Full text of DOI:10.1111/j.1755-0238.2000.tb00182.x

216
Effect of shoot trim m ing on potted grapevines
Australian Journal of Grape and Wine Research 6, 216–226, 2000
Grow th , p h otosyn th esis an d crop p in g of p otted grap evin es
(Vitis vinifera L. cv. Cabern et Sau vign on )
in relation to sh oot trim m in g
STEFANO PO NI and ELISA GIACHINO
Istituto di Frutti-Viticoltura, Università Cattolica del Sacro Cuore, 29100 Piacenza, Italy
Corresponding author: Prof. Stefano Poni, facsimile + 39 523 599268, email sponi@pc.unicatt.it
Abstract
The present study was conducted to evaluate how changes in leaf area affected vine growth, yield and
grape quality of five-year-old potted Cabernet Sauvignon grapevines. At the beginning of flowering
vines were randomly assigned to the following five treatments: untrimmed (control); shoot trimmed at
either node 12 (T12) or node 6 (T6) with laterals either retained (R) or excised (X). Those four
manipulations are abbreviated to: T12LR, T12LX, T6LR and T6LX, respectively.
Total leaf area per vine was significantly lowered in T12LX and T6LX as compared to the other
treatments, whereas lateral formation was able to offset foliage loss due to trimming in T12LR and T6LR
with respect to control vines. T6LR also showed a more prolonged lateral node production. Yield per vine
and its components did not differ significantly among treatments except for berry size, which was reduced
in T6LR and T6LX. Grape ripening was severely retarded in T6LX, as shown by lower °Brix, pH, colour
and phenolics, and higher TA, tartrate and malate. A maturity delay was also shown in T6LR as lower
soluble solids and total anthocyanins per berry in comparison with untrimmed vines. No difference in
grape quality versus control was shown by the T12 treatments. Post-trimming assimilation rates (A)
clearly indicated a large compensation capacity of retained main leaves despite their mean age being
higher than that calculated for main leaves sampled the same day on control vines. The assimilation rates
recorded on lateral leaves increased proportionally with lateral shoot size and inversely to the number of
main leaves retained with trimming.
Based on present results, both the area and photosynthetic effectiveness of source leaves will drive
overall vine responses to shoot trimming. For example, T6LX showed the worst performance with respect
to the other treatments, in agreement with lowest leaf area, leaf-to-fruit ratio and oldest canopy.
However, T6LR had a somewhat retarded ripening despite its non-limiting leaf-to-fruit ratio, relatively
young canopy and maximum whole-canopy photosynthesis and efficiency at veraison. Under such
circumstances, duration of growth and possible competition with the berry sugaring process may have
played a role.
Abbreviation s
PI plastochron index; LPI leaf plastochron index; LA leaf area; DAB days after budburst;
NCER net carbon exchange rate; A CO2 assimilation; gs stomatal conductance; W dry weight per unit leaf area.
Keywords: shoot growth, canopy age, leaf-to-fruit ratio, gas-exchange, yield components, summer pruning,
berry ripening, source-sink balance.
In trod u ction
invasion of the alleyway by excessively vigorous shoots of
grapevines grown on trellises featuring no catch wires
(e.g. Geneva Double Curtain and Single Wire Trellis).
Shoot trimming is also applied to vertically shoot-
positioned training systems, to limit elongation of shoots
which typically outgrow the top wire and start to bend
downwards, thereby casting shade above the fruiting and
renewal area.
Summer pruning is one component of canopy manage-
ment techniques which can be helpful in controlling
grapevine vegetative growth and promoting canopy
ventilation around bunches in medium to high vigour
sites (Smart 1985, Koblet 1987, Jackson and Lombard
1993). One of the more extensively applied summer
pruning operations is shoot trimming, which consists of
removing shoot tips and of a variable number of under-
lying young leaves. This operation is designed to prevent
Changes in canopy morphology and physiology
brought about by shoot trimming are dramatic, and

Poni & Giachino
Effect of shoot trim m ing on potted grapevines 217
dynamically affect both amount and effectiveness of
source leaves (Poni and Intrieri 1996). Total-canopy light
interception is initially lowered upon the removal of the
apical shoot leaves, but subsequently recovers. The extent
of recovery depends upon the amount and duration of
lateral regrowth. Similarly, a canopy suddenly ages when
trimmed due to removal of the youngest leaves. Such a
canopy then rejuvenates via production of new leaves
from lateral shoots. The speed and duration of vegetative
growth, leaf-to-fruit ratio, leaf and cluster exposure and
the fraction of canopy leaf area represented by lateral
shoots, all change as a function of shoot trimming.
While the relationship between leaf ageing and
photosynthesis in untrimmed shoots has been widely
investigated (Kriedemann et al. 1970, Hunter and Visser
1988, Poni et al. 1994, Schultz et al. 1996), less attention
has been devoted to the same relationship in trimmed
shoots and the results appear controversial. Kriedemann
and Lenz (1972) and Höfacker (1978) have shown no
consistent effects on the photosynthesis of the retained
leaves after tip excision of Müller-Thurgau, Alicante and
Riesling shoots; however a defoliation study carried out
on Pinot Noir shoots topped at 12 nodes (Candolfi-
Vasconcelos and Koblet 1991) indicated a marked,
though temporary, photosynthetic compensation by the
retained main leaves that is shown to increase in the
absence of laterals. However, these workers did not report
gas exchange data for untrimmed shoots subjected to the
same defoliation levels.
More recent work has focused on the recovery of sun-
light interception following shoot trimming of grapevine
canopies with different trellis designs (Poni et al. 1996).
Of sunlight intercepted, laterals accounted for 45% in
upright canopies versus 22% in a GDC-trained canopy. A
condition that often occurs as a result of shoot trimming
is re-exposure of previously shaded leaves to full sun-
light. This effect has not been investigated in detail,
although a paper by Silvestroni et al. (1993) has shown
consistent photosynthetic recovery and delayed ageing
for leaves re-exposed to high light after experiencing a
period of shade. In general, due to the complexity of the
physiological changes induced at the canopy level by
shoot topping, a better understanding of the underlying
mechanism would be achieved through direct measure-
ments of whole-canopy gas exchange rather than relying
solely upon traditional single leaf determinations.
