Rootstock Effects on Deficit-Irrigated Winegrapes in a

Dry Climate: Vigor, Yield Formation, and Fruit Ripening

Markus Keller,1* Lynn J. Mills,2 and James F. Harbertson3
Abstract: A rootstock field trial was conducted in the Yakima Valley, southeastern Washington, with three Vitis
vinifera cultivars (Merlot, Syrah, Chardonnay). Vines were grown on their own roots or field-grafted to the rootstocks
5C, 99R, 140Ru, 1103P, 3309C, and an unnamed rootstock from Cornell University (here termed 101CU) that is a
likely sibling or seedling of 101-14 Mgt. Repeated scion dieback due to cold injury to 99R led us to abandon this
rootstock. Vine phenology, vigor, water status, yield formation, and fruit ripening and composition were evaluated
during three years beginning in the vineyards ninth year. Own-rooted Merlot and Chardonnay grew more shoots
than grafted vines, and 140Ru and 1103P tended to reduce pruning weights. However, 3309C was the rootstock associated with the highest pruning weights in Syrah and the lowest in Chardonnay. Rootstocks usually did not impact
vine phenology, fruit set, and plant water status, although there was a trend for stem water potential to be highest
with 3309C and lowest with 5C. The rootstock effect on yield formation depended on the scion cultivar, and variations in different yield components often cancelled out each other, but 3309C (Merlot and Syrah), 5C (Merlot and
Chardonnay), and own roots (Chardonnay) were often associated with high yields. Nevertheless, the rootstocks had
only minor effects on fruit ripening and did not consistently alter soluble solids, TA, K+, or anthocyanin pigments,
but the pH was higher in fruit from own-rooted vines compared with grafted Merlot and Chardonnay. Overall, scion
effects and differences due to yearly climate variation far outweighed any differences due to rootstock.
Key words: cultivar, fruit composition, fruit set, grape berry, growth, rootstock, vigor, Vitis vinifera, yield components

Crosses of diverse North American Vitis species are used

as rootstocks in the majority of vineyards throughout the
world as the sole feasible means to prevent vineyard decline
due to infestation of susceptible European winegrapes (Vitis
vinifera L.) by phylloxera (Daktulosphaira vitifoliae Fitch).
Rootstocks are also used for their resistance to or tolerance of
nematodes, adverse soil conditions such as drought, waterlogging, high or low pH, or salinity, and their ability to influence
vine vigor and fruit ripening (Currle et al. 1983, Pongrcz
1983, Galet 1998, Whiting 2004). Although the compounds
responsible for fruit composition are mostly determined by
the genotype of the scion (e.g., Gholami et al. 1995), rootstocks may alter fruit composition indirectly by influencing
scion vigor, canopy configuration, yield formation, and nutrient uptake (Schumann 1974, Ruhl et al. 1988, Keller et al.
2001a, 2001b).

Despite the presence of phylloxera in the region and unlike

most of the worlds grapegrowing areas, the vast majority of
vineyards in eastern Washington State are planted to vines
on their own roots. Vineyards in this arid region (<300 mm
annual precipitation) are typically drip-irrigated using deficitirrigation strategies, which are used as a tool to control canopy development and fruit ripening (Wample and Smithyman
2000, Keller et al. 2008). The main reason for growers reluctance to adopt rootstocks as a cultural practice is the periodic
occurrence of very cold winter temperatures leading to cold
injury in grapevines. This is of particular economic concern
for grafted vines (Folwell et al. 2001), which cannot simply
be retrained from suckers following lethal cold injury to the
trunk. Although the ability of Washingtons wine industry to
remain competitive is dependent upon the consistent production of high-quality fruit to make high-quality wines, there
is no local experience with the performance of grafted vines.
This lack of familiarity may leave the industry vulnerable to
the inadvertent spread of phylloxera, however unlikely such
a scenario may seem. To address this issue, a task force was
assembled in 1992 that recommended that Washington State
University begin a research program to evaluate rootstock
adaptability to and performance under local climatic and
edaphic conditions. The rootstocks V. berlandieri V. riparia
Teleki 5C (5C), V. berlandieri V. rupestris 99 Richter (99R),
140 Ruggeri (140Ru), 1103 Paulsen (1103P), V. riparia V.
rupestris 3309 Couderc (3309C), and an unnamed rootstock
selection from Cornell University were chosen for evaluation.
A rootstock field trial was planted in 1999, and evaluation
of scion performance began in 2002. In addition to the six
rootstocks, the three V. vinifera cultivars that were used as
scions (Merlot, Syrah, Chardonnay) were also planted on their

Professor of Viticulture, 2Research Technology Supervisor, Department of

Horticulture and Landscape Architecture, and 3Associate Professor of Enology, School of Food Science, Irrigated Agriculture Research and Extension
Center, Washington State University, 24106 N. Bunn Road, Prosser, WA 99350.
*Corresponding author (email: mkeller@wsu.edu; fax: 509 786-9370)
Acknowledgments: This work was funded by WSUs Agricultural Research
Center, project WNP00673, and by the Washington Wine Advisory Committee program. Plant material was donated by Ste. Michelle Wine Estates and
Inland Desert Nursery. Trellis materials were donated by Quiedan Company.
The authors thank R.L. Wample for initiation of the project and A. Kawakami,
C. Longoria, M. Mireles, and E. Harwood for technical assistance.
Manuscript submitted Aug 2011, revised Oct 2011, accepted Oct 2011
Copyright 2012 by the American Society for Enology and Viticulture. All
rights reserved.
doi: 10.5344/ajev.2011.11078
1

29
Am. J. Enol. Vitic. 63:1 (2012)

30 Keller et al.

own roots to permit comparison of vines grafted to rootstocks

with own-rooted vines that remain the industry standard. The
purpose here is to describe rootstock effects and scion rootstock interactions on scion growth, yield formation, sourcesink relations, and fruit ripening under conditions of deficit
irrigation. A companion study evaluated rootstock effects on
fruit and wine composition. The findings of that study are reported in a separate publication (Harbertson and Keller 2012).

