horticulturae

Article
Rootstocks Impact Yield, Fruit Composition, Nutrient
Deficiencies, and Winter Survival of Hybrid Cultivars in
Eastern Canada
Caroline Provost *, Alexander Campbell and François Dumont

Centre de Recherche Agroalimentaire de Mirabel, 9850 Rue Belle-Rivière, Québec, QC J7N 2X8, Canada;
acampbell@cram-mirabel.com (A.C.); fdumont@cram-mirabel.com (F.D.)
* Correspondence: cprovost@cram-mirabel.com; Tel.: +1-450-434-8050 (ext. 6064)

Abstract: Grafting cold-hardy hybrid grapevines may influence their attributes under different
pedoclimatic conditions and may also contribute to cold-hardiness, influence plant physiology, and
affect yield and fruit composition. In a six-year study, we evaluated bud survival, plant development,
nutrient deficiencies, yield, and fruit composition for three cold-hardy grape varieties: Frontenac,
Frontenac blanc, and Marquette. The grape varieties were grafted on four rootstocks: 3309C, SO4,
Riparia Gloire, and 101-14. The final combinations were own-rooted. The six-year research period
indicated that cold-hardy hybrids were affected differently by each rootstock. Magnesium deficiency
was lower for grafted Frontenac and Frontenac blanc compared with own-rooted vines, but bud
survival and grapevine development were not affected by rootstock. Moreover, results related to yield
components showed that there are significant differences between rootstocks and own-rooted vines.
Frontenac was the least affected grape variety compared to Frontenac blanc and Marquette, where





 only cluster weight and berry weight were impacted. Overall, for the two Frontenac varietals, we
also observed a greater maturity for fruits of vines grafted on 101-14 and 3309C compared with own-
Citation: Provost, C.; Campbell, A.;
Dumont, F. Rootstocks Impact Yield,
rooted vines. Grafting affected fruit composition for Marquette differently, where the lowest grape
Fruit Composition, Nutrient maturity was observed for fruits on vines grafted on SO4. This study demonstrates that rootstocks
Deficiencies, and Winter Survival of affect cold-hardy hybrids, highlighting their potential under eastern North American conditions.
Hybrid Cultivars in Eastern Canada.
Horticulturae 2021, 7, 237. https:// Keywords: cold-hardy hybrid; rootstock effect; cold climate; Frontenac; Marquette
doi.org/10.3390/horticulturae7080237

Academic Editor: Massimo Bertamini

1. Introduction
Received: 15 July 2021
Growing grapes in cold climates presents several challenges to overcome. Grape
Accepted: 6 August 2021
production is a relatively recent industry in eastern Canada, and growers must adapt their
Published: 10 August 2021
techniques to achieve high grape quality at the end of the season. Cold injury to grapevines,
short growing seasons, and soil conditions that are often too fertile and poorly drained
Publisher’s Note: MDPI stays neutral
are just a few examples of factors that affect grapevine production and limit the choice
with regard to jurisdictional claims in
of grape variety when establishing a vineyard [1,2]. Pedoclimatic conditions found in
published maps and institutional affil-
iations.
Quebec (eastern Canada) limit the choice of grape varieties that can be used; therefore,
winegrowers are often restricted to grape varieties tolerant to extreme winter temperatures
and spring frosts, but also those capable of reaching optimum berry maturity at the end of
the season [2]. While genetics determines the ultimate degree of cold-hardiness expression,
the environment, as well as cultural practices and pest management, affect that expression.
Copyright: © 2021 by the authors.
Cold injury and disease resistance studies have helped lead breeding programs in eastern
Licensee MDPI, Basel, Switzerland.
North America and have led to the development of several hybrid cultivars with high cold
This article is an open access article
hardiness [3].
distributed under the terms and
conditions of the Creative Commons
Rootstocks allow growers to plant varieties that become better adapted and more
Attribution (CC BY) license (https://
efficient in specific soil and climatic conditions and improving the scion/rootstock combi-
creativecommons.org/licenses/by/ nation optimizes their adaptation. Though some cold-hardy hybrids have been grafted and
4.0/). studied, this is not a common practice for hybrid cultivars as rootstocks are typically used

Horticulturae 2021, 7, 237. https://doi.org/10.3390/horticulturae7080237 https://www.mdpi.com/journal/horticulturae

Horticulturae 2021, 7, 237 2 of 13

for Vitis vinifera. In recent years, some studies have been carried out in British Columbia
(Canada), Ontario (Canada), New York (USA), and Missouri (USA) to assess the benefits of
using rootstocks for hybrid grape varieties grown in cold climates [4–10].
Some studies have noted that rootstocks can influence scion cold-hardiness through
faster cold acclimation periods [6,11]. Other studies have observed no difference in cold-
hardiness according to rootstock across multiple scion/rootstock combinations [12,13].
Rootstocks can also influence vine vigor since it is the root system that provides the
plant with water and mineral uptake essential to its growth and harbors the majority of
nutritional reserves that are stored during the winter season [14]. Some rootstocks enhance
the physiological development of the vine and can ensure optimal ripening of the grafted
grape variety [7,14,15]; thus, rootstocks also have an impact on yield and berry quality.
Studies have shown that there is a significant interaction between grape varieties and
rootstocks related to yield, the accumulation of sugars in berries, the chemical composition
of the berries, and the aromas [5,7,15,16]. Others have observed more variable results,
where grafted plants are often similar to those that are own-rooted [15].
Grapevine grafting may influence grape production in specific soil and climate con-
ditions, specifically in an emergent grapevine production region such as Quebec. This
project evaluated the effects of grafting on cold-hardiness, grapevine development, grape
maturation, yield, and berry chemistry of cold-hardy hybrids. These results can be used by
growers, stakeholders, nurseries, and researchers for development of the wine industry in
eastern Canada.