Although whole-vine gas exchange systems have also
been tested and used on grapevine (Edson et al. 1993,
Poni et al. 1997), to our knowledge there has not been
any application specifically aimed at evaluating the
response to shoot trimming.
with pruning severity, thus increasing variability in vine
performance. While there is evidence that late and severe
pruning can be the most limiting for vine growth and
grape maturity (Peterson and Smart 1975, Koblet 1987,
Poni and Intrieri 1996), contradictory outcomes have
been reported in regard to earlier trimming as related to
its severity. Reynolds and Wardle (1989 a,b) have report-
ed minimal reduction in vine capacity, no differences in
grape quality and improvements in canopy characteristics
for vines hedged post-bloom at 5 leaves as compared to
unhedged. Conversely, grape berry sugar and colour
development were impaired in Shiraz grapevines when
only two leaves above the distal bunch were retained
regardless of timing of shoot trimming (Peterson and
Smart 1975). In another comparison, trimming shoots to
about the 15th node at 4 and 8 weeks post-bloom invari-
ably reduced pruning weight, berry weight and soluble
solids as compared to untrimmed Sauvignon Blanc vines
(Kliewer and Bledsoe 1987), whereas a similar shoot
trimming severity did not affect yield and grape quality in
other cases (Wolf et al. 1986, Intrieri 1994). Indeed, these
contradictory results may in part reflect differences due to
scion/rootstock combinations and site vigour, but also
suggest that the understanding of canopy physiology as
affected by shoot trimming needs to be improved.
Our present purpose was twofold: (1) evaluate the
vine performance of Cabernet Sauvignon grapevines
subjected to various shoot trimming treatments and
determine their relatedness to the amount and quality of
source; and (2) gather a body of basic information which
would help in predicting Cabernet Sauvignon grapevine
behaviour following different severities of shoot trim-
ming.
Materials an d m eth od s
Plant material and experimental layout
The study was conducted on five-year-old potted Caber-
net Sauvignon (Vitis vinifera L.) grapevines grafted onto
SO4 rootstocks, and grown outside in 45 L pots filled
with a mixture of sand, peat and soil (1.5:1:2.5 by vol-
ume). Vines were winter-pruned to retain 3–4 fruiting
spurs and arranged in two, north-south oriented rows of
15 plants each. Two weeks after budburst, shoot and
inflorescence number per vine were counted to check
uniformity, and each vine was randomly assigned to the
following treatments within a completely randomised
design: an untrimmed control (C), trimmed immediately
above node 12 with lateral shoots either retained (R) or
excised (X) (T12LR; T12LX) and trimmed immediately
above node 6 with lateral shoots either retained or
excised (T6LR, T6LX). Each treatment had 6 vine repli-
cates and shoot trimming was performed at the beginning
of flowering (26 May) when the main shoots had formed
an average number of 14–16 unfolded leaves.
The general picture emerging from the large body of
work conducted on the effects of different timings of
shoot topping on vine growth and grape quality shows
preference for a shoot cut applied once early in the season
(e.g. fruit set), thereby allowing a fairly high number of
lateral leaves to reach maturity around veraison
(Reynolds and Wardle 1989a, Poni and Intrieri 1996,
Keller et al. 1999) and offsetting the loss in functional leaf
area. However, the timing of shoot trimming interacts
Vines were irrigated to pot capacity twice a day from
fruit-set till harvest (2 September) to avoid any inter-
ference due to temporary water stress. Pot sides were
wrapped with foil to minimise radiation-induced heating
of the root system. Five grams of urea per plant were
added to each pot a week after budburst and no further

218
Effect of shoot trim m ing on potted grapevines
Australian Journal of Grape and Wine Research 6, 216–226, 2000
fertilisation was applied throughout the rest of the season.
Downy and powdery mildew were controlled by spraying
on a calendar basis. Vines were protected against hail and
bird damage with a white net, thereby reducing incoming
photosynthetically-active radiation (PAR) by about 10% .
Yield, grape ripening and must quality
The onset of veraison was estimated by visual scoring
three times throughout the season (104, 107 and 110
DAB) as per cent of berries showing initial colour appear-
ance. Veraison date was estimated to occur when at least
10% of berries had shown initial colouring.
Yield and total cluster number per vine were
recorded at harvest (2 September, 150 DAB). Two 50-
berry samples per vine were taken concurrently to
ensure that the various positions within cluster (top,
mid, bottom) and exposures (internal or external
berries) were represented. The first set of berry samples
was weighed and stored at –20°C for subsequent
colour and phenolic analysis, while the second set was
immediately processed. The concentration of total sol-
uble solids (°Brix) was determined by a temperature-
compensating Atago refractometer and total sugar per
vine was calculated as °Brix × yield per vine. Titratable
acidity (TA) was measured by titration with NaOH
0.1N to the end point of pH 8.2 and was expressed as
tartaric acid equivalent. Tartrate was assessed accord-
ing to the colorimetric method based on silver nitrate
and ammonium vanadate reactions (Lipka and Tanner
1974). Malate was determined with a Boehringer kit
which utilises the enzyme L-malic dehydrogenase to
catalyse the reaction between malic and nicotinamide
adenine dinucleotide (NAD+), the latter two forming
oxaloacetate and the reduced form of the dinucleotide
(NADH). The extent of the reaction is measured
spectrophotometrically by change in absorption at 340
nm from the reduction of NAD+ to NADH. Potassium
was measured on a 0.5 mL must sample by atomic
absorption spectroscopy.
Total anthocyanins and phenolics were determined
after Iland (1988) and modifications suggested by the
same author thereafter (Iland, personal communication).