Materials and Methods

Vineyard site, plant material, and management. The
experiment was conducted in a vineyard at the Irrigated Agriculture Research and Extension Center near Prosser, WA
(461740N; 1194437W; elevation 365 m), from 2007
through 2009. Vines were planted with 1.83 m between vines
in north-south-oriented rows spaced 2.74 m apart on a 2%
south-facing slope. The soil is a well-drained, uniformly deep
(>1 m) Shano silt loam, pH 8.0, with 0.25% organic matter and an estimated soil water content ( v) of ~25% (v/v) at
field capacity and ~8% at permanent wilting point (vineyard
4 in Davenport et al. 2008). Merlot, Syrah, and Chardonnay
were evaluated on their own roots (OR) or grafted to 5C,
99R, 140Ru, 1103P, 3309C, and an unnamed rootstock received from Cornell University. Rootstocks were propagated
by aseptic shoot-tip culture to eliminate crown gall bacteria
(Agrobacterium vitis), planted in an increase block in 1998,
and their identity was confirmed by DNA typing (Foundation Plant Services, UC Davis, CA). Although the selection
from Cornell University was initially identified as V. rupestris
V. riparia 101-14 Millardet and de Grasset (101-14 Mgt),
subsequent evaluation revealed that it was not 101-14 Mgt
nor any other commercially available rootstock, but a likely
sibling or seedling of 101-14 Mgt (hereafter termed 101CU;
P. Cousins and M.A. Walker, personal communication, 2010).
Rooted dormant cuttings were planted in 1999 and grafted
with certified nursery material by chip-budding in 2002. Cold
injury due to unseasonably low temperatures in late October
of both 2002 and 2003 necessitated regrafting of many vines
in 2003 and 2004 (Keller et al. 2007). The vines were trained
to two trunks and bilateral cordons at a height of 95 cm and
winter-pruned to two-bud spurs, leaving ~25 buds (excluding
basal buds) per vine. Shoots were loosely positioned between
two pair of foliage wires placed 35 cm (25 cm apart) and 70
cm (5 cm apart) above the cordon. No shoot thinning, hedging, or other canopy management practices were applied to
permit full expression of potential rootstock effects.
The vineyard was drip-irrigated using pressure-compensated emitters with a flow rate of 2 L/hr, spaced 90 cm apart.
Irrigation was applied if necessary between budbreak and
bloom to avoid plant water stress, then water was withheld
through mid-July to achieve control of shoot growth, after
which irrigation was applied approximately once weekly
through summer and less frequently during the cooler ripening period. The initial goal for the fruit set to veraison period
was to maintain a target v 11% (averaged over the top 90
cm, for measurement see below) for Chardonnay and Merlot
and 10% for Syrah because of the more vigorous shoot growth

of the latter. Given the very low vigor at this site, the target v
was increased to 1112% in 2008 and to 1314% in 2009. The
amount of irrigation water (IW in mm) to be applied for each
irrigation set was calculated from measured v (converted to
mm), rainfall (RF), and crop evapotranspiration (ETc): IW =
target v measured v RF + ETc. In addition, ETc = 0.8
Kc ET0, where Kc was the published V. vinifera crop coefficient (Evans et al. 1993) for appropriate cumulative growing
degree days (GDD, see below) and ET0 was the pan (grass)
evapotranspiration for the preceding irrigation interval. Following irrigation near veraison and during early ripening,
the soil was again permitted to dry down to encourage cold
acclimation. After harvest, irrigation was applied to replenish
v 18% to minimize cold injury to roots in winter.
Nitrogen fertilizer (NH4NO3(NH2)2CO) was applied annually at a rate of ~20 kg N/ha by fertigation; the rate was split
between the six-leaf and bloom stages. Because some vines
showed symptoms of potassium deficiency in 2008, potassium fertilizer (K 2SO 42MgSO 4) was shanked ~10 cm into
the soil on both sides of each vine row after harvest of 2008
and 2009 at a rate of ~170 kg K/ha. Vineyard floor management consisted of mowing a permanent cover crop and a 120
cm under-vine herbicide strip.
Measurements. Meteorological conditions were monitored using daily raw data derived from a Washington State
University AgWeatherNet weather station that has been in operation since 1989 and is located at the same elevation <1 km
to the east of the trial site. Growing-season heat units were
estimated as GDD > 10C accumulated from 1 Apr through
31 Oct, using daily mean temperatures calculated from daily
maximum (Tmax) and minimum temperatures (Tmin). Neutron
probes (503 DR Hydroprobe; CPN International, Concord,
CA) were used to monitor v. One (2007 and 2008) or two
(2009) PVC probe-access tubes were installed in each scion/
rootstock combination to a soil depth of 1 m beneath the
drip line and equidistant between drip emitters. In addition,
stem water potential (i.e., petiole xylem pressure, x) was
measured using a pressure chamber (PMS Instrument Co., Albany, OR) on at least four leaves per treatment replicate. Fully
expanded, sun-exposed leaves were measured after they had
been enclosed in aluminum-coated plastic bags for >30 min
between 11:00 and 15:00 LST. Measurements were conducted
four times before and once after veraison in 2007, four times
each before and after veraison in 2008, and weekly from fruit
set through harvest in 2009.
Vine phenology was monitored at least weekly. Flowers
per cluster and percent fruit set were estimated by counting
abscised flower caps collected in gauze bags (1 mm perforations) and counting the berries of the same clusters (Keller et
al. 2010). Average flower size for each cluster was estimated
by drying (60C) and weighing the collected flower caps, assuming that cap weight is proportional to flower weight and,
hence, size (Keller et al. 2010). Yield, clusters per vine, and
mean berry weight were determined at harvest and used to
estimate clusters per shoot and berries per cluster. Pruning
weights were recorded during winter pruning, and canes were
counted at the same time.

Am. J. Enol. Vitic. 63:1 (2012)

Rootstock Effects on Vine Performance 31

Fruit ripening was assessed by biweekly sampling beginning during the lag phase of berry growth. Five berries were
plucked from each of five clusters per replicate, alternately
from the top, middle, and bottom of each cluster, and kept
in a zip-lock bag on ice. At harvest, which occurred on the
same day for all rootstocks within a scion cultivar, 100 berries were collected per replicate. Berry samples were weighed
and analyzed the following day for total soluble solids (TSS),
titratable acidity (TA), pH, and anthocyanin color (Harbertson
and Keller 2012). Juice potassium concentration ([K+]) was
measured in 2007 and 2009 harvest samples as described by
Harbertson and Harwood (2009). Additional fruit composition
data and winemaking procedures and results are reported in
a companion paper (Harbertson and Keller 2012).
Experimental design and data analysis. The experiment
was designed as a split-plot with each of the three cultivars
randomly assigned to both of two adjacent 15-row blocks and
the seven rootstocks (one own-rooted and six grafted treatments) assigned to five subplots within each cultivar main
plot. Each cultivar plot consisted of five rows (60 vines/row),
and each rootstock was replicated once (7 vines/rootstock)
in each row. There were five or six own-rooted buffer vines
at either end of the row and five buffer rows on either side
of the experimental unit. All measurements were taken on
three interior vines (data vines), flanked by two buffer vines
of the same rootstock on either side of each of the 10 scion/
rootstock replicates. Vegetative and yield component data
were collected separately for each data vine. Fruit set was
estimated on both clusters of one two-cluster shoot on one
vine of five scion/rootstock replicates. Fruit composition data
were collected as composite samples from the data vines of
each replicate.
All data were analyzed using Statistica (version 10; StatSoft, Tulsa, OK). Results were first analyzed as a split-splitplot design using four-way (year block cultivar rootstock) analysis of variance (ANOVA) and F-test. Because
the block effect was almost never significant and cultivar
rootstock interactions were almost always significant, data
were next subjected to three-way (year cultivar rootstock)
ANOVA. Three-way interactions were almost never significant, but year and cultivar effects and year cultivar interactions were almost always significant and often failed Levenes
test due to differences in variance among years. Therefore,
data were also analyzed by two-way ANOVA using the general linear model procedure. This analysis was performed
by cultivar (year rootstock) to test for consistency of rootstock effects within cultivars over time and by year (cultivar
rootstock) to test for consistency of rootstock effects across
cultivars. Duncans new multiple range test was used for posthoc comparison of significant treatment means, and orthogonal contrasts were used to compare own-rooted vines with
grafted vines for each cultivar. The v, x, berry weight, and
fruit composition data were analyzed with a repeated measures design. Individual pH values were converted to [H+] for
statistical analysis, and the reported means were recalculated
from means of [H+]. Correlation analysis was used to compare
relationships between selected pairs of variables.