2. Materials and Methods

All trials were conducted at the experimental vineyard of the Centre de recherche
agroalimentaire de Mirabel (CRAM) located in the municipality of Oka, Quebec, Canada
(45◦ 300 N, 74◦ 4.20 W). The region’s climate is characterized by cold winters with tempera-
tures reaching as low as −30 ◦ C, short growing seasons determined in part by days without
frost (generally 155 to 200 days calculated from the last spring frost to the first fall frost),
and also hot summers that accumulate 1295–1450 growing degree days (base 10, mean
of the last 10 years, 1365 GDD) (Table 1). The climate is also humid, with mean annual
precipitation of 790 mm of rain during the growing season (snow excluded). The vineyard
soil type is a gravelly loam, and plots are located on an 8% slope.

Table 1. Characteristics of grape varieties.

Scion Origin Hardiness GDD at Harvest (Base 10) Vigor Mean Yield Deficiency
Vitis riparia 89
Frontenac −30 to −34 ◦ C 1250 High 8 to 12 T ha−1 Mg
× Landot 4511
Mutation from
Frontenac blanc −30 to −34◦ C 1150 High 8 to 12 T ha−1 Mg
the Frontenac
Mn 1094 ×
Marquette −30 to −34◦ C 1100 High 6 to 10 T ha−1
Ravat 26,212
Sources: [1,17,18].

Mature dormant canes of three cold-hardy hybrids were collected in October 2011 from
the CRAM vineyard and provided to a commercial nursery for bench grafting. Vines were
grown for a year in the nursery (2012) and shipped for planting in spring 2013 as dormant
vines. Grafted vines were planted in June 2013. The experimental design is composed
of four replicates (plots) for each of the scion/rootstock combinations (3 grape varieties,
5 root systems). Three cold-hardy hybrid varieties were used: Frontenac, Frontenac blanc,
and Marquette (Table 1), and five root systems were evaluated: Couderc 3309 (3309C),
Sélection Oppenheim 4 (SO4), Riparia Gloire (RP), Millardet et de Grasset 101-14 (101-14),
and own-rooted (Table 2). Hybrid cultivars were chosen on the basis of yield and quality
components as well as land use by local growers. Rootstocks were selected on the basis
of qualities known to be imparted on scions as well as availability and grower selection.
Horticulturae 2021, 7, 237 3 of 13

Each plot included 10 grapevines, for a total of 40 vines per combination. The four blocks
containing the combinations were implanted according to a complete random distribution.
Rows were oriented North–South, and the vines were planted to 1.20 × 2.44 m spacing
within and between the rows. Grapevines were trained to a bilateral cordon and vertical
shoot positioning system. An initial pruning was performed during the month of April,
and the final pruning was completed in May, after the risk of spring frost had passed, to
leave 16 nodes per vine. In 2015, the first small harvest was collected. Data were collected
from April 2014 to October 2019 (six growing seasons).

Table 2. Characteristics of rootstocks.

Rootstock Origin Vigor Soil Adaptation Nutrient Absorption

Adapted to various types of soils
Absorbs magnesium well,
Couderc 3309 V. riparia × (deep, sandy-clay, silty-clay, little
Medium and low absorption of
(3309C) Vitis rupestris limestone) and well-drained.
potassium
High tolerance to soil acidity.
Adapts to various types of soils
(sandy, clay-limestone, medium
Sélection Vitis berlandieri × Badly assimilates
Medium to high or low fertility), best results in
Oppenheim 4 (SO4) V. riparia magnesium
well-drained, moist, and
rich soils.
All non-calcareous, rich, and
fresh soils. Easily absorbs potassium
Riparia Gloire (RP) V. riparia Low Adapted to acidic soils. and low absorption of
Not suitable for too clayey and magnesium
compact soils.
Millardet et de
V. riparia × Deep and clayey soils.
Grasset 101-14 Medium Absorbs magnesium well
V. rupestris Sensitive to soil acidity.
(101-14)
Sources: [9,17,19].

The between row vineyard floor consisted of a permanent cover crop, and herbicides
were used under the row (three treatments per year) to control weeds Canopy management
practices (hedging, shoot positioning, shoot thinning, leaf removal) were performed all
season according to integrated pest management practices. To prevent severe infestations
and heavy losses in the plots due to disease and insect damage, we applied chemical sprays
as recommended by an agronomist and followed integrated pest management practices.

2.1. Viticultural Parameters

Data were collected throughout the growing season and measured on the six central
plants of each plot. Several parameters were monitored: (a) bud survival, where bud
break was evaluated on 6 buds from two canes per vine to determine winter mortality;
(b) grapevine phenology using the BBCH scale [20] with observations twice a week from
early April to early June, and once a week from June to September; (c) nutrient deficien-
cies (e.g., nitrogen, magnesium, manganese) were evaluated at three time points during
the growing season using the Horsfall–Barratt grade scale [21]; (d) grapevine vigor was
evaluated once a year (in July) using three parameters: shoot length on two canes, trunk
diameter, and leaf area index (LAI) (Li-Cor LAI-2200C Plant Canopy Analyzer). At the end
of the growing season, berry maturity was followed (pH, total acidity (TA)and total soluble
solids (TSS)) using weekly chemical analyses on 100 berries from the end of August to the
end of September. The optimum harvest times were determined using maturity monitoring.
Measurements taken at harvest include yield as kilograms per vine, clusters per vine and
berry weight, calculated from random sampling of 100 berries within the sampled vines.
Cluster weight was then determined from these data. Chemical composition of fruit at har-
vest was analyzed using a random sampling of 200–300 berries. All the chemical analyses
were performed on fresh juice by using a wine titrator for titratable acidity (Hanna, model
Horticulturae 2021, 7, 237 4 of 13

HI 84102), a refractometer for soluble solids (Hanna, model HI96811), and a pH-meter
(Hanna, model HI9124).