The 50-berry samples were left to thaw and then
homogenised at high speed (20000 rpm) with an Ultra-
Turrax homogeniser for 1 minute. Two grams of the
homogenate were transferred to a pre-tared centrifuge
tube, enriched with 10 mL aqueous ethanol (50% , pH
5.0), capped and mixed periodically for an hour before
centrifugation at 3500 for 5 minutes. A portion of the
extract (0.5 mL) was added to 10 mL 1M HCl, mixed,
left to stand for three hours and then absorbance values
registered at 520 nm and 280 nm as taken on a Kontron
spectrophotometer. Total anthocyanins and phenolics
were expressed as mg per berry.
Vegetative growth and canopy age assessment
Six shoots per vine borne on distal spur position were
marked 20 days after budburst (DAB) and used for
growth and age assessment. Budburst was estimated as 5
April on the basis that more than 50% of the total bud
population had by then reached the ‘woollen’ stage
(Baggiolini 1952) The age of each main leaf was defined
according to the plastochron index (PI). We nominated a
reference lamina length of 20 mm. Cabernet Sauvignon
leaflets 10 to 15 mm long show complete unfolding but
by 20 mm, leaves can be measured without mechanical
damage. The number of leaves longer than the reference
20 mm and the length of two consecutive leaves, one
less than 20 mm and the other greater than 20, were
measured on each marked shoot at weekly intervals dur-
ing linear shoot growth to calculate PI after Erickson and
Michelini (1957). The length of this phase was obviously
limited to the interval between budburst and shoot
trimming for all treatments except control, whose linear
growth phase extended to about 75 DAB. Mean shoot PI
per treatment was then plotted versus time and the reci-
1
b
procal of the linear regression coefficient ( ) calculated to
represent the number of days elapsing between the
appearance of two consecutive leaves on the main stem.
The leaf plastochron index (LPI) was then computed as
PI-i, where i is the serial number of the leaf from the
base towards the shoot tip and leaf age finally expressed
1
in days as LPI × .
b
The age of each lateral leaf forming along the main
shoot was calculated according to the same method as
per the phase of linear growth. From growth cessation
onward the age of all leaves was updated chronologically.
A special case applied to those laterals that had already
appeared on the main stem before trimming and did not
grow further. The age of these leaves was estimated using
1
b
the mean calculated for other laterals borne on the
same vines; thereafter age was updated chronologically.
Canopy age at specific dates was calculated by averaging
age values from single leaves.
Estimation of total leaf area per vine removed by trim-
ming was performed on the basis of the leaf area/dry
weight relationship. Five and twenty-five leaf disks (1.9
cm diameter) per vine were taken from the removed leaf
area of the T12 and T6 treatments and dried in an oven at
70°C to constant weight. Remaining leaves were dried as
well, and total leaf area calculated accordingly.
One week after harvest (9 September, 157 DAB) each
vine was defoliated and the total number and fresh
weight of main and lateral leaves recorded. One disk (1.9
cm diameter) per leaf was then immediately taken to
provide sub-samples which were weighed, dried in an
oven at 70°C and then re-weighed. The dry weight per
unit leaf area (W) was calculated from leaf disk data.
Single-leaf and whole-canopy gas exchange.
On the day before trimming treatments were imposed,
assimilation rate (A) and stomatal conductance (gs) of
every other main leaf from shoot base towards the apex
of a single shoot per vine were measured under saturat-
ing light (10.00 am to 4.00 pm) with a portable, flow-
through CIRAS-1 (PP-System, Hertfordshire, UK) gas-
exchange system featuring
a broad-leaf chamber
having a window of 2.5 cm2. Air flow was adjusted to 300
mL/min and all readings were taken at ambient relative
humidity. All measured leaves were generally well-

Poni & Giachino
Effect of shoot trim m ing on potted grapevines 219
Table 1. Vegetative growth of potted Cabernet Sauvignon vines left untrimmed or subjected to various shoot trimming
treatments. Data are given on a per vine basis. T12LR = trimmed at 12 nodes with laterals retained; T12LX = trimmed
at 12 nodes with laterals excised; T6LR = trimmed at 6 nodes with laterals retained; T6LX = trimmed at 6 nodes with
laterals excised.
Sh oot
LA rem oved
(d m 2)
Total n od es
(n )
Total LA
(m 2)
Main LA
(m 2)
Lateral LA
(m 2)
Main leaf size
(cm 2)
Lateral leaf
size (cm 2)
n u m ber (n )
Untrimmed
T12LR
11.8
10.0
10.2
11.8
11.0
ns
–
403 a
381 a
122 b
340 a
66 c
*
2.81 a
2.70 a
1.68 b
2.24 ab
0.90 c
*
2.10 a
1.57 b
1.68 b
0.82 c
0.90 c
*
0.71 b
98.7 b
136.1 a
138.4 a
122.8 a
136.7 a
*
39.0 b
1.04 b
0.87 b
8.06 a
7.76 a
*
1.13 ab
41.2 b
T12LX
–
–
T6LR
1.42 a
49.2 a
T6LX
Significancea
–
*
–
*
a
Mean separation within column by Student Newman Keuls test. *, ns: significant at P < 0.05, or not significant, respectively
exposed to sunlight at the time of measurements. Leaves
partially shaded before measurements were oriented
towards the sun and allowed to adjust for at least one
minute before being clamped. The second set of single-
leaf gas-exchange readings was run on the same shoots
on 20 July (56 days after trimming) and was also extend-
ed to lateral leaves. All main leaves were measured on
the T6 treatments, whereas every other main leaf was
sampled in the T12 treatments. Two lateral shoots (the
distal and one underneath it) were measured in T6 and
three lateral shoots representative of basal, median and
apical positions were measured in T12.
