Soluble Solids, Acidity, Canopy Fruit Distribution, and Disease Susceptibility of Selected Grape Cultivars in Quebec

ABSTRACT

Twenty grapevine genotypes (‘Chancellor’, ‘Delisle’, ‘ES-6–12–28’, ‘ES-4–7–25’, ‘GR-7’, ‘Hibernal’, ‘Sabrevois’, ‘Kay Gray’, ‘Lucie Kuhlmann’, ‘Michurinetz’, ‘Okanagan Riesling’, ‘Prairie Star’, ‘St. Croix’, ‘St. Pepin’, ‘Seyval Noir’, ‘Seyval Blanc’, ‘SV-18–307’, ‘Vandal-Cliche’, ‘Vidal Blanc’, and ‘Siegerrebe’) were evaluated under different winter protection methods in Frelighsburg, Quebec, Canada. The effects of these methods on soluble solids, acidity, fruit canopy distribution, and susceptibility to diseases were evaluated. Significant differences in juice composition was observed among the tested cultivars, and a significant interaction was observed between cultivar and sampling date, indicating that the effects of sampling date and cultivar are not independent. SSC/acid ratio increased with a corresponding decrease in acidity and the hardy and semi-hardy cultivars Lucie Kuhlmann, Michurinetz, and Geneva Red produced the highest °Brix values. None of the tender cultivars had values exceeding 19.5 °Brix. A decrease in acidity was observed for all cultivars as ripening progressed except for ‘Seyval Blanc’, ‘St. Pepin’, ‘St. Croix’, and ‘SV-18307’, which showed little or no reduction in acidity during the last three sampling dates. Under the climatic conditions observed in this study, ‘Prairie Star’, ‘ES-4–7–25’, ‘Geneva Red’, ‘St. Pepin’, ‘Delisle’, ‘ES-6–12–28’, ‘Vandal Cliche’, ‘Kay Gray’, ‘Lucie Kuhlmann’, ‘Okanagan Riesling’, and ‘SV-18–307’ had acceptable SSC and TA values. No clusters were observed at a wire level above 175 cm in any of the winter protection systems. In the M1 and M2 treatments, almost all the cultivars produced the highest proportion of clusters at a height of 80 to 125 cm and minimum fruit clusters close to the ground. Unlike the M1 and M2 methods, the M3 winter protection approaches produced a wide distribution of fruit in the canopy. ‘Michurinetz’ had the highest powdery mildew infection, followed by ‘Siegerrebe’ and ‘Lucie Kuhlmann’, whereas ‘Prairie Star’, ‘ES 4–7–25’, ‘St. Croix’, ‘St. Pepin’, ‘Vandal Cliche’, ‘Hibernal’, ‘Okanagan Riesling’, and ‘Seyval Noir’ exhibited low susceptibility. No powdery mildew symptoms were noted in ‘Sabrevois’, ‘Delisle’, ‘Kay Gray’, ‘ES-6–12–28’, ‘Chancellor’, ‘SV-18307’, or ‘Seyval Blanc’.

KEYWORDS:

• Vitis spp.
• winter hardiness
• protection against cold
• grape yield
• juice composition

INTRODUCTION

Grape production for wine-making is a young industry in Quebec and is based primarily on French–American hybrid cultivars and, to a lesser extent, on Vitis vinifera cultivars. The performance of some of these cultivars from the standpoint of phenology, agronomic characteristics, and cold hardiness has been investigated in the northern Canadian climate, specifically in Quebec and Ontario, as well as in the United States in Minnesota, Indiana, Michigan and Ohio (Bordelon, Ferree et al., 1997; Bordelon, Henick-Kling et al., 1997; Hemstad and Luby, 2000; Khanizadeh et al., 2004, 2005; Rekika et al., 2005). Limited information is available on the performance of new cultivars in regard to their soluble solids concentration (SSC), disease susceptibility, titratable acidity (TA), and fruit distribution during the growing season and at harvest time in northern Quebec, where the growing season is very short and is characterized by severe temperature fluctuations in the fall.