2.2. Statistical Analysis

The results for the different parameters were analyzed separately for each grapevine
variety. A generalized linear mixed model (GLMER) for binomial distribution was imple-
mented to test the effect of rootstocks, year, and the interaction of rootstock x year on bud
survival related to winter injuries. The plot nested in the year was included in the model.
The statistical significance of the fixed effect was estimated using a likelihood ratio test
(LRT) for chi-squared distribution. The levels of nutrient deficiencies were tested using
a GLMER model for Poisson distributed data to test the effect of rootstocks, year, and
the interaction of rootstock × year. The fixed effect rootstock and the random effect plot
nested in the year were included in the model. A Tukey’s test using the glht function in R
(package multcomp) was used for comparison among treatments. Data related to harvest
components and fruit composition were analyzed using two-way ANOVA with rootstock,
year, and interaction as fixed parameters. The analyses were performed in R (R Core Team
2017) using the functions of the lme4 library.

3. Results
The results presented are the first, and relevant conclusions will come in the future
with additional years of observations. Data related to cold-hardiness, developmental stages,
and nutrient deficiencies are presented as the average value for six years and, for data
related to yield and fruit composition, as the average for five years, from the first harvest
in 2015 until 2019. The annual growing season effect was observed in years with shorter
or longer than normal GDD accumulation (Table 3). The shortest growing season was
observed in 2018 with 1253 GDD and 177 days without frost; the seasons with the highest
GDD being noted in 2015 and 2016.

Table 3. Climatic conditions in Oka vineyard during 2014 to 2019.

GDD (Base10) Precipitations (mm) Days without Frost

Year
1 March to 30 October 1 March to 30 October
2019 1305 630 186
2018 1253 550 177
2017 1373 879 190
2016 1424 901 179
2015 1429 923 190
2014 1395 450 202

3.1. Bud Survival

Bud survival was not significantly affected by rootstock (Table 4). Statistical analysis
showed that bud survival after winter for the three cold-hardy hybrids were similar among
rootstock and own-rooted vines. Seasonal effects on bud survival across all three grape
varieties were also observed; as the winters in 2014 and 2018 caused more bud damage
than winters in 2015, 2016, 2017, and 2019.

3.2. Grapevine Development

Grafting had no effect on vine physiology during the spring nor for the remainder of
the season, save for one exception during early season growth. In early May of 2017, we
observed a faster development for Marquette vines grafted on Riparia Gloire and SO4 than
for other rootstocks or own-rooted vines (data not shown). Two weeks later, no difference
in the development of the vine was observed (p = 0.0021), and that tendency was not
maintained in subsequent years. The BBCH stage 5 ‘wool stage’ was observed for the two
Frontenac varieties at the beginning of May, stage 9 ‘bud burst’ around mid-May, flowering
stage 65 near mid-June, and ripening at the beginning of August.
Horticulturae 2021, 7, 237 5 of 13

Table 4. Effect of rootstock on bud survival of the three cold hardy hybrids.

Bud Survival (%)

Rootstock Frontenac Frontenac Blanc Marquette
101-14 82.47 78.16 82.12
3309C 88.93 87.69 82.18
Rootstock Own-rooted 90.91 88.96 83.55
Riparia gloire 86.93 87.69 86.88
SO4 87.25 86.32 83.59
2014 66.25 63.25 67.11
2015 90.63 89.27 88.05
2016 90.63 89.71 89.82
Year
2017 97.36 97.81 96.96
2018 84.06 80.80 71.71
2019 91.67 91.26 84.87
Rootstock 0.83 0.42 0.91
p-value Year 0.19 0.15 0.64
Roostock × Year 0.77 0.91 0.92

The grapevine vigor was affected by the rootstock and year (Table 5). For all the
grapevine varieties, the trunk diameter increased yearly after plantation. For Frontenac
and Frontenac blanc, shoot length and LAI were lower during summer in 2016 and 2017
than during other growing seasons. For Marquette, seasons 2015, 2016 and 2017 resulted
in a lower shoot length and LAI. The rootstocks affected the Frontenac grapevine vigor
where grating on Riparia Gloire resulted in a lower shoot length, trunk diameter, and LAI.
LAI was also weak for own-root vines. Vigor of Frontenac blanc was low on rootstock
101-14 and moderately low (trunk diameter and LAI) on Riparia Gloire. Vigor parameters
showed different results for Marquette. Shoot length was lower on 3309C and 101-14, the
trunk diameter was weak on Riparia Gloire and 101-14, and the lowest value of LAI was
observed on Riparia Gloire.

Table 5. Effect of rootstock on grapevine vigor of the three cold hardy hybrids.