Results
Weather, soil moisture, and vine water status. Among
the three growing seasons, 2007 and 2008 were below and
2009 was above the 22-year average in terms of heat accumulation from 1 Apr through 31 Oct (Figure 1). Mean Tmax /
Tmin between budbreak (phenological stages were averaged
for the three cultivars) and bloom was similar among years,
varying only from 22.3/7.4C (2007) to 22.8/7.9C (2009).
The Tmax /Tmin range during bloom-fruit set was more pronounced: 23.1/8.3C (2007) to 26.8/10.2C (2008). The variation of 29.3/13.5C (2007) to 30.1/13.0C (2009) was again
low between fruit set and veraison but significant from veraison to harvest, ranging from 22.4/9.0C (2008) to 27.3/10.9C
(2009). While 2007 and 2008 had similar numbers of hot (Tmax
> 30C) and very hot (Tmax > 35C) days during the growing
season, 2009 had considerably more hot and very hot days,
most of which occurred between fruit set and veraison (Table
1). 2008 had the most cool (Tmax < 15C) and very cool (Tmax
< 10C) days in spring, and 2009 had several very cool days
in fall. The first fall frost occurred between 1 d before (2009)
and 16 d after (2007) the harvest of Syrah, which was always
the last cultivar to be harvested. Precipitation was below average in all three years, and there was very little rainfall during
the growing season (Table 1).
At budbreak, v of the top 90 cm of soil varied from considerably below (2007: 17.5% v/v; 2008: 18.9%) to slightly
below (2009: 22.6%) field capacity. Because of minimal rainfall, the subsequent v pattern mostly reflected the seasonal
irrigation strategy. In 2007 the soil began to dry down immediately after budbreak, whereas in 2008 and 2009 more
frequent irrigation kept v high through fruit set (Figure 2). In
all years, v reached a temporary minimum before veraison,
but v was lower ( p < 0.001) throughout the 2007 growing
season than in the other two years except for a strong temporary increase due to irrigation at veraison. Each year, and as
intended by the irrigation strategy, the soil under Syrah was
usually 1% (v/v) drier than that under Merlot and Chardonnay ( p < 0.05). Across the three scion cultivars, 1103P was

Figure 1 Growing degree day accumulation (base 10C) in Prosser, WA,

from 1 Apr to 31 Oct 2007 through 2009.

Am. J. Enol. Vitic. 63:1 (2012)

32 Keller et al.

the rootstock that was associated with the lowest v, which

was on average ~1.2% (v/v) lower than with other rootstocks
and own-rooted vines ( p < 0.01, data not shown). The only
other significant rootstock effect was the trend in 2009 toward
slightly elevated v with 140Ru ( p < 0.01). Each year, however, the spatial variation in v due to varying soil properties
across the vineyard block was usually greater than that due
to either scion or rootstock cultivar.
In 2008 and 2009, but not in 2007, there were significant
positive correlations between v and x for all three scion
cultivars; the strength of the relationship varied among cultivars as well as between years (0.36 < r < 0.82, p < 0.05).
When the x data were averaged for the pre- or postveraison
berry development phases, there were few and inconsistent
differences among scion cultivars (Table 2) and none among
rootstocks (data not shown). Seasonal trends and mean values
of x were rather similar among scion cultivars in 2007, but
Syrah maintained somewhat higher x after veraison in 2008
than did the other cultivars (Table 2). In 2009 Chardonnay
sustained the highest x after veraison. Evaluating individual
measurement dates uncovered a few significant but small differences among rootstocks (data not shown). All three cultivars maintained the highest midday x on 3309C throughout

most of the 2007 growing season ( p < 0.05). In 2008, vines

(especially Syrah) grafted to 5C had a lower x compared
with other rootstocks (p < 0.05). In 2009, 3309C (along with
140Ru) again led to the highest x, while 5C and 101CU were
associated with the lowest x (p < 0.001). Own-rooted vines
did not differ from grafted vines in any cultivar or year.
Vine growth. One of the rootstocks, 99R, was eliminated from the evaluation because both the rootstock itself
and the scions grafted to it often died back during the winter
Table 2 Effect of scion cultivar on average midday stem water
potential (x) during fruit ripening of field-grown grapevines in the
Yakima Valley, WA (all se 0.05 MPa).
Scion
Merlot
Syrah
Chardonnay
Signfa

2007
-0.83 b
-0.71 a
-0.77 ab
0.070
b

x (MPa)
2008

2009

-1.18 b
-0.99 a
-1.17 b
0.012

-1.26 b
-1.30 b
-1.01 a
<0.001

Significance (p value) of cultivar effect. Preveraison means were

similar for all cultivars (average -0.81 MPa in 2007; -0.84 MPa in
2008; -1.01 MPa in 2009).
bMeans within columns followed by different letters differ significantly
at p < 0.05 by Duncans new multiple range test.
a

Table 1 Meteorological data from the Washington State University AgWeatherNet Roza weather station near Prosser, WA
(<1 km east of vineyard site).
Year
2007
2008
2009
19892010
a
b

GDD (C)
1314
1333
1481
1409

>30C PV/RP
26/8
30/3
33/14
38

Seasonal temperature (d)b

>35C PV/RP
<15C S/F
1/0
5/0
11/2
7

16/19
23/13
14/12
13/11

<10C S/F
0/0
6/0
2/6
1/2

Precipitation (mm)
Annual
Seasonala
152
117
135
227

70
45
64
111

Cumulative growing degree days (>10C) and rainfall from 1 Apr to 31 Oct.
Number of days from 1 Apr to 31 Oct with maximum temperatures greater or lower than four threshold temperatures (PV: preveraison/RP:
ripening; S: spring/F: fall).