When canopy growth was almost completed in all
treatments (late July), one vine per treatment was
randomly singled out from the batch of 30 and used
for whole-canopy gas exchange readings. Measure-
ments were taken using a custom-built, flow-through
whole-canopy gas exchange system set up to run con-
tinuous, automated and simultaneous net carbon
exchange rate (NCER) readings on four canopies. The
system features two air-feed centrifugal blowers, four
flexible, inflated, transparent polyethylene chambers,
a rugged infrared gas analyser and a CR10 data logger
(Campbell Scientific, Leicestershire, UK) for data stor-
age and processing. More details about system set up
and functioning can be found in Poni et al. (1997).
Air-flow fed to the chamber was adjusted to 15–20 L/s
to prevent the temperature inside the chamber
exceeding the external air by more than 1.5°C; the
measurements were taken continually from 25 July
to 13 August (111–130 DAB). To solve the mismatch
between the number of treatments (five) and the
number of vines the system can handle (four), the
trimmed treatments were rotated at 4–5 day intervals
and the untrimmed vine kept as it was. Data were
automatically recorded at 10 min intervals and, to
allow comparison with A rates, whole-canopy NCER
(µmol CO2/s) was also expressed on a per unit leaf
area basis (µmol CO2/m2s).
after checking for normality, and mean separation was
performed by the Student-Newman-Keuls (SNK) test at
the 5% level. Regression analysis was used for quantita-
tive data types. Variation around means was shown as 2 ×
standard error (SE) where appropriate.
Resu lts
Shoot growth and vegetative development
While shoot number per vine did not differ among treat-
ments, all remaining vegetative parameters were affected
by shoot trimming. Final total nodes and leaf area per
vine were the lowest for T6LX, intermediate for T12LX
but did not statistically differ for untrimmed, T12LR and
T6LR vines (Table 1). The amount of total leaf area of
T6LX was similar to the amount of foliage removed with
trimming. Laterals contributed to final leaf area for 25% ,
42% and 63% in untrimmed, T12LR and T6LR, respec-
tively. Lateral leaf size was larger in T6LR as compared to
untrimmed and T12LR, whereas main leaf size was
smaller in control vines versus all trimmed treatments
(Table 1).
Changes in the number of fully expanded leaves per
shoot over the season indicated that shoot growth cessa-
tion occurred in the untrimmed vines at about 80 DAB,
or 25 days after trimming (Figure 1). A similar pattern
was observed for T12LR, whose post-trimming lateral
regrowth fully offset the main leaf removal. Conversely,
T6LR showed a temporary decrease in the total number
of expanded leaves one week after trimming but also
displayed the strongest post-trimming lateral production,
which continued to about 10 days after veraison.
Canopy age dynamic was markedly affected by shoot
trimming, as expected (Figure 2). Untrimmed vines had
the slowest canopy ageing and T6LX the fastest. Mean
canopy age at harvest, including contribution of both
main and lateral leaves, was 102 and 132 days for
untrimmed and T6LX, respectively. Trends of canopy
ageing for T12LR and T6LR were very similar and T12LX
was intermediate with respect to them and T6LX.
Plots were also drawn (Figure 3) to show variation
within the season in the number of main and lateral
unfolded leaves per shoot and their respective ages. At
growth cessation, the mean age of main leaves was about
Data analysis
Statistical analysis was carried out using the SAS soft-
ware package (SAS Institute, Cary, NC, USA). All data
were subjected to one-way analysis of variance (ANOVA)

220
Effect of shoot trim m ing on potted grapevines
Australian Journal of Grape and Wine Research 6, 216–226, 2000
Untrimmed
T12LR
Untrimmed
T12LX
trimming
veraison
T6LR
T6LX
veraison
harvest
Main
Laterals
TW12LR
Main
Days from budburst
Laterals
trimming
Figure 1. Seasonal dynamic of the total number of expanded leaves
per shoot (main plus laterals) recorded for untrimmed and trimmed
Cabernet Sauvignon grapevines. Vertical bars indicate the standard
error (SE) of a difference between any two treatments means
calculated as √(2s2/r), where s2 is the error mean square and r is the
number of replicates. The size of the vertical bars at the pre-trimming
dates was smaller than symbol size.
TW6LR
Main
Untrimmed
T12LR
T12LX
T6LR
Laterals
trimming
T6LX
harvest
trimming
veraison
Days from budburst
Figure 3. Seasonal evolution of the total number of unfolded leaves
on main and lateral shoots (solid lines) and of their respective ages
(broken lines) for untrimmed (top), T12LR (middle) and T6LR
(bottom). Vertical bars indicate 2SE for means of unfolded leaves.
Bars are not shown when smaller than symbol size. Behaviour of
T12LX and T6LX is almost identical to trends for main leaves
reported in figures 3 middle and bottom.
Days from budburst
Figure 2. Seasonal progression of canopy age including contribution
of lateral leaves. Treatments were * significantly different at P < 0.05
or ns, not different.
40 days in untrimmed vines (Figure 3 top). There was
very little lateral growth on control vines, and as a con-
sequence, lateral leaf ageing increased on a chronological
basis (Figure 3 top), varying from 5 (date of trimming) to
100 days (harvest). Laterals were moderately promoted
by shoot trimming in T12LR since a steady leaf number of
four had already been reached about 25 days before
veraison (Figure 3 middle). The laterals’ ageing pattern
was similar to that described for untrimmed vines.
Trimming in this treatment (T12LR) caused an abrupt
increase of main leaf age from 20 to 33 days (Figure 3
middle). Laterals were more vigorously promoted by
trimming in T6LR and a constant leaf number (6.5) was
only reached in post-veraison (Figure 3 bottom). Due to
this effect, leaf age of laterals formed on the T6LR vines
averaged 10 days less than the age recorded on un-
trimmed and control plants. Trimming caused a sudden
increase in age from 20 to about 40 days.
Untrimmed
T12LR
T6LR
Lateral insertion along main shoot
Figure 4. Variation of expanded leaves per lateral shoot against lateral
insertion on the main shoot (solid lines). Regression equations were:
y = 0.62 + 2.38(1+((x-5.6)/4.5)2), R2 = 0.94 (untrimmed); y = 0.3 +
1.46x – 0.25x2 + 0.014x3, R2 = 0.88 (T12LR); y = 2.25 + 0.052x3, R2
= 0.98 (T6LR). Mean lateral age at each position is also reported for
comparison at top of graph (broken lines).