Fruit maturity is an important factor influencing the quality of juice and wine, and it is known, for example, that under-mature grapes may yield watery wine with high acidity (Sharma et al., 1997). Various criteria have been developed for monitoring grape maturation and identifying the optimum harvest date. The SSC, TA, pH, and sugar/acid ratio are the most commonly used indicators (Ahmedulah and Himelrick, 1989; Morris et al., 1984). Amerine et al. (1980) showed that the °Brix/acid ratio can be used as a measure of wine quality. Ough and Alley (1970) reported that ‘Thompson Seedless’ grapes are at optimum quality with a °Brix/acid ratio of 30 to 32. In Ohio, Gallander (1983) found that mid-maturity ‘Vidal Blanc’ grapes produced better quality wine than early- or late-maturity fruit. Coombe et al. (1980) found that for dry table wines, pH is a better indicator of wine quality than °Brix/acid, °Brix × acid, or °Brix × pH. Although the pH level is important, pH is more difficult to adjust in the winery than sugar and acidity, and wines with a pH higher than 3.6 are potentially unstable (Amerine et al., 1980). It was concluded that the level of sugar and acid that determines ripeness may vary among cultivars and that the achievement of mature fruit composition values is not directly related to varietal character (Howell et al., 1998; Plocher and Parke, 2001). According to Coombe et al. (1980), no single parameter should be given priority and the use of only one parameter to predict optimum wine grape maturity does not always give satisfactory results. Several studies have been conducted on factors such as site selection and cultural practices that affect grape maturation and the composition and quality of grape wine (Khanizadeh et al., 2005; Rekika et al., 2005; Reynolds et al., 1995). It has been reported that American cultivars tend to have lower acidity, while the French–American hybrids have more acidity in cool climates such as those of the central and eastern United States (Clore et al., 1976; Gallander, 1983).

Diseases, such as powdery mildew, downy mildew, black rot, and crown gall, are the primary limiting factors of grapevine growth around the world (Funt et al., 1997). Most of the disease-causing organisms thrive in warm, humid conditions and can reduce yields and affect the quality of juices and wines (Roper et al., 1998). The American grape cultivars have greater disease resistance than the V. vinifera cultivars, although within-cultivar differences do exist (Roper et al., 1998).

In addition to climatic and varietal factors, many other factors can affect the incidence of disease, including site selection, vine vigor, canopy density, and pruning severity (Wolf et al., 1999; Wolf and Warren, 2000).

The present investigation was undertaken to determine optimum harvest dates, the effect of three winter protection methods on canopy fruit distribution, and the relative disease susceptibility of 20 grape cultivars believed to hold promise for the viticulture industry of the northeastern part of central Canada.

MATERIALS AND METHODS

This experiment was conducted on 20 nongrafted grape cultivars, including various interspecific hybrids and one V. vinifera type (Table 1). The cultivars had previously been classified as hardy, semi-hardy, or tender based on their field performance under cold climate conditions (Khanizadeh et al., 2005; Table 1).

TABLE 1. List of the 20 grape (Vitis spp.) cultivars tested at the Frelighsburg research substation

Cultivar	Origin	Parentage	Winter hardiness literature
Sabrevois (ES-219)	United States	(Minn. 78 × Rosette) × (Minn. 78 × Seneca)	H ^z
Prairie Star (ES-3247)	United States	ES 2–7–13 × ES 2–8–1	H ^z
ES-4725	Canada (H. Fisher)	ES 2–12–27 × St. Croix	H ^z
Delisle (ES-7541)	Uunited States	ES 2–2–22 × Esprit	H ^y
Michurinetz	Russia	V. amurensis × Getsh	H ^z
St. Croix	United States	(Minn. 78 × Rosette) × (Minn. 78 × Seneca)	H ^z
St. Pepin	United States	(Minn78 × Siebel 1000) × Seyval	H^z,y
Vandal Cliche	Canada	Vandal 63 × Vandal 163	H ^z
Kay Gray	United States	(Minn. 78 × Golden Muscat) × Unknown	H ^z , ^y
ES-6–12–28	Canada (H. Fisher)	ES 5–14 × open pollination	—
Geneva Red (GR-7)	United States	Buffalo × Baco noir	H/SH ^x
Lucie Kuhlmann	France	Mg 101-14 S.P. × Goldriesling	SH ^y
Okanagan Riesling	Unknown	—	—
Seyval Noir	France	—	SH ^w
Chancellor	France	Seibel 5163 × Seibel 880	SH ^z , ^y , ^x , ^w
Seyval Blanc	France	Seibel 5656 × Seibel 4986 (Rayon d'Or)	SH ^z , ^y , ^x , ^w
SV-18307	France	Seibel 7053 × Seyve Villard 12–375	T ^w
Vidal Blanc	France	St. Emilion × Seibel 4986 (Rayon d'Or)	SH ^v /T ^w
Hibernal (GM-322)	Germany	Chancellor × Reisling	T ^z
Siegerrebe	Germany	Gewürztraminer × Madeleine Angevine	T ^u
^z Plocher and Parke (2001).
^y Rekika et al. (2005).
^x Rekika et al. (2005).
^w Dubois and Deshaies (1997).
^v Bordelon, Ferree, et al. (1997).
^uhttp://www.nysaes.cornell.edu/hort/faculty/pool/vinfvar/vardescs/siegerrbe.html
H = hardy, SH = semi-hardy, T = tender.

The study was carried out at Agriculture and Agri-Food Canada's research substation in Frelighsburg, Quebec (45°N, 72°W, and 205 m elevation), which has a sandy loam soil containing pebbles and gravel and a pH of 6.0. The site is sloped, allowing good cold air drainage, and it has a windbreak to the south.