Figure 2 Influence of growing season and scion cultivar on the volumetric soil water content in the top 90 cm (means se) of a deficit-irrigated rootstock
trial block in Prosser, WA, in 2007 (n = 5), 2008 (n = 5), and 2009 (n = 10; BB: budbreak, B: bloom, V: veraison, H: harvest).
Am. J. Enol. Vitic. 63:1 (2012)

Rootstock Effects on Vine Performance 33

following grafting. Those vines that survived the first two

years after grafting have had no further problems with winter
survival, probably because once established, the woody rootstocks and grafts no longer suffered from the late maturation
that characterized their green shoots. Among the remaining
rootstocks (including own-rooted vines) there was no consistent effect on scion phenology in any cultivar (data not
shown). However, own-rooted Merlot and Chardonnay had
a greater capacity for growth than did grafted vines. Across
the three years and despite efforts to prune to similar bud
numbers, these cultivars grew on average 52% more shoots
(21/m) on their own roots than when they were grafted (14/m;
Table 3). Merlot and Chardonnay grafted to 5C and 101CU
usually grew intermediate shoot numbers. These differences
decreased from 2007 to 2009 as the vines matured. No such
rootstock effect was observed with Syrah as the grafting partner; all combinations grew ~15 shoots/m of canopy (Table 3).

Table 3 Effect of rootstock on measures of vine vigor

and balance of three scion cultivars in the Yakima Valley, WA,
over three years.
Pruning wt
(g/m)
Merlot
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009
Syrah
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009
Chardonnay
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009
Signfa
SR
YS
YR

246
254
177
184
230
253

ab
a
b
b
a
a

218
236
219

Cane no.
(canes/m)
20
16
13
14
15
16

a
b
c
c
bc
b

Cane wt
(g)
12.8
16.8
13.7
13.9
15.7
15.9

c
a
c
bc
ab
ab

Yield:
pruning wt
10.1
13.0
15.0
12.4
16.0
10.4

d
bc
ab
cd
a
cd

19 a
13 b
14 b

11.8 c
17.6 a
15.0 b

7.0 c
17.2 a
13.2 b

301
351
306
246
393
306
288
322
335

bc
ab
bc
c
a
bc

16
17
14
16
17
16
18
15
15

ab
a
b
ab
ab
ab

19.9
19.8
19.3
15.1
21.4
18.0
17.2
20.1
19.4

ab
ab
ab
c
a
bc
b
a
a

7.3
8.9
14.2
11.0
14.5
11.3
6.7
15.5
10.4

d
cd
ab
bc
a
abc
c
a
b

442
390
211
233
195
326
245
321
340

a
ab
c
c
c
b
b
a
a

23
17
13
15
14
16
22
13
14

a
b
d
cd
d
bc
a
b
b

20.3
22.6
16.1
15.3
14.0
19.1
11.1
20.7
21.9

ab
a
bcd
cd
d
abc
b
a
a

7.3
9.0
16.9
10.7
16.0
9.2
8.9
12.9
11.1

c
bc
a
b
a
bc
b
a
a

<0.001
0.053
0.017

<0.001
<0.001
0.301

<0.001
<0.001
0.097

0.195
<0.001
0.031

Significance (p value) of scion (S) rootstock (R), year (Y) S, and

Y R interactions.
bRootstock and year means within columns followed by different letters
differ significantly at p < 0.05 by Duncans new multiple range test.
a

Shoot numbers varied more than 10-fold but were strongly

correlated between years in all scion/rootstock combinations
(0.77 < r < 0.81, p < 0.001), indicating that the spatial variation within this vineyard was dominant over the temporal
variation. While shoot number may be taken as a measure
of vine capacity, average cane weight at pruning is a better indicator of shoot vigor. These two variables are usually
inversely related (i.e., vines that grow more shoots grow less
vigorously), but in this study there was no consistent association between shoot number and cane weight. Cane weights
were lowest after the 2007 growing season and similar in
the other two years (Table 3). Syrah had heavier canes than
Merlot and Chardonnay in 2007, and Merlot had lighter canes
than the other cultivars in 2008 and 2009 ( p < 0.001). Merlot produced heavier canes on 5C, 101CU, and 3309C than
on the other rootstocks or own roots, whereas 1103P led to
lower cane weights compared with other rootstocks in Syrah.
Chardonnay canes were heaviest in own-rooted vines, 5C, and
101CU. In all three cultivars, the variation in pruning weight
was somewhat more closely associated with differences in
cane weight (0.60 < r < 0.86, p < 0.001) than with differences
in cane number (0.46 < r < 0.69, p < 0.001).
In all scion cultivars and rootstocks, pruning weight was
positively correlated with the previous winters pruning
weight. The contribution of the variation in pruning weight
in one year to that in the following year increased from 2007
to 2009: r = 0.50 0.70 for Merlot; r = 0.55 0.83 for Syrah;
and r = 0.54 0.87 for Chardonnay (all p < 0.001). These
results show that larger vines remained larger over time and
that within-vineyard variation changed little from year to year.
Merlot consistently had the lowest pruning weights, and Syrah
had the highest pruning weights in 2007 but was similar to
Chardonnay in 2008 and 2009 (Table 3). While Merlot pruning weights did not exceed 0.7 kg/m of canopy, some Syrah
and Chardonnay vines reached pruning weights of up to 1.6
kg/m. However, the mean ( se) pruning weight varied only
from 0.22 0.01 to 0.34 0.02 kg/m across scion cultivars and
years. The rootstock effect was significant in 2008 and 2009,
which resulted in a significant year rootstock interaction
(Table 3). Because the scion rootstock interaction was also
significant, the rootstock effect was analyzed separately for
each cultivar. In Merlot, 140Ru and 1103P decreased pruning
weights by 27% compared with other rootstocks and ownrooted vines (Table 3). Syrah had the lowest pruning weights
when grafted to 1103P and the highest on 3309C. Chardonnay pruning weights were 49% lower with 3309C, 140Ru, and
1103P compared with 5C and own-rooted vines.
Yield formation and vine balance. A vines yield potential at the beginning of a growing season may be estimated
from the number of clusters per vine (shoots/vine clusters/
shoot) and the average number of flowers per cluster (inflorescence size). Annual variation dominated the total variation
in cluster numbers. Despite higher shoot numbers, there were
generally fewer clusters per vine in 2007 than in 2008 and
2009, with a range among means of 1.6-fold in Merlot, 1.8fold in Syrah, and 1.3-fold in Chardonnay (Table 4). There
was a significant year rootstock interaction across but not

Am. J. Enol. Vitic. 63:1 (2012)