The gradient of lateral development as a function of

Poni & Giachino
Effect of shoot trim m ing on potted grapevines 221
Table 2. Yield per vine and components of yield recorded at harvest on the potted Cabernet Sauvignon vines left
untrimmed or subjected to various shoot trimming treatments. See Table 1 for explanation of treatment codes.
Yield /vin e (g)
Clu ster n u m ber
p er vin e (n )
Clu ster w eigh t (g)
Berry w eigh t (g)
Berry n u m ber p er
clu ster (n )
Untrimmed
T12LR
1688
2186
1706
1985
1767
ns
15.5
16.0
14.8
16.7
15.3
ns
109
138
117
121
115
ns
1.53 a
1.51 a
1.51 a
1.36 b
1.24 c
*
83
94
T12LX
87
T6LR
114
101
ns
T6LX
a
Significance
a
Mean separation within column by Student Newman Keuls test. *, ns: significant at P < 0.05, or not significant, respectively
Table 3. Properties of must quality recorded at harvest on potted Cabernet Sauvignon vines left untrimmed or sub-
jected to various shoot trimming treatments. See Table 1 for explanation of treatment codes.
Solu ble solid s
(°Brix)
p H
TA
(g/L)
Tartrate
(g/L)
Malate
(g/L)
Ph en ols
(m g/berry)
An th ocyan in s
(m g/berry)
K+
(m g/L)
Untrimmed
T12LR
19.1 a
19.2 a
18.9 a
17.9 b
14.6 c
*
3.51 a
3.44 a
3.45 a
3.37 ab
3.32 b
*
5.91 b
6.63 b
6.63 b
7.18 ab
9.41 a
*
5.8 b
5.8 b
5.8 b
6.7 b
8.2 a
*
2.2 b
2.9 b
2.8 b
3.3 b
4.2 a
*
4.02 a
3.36 ab
3.69 a
3.17 ab
2.58 b
*
1.52 a
1.27 ab
1.28 ab
1.05 b
0.58 c
*
1844
1819
1694
1742
1998
ns
T12LX
T6LR
T6LX
Significancea
a
Mean separation within column by Student Newman Keuls test. *, ns: significant at P < 0.05, or not significant, respectively.
position along the main shoot (Figure 4) showed an
exponential increase in the number of expanded leaves
from base towards apex for T6LR at harvest. Accordingly,
mean age of the laterals borne at the distal node was only
78 days as compared to the 100 days of leaves located at
position 2. A similar, albeit less pronounced, pattern was
shown by T12LR, whose distal lateral shoot was notably
more vigorous and younger than the lateral shoots below
it. Due presumably to developmental influences exerted
by the intact shoot tip, the pattern of lateral growth along
the main stem was reversed in untrimmed vines and, in
spite of a generally weak lateral growth, the maximum
number of expanded leaves was reached by laterals
inserted at nodes 5–7 (Figure 4).
and tartrate as compared to the T12 and untrimmed
treatments. T6LR had lower total anthocyanins than
untrimmed on a per berry basis. This difference became
non significant when berry pigmentation was expressed
as mg/g of fresh weight (data not shown) due to lower
berry size of T6LR versus untrimmed (Table 2). The T12
treatments had a ripening pattern similar to untrimmed
vines. Potassium concentration of musts did not differ
among treatments, although T6LX showed higher values
in spite of a lower pH.
Cropping
Yield per vine did not differ statistically among treatments
(Table 2). This lack of significance in the amount of crop
per vine was reflected in similar cluster number, berry
number per cluster and cluster weight. A consistently
lower berry weight was shown by the T6 treatments as
compared to untrimmed and T12 treatments (Table 2).
The threshold per cent of coloured berries for the
onset of veraison was reached by all treatments but T6LX
on 20 July, the latter reaching the required level with a
5–day delay. At harvest, must soluble solids (°Brix) were
significantly lowered by the T6 treatments in comparison
with untrimmed and T12 treatments (Table 3). However,
this difference was much more pronounced for T6LX (4.5
°Brix less than control) than for T6LR (1.2°Brix less than
control). T6LX also showed a markedly delayed ripening
as lower pH, and anthocyanins and higher TA, malate
T12LX
Untrimmed
T6LR
T12LR
T6LX
Leaf position along the main shoot (n)
Figure 5. Variation of single leaf assimilation (µmolCO /m2s) against
2
position on main shoot evaluated the day before trimming. Data in all
treatments were fitted by a quadratic equation (y = a + bx + cx2). R2
values were 0.93, 0.92, 0.98, 0.93 and 0.95 for untrimmed, T12LR,
T12LX, T6LR and T6LX, respectively. Inner x-axis also shows mean
leaf age per position.

222
Effect of shoot trim m ing on potted grapevines
Australian Journal of Grape and Wine Research 6, 216–226, 2000
Table 4. Assimilation (A) and stomatal conductance (gs) rates and mean leaf age (days) recorded on either main (pre
and post-trimming) and lateral (post-trimming) leaves at different positions along the stem for each treatment. Last col-
umn reports total canopy assimilation (TCA) estimated from the mean of single-leaf readings at post-trimming and final
total LA. See Table 1 for explanation of treatment codes.
