict of interest: Water conservation and quality
enhancement → Deficit irrigation → Stomata close
→ Canopy heats up
• Heat mitigation → Consequences?
➢ Shade netting: Expensive (~$30,000/ha), less light → Lower photo-
synthesis → Yield, quality?
➢ Overhead sprinklers: More water → May compromise deficit irrigation
goals → Higher vigor, berry splitting, bunch rot
➢ Heat-tolerant varieties: Requires breeding, field grafting, replanting
➢ Vineyard relocation: Requires vineyard removal and redevelopment
• Urgent needs:
➢ Better knowledge of existing varietal diversity (responses to heat and
drought stress)
➢ Variety-specific, cost-effective irrigation and heat mitigation strategies
20
103/3/2020
Mitigating heat stress: Canopy cooling
5.7 L/h @ 32 PSI
ON (dry) OFF (wet)
ON (35ºC) OFF (32ºC)
• Novel mist-type evaporative cooling system
• Misting nozzles on drip tube attached to foliage wire on west side
• Feedback controls maintain temperature, avoid leaf wetness, water runoff
• >90% reduction in water use compared with overhead sprinklers
• Canopy temperature maintained around 32–35°C during heat waves
• No effect on disease incidence, yield, berry weight, TSS, TA, but lower pH
21
Acknowledgments: Thank you!
People:
• Esther Hernández
• Ben-Min Chang
• Nataliya Shcherbatyuk
Funding: • Joelle Martinez
• 9th ITGS • Yun Zhang
• Specialty Crop Block Grant Program • Noorani Barkat
• Washington State Grape & Wine • Lynn Mills
Research Program • Alan Kawakami
22
113/3/2020
It’s in the book
Third Edition, 2020
Academic Press
(Elsevier) or Amazon
23
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