34 Keller et al.

within scion cultivars, indicating that the rootstock effect on

cluster numbers of each scion was relatively consistent over
time. Merlot produced fewer clusters when grafted to 1103P
and 140Ru compared with other rootstocks and own-rooted
vines, Syrah was most productive on 3309C, and Chardonnay produced the fewest clusters on 140Ru and the most on
its own roots (Table 4). Merlot had the fewest flowers per
cluster in 2007 and the most in 2008, while inflorescence
size varied little from year to year in Syrah and Chardonnay
(Table 5). Chardonnay had the largest flowers, followed by
Syrah and finally Merlot (p < 0.001). Across scion cultivars,
f lowers were 23% smaller in 2007 than in 2008 and 2009
(Table 5), and 1103P was often associated with smaller flowers compared with other rootstocks and own-rooted vines ( p
< 0.01). Whereas there was no significant rootstock effect on
Merlot and Chardonnay inflorescence size, Syrah tended to
produce more flowers per inflorescence on 5C and 101CU
than on its own roots (p < 0.05). Merlot had more flowers per
Table 4 Effect of rootstock on yield and its components of three
scion cultivars in the Yakima Valley, WA, over three years.
Yield b
Clusters
(kg/vine)
/vine

Cluster
wt (g)

Berries
/cluster

Berry
wt (g)

Merlot
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009

4.50
5.26
4.29
4.05
5.44
4.65
2.70
6.24
4.86

bc c
ab
c
c
a
abc
c
a
b

73
69
59
58
69
67
48
75
72

a
a
b
b
a
ab
b
a
a

57
74
66
63
75
66
56
76
67

c
a
b
bc
a
b
c
a
b

57
71
61
64
66
64
64
67
61

c
a
bc
b
ab
b
ab
a
b

0.98
1.06
1.10
1.04
1.16
1.03
0.85
1.19
1.11

c
bc
ab
bc
a
bc
c
a
b

Syrah
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009

3.84
5.11
5.15
4.34
7.05
4.64
3.40
6.90
4.41

c
b
b
bc
a
bc
c
a
b

51
54
54
52
67
55
42
75
47

b
b
b
b
a
b
b
a
b

70
88
85
79
97
76
73
86
87

d
b
bc
bcd
a
cd
b
a
a

59
78
69
68
76
62
68
66
72

d
a
bc
c
ab
cd
ab
b
a

1.21
1.15
1.26
1.16
1.32
1.24
1.14
1.32
1.21

bc
c
ab
bc
a
ab
c
a
b

Chardonnay
Own roots
5C
140Ru
1103P
3309C
101CU
2007
2008
2009

5.37
5.25
3.83
4.14
4.17
4.35
3.77
4.86
4.92

a
a
b
b
b
b
b
a
a

91
79
65
68
70
73
64
77
82

a
b
c
bc
bc
bc
b
a
a

57
65
55
57
54
56
57
58
58

b
a
b
b
b
b

58
58
54
59
52
55
67 a
49 c
55 b

Signf a
SR
YS
YR

<0.001
<0.001
0.019

<0.001
<0.001
0.012

<0.001
<0.001
<0.001

<0.001
<0.001
0.398

1.01
1.11
1.05
1.04
1.03
1.07
0.85 c
1.20 a
1.08 b
0.016
<0.001
0.015

Significance (p value) of scion (S) rootstock (R), year (Y) S, and

Y R interactions.
b
Yield in t/ha can be obtained by doubling the number in kg/vine.
c
Rootstock and year means within columns followed by different letters
differ significantly at p < 0.05 by Duncans new multiple range test.
a

cluster than Syrah and Chardonnay, but Syrah set more fruit
than did Merlot and Chardonnay (Table 5). The percentage
fruit set in Merlot and Syrah was lowest in 2008 and highest in 2009 ( p < 0.001), while Chardonnay fruit set varied
little from year to year. The rootstock did not alter fruit set
in Syrah, but own-rooted Merlot set ~8% more fruit than did
its grafted counterparts (p < 0.05), whereas Chardonnay had
~9% lower fruit set on 140Ru than on other rootstocks or own
roots (p < 0.05). In Merlot and Syrah, the number of berries
per cluster was not a reliable indicator of fruit set (r < 0.11,
n.s.), but instead was more closely associated with the number
of flowers per cluster (r > 0.64, p < 0.001). In Chardonnay,
both flower number (r = 0.43, p < 0.001) and percentage fruit
set (r = 0.48, p < 0.001) contributed equally to the variation
in berry number.
Except in own-rooted vines of all cultivars, cluster weights
varied far less from year to year than did cluster numbers
(Table 4). Because of compensating effects of flower numbers and fruit set, the number of berries per cluster was much
less dependent on seasonal effects than on scion cultivar and
rootstock, although the interannual variation was quite pronounced (1.4-fold) in Chardonnay (Table 4). Chardonnay had
fewer berries per cluster (56 1.2) than Merlot (64 0.9) and
Syrah (69 1.2). Own-rooted Merlot and Syrah had fewer
berries per cluster than grafted vines, while vines on 5C and
3309C typically had the most berries per cluster (Table 4). The
variation in berry weights was again dominated by seasonal
effects: berries were smallest in 2007 and largest in 2008 with
a mean range of 1.4-fold in Merlot and Chardonnay and 1.2fold in Syrah (Table 4). Syrah consistently had heavier berries
than the other cultivars (p < 0.001). Merlot and Syrah gener-

Table 5 Inflorescence and flower size (estimated from dry

weights of collected flower caps) and fruit set of three scion
cultivars in the Yakima Valley, WA, over three years.
Flowers
/cluster

Flower size
(mg)

Fruit set
(%)

Merlot
2007
2008
2009

265 c c
475 a
358 b

0.30 c
0.40 a
0.37 b

38 b
33 c
43 a

Syrah
2007
2008
2009

233
264
245

0.32 c
0.44 a
0.42 b

57 ab
53 b
61 a

Chardonnay a
2008
2009

261
258

0.56
0.59

39
42

<0.001
0.076
0.270
<0.001
0.056

<0.001
0.005
0.479
<0.001
0.230

<0.001
0.408
0.580
0.351
0.291

Signf b
S
R
SR
YS
YR

Flower caps not collected for Chardonnay in 2007.