Pre-trim m in g – Main leaves
gs Age
(µm ol/m 2s) (m m ol/m 2s) (d ays)
Post-trim m in g – Main leaves
gs Age
(µm ol/m 2s) (m m ol/m 2s) (d ays)
Post-trim m in g – Laterals
gs Age
(µm ol/m 2s) (m m ol/m 2s) (d ays)
Estim ated
A
A
A
TCA
(µm ol/s)
Untrimmed
T12LR
8.7
7.1
9.2
8.5
8.6
ns
106 b
80 b
136 a
105 b
101 b
*
21
20
19
20
20
ns
7.1 b
7.6 b
11.7 a
10.4 a
11.1 a
*
74 d
117 c
153 b
166 b
203 a
*
49 c
70 b
69 b
78 a
78 a
*
5.9 c
58 c
147 b
–
57 a
56 a
19.1 b
21.9 ab
19.6 b
26.7 a
10.0 c
*
8.9 b
T12LX
–
T6LR
12.8 a
216 a
–
47 b
*
T6LX
–
*
a
Significance
*
a
Mean separation within column by Student Newman Keuls test. *, ns: significant at P < 0.05, or not significant, respectively
Table 5. Mean and maximum canopy NCER per unit leaf area, whole-canopy NCER and other canopy efficiency para-
meters measured or estimated for potted Cabernet Sauvignon vines left untrimmed or subjected to various shoot trim-
ming treatments. See Table 1 for explanation of treatment codes.
Mean
NCER
Maxim u m
NCER
Mean w h ole-
can op y NCERb
(µm ol/s)
W – m ain
(m g/cm 2)
W – laterals Leaf-to-fru it
ratio
Total su gar
p er vin e
(g)
(µm ol/m 2s)
(µm ol/m 2s)
(m g/cm 2)
(cm 2/g)
Untrimmed
T12LR
3.1 b
3.5 b
4.4 a
4.6 a
4.6 a
*
5.4 c
6.2 b
7.4 ab
8.1 a
8.6 a
*
8.8 ab
9.4 a
7.3 b
10.4 a
4.1 c
*
7.4
7.3
7.4
7.0
7.4
ns
6.3
6.4
–
17.3 a
12.6 b
10.3 b
11.1 b
5.2 c
*
321 ab
419 a
322 ab
356 ab
248 b
*
T12LX
T6LR
6.3
–
T6LX
a
Significance
ns
a
b
Mean separation within column by Student Newman Keuls test. *, ns: significant at P < 0.05, or not significant, respectively
Adjusted over mean total leaf area per vine as reported in Table 1.
Leaf gas exchange
in all treatments, although this pattern was slightly more
pronounced in the T6 and the T12LX treatments. A rates
and leaf position on the lateral stems (Figure 6 bottom)
were not significantly correlated with position for
untrimmed and T12LR vines, whereas A rates measured
on basal lateral leaves in T6LR were consistently lower
than those found for upper leaves.
Assimilation (A) measured before trimming on main
leaves at similar leaf age (≈ 20 days) did not differ among
treatments (Table 4). Variation in A as a function of main
leaf position along shoot (Figure 5) showed a quadratic
relationship for all treatments with a maximum located
between nodes 4–7, where leaves of age varying from 22
to 31 days were located. Assimilation rates diminished
sharply towards the shoot apex for leaves of decreasing
age. A decrease of net assimilation was also shown for
basal leaves at positions 1 and 2.
Subsequent to trimming, main leaf A rates were
similar in untrimmed and T12LR, even though leaves of
the latter treatment were 20 days older (Table 4). At very
similar age levels, post-trimming A and gs on main leaves
in T12LX showed a substantial increase compared to
T12LR. The same A levels as T12LX were also maintained
by main leaves of T6 treatments, despite a further
increase in age of about 10 days. T6LX showed similar A
rates to T6LR but a significantly higher gs.
Canopy gas exchange
Estimated maximum total canopy assimilation (TCA), cal-
culated on the basis of A rates measured at veraison and
final total leaf area, indicated T6LR as the most efficient
treatment and T6LX as the least efficient (Table 4).
Untrimmed and T12 treatments were somewhat inter-
mediate, although it is worth noting that estimated TCA
was lower in control and T12LX vines as compared to
T6LR.
Mean and maximum whole-canopy NCER per unit
leaf area (direct measurement) resulted in higher values
for both T6 treatments and T12LX as compared to the
others, whereas NCER per vine did not differ between
control and treatments bearing laterals (Table 5). Whole-
canopy NCER was greatly reduced in T6LX and, to a
much lesser extent, in T12LX. The total leaf-to-fruit ratio
was highest in untrimmed vines, lowest in T6LX and
intermediate for the remaining treatments (Table 5). No
differences among treatments were shown with regard to
Subsequent to trimming, lateral leaf A rates increased
according to severity of shoot trimming, and values
measured on T6LR were double those recorded on
untrimmed vines. The same pattern also held for gs rates
(Table 4).
Assimilation rates by main leaves subsequent to trim-
ming (Figure 6 top) increased from basal to distal nodes

Poni & Giachino
Effect of shoot trim m ing on potted grapevines 223
sugar per vine values, i.e. high canopy efficiency. Despite
the fact that canopy age was slightly higher in T12LR as
compared to untrimmed vines over the season, the
T12LR benefited from a well-balanced lateral regrowth.
The amount of laterals promoted after trimming in T12LR
was sufficient to fully offset the previous foliage loss and
vigour was calibrated so that growth could occur
throughout stage I and II of berry growth with no inter-
ference with the process of berry sugaring (Figure 1 and
Table 1). Furthermore, the T12 cut was able to trigger
photosynthetic compensation on both main and lateral
leaves so that TCA and whole-canopy NCER were not
lowered as compared to control vines. Negative results
reported in the literature for similar shoot trimming
severities carried out later in the season (Kliewer and
Bledsoe 1987, Koblet 1987) may relate primarily to in-
adequate lateral regrowth (i.e. too weak) and meagre
photosynthetic compensation. The similarity in the vine
performance between T12LR and untrimmed vines also
points out the limited value of total leaf area-to-fruit ratio
(Table 5) as a predictor of grape quality (untrimmed had
a significantly higher ratio), thereby justifying the need to
assess also the ‘quality’ of the source, i.e. the ‘effective’
leaf area-to-fruit ratio.