Frontenac Frontenac Blanc Marquette

Shoot Trunk Shoot Trunk Shoot Trunk
Leaf Area Leaf Area Leaf Area
Rootstock Length Diameter Length Diameter Length Diameter
Index Index Index
(cm) (cm) (cm) (cm) (cm) (cm)
101-14 189.94 17.82 a 4.65 ab 161.28 a 16.50 ab 4.17 bc 170.81 a 15.48 bc 4.75 abc
3309C 187.57 18.01 a 4.90 a 174.07 ab 17.91 a 4.49 abc 169.84 a 17.35 a 5.01 bc
Rootstock Own-root 186.60 17.56 a 4.21 c 190.78 c 17.67 a 4.80 a 185.66 b 17.24 ab 4.62 ab
Riparia
174.71 14.92 b 4.35 bc 178.73 bc 15.98 b 4.08 c 172.44 a 14.88 c 4.40 a
Gloire
SO4 183.73 16.93 a abc b ab ab b 18.17 a 5.23 c
4.58 175.56 17.05 4.61 188.27
2014 214.67 a 9.26 a 188.60 ab 8.95 a 220.31 a 8.97 a
2015 180.68 bc 13.81 b 175.88 bc 13.88 b 166.86 c 13.87 b
2016 169.04 bc 16.20 c 3.93 a 166.03 cd 16.61 c 3.67 a 166.03 c 16.54 c 4.00 a
Year
2017 160.87 c 19.15 d 3.91 a 159.36 d 19.34 d 4.02 a 150.14 d 17.81 c 4.58 b
2018 198.23 ab 21.69 e 5.15 b 192.59 a 22.16 e 5.04 b 189.95 b 21.51 d 5.32 c
2019 184.99 bc 21.77 e 5.15 b 174.05 bcd 21.20 e 5.04 b 171.70 c 21.62 d 5.32 c
Rootstock 0.4874 <0.0001 <0.0001 <0.0001 0.0025 0.0001 <0.0001 <0.0001 <0.0001
p-value Year <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
Roostock
0.3332 0.3731 0.0581 0.0744 0.9167 0.4584 0.0013 0.1013 0.6048
× Year
Values followed with a different letters in each column (section ‘Rootstock’ and ‘Year’, separatly) were significantly different according
to ANOVA.
Horticulturae 2021, 7, 237 6 of 13

3.3. Nutrient Deficiencies

When present, nutrient deficiencies were recorded for magnesium, nitrogen, potas-
sium, and manganese. No deficiency in potassium was observed, and only a few plants
showed manganese deficiencies. Nitrogen deficiency was very uncommon as well—we
observed between two and eight vines yearly affected by nitrogen deficiency, mainly those
grafted to rootstock 101-14. The main nutrient deficiency noted was for magnesium on the
two Frontenac varieties (Table 6). Vines of Frontenac showed higher magnesium deficiency
for own-rooted vines and vines grafted on SO4 compared to vines grafted on Riparia
Gloire, 101-14, and 3309C. The least magnesium-deficient vines were grafted on 3309C.
For Frontenac blanc, low magnesium deficiency was observed for vines grafted on 3309C,
intermediate deficiency was obtained on vines grafted on 101-14 and Riparia Gloire, and
the highest level of magnesium deficiency was noted for own-rooted vines and vines
grafted on SO4. The Marquette variety showed lower levels of magnesium deficiency than
Frontenac, although, again, significantly higher deficiency was observed for vines grafted
on SO4 than for vines grafted on 101-14 and 3309C. The growing season also affected
magnesium deficiency.

Table 6. Effect of rootstock on nutrient deficiencies of the three cold hardy hybrids.

Level of Magnesium Deficiency

(Horsfall–Barratt Grade Scale)
Rootstock Frontenac Frontenac Blanc Marquette
101-14 2.22 b 2.02 b 0.79 a
3309C 1.35 a 1.49 c 0.76 a
Rootstock Own-rooted 3.59 c 2.88 ab 0.86 ab
Riparia gloire 2.66 b 2.35 b 1.07 ab
SO4 3.51 c 3.15 a 1.78 b
2014 0.84 0.78 0.80
2015 1.00 0.95 0.95
2016 5.49 5.18 1.78
Year
2017 0.81 0.66 0.03
2018 3.55 3.03 0.65
2019 4.31 3.74 2.21
Rootstock <0.0001 0.0001 0.02
p-value Year 0.08 0.10 0.99
Roostock × Year 0.01 0.006 0.25
Values followed with a different letters in each column (section ‘Rootstock’ and ‘Year’, separatly) were significantly
different according to GLMER model.

3.4. Yield Components and Fruit Composition

The five-year observation period showed different significant effects for rootstocks
and growing season on yield and quality for the three grape varieties.

3.4.1. Frontenac
Rootstocks affected some yield components and fruit composition parameters for
Frontenac, and we observed a significant effect of the growing season (Table 7). Statistical
analysis showed that the rootstocks affect cluster weight, berry weight, soluble solids,
and pH. Vines grafted on Riparia Gloire produced the heaviest clusters, followed by own-
rooted vines and vines grafted on 3309C, while the lightest clusters were produced on vines
grafted to SO4. Across all combinations, cluster weight varied from 93.60 g to 105.01 g.
Significant differences for berry weight were noted between rootstocks: the lowest berry
weights were for vines grafted on 101-14 and 3309C, and the highest for own-rooted vines,
ranging from 1.10 to 1.26 g. The number of clusters and yield were not significantly affected
by rootstocks. The average number of clusters varied between 30 to 33 clusters, and
each grapevine produced slightly more than 3 kg. Rootstocks affected fruit composition
Horticulturae 2021, 7, 237 7 of 13

for soluble solids and pH, although titratable acidity was not affected. Higher levels of
soluble solids were seen for vines grafted on 101-14, 3309C, and Riparia Gloire compared
to own-rooted vines. Results for pH followed the same trends as soluble solids.

Table 7. Effect of rootstock on yield quantity and fruit composition of grapevine ‘Frontenac’.