Significance (p value) of scion (S) and rootstock (R) effects and S
R, year (Y) S, and Y R interactions.
cYear means within columns followed by different letters differ significantly at p < 0.05 by Duncans new multiple range test.
a
b

Am. J. Enol. Vitic. 63:1 (2012)

Rootstock Effects on Vine Performance 35

ally produced slightly heavier berries on 3309C than on other

rootstocks or on their own roots. Consequently, own-rooted
Merlot and Syrah tended to have the smallest clusters, and
vines grafted to 5C and 3309C the largest (Table 4). In Merlot, the latter two rootstocks were also associated with 21%
higher yields compared with other rootstocks or own roots,
whereas Syrah on 3309C produced 61% more crop than on
other rootstocks or own roots. Rootstocks did not influence
berry numbers and berry weights on Chardonnay clusters.
Nonetheless, yields of own-rooted and 5C-grafted Chardonnay
were 28% higher in comparison with other rootstocks (Table
4). Across scion cultivars, own-rooted vines produced lower
yields than grafted vines in 2007 but not in 2008 and 2009.
Average yields in all three cultivars and across rootstocks were
lowest in 2007, but the annual variation was more pronounced
in Merlot (2.3-fold) and Syrah (2-fold) than in Chardonnay
(1.3-fold). Merlot and Syrah yields were highest in 2008, while
Chardonnay yields were similar in 2008 and 2009.
Most of the variation in the yield:pruning-weight ratio
(Y/P) was due to seasonal effects followed by rootstock effects. The Y/P was generally lowest in 2007 and highest in
2008 (Table 3); the mean varied 2.5-fold in Merlot, 2.3-fold in
Syrah, and 1.4-fold in Chardonnay. All three scion cultivars
had higher Y/P on 3309C and 140Ru than on other rootstocks
(Merlot +35%, Syrah +49%, Chardonnay +81%; p < 0.001),
with own-rooted vines consistently at the low end (Table 3).
For all cultivars, there were significant positive correlations
between pruning weight and cluster number as well as yield
in the following season, and these correlations generally became stronger over time (data not shown). Although yields on
an individual vine basis varied from 0 to 34 t/ha in Merlot,
from 0 to 40 t/ha in Syrah, and from 0 to 25 t/ha in Chardonnay, there was no sign of higher yields leading to lower
pruning weights. On the contrary, higher-yielding vines were
associated with higher pruning weights the following winter: r = 0.67 for Merlot, r = 0.72 for Syrah, and r = 0.75 for
Chardonnay (all p < 0.001). Thus, larger vines had a greater
yield potential than smaller vines, and higher yields did not
compromise vine size and capacity for the subsequent year.
Fruit ripening and composition. Variation in fruit ripening was dominated by scion and year effects. Rootstocks contributed little to this variation and to within-vineyard variation (data not shown). Sugars typically accumulated rapidly
during the first 30 to 35 days of the ripening period, but accumulation slowed markedly thereafter and effectively ceased
40 days after veraison in Chardonnay, 40 to 45 days after
veraison in Merlot, and 45 to 50 days after veraison in Syrah.
The rate of sugar accumulation (Brix/d) was positively correlated with the rate of organic acid degradation (g TA/L/d),
but the degree of this association varied by cultivar: r = 0.58
for Merlot; r = 0.29 for Syrah; r = 0.88 for Chardonnay (all p
< 0.001). The low yields in 2007 and, to a lesser extent, the
high temperatures in 2009 accelerated sugar and anthocyanin
accumulation and acid degradation compared with 2008 in
Merlot and Syrah, but merely advanced the onset of ripening
in Chardonnay. Although berries of all cultivars also had a
higher pH during the initial ripening phase of 2009, pH was

lower during that period when compared at similar TA or TSS

concentrations (p < 0.001). While TA declined rapidly during
the early ripening phase, the decrease slowed around 16 to
18 Brix and essentially ceased at ~20 to 21 Brix, irrespective
of cultivar, rootstock, and year. Nonetheless, pH consistently
continued to increase to at least 24 to 26 Brix. Over the entire
ripening period, correlations between TSS and pH (transformed to [H+]) were generally higher (r > 0.92, p < 0.001) and
less variable from year to year than were correlations between
TA and pH (r > 0.84, p < 0.001). Anthocyanins in Merlot and
Syrah berries increased during ripening but usually reached
a plateau at 22 to 24 Brix. In Syrah this plateau shifted to 28
Brix in 2007, when anthocyanins accumulated more slowly
but to a similar final level compared with the other years.
With few exceptions there was no clear rootstock effect
on sugar and anthocyanin accumulation or organic acid degradation in the fruit (data not shown). Significant scion
rootstock and year rootstock interactions indicated that
rootstock effects were neither consistent among scion cultivars nor among growing seasons within a cultivar. In 2007,
fruit from Syrah on 3309C had lower TSS and pH throughout
most of ripening compared with other rootstocks and own
roots ( p < 0.05) and began the ripening phase with higher
TA than own-rooted Syrah (p < 0.01). In 2008, grapes from
own-rooted Merlot had the highest pH throughout ripening,
and the difference increased over time ( p < 0.001). Ripening grapes from own-rooted Syrah had higher TSS than did
grapes from grafted Syrah ( p < 0.001); the former, together
with 5C, also had the lowest TA ( p < 0.05), highest pH ( p
< 0.01), and highest anthocyanin concentrations ( p < 0.001).
Sugar accumulation and acid degradation in Chardonnay was
faster on its own roots, 101CU, and 140Ru than on the other
rootstocks (p < 0.05), and grapes from own-rooted Chardonnay had a higher pH throughout ripening (p < 0.001). In 2009,
140Ru was associated with more rapid acid degradation than
1103P and 5C in Syrah, and 140Ru and 1103P led to faster
acid degradation compared with other rootstocks or own roots
in Chardonnay (p < 0.05). The pH increased more slowly in
grapes from own-rooted compared with grafted Chardonnay,
but it started from a higher level at veraison ( p < 0.05). In
Merlot, by contrast, the pH was similar across rootstocks at
veraison, but increased more rapidly in own-rooted vines (p <
0.001). Berries from Syrah grafted to 101CU had the highest
anthocyanin concentrations throughout ripening (p < 0.01).
For the most part, differences in fruit composition among
rootstocks disappeared by harvest (Table 6; rootstock data not
shown). However, there was a significant scion rootstock
interaction on pH: each year fruit from own-rooted Merlot
and Chardonnay had the highest pH (p < 0.001), but that was
not true for Syrah. Merlot grafted to 140Ru consistently had
the lowest pH (0.2 units below own-rooted vines) followed by
3309C ( p < 0.001); 3309C also consistently led to a slightly
lower pH in Syrah (p < 0.05), but there were no differences
among rootstocks in grafted Chardonnay. The pH was always
positively correlated with [K+] (0.32 < r < 0.70, p < 0.001 to
0.05) and often but not always inversely correlated with TA
(-0.89 < r < 0.05, p < 0.001 to 0.75). Fruit from Merlot on its

Am. J. Enol. Vitic. 63:1 (2012)