Untrimmed
T6LR
T12LR
T6LX
T12LX
Leaf position along the main shoot (n)
Untrimmed
T12LR
T6LR
Quite satisfactory results were achieved in the present
study by the T12LX treatment, which closely paralleled
the untrimmed vines as total sugar per vine. This out-
come primarily relies on the ability of the T12LX vines to
compensate for the permanent removal of leaf area by
the increased photosynthesis of the retained main leaves.
Both TCA and whole-canopy NCER rates, which were
similar to control vines (Tables 4 and 5), confirm this
effect. Similar findings were also reported by Candolfi-
Vasconcelos and Koblet (1990) for shoots deprived of
laterals and trimmed to 16 nodes as compared to un-
trimmed. Although these authors did not assess gas
exchange, they provide evidence that compensation in
main leaves occurred both as retarded leaf senescence
and abscission. The latter aspect could not be determined
in the present study, although the much higher post-
trimming A rates recorded in T12LX as compared to
untrimmed, in spite of leaves 20 days older, strongly
confirm an alteration of the late-season leaf senescence
pattern (Table 4).
Leaf position along the lateral shoot (n)
Figure 6. Variation of single leaf assimilation (µmolCO /m2s) against
2
position on main (top) and lateral (bottom) shoots evaluated at
veraison (55 days after trimming). Regression equations for main
leaves were: 1/(0.12 + 0.16/x), R2 = 0.67 for untrimmed; y = exp
(2.33 – 1.61/x), R2 = 0.97 for T12LR; y = exp (2.55 – 1.71/ x2), R2 =
0.93 for T12LX; y = exp (2.5 – 1.95/x2), R2 = 0.91 for T6LR; y = exp
(2.58 – 0.5/x), R2 = 0.90 for T6LX. Regression equation for lateral
leaves of T6LR (bottom) was: y = 1/(0.069 + 0.11exp (-x)), R2 =
0.93. A and leaf position on laterals were not significantly correlated
in untrimmed and T12LR.
dry weight per unit leaf area (W) for both main and
lateral leaves. Total sugar per vine was maximum in
T12LR, intermediate in untrimmed, T12LX and T6LR and
lowest in T6LX (Table 5).
Discu ssion
The T6LR treatment had a somewhat contradictory
behaviour if vine potential and actual grape ripening are
compared. Laterals promoted by this treatment were
highly vigorous (the lateral-to-main leaf area ratio was
1.7 as compared 0.7 for T12LR), so that total leaf area per
vine was similar to untrimmed vines (Table 1). Severe
trimming also achieved two concurrent, positive physio-
logical responses: consistent photosynthetic compensa-
tion in the retained main leaves and very high A rates on
well-developed lateral leaves. Here the contribution of a
considerable amount of relatively young lateral leaves
from veraison onward seems of primary importance
(Figure 4). These factors summed up to give T6LR the
highest TCA and mean whole-canopy NCER rates. Yet,
total sugar per vine was not the highest and both soluble
solids and total anthocyanins were significantly lower
In agreement with previous studies (Peterson and Smart
1975, Koblet 1987, Reynold and Wardle 1989a, Intrieri
1994) trimming at different severities with or without
maintenance of laterals did not markedly affect yield per
vine, but it abruptly changed the amount and quality of
the source, generating in turn consistent differences in
must quality. The overall effects on grape ripening
observed in this study made it possible to identify three
major aspects: (1) an unchanged ripening course for the
T12 treatments as compared with untrimmed vines; (2) a
slight delay in berry maturity for T6LR compared to
untrimmed vines manifested as lower soluble solids and
berry colour; and (3) unripe berries in T6LX.
The T12LR treatment showed a series of positive
features that can readily explain the maximum total

224
Effect of shoot trim m ing on potted grapevines
Australian Journal of Grape and Wine Research 6, 216–226, 2000
than in untrimmed vines. Although the role of mature
laterals as contributors to canopy photosynthesis from
veraison onward has already been widely emphasised
(Hale and Weaver 1962, Koblet 1969 and 1987, Poni and
Intrieri 1996), our data suggest that laterals acted as
partial sinks even after veraison, thereby diverting some
carbohydrates away from basipetal movement, and into
bunches. Two main results support this interpretation:
(1) lateral growth extended in T6LR beyond veraison
(Figure 1) and (2) berry size in T6LR was smaller than in
untrimmed and T12 treatments. Smaller berries suggest
that berry development was directly affected by other
competitive sinks (Table 2). These findings are in partial
disagreement with those reported by Reynolds and
Wardle (1989b), who noted no harmful effects on berry
ripening for a 5-leaf post-bloom trim on a three-year
basis. Once again, though, the lateral-to-main leaf area
ratio for that specific treatment in their study was about
0.63, therefore much less than the ratio found in our
study (1.7).
Treatment T6LX had an expected adverse impact on
fruit ripening in spite of a marked photosynthetic com-
pensation by the retained main leaves (Table 4).
However, TCA and whole-canopy NCER clearly indicated
the occurrence of a severe source limitation. Due to the
particularly sparse and open canopy of this treatment,
the total leaf-to-fruit ratio may represent a reliable
indicator of the effective leaf area-to-fruit ratio, thus con-
firming that higher amounts of functional leaf area are
generally required to adequately ripen a gram of fresh
fruit mass in grapevine (Kliewer and Weaver 1971).
Results in the present study also provide novel infor-
mation about the modification of the canopy ageing
pattern and gas-exchange response at both the single and
the whole canopy level as related to trimming severity. In
general, the leaf ageing pattern along the main shoot,
assessed as changes in A, confirmed previous findings by
Kriedemann et al. (1970) and Poni et al. (1994), with
very low rates for rapidly expanding apical leaves and a
fairly precocious, though moderate, decline for basal
leaves (Figure 5). Yet it should be noted that the lower A
rates recorded for leaves at positions 1 and 2 before trim-
ming may also relate to abnormalities in lamina growth
and function of these pre-formed leaves and to such
spatial effects as partial shading cast by upper leaves.