Frontenac
Average Soluble Titratable
Cluster Berry Yield Yield
Rootstock Number of Solids pH Acidity (g·L−1
Weight (g) Weight (g) (kg·vine−1 ) (t·ha−1 )
Cluster (pcs) (◦ Brix) tar. ac.)
101-14 32.31 96.22 bc 1.10 a 3.16 10.66 24.77 a 3.22 a 12.89
3309C 32.78 101.72 abc 1.14 ab 3.33 11.22 24.23 a 3.20 a 13.20
Own-
30.88 102.22 ab 1.26 c 3.19 10.74 21.98 c 3.13 b 13.91
Rootstock rooted
Riparia
30.75 105.01 a 1.17 b 3.44 11.58 23.94 ab 3.18 ab 13.26
Gloire
SO4 31.58 93.6 c b 3.04 10.25 bc 3.18 a 13.67
1.19 22.88
2015 25.00 a 85.62 a 1.00 a 2.16 a 7.29 a 24.23 a 3.58 a 11.18 a
2016 35.97 b 106.41 b 1.27 c 3.77 b 12.70 b 24.73 a 3.20 b 13.21 bc
Year 2017 29.75 c 80.92 a 1.13 b 2.42 ac 8.14 ac 21.53 b 3.12 c 12.14 ab
2018 24.64 a 106.36 b 1.23 c 2.66 c 8.97 c 23.73 a 3.20 b 13.91 c
2019 42.98 d 119.70 c 1.22 c 5.15 d 17.36 d 23.76 a 2.90 d 15.95 a
Rootstock 0.4571 0.0010 <0.0001 0.1150 0.1150 <0.0001 <0.0001 0.2419
p-value Year <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
Roostock ×
0.4765 0.0602 0.3386 0.0268 0.0268 0.5083 0.2806 0.8173
Year
Values followed with a different letters in each column (section ‘Rootstock’ and ‘Year’, separatly) were significantly different according
to ANOVA.

Growing season also affected yield components and fruit composition (Table 7). The
highest yields were obtained during 2019 and 2016; the first harvest in 2015 was the lowest;
yields during 2017 and 2018 were intermediate. We do not have a constant trend between
years for the number of clusters, cluster weight, and berry weight. The number of clusters
ranged from 24 to 43 clusters, and the lowest number of clusters was observed during 2015
and 2018. The high number of clusters noted for 2019 may be related to the high yield. The
cluster weight varied from 80.92 g in 2017 to 119.70 g in 2019, and the berry weight was
the lowest during 2015. The heaviest berries were noted during the 2016 growing season.
Lastly, berry chemistry was also affected by growing season. Statistical analyses showed
that soluble solids were similar for the growing seasons of 2015, 2016, 2018, and 2019,
varying from 23.73 to 24.73 ◦ Brix; only 2017 showed a lower sugar content with 21.53 ◦ Brix.
pH was lowest in 2019, and highest during 2015. Titratable acidity was very high during
2019, and the lowest value was seen for the first harvest in 2015.

3.4.2. Frontenac Blanc

The rootstocks had a greater impact on Frontenac blanc than on the Frontenac variety.
We observed a significant effect of the rootstocks and growing season on all the studied
parameters, except for the average number of clusters (Table 8). The cluster weight ranged
from 87.64 to 110.70 g and differed significantly between rootstocks. Vines grafted on
SO4 had significantly lighter clusters than those grafted on Riparia Gloire, 3309C and
own-rooted vines. The heaviest clusters were observed on own-rooted vines. Statistical
analyses showed significantly higher berry weight for own-rooted vines and vines grafted
on Riparia Gloire compared to rootstocks 3309C, 101-14, and SO4. Yield ranged from 3.10
to 3.87 kg per vine and was highest for own-rooted vines, while vines grafted on 101-14
and SO4 recorded the lowest yields. Fruit composition was related to grape maturity,
where the lowest grape maturity was observed for own-rooted vines with low soluble
solid concentration and high titratable acidity. All vines grafted on the four rootstocks
showed similar fruit composition at harvest, with soluble solid values ranging from 23.27
to 24.18 ◦ Brix and titratable acidity between 13.06 and 13.63 g/L.
Horticulturae 2021, 7, 237 8 of 13

Table 8. Effect of rootstock on yield quantity and fruit composition of grapevine ‘Frontenac blanc’.

Frontenac Blanc
Average Soluble Titratable
Cluster Berry Yield Yield
Rootstock Number of Solids pH Acidity (g·L−1
Weight (g) Weight (g) (kg·vine−1 ) (t·ha−1 )
Clusters (pcs) (◦ Brix) tar. ac.)
101-14 31.20 96.05 ab 1.09 a 3.12 ab 10.53 ab 23.76 a 3.15 a 13.22 a
3309C 34.31 104.16 bc 1.11 a 3.66 bc 12.33 bc 24.18 a 3.09 ab 13.06 a
Own-
34.91 110.70 c 1.25 b 3.87 c 13.06 c 21.02 b 3.05 b 14.56 b
Rootstock rooted
Riparia
32.35 99.59 b 1.21 b 3.36 abc 11.33 abc 23.27 a 3.09 ab 13.63 a
Gloire
SO4 34.76 87.64 a 1.09 a 3.10 a 10.46 a 23.51 a ab 13.42 a
3.10
2015 26.08 a 80.80 a 1.03 a 2.21 a 7.45 a 25.14 a 3.44 a 10.89 a
2016 36.58 b 103.62 b 1.27 c 3.75 c 12.62 c 23.48 b 3.06 c 14.85 b
Year 2017 24.53 b 84.53 a 1.09 a 2.93 b 9.87 b 21.97 c 3.10 bc 11.45 a
2018 25.55 a 106.78 b 1.16 b 2.73 ab 9.20 ab 23.48 b 3.14 b 14.09 b
2019 45.12 c 123.18 c 1.22 bc 5.58 d 18.79 d 22.17 c 2.82 d 15.94 c
Rootstock 0.1203 <0.0001 <0.0001 0.0003 0.0003 <0.0001 0.0082 <0.0001
p-value Year <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
Roostock ×
0.1246 0.1763 0.1875 0.3161 0.3161 0.6921 0.3680 0.9921
Year
Values followed with a different letters in each column (section ‘Rootstock’ and ‘Year’, separatly) were significantly different according
to ANOVA.