36 Keller et al.

own roots had the lowest TA, while 140Ru was consistently
associated with the highest TA at harvest ( p < 0.001). No
significant differences were found among rootstocks for any
other fruit composition variable in any scion cultivar.
The following relationships partly reflected the low crop
and associated rapid ripening in 2007, but correlations of similar magnitude and direction as those reported across years
were often found within years. Across years there were negative correlations between yield and TSS (Merlot: r = -0.60;
Syrah: r = -0.52; Chardonnay: r = -0.26; all p < 0.001) and
between yield and pH (Merlot: r = -0.38; Syrah: r = -0.53;
Chardonnay: r = -0.24; all p < 0.01) but not TA. Somewhat
weaker negative correlations were also found between Y/P
and TSS for Merlot (r = -0.51, p < 0.001) and Syrah ( r = -0.48,
p < 0.001), but not for Chardonnay. Still the pH decreased
with increasing Y/P in all cultivars (Merlot: r = -0.51; Syrah:
r = -0.24; Chardonnay: r = -0.42; all p < 0.01), while [K+]
decreased significantly only in Merlot (r = -0.34, p < 0.001)
and Syrah (r = -0.21, p < 0.001). The pH increased as canopy
density (shoots/m) increased in Merlot (r = 0.50, p < 0.001)
and Chardonnay (r = 0.39, p < 0.001), but not in Syrah. This
association was partly driven by the higher shoot number
(Table 3) and higher pH of own-rooted Merlot and Chardonnay compared with grafted vines.
There were positive correlations between average postveraison (but not preveraison) x and TSS (Merlot: r = 0.46;
Syrah: r = 0.38; Chardonnay: r = 0.59; all p < 0.01). Yet TA
was positively correlated with both preveraison x (Merlot:
r = 0.58; Syrah: r = 0.55; Chardonnay: r = 0.59; all p < 0.001)
and postveraison x (Merlot: r = 0.64; Syrah: r = 0.42; all p
< 0.01; Chardonnay: n.s.). Anthocyanins were negatively correlated with both preveraison x (Merlot: r = -0.51; Syrah: r
= -0.46; all p < 0.001) and postveraison x (Merlot: r = -0.70;
Table 6 Basic fruit composition at harvest of three scion cultivars
in the Yakima Valley, WA, over three years.

Merlot
2007
2008
2009
Syrah
2007
2008
2009
Chardonnay
2007
2008
2009
Signfa
S
R
SR
YS
YR

TSS
(Brix)

TA
(g/L)

pH

K+
(g/L)

25.2 ab
23.4 c
24.5 b

8.06 a
6.78 b
5.89 c

3.61 a
3.52 b
3.54 b

2.04 a

26.7 a
22.1 c
24.5 b

8.33 a
8.43 a
6.95 b

3.54 b
3.49 c
3.61 a

1.58 b

25.4 a
23.2 b
23.5 b

8.47 b
9.07 a
8.01 b

3.39 a
3.27 c
3.35 b

1.15

0.055
0.288
0.698
<0.001
0.263

<0.001
0.083
0.019
<0.001
0.905

<0.001
<0.001
<0.001
<0.001
0.633

<0.001
0.072
0.949
<0.001
0.204

1.69 b

1.89 a

1.25

Significance (p value) of scion (S) and rootstock (R) effects and S

R, year (Y) S, and Y R interactions.
bYear means within columns followed by different letters differ significantly at p < 0.05 by Duncans new multiple range test.
a

Syrah: r = -0.46; all p < 0.001). In Syrah, but not in the other
cultivars, fruit [K+] increased as x decreased both preveraison (r = -0.84, p < 0.001) and postveraison (r = -0.76, p <
0.001), which was coupled to an increase in pH with decreasing preveraison x (r = -0.54, p < 0.001) and postveraison x
(r = -0.31, p < 0.05). Yet, none of these associations between
plant water status and fruit composition were altered by grafting or the rootstocks used in this study.

Discussion
This three-year trial in a deficit-irrigated vineyard tested
the inf luence of six rootstocks, in comparison with ownrooted vines, on water use, growth, yield formation, and
fruit ripening of three V. vinifera cultivars. From an economic perspective, we currently cannot recommend planting
99R or other rootstocks with very long vegetative cycles in
areas with short growing seasons and cold winters because
their late shoot maturation appears to be associated with
late cold acclimation and hence poor initial graft survival in
winter. Overall, the remaining rootstocks induced few, and
often minor, differences in scion performance. This finding
was true not only for the variation among the different rootstocks, but also for the variation introduced by grafting in
comparison with own-rooted vines. The variation of most
variables evaluated here was clearly dominated by annual
climate variation, spatial differences across the vineyard, and
differences among scion cultivars. Where rootstock effects
were significant and consistent from year to year, there also
often was significant scion rootstock interaction, indicating that scion cultivars modified the rootstock impact. Based
on v measurements, 1103P appeared to be associated with
somewhat higher soil water use, but that was not reflected in
x measurements. The latter indicated that vines grafted to
3309C tended to maintain slightly higher and those grafted to
5C slightly lower water status than other vines. Other studies found no or inconsistent rootstock effects on vine water
status (estimated as midday leaf ) in Chardonnay (Stevens et
al. 2008), Syrah (Stevens et al. 2010), or Cabernet Sauvignon
(Nuzzo and Matthews 2006, Williams 2010). However, our
measures of vine vigor, such as shoot number, cane weight,
and pruning weight, suggested that own-rooted vines were
more vigorous than were grafted vines and 1103P consistently
induced low vigor; 5C was often grouped with own-rooted
vines and 140Ru with 1103P. The >50% higher shoot number
of own-rooted Merlot and Chardonnay compared with grafted
vines was especially striking. In contrast, 3309C was associated with high vigor in Syrah, intermediate vigor in Merlot,
and low vigor in Chardonnay. However, over the three years
both pruning weights and cane weights generally remained
low by published standards.
Optimum pruning weights are thought to be in the range
of 300 to 600 g/m of canopy, and optimum cane weights fall
in the range of 20 to 40 g (Smart 1985, Smart et al. 1990). All
three scion cultivars used here had yearly average values near
or below the lower limit of these ranges, and no rootstock was
associated with values that exceeded their upper limit in any
cultivar. In addition, despite considerable variation among

Am. J. Enol. Vitic. 63:1 (2012)