However, the relationship between leaf photosynthesis
and age was markedly altered by shoot trimming, as is
very clearly shown by the progressive increase of post-
trimming A rates in untrimmed, T12 and T6 which
occurred against the age gradient. This suggests that the
leaf senescence pattern in grapevine can be substantially
modified by management factors (such as shoot trim-
ming) and lead to marked changes in the source-sink
balance.
ly promote post-trimming A rates in T12LX as compared
to T12LR, although this did not hold true for the T6 treat-
ments. As recorded by Candolfi-Vasconcelos and Koblet
(1991) and Hunter and Visser (1988) in defoliation studies,
an increase in stomatal conductance was generally
observed in all our trimmed treatments, suggesting the
validity of the ‘transpiration-stream’ partitioning hypo-
thesis (Flore and Lakso 1991). According to this hypo-
thesis, a source reduction (carried out either by shading
or leaf removal) would allow the remaining leaves to
benefit from an increased root supply of water, nutrient
and hormones, generating in turn higher stomatal con-
ductance and photosynthesis. However, it is clear from
our data that gs did not have complete control over A, as
can be judged from comparisons within the T6 treatments
where no gain in A was observed in T6LX despite a sig-
nificant further rise in gs. (Table 4). This effect resembles a
response to defoliation reported by Candolfi-Vasconcelos
and Koblet (1991), which showed that the photosynthetic
compensation of two very severe defoliation levels (only
3 or 6 leaves maintained on main shoots) versus a 12
node cut was very pronounced up to 3 weeks after
treatment, negligible at 8 weeks and reversed thereafter,
suggesting that severely defoliated plants get ‘exhausted’
before the others. Since our readings were taken about
8 weeks after trimming, it is likely that assimilation
measured on T6LR, the most source-limited treatment,
was already declining towards values similar to those
recorded on less source-limited treatments (namely T6LR
and T12LX).
Data reported in the present study for direct measure-
ments of whole-canopy NCER also highlight the impor-
tance of their association with single leaf readings when
the treatments are supposed to cause modifications at the
canopy level. Mean NCER per unit leaf area showed
moderate photosynthetic compensation in T12LR and a
more pronounced carbon gain in the remaining treat-
ment. Although this trend was also outlined by the
single-leaf readings, it is physiologically sound that these
differences were confirmed from a measurement which
integrates all effects due to different leaf exposures and
ages. The estimated mean whole canopy NCER (Table 5)
also paralleled quite closely the TCA values (Table 4) with
one significant exception regarding T6LR, for which TCA
seemed to overestimate the actual canopy photosynthesis.
We must emphasise that the single-leaf readings taken on
well-exposed, healthy leaves invariably tend to over-
estimate actual photosynthesis since only a portion of
leaves in a canopy can be under those conditions at any
given time of day. Therefore, it is likely that the whole
canopy NCER reading may have detected an effect of
diurnal shading on basal leaves by the overlying lateral
shoots, which could not have been sensed by single
strategic measurements.
The photosynthetic compensation that took place as a
reaction to trimming was, however, variable in regard to
severity and presence/absence of laterals, and showed
contrasting correlation with stomatal conductance (gs).
In agreement with Candolfi-Vasconcelos and Koblet
(1990), the absence of laterals was actually able to strong-
The maximum whole canopy NCER rates per unit leaf
area (Table 5, column 2) were approximately 73% of the
mean, post-trimming single leaf rates reported in Table 4.
This difference, due to the inclusion of shaded leaves,
clusters and stems within the gas exchange chamber,
matches quite closely the value (65% ) found for potted

Poni & Giachino
Effect of shoot trim m ing on potted grapevines 225
Flore, J.A., and Lakso, A.N. (1990) Environmental and physiological
regulation of photosynthesis in fruit crops. Annual Review of
Horticultural Science 11, 111–157.
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on direction of translocation of photosynthate in Vitis vinifera.
Hilgardia 33, 89–141.
Cabernet Sauvignon vines of similar size (Al-Hazmi et
al. 1997). Overall, whole canopy and single-leaf gas
exchange readings were well paralleled in the present
study since vines had rather open canopies, relatively low
crop load and little shoot and trunk weight.
Hofäcker, W. (1978) Investigation on the photosynthesis of vines.
Influence of defoliation, topping, girdling and removal of grapes.
Vitis 17, 10–22.
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leaf position and development stage on the vine on the photo-
synthetic activity of Vitis vinifera L. cv. Cabernet Sauvignon. South
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In extrapolating from this pot study to vineyard situa-
tions, we offer the following comments. Although our
vines showed a moderate vine capacity (estimated from
total LA levels) and crop load, the vigour of individual
untrimmed shoots was fairly high and the amount of
lateral regrowth induced by the T6 treatment was com-
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Our data indicate that an early trimming that pre-
serves at least 12 main leaves is a ‘safe’ and advisable
choice in vigorous Cabernet Sauvignon grapevines. This
trimming severity would have the advantage of ensuring
a sufficient amount of source foliage for crop ripening
even if followed by weak or even no lateral regrowth (a
case which may occur when dry weather follows trim-
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especially in very vigorous sites, only when strictly nec-
essary, since it may cause too vigorous a lateral regrowth
with growing tips on the vine well beyond veraison. On
the other hand, a severe cut may also lead to excessive
source limitation in dry seasons and/or excessive crop
load.
Ack n ow led gem en ts
We thank Mr G. Bruzzi for technical assistance in data
recording and lab analyses and Dr E. Magnanini for
invaluable help in setting up the whole-canopy gas-
exchange system. We are also indebted to Prof. C. Intrieri,
Dipartimento di Colture Arboree, University of Bologna,
for lending the CIRAS-1 apparatus.
Peterson, J. R., and Smart, R.E. (1975) Foliage removal effects on
‘Shiraz’ grapevines. American Journal of Enology and Viticulture
26, 119–123.
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Manuscript received: 17 May 2000
Amended version received: 11 September 2000