Similarly to Frontenac, growing seasons affected yield components and fruit com-
position (Table 8). The years with the highest yield were 2019 and 2016, the lowest yield
was collected during 2015, and the growing seasons 2017 and 2018 had intermediate yield.
Yield may be related to the number of clusters, cluster weight, and berry weight which
were higher during the 2019 and 2016 seasons compared to the other three growing seasons.
Berry chemistry showed that the greatest maturity (expressed as a ratio of TSS/TA) was
obtained during 2015 with the highest soluble solids level and the lowest titratable acidity
value. During 2016 and 2018, we observed high sugar values but also high titratable
acidity levels. In 2017, the level of soluble solids was low as was titratable acidity; dur-
ing the 2019 growing season, we noted low soluble solid levels and very high values for
titratable acidity.

3.4.3. Marquette
Of the studied varietals, Marquette was the most affected by grafting and growing
season (Table 9). Statistical analyses demonstrated the greatest yield on own-rooted vines
and those grafted on Riparia Gloire and 3309C. Yield per vine was directly related to the
number of clusters that were higher for the same rootstocks. Cluster weight from vines
grafted on 101-14 was lower than from vines grafted on Riparia Gloire. Berry weight varied
from 1.19 to 1.37 g, with the heaviest berries on own-rooted vines and grafted on Riparia
Gloire; the lightest berries were noted on rootstock 101-14. The highest productive years
were 2016 and 2019, followed by 2017, 2015, and 2018 (Table 7). The number of clusters is
related to yield obtained for each year: a higher number of clusters was observed during
2016, 2019, and 2017, and lower numbers during 2015 and 2018. Cluster weight varied
from 80.80 g in 2015 to 123.18 g in 2019. Berries were heavier in 2016 and 2019 and lighter
in 2017 and 2015.
The rootstocks also affected Marquette fruit composition at harvest. The soluble solid
content was higher for vines grafted on rootstocks than for own-rooted vines. The titratable
acidity was then linked to sugars, as we observed lower levels of titratable acidity on
grafted vines compared to own-rooted. Berry maturity at harvest was also affected by
growing season. The highest soluble solid concentration was noted in 2015; intermediate
levels were observed during 2016 and 2018, and the lowest levels were found in 2019 and
2017. Titratable acidity was highest during the growing seasons 2019, 2016, and 2018, and
lowest in 2017 and 2015.
Horticulturae 2021, 7, 237 9 of 13

Table 9. Effect of rootstock on yield quantity and fruit composition of grapevine ‘Marquette’.

Marquette
Average Soluble Titratable
Cluster Berry Yield Yield
Rootstock Number of Solids pH Acidity (g·L−1
Weight (g) Weight (g) (kg·vine−1 ) (t·ha−1 )
Clusters (pcs) (◦ Brix) tar. ac.)
101-14 29.98 ab 60.68 a 1.19 a 1.86 a 6.27 a 24.61 b 3.31 10.78 ab
3309C 32.70 a 71.02 ab 1.27 b 2.32 c 7.83 c 25.21 ab 3.27 10.51 a
Own-
31.35 a 70.09 ab 1.37 c 2.20 bc 7.40 bc 24.95 ab 3.24 11.20 b
Rootstock rooted
Riparia
31.45 a 80.35 b 1.35 c 2.40 c 8.07 c 25.26 a 3.23 11.21 b
gloire
SO4 b ab bc ab ab 23.45 c 3.23 11.85 c
26.95 71.74 1.32 1.99 6.70
2015 26.37 b 89.18 a 1.14 a 2.16 b 7.26 b 25.74 a 3.72 a 7.88 a
2016 36.63 a 68.95 b 1.44 c 2.53 a 8.53 a 25.42 a 3.16 c 12.03 c
Year 2017 33.97 a 65.02 bc 1.27 b 2.22 b 7.48 b 24.39 b 3.43 b 9.01 b
2018 20.05 c 58.25 c 1.28 b 1.26 c 4.25 c 23.72 c 3.07 d 12.58 c
2019 35.32 a 75.16 b 1.39 c 2.66 a 8.95 a 24.45 b 2.98 e 13.45 d
Rootstock <0.0001 0.0002 <0.0001 <0.0001 <0.0001 <0.0001 0.0972 <0.0001
p-value Year <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
Roostock ×
<0.0001 0.0003 0.6467 <0.0001 <0.0001 0.2392 0.1267 0.0936
Year
Values followed with a different letters in each column (section ‘Rootstock’ and ‘Year’, separatly) were significantly different according
to ANOVA.

4. Discussion
Vines were planted in 2013, and results are more representative after a few years
of production as grapevines became more established. The results obtained provide an
interesting portrait of the impact of grafting on three cold-hardy hybrid varieties. The
four rootstocks affected viticultural and physiological components, and some trends can
be observed.