Rootstock Effects on Vine Performance 37

vines, the average shoot number per unit cordon length, a

measure of canopy density, was close to the optimum of 15
shoots/m. This suggests that in dry climates vine vigor is
predominantly controlled by water deficit (and hence by irrigation), with rootstocks having only a minor effect. Moreover, the overall direction of this effect was generally one
of lower vigor compared with own-rooted vines; rootstocks
such as 1103P and 140Ru may decrease both scion capacity
and vigor. However, 1103P and 140Ru led to higher vigor
than did 5C in unirrigated Cabernet Sauvignon (Nuzzo and
Matthews 2006). A recent field trial, conducted under similar
climatic conditions, uncovered no differences in scion vigor
among irrigated own-rooted Malbec and Malbec grafted to
140Ru, 1103P, 3309C, among other rootstocks (Di Filippo
and Vila 2011).
Of the rootstocks tested in the present study, the viticultural literature often classifies 140Ru as drought tolerant, 99R
and 1103P as intermediate to tolerant, 3309C as less to poorly
tolerant, and 5C as poorly drought tolerant (e.g., Galet 1998,
Whiting 2004). Yet, 99R, 1103P, and 3309C were reported to
be quite drought tolerant when grafted to nonfruiting Cabernet Sauvignon and grown in sand in small pots (Carbonneau
1985). More recently, 140Ru and 1103P, and in some cases
5C, were found to tolerate water deficit equally well when
grafted to mature, fruit-bearing Chardonnay (Stevens et al.
2008), Syrah (Stevens et al. 2010), or Cabernet Sauvignon
(Williams 2010). With the exception of the Malbec trial mentioned above, none of these studies included own-rooted vines
for comparison. Because of its geographic origin, V. vinifera
is likely to be more drought tolerant than many American
Vitis species. Consequently, rootstocks derived from American species might tend to reduce vigor and/or vine capacity
relative to own-rooted vines in arid regions, where the soil
dries down sufficiently to permit implementation of deficit
irrigation strategies. The low overall vigor in this study was
also the reason for the high Y/P ratios, especially for grafted
vines. Rather than being generally overcropped, these vines
might have been classified as undervigorous.
Low v or low temperature evidently did not limit fruit set
in any year; percentage fruit set in 2007 was similar to other
years, although 2007 had the lowest v between budbreak
and veraison and the lowest temperature during bloom. The
low yield in 2007 was a consequence of low bud fruitfulness
combined with low berry weights that resulted from low soil
moisture (McCarthy et al. 1997). Much of the difference in
berry size may have been established before bloom, as demonstrated by the smaller flower size in 2007 compared with
the other years. Thus, while the water deficit was not severe
enough to reduce fruit set, it may have been sufficient to
limit flower size and hence berry size (cf. Keller et al. 2010).
Rootstock effects on yield formation varied by scion cultivar,
but 3309C and 5C were often associated with high yields.
Yield differences arose from a combination of rootstock effects on cluster number, inflorescence size (flower number),
fruit set, and berry growth. For instance, high yields of Merlot on 3309C were mostly a result of higher berry weights,
whereas on 5C they were due to higher berry numbers per

cluster; other rootstocks had inconsistent and opposing impacts on different yield components. In Syrah, 3309C resulted
in the most clusters with the most f lowers and hence berries, and the heaviest berries. In Chardonnay, on the other
hand, 140Ru reduced the yield potential by decreasing both
cluster number and fruit set, but compensatory processes in
other yield components masked this rootstock effect so that
final yields were similar across all rootstocks and own-rooted
vines. The yield-promoting influence of 3309C on Merlot and
Syrah contrasts with a cool/humid-climate rootstock trial
with Mller-Thurgau (Keller et al. 2001a), in which 3309C
decreased both berry number per cluster (an effect it shared
with 140Ru) and berry weight. In other dry-climate field trials
that included some of the rootstocks used in this study with
irrigated Chardonnay (Stevens et al. 2008), Syrah (Stevens et
al. 2010), Cabernet Sauvignon (Williams 2010), Malbec (Di
Filippo and Vila 2011), or unirrigated Cabernet Sauvignon
(Nuzzo and Matthews 2006), rootstock effects on yield and
its components tended to be minor and, although sometimes
significant, were often inconsistent between years.
Although rootstocks may sometimes lead to considerable
differences in scion yield, seasonal effects have long been
deemed to strongly outweigh their influence on fruit composition (Schumann 1974). The outcomes from the present
field trial confirmed this notion. Nuzzo and Matthews (2006)
found that fruit ripening of Cabernet Sauvignon was quite
insensitive to rootstock. Few and inconsistent rootstock effects on fruit composition were measured in a recent field
trial that included own-rooted Malbec vines (Di Filippo and
Vila 2011). Similar to our study, Ruhl et al. (1988) found
that rootstock effects on TSS were inconsistent and that the
pH was higher in grapes from own-rooted compared with
grafted Chardonnay but not Syrah. These authors also reported a positive correlation between juice K+ (and in some
cases Na+) and pH. Potassium, sodium (Na+), and other metal
cations may substitute for H+, which increases the pH and
thus counters the influence of organic acids (Boulton 1980a,
1980b). The higher pH of Merlot and Chardonnay fruit from
own-rooted vines in our study might have been a consequence
of greater canopy density (Smart et al. 1985, Morrison and
Noble 1990) resulting from the high shoot number of these
vines. However, [K+] was not significantly higher in juice
from own-rooted vines. Gong et al. (2009) found similar K+
but higher Na+ concentrations in fruit from own-rooted Syrah
and Chardonnay compared with grafted vines, but we did not
measure Na+. While grafting might have indirectly influenced
fruit pH via canopy alterations in Merlot and Chardonnay, the
pH was instead altered by vine water status, irrespective of
rootstock, in Syrah.
The rates of sugar accumulation and organic acid (presumably malate) catabolism decreased and eventually ceased
during the late ripening period. These changes were likely
associated with declining sink strength of the berries ~30 d
after veraison and with declining temperatures in the fall. The
continued increase in pH at that time may have been a consequence of continued K+ (and perhaps some Na+) influx via
the phloem (Rogiers et al. 2006). Moreover, the concomitant

Am. J. Enol. Vitic. 63:1 (2012)

38 Keller et al.

decrease of TSS, K+, and pH with increasing yield and Y/P

is in agreement with earlier research (Hepner and Bravdo
1985) and indicates that higher yields and crop loads reduced
phloem inf lux per berry. It appears that the more heavily
cropped vines were source-limited, which is in agreement
with the low pruning weights in this trial. This conclusion is
further corroborated by the association between postveraison
x and TSS and suggests that implementation of deficit irrigation in this vineyard restricted vine growth, and consequently
functional leaf area, considerably more than yield formation
(Eibach and Alleweldt 1985).

Conclusions
The field performance of three V. vinifera cultivars (Merlot, Syrah, Chardonnay) was evaluated on six rootstocks and
on their own roots in arid eastern Washington for three years.
One rootstock (99R) was abandoned because of its poor winter survival as a result of its long vegetative period. Thus,
rootstocks with similar characteristics cannot be recommended for regions with short growing seasons and cold winters.
The remaining rootstocks induced few, and often minor, differences in scion performance. For the most part, the variation in growth, yield formation, and fruit ripening and composition was dominated by scion cultivar, spatial differences
across the vineyard site, and climate variation among years.
Although own-rooted vines grew more shoots than grafted
vines, and 140Ru and 1103P tended to reduce scion vigor, the
rootstocks generally did not impact vine phenology, fruit set,
and plant water status. The influence of rootstocks on yield
formation depended on the scion cultivar, but 3309C and 5C
were often associated with high yields. Nevertheless, the rootstocks had only minor effects on fruit ripening and did not
consistently alter soluble solids, TA, K+, or anthocyanin pigments, although the pH tended to be higher in fruit from ownrooted compared with grafted vines. It appears that in this
dry climate vine vigor, reproductive performance, and fruit
composition were mostly controlled by water deficit, through
the implementation of deficit irrigation, while rootstocks had
minor effects that often depended on their grafting partner.

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