4.1. Bud Survival

Our results obtained for Frontenac, Frontenac blanc, and Marquette did not show a
significant effect of rootstock on bud survival. The processes involved in bud survival and
influenced by rootstock may be set by direct or indirect effects and could therefore also be
related to factors such as vine growth, vine acclimation, and nutrient deficiency. The impact
of rootstock on bud survival, however, is not consistent in the literature—some studies
demonstrated an influence of rootstock on bud survival and others did not. Sabbatini
and Howell [22] demonstrated that bud survival of grafted Vidal and Marechal Foch was
influenced by the scion, and determined that no rootstock effect was observed. The same
tendency was observed by Hoover et al. [6] with the cultivar St-Pepin grafted on five
rootstocks. On the other hand, Striegler and Howell [12] observed that rootstocks could
increase the bud survival of Seyval, with the most promising results coming from pairings
with rootstock 3309 C. They noted the limited impacts of rootstock on bud survival and
instead showed that, for some rootstocks, the vine size of grafted vines had a greater effect
on bud survival. Hence, bud survival was influenced by indirect effects of grafting and
was not directly related to the change in root system. These mixed findings are somewhat
unsurprising given that commonly used rootstocks were developed to either mitigate soil
biochemistry on vine development or enhance those same features. Rootstocks are not
sought after nor principally known for their ability to impart freeze tolerance and improve
cold hardiness of grapevines.

4.2. Grapevine Development

Vine physiology is causally linked to the characteristics of the scion, and the observa-
tions made throughout the trial period are in accordance with seasonal vine development
for these three grape varieties. Howell [23] also noted that rootstocks did not impact
Horticulturae 2021, 7, 237 10 of 13

growth stages or seasonal vine development. Grafting had no effect on the phenology of
interspecific hybrid vines under the conditions evaluated in this study.
The effect of rootstock on vine vigor showed that each variety was influenced dif-
ferently by rootstock, but a tendency to lower vigor when grafted on Riparia Gloire was
observed. Moreover, vigor was low for Frontenac blanc grafted on 101-14, and a weak
vigor of Marquette was noted on rootstocks 3309C and 101-14. Rootstocks attribute a dif-
ferent influence on the vigor of grape varieties [9,10]. Following its establishment in 2013,
rootstock 3309C was the one that generally produced a greater grapevine vigor, while vine
grafted on 101-14 and Riparia Gloire rootstocks presented a reduced vigor. In subsequent
growing seasons, where the vines were more established, it is difficult to draw a clear
picture of the effects of rootstocks on the growth of the vines. According to the literature,
rootstocks 3309C, 101-14, and SO4 are medium-vigor rootstocks, while Riparia Gloire is a
low-vigor rootstock [9,19]. The study of Reynolds and Wardle [8] with interspecific hybrids
also showed a variable effect of rootstock on vine vigor according to the combination
of scion/rootstock. For example, De Chaunac and Marechal Foch grafted on Kober 5BB
presented lower weight of cane pruning, and Seyval blanc showed lower pruning weight
on own-root, SO4, and Kober 5BB. Hoover et al. [6] also observed an effect of rootstock on
grapevine vigor. St-Pepin grapevine grafted on rootstock 3309 C and ES15-53 resulted in a
heavier pruning weight than vine grafted on MN Rip 64 and MN 1065. On the other hand,
Striegler and Howell [12] did not show a significant effect of rootstock on vine size and
canopy development. Grapevines grafted on Seyval, Kober 5BB, and 3309 C had a similar
vine size as the own-root vines.

4.3. Nutrient Deficiencies

The results demonstrate that magnesium deficiencies were more prevalent for the two
Frontenac varieties compared to Marquette. Magnesium deficiency is frequently observed
in vineyards, and several grape varieties even require higher magnesium uptake [17,24].
Overall, grafting improves the absorption of magnesium for several grape varieties, in-
cluding the two Frontenac. Our results demonstrate that the most effective rootstocks
for absorbing magnesium were 3309C and 101-14. These results are consistent with the
descriptions of rootstocks found in the literature, where the rootstocks that are known
to absorb magnesium more easily are 3309C and 101-14, while Riparia Gloire and SO4
rootstocks assimilate magnesium less easily [9,10].

4.4. Yield Parameters

Results related to yield components revealed significant differences between root-
stocks and own-rooted vines. Frontenac was the least affected grape variety compared to
Frontenac blanc and Marquette; only cluster weight and berry weight were impacted. For
Frontenac blanc and Marquette, higher yields were observed on own-rooted vines and
vines grafted on 3309C and Riparia Gloire. The number of clusters and cluster weight were
generally higher for vines grafted on Riparia Gloire and 3309C, as well as on own-rooted
vines. Other studies observed an effect of rootstocks on yield components for hybrid
varieties [5,6,8,12,22,25]. Hoover et al. [6] demonstrated that there were few significant
difference in yield and fruit composition among the scion/rootstock combinations for
St-Pepin. However, Kaplan et al. [25], Harris [5], and Striegler and Howell [12] have shown
a significant impact of rootstock on yield for Regent, Norton, and Seyval grape varieties,
where higher yields were produced by vines grafted on Kober 5BB, 125AA, and 110R,
respectively. Reynolds and Wardle [15] evaluated the effect of four rootstocks (compared
to own-rooted vine) for nine hybrid varieties in British Columbia and the northwestern
United States. Grapevine varieties studied were Chardonnay, Gewurztraminer, Ortega,
Riesling, De Chaunac, Maréchal Foch, Okanagan Riesling, and Seyval blanc on rootstocks
3309C, 5BB, 5C, and SO4. For all scion/rootstock combinations, the results demonstrated
weak-to-moderate effects of the rootstocks on yield. For example, grafting of De Chaunac,
Okanagan Riesling, Gewurztraminer, and Riesling had no effect on yields or on the number
Horticulturae 2021, 7, 237 11 of 13

of clusters. Varieties most affected were Maréchal Foch and Chardonnay, where yields
were higher on rootstock 5BB, while higher yields for Seyval blanc were observed for vines
grafted on 3309C compared to SO4. The higher yield was mainly related to the number of
clusters, which is higher per vine for these scion/rootstock combinations. Cluster weight is
also sometimes affected by rootstock; however, results are often less correlated with yields
than can be the number of clusters.
Yields observed for the three grape varieties were comparable to yields noted in other
studies with these hybrid grape varieties under northeastern conditions [17,18,26–29]. The
two Frontenac varieties are considered as productive varieties capable of averaging 10 to
12 t/ha, and growers may easily obtain higher yield with less consequent bud removal.
Marquette is a little less productive and we generally reach between 6 to 8 t/ha. These three
cold-hardy hybrids are found in many vineyards in eastern North America. In Quebec,
Frontenac, Frontenac blanc, and Marquette are three grape varieties among the top 5 found
in vineyards, representing 27.8% of the growing area with an estimated growing area of
534 acres [30]. Across the upper Midwestern United States and New England, 7580 acres
out of a total of 55,500 acres are used for the production of cold-hardy hybrid grapes [31].
Marquette (24%) and Frontenac (17%) are two of the four most commonly planted cold-
hardy hybrids grape in Minnesota, along with Frontenac gris and La Crescent [31,32].

4.5. Fruit Composition

Chemical analysis demonstrated similar values for these hybrids in cold climates,
soluble solids ranging from 20 to 26 ◦ Brix, pH between 2.86 to 3.4, and titratable acidity
from 10 to 20 g/L of tartaric acid for Frontenac and Frontenac blanc; between 22 to 30 ◦ Brix,
pH ranging from 2.84 to 3.5, and 8.2 to 13 g/L of tartaric acid for Marquette [18,33–36].
Overall, for the two Frontenac grape varieties, we observed a low soluble solid content,
low pH, and a high titratable acidity for fruits on own-rooted vines compared to grafted
vines on rootstocks 101-14 and 3309C. Grafting affected fruit composition for Marquette
differently, where the lowest grape maturity was observed for fruits on vines grafted on
SO4. Soluble solids and titratable acidity are significant indicators of grape ripening and
fruit quality. Obtaining higher soluble solid content on grafted vines was also observed
by Reynolds and Wardle [15] for Okanagan Riesling, Seyval blanc, and Chardonnay on
rootstocks 5BB, SO4, and 3309C. Kaplan et al. [25] also observed an effect of rootstock on
sugar content, where the lowest value was noted for rootstock 101-14 compared to others
(SORI, 161-49C, 5BB, SO4, 125AA, and own-rooted). However, in several cases, grafting has
shown no influence on the sugar content of juice at harvest, and this was found for several
grape varieties (St. Pepin, De Chaunac, Maréchal Foch, Verdelet, Gewurztraminer, Riesling,
Cabernet Franc, and Chardonnay) [6,7,15]. Similar results have been noted by other authors,
where grafting has little or variable effects on the pH and titratable acidity of musts at
harvest [6,7,15]. Regarding titratable acidity, rootstock affected all three grape varieties
studies. Reynolds and Wardle [15] also noted a lower titratable acidity on grafted vines
compared to own-rooted vines for the Okanagan Riesling and Verdelet grape varieties.
For the six years studied, we observed a seasonal effect on yield components and fruit
composition. The 2015 growing season was the first harvest for the vines, and the low
yield that season was coupled with a long and hot growing season (1429 GDD), resulting
in grapes with high soluble solid content and low acidity. The most productive years were
2016 and 2019, with the highest yields and number of clusters; however, fruit composition
was unbalanced, with a normal soluble solids content but high level of titratable acidity.
The growing seasons of 2016 and 2019 were good growing seasons regarding GDD, but the
high yield may have reduce the capacity of the vines to reduce fruit acidity [19]. Finally,
the shortest growing season was observed during 2018, and we also noted more bud
damage (not significant) for Marquette, resulting in a low yield with low sugar content and
high acidity.
Horticulturae 2021, 7, 237 12 of 13

5. Conclusions
Grape rootstocks have been used in Europe since the end of the 19th century with Vitis
vinifera to fight against phylloxera and nematode-infested soils or to adapt grapevines to
specific soil conditions. However, although several studies have demonstrated the impact
of rootstocks in improving vine performance and fruit composition, mainly for V. vinifera,
the number of studies investigating their impact on hybrids grape varieties still remains
very limited. This study has demonstrated that rootstocks may affect cold-hardy hybrids
in different ways, and some of them showed higher potential than others for use in eastern
North American conditions. The study of cold-hardy hybrids in eastern Canada is still
relatively recent and more work needs to be done to improve knowledge about these grape
varieties under specific growing conditions. Moreover, while rootstocks have since been
shown to impart other adaptations to V. vinifera, the original use was never meant to impart
cold-hardiness adaptations. Further research into the matter should test new and novel
rootstocks that were developed specifically for and from North American hybrid cultivars.

Author Contributions: Conceptualization, C.P.; methodology, C.P.; validation, C.P.; formal analysis,
C.P., A.C. and F.D.; investigation, C.P.; resources, C.P.; data curation, C.P. and A.C.; writing—original
draft preparation, C.P.; writing—review and editing, C.P., A.C. and F.D.; supervision, C.P.; project
administration, C.P.; funding acquisition, C.P. All authors have read and agreed to the published
version of the manuscript.
Funding: Funding of this project has been provided in part through the AgriScience program-cluster
on behalf of Agriculture and Agri-Food Canada.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors wish to thank Richard Bastien and Jérémie d’Hauteville for their
expertise. We also thank Richard Kamal, Stefano Campagnaro, and Pascale Boulay for their techni-
cal support.
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or
in the decision to publish the results.

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