The 20 cultivars were evaluated using four winter protection methods as described previously (Khanizadeh et al., 2005). In method 1 (M1), the canes were left attached to the trellis with no winter protection of any sort. Only hardy and semi-hardy cultivars were used in this treatment. In method 2 (M2), half the canes were pinned to the ground, which was covered by snow in the winter. The remaining canes, which served as a control, were left attached to the trellis without protection. Only hardy and semi-hardy cultivars were assigned to this treatment. In method 3 (M3), all the canes were removed from the trellis, laid on the ground, and covered with geotextile fabric (Polyester, Arbotex Plast 0100, 2 m × 50 m). This method was used for hardy, semi-hardy, and tender cultivars. Method 4 (M4), which was used only for ‘Seyval Blanc’ (the most widely grown cultivar in Quebec), consisted in burying the canes with 0.35 m of soil taken from between the rows. All the winter protection methods were applied in late fall when the vines had lignified and day and night temperatures were approximately 0°C, in order to avoid etiolation and continuous growth.

The experimental design for the trial was an unbalanced, randomized, incomplete block design, using a split plot with winter protection as the main plot and cultivar as the subplot, with four replications (blocks). Each replication had five vines spaced 1.5 m apart in the row and 3 m between the rows. The cultivar replications were randomized within each winter protection method.

The training system consisted of four horizontal wires attached to 1.8-m cedar posts at a height of 45, 80, 125, and 175 cm above the ground (Fig. 1). Pruning was done in keeping with the needs of the winter protection system. Hardy and semi-hardy cultivars were trained using the Mini-J-Style training system, whereas tender cultivars were trained using the fan training system. All the cultivars were cane-pruned and had multiple trunks.

FIGURE 1. Schematic diagram of the trellis used and the distance between the wires.

Assessments

Grape Maturation and Berry Composition

Maturation was checked at weekly intervals, from shortly after veraison in late August until mid-October during the 2000 season. Representative samples of 24 berries were harvested randomly on two outer vines in the plot from 30 Aug. to 17 Oct. 2000. Samples were sealed in polyethylene bags and stored at −20°C for later analysis. The frozen samples were thawed at 5°C in a cold room overnight and then juiced. The soluble solids concentration (SSC, °Brix) was measured in clear juice using a digital refractometer (Abbe Mark II, Baxter Division Canlab, Mississauga, Ontario, Canada), and titratable acidity (TA) was determined by titrating a 5-mL juice sample with 0.1 N NaOH to a pH of 8.1 (665 Dosimat, Metrohm Ltd., Herisau, Switzerland).

Fruit Distribution

On July 11, fruit distribution in the canopy was evaluated visually on the five middle vines in the plot using a thin, 2-m-long piece of wood. Measurements were made three times in the middle of the row, and the percentage of clusters present at each wire level was scored using the following scale: 0 = no clusters: (0%); 1 = very few clusters: (10–20%); 2 = small proportion of clusters (20–40%); and 3 = majority of clusters (>50%). The wire levels were measured in centimeters starting from the ground (L1 = 0–45 cm, L2 = 46–80 cm, L3 = 81–125 cm, L4 = 125–175 cm, and L5 >175 cm; Fig. 1).

Resistance to Fungal Diseases

In 2001, chemical treatments were not applied to the vines in order to permit assessment of their susceptibility to powdery mildew, downy mildew, and Botrytis. Resistance to fungal diseases (powdery mildew and downy mildew) was assessed visually based on the density of symptoms observed on the petioles, leaves, shoots, clusters, and canes during fruit ripening. Disease susceptibility was rated as follows: += slightly susceptible or sensitive; ++= moderately susceptible or sensitive; +++= highly susceptible or sensitive; −= relatively low susceptibility.

Statistical Analysis

Data were analyzed using SAS software (SAS, 1989), and the means were separated using the least significant difference test (lsd). Rank data were transformed using the arcsine transformation, but the results are presented as ranks for the sake of simplicity.

RESULTS AND DISCUSSION

Fruit Maturity and Juice Composition

There were significant differences in juice composition (SSC and TA) among the cultivars within the sampling dates, and a significant interaction was observed between cultivar and sampling date, indicating that the effects of sampling date and cultivar are not independent. A two-way table was therefore used to examine the effect of the cultivar/sampling date combination on the measured variables (Table 2). Fruit maturity was monitored from the last week of August until 17 Oct., when the grapes were harvested (Table 2). SSC and SSC/acid ratio (data not shown) increased with a corresponding decrease in acidity. Among the cultivars tested, the hardy and semi-hardy cultivars Lucie Kuhlmann, Michurinetz, and Geneva Red produced the highest °Brix values (23.3, 22.6, and 22.3, respectively). The lowest °Brix values were observed in the fruit of ‘Vandal Cliche’ (14.8) and ‘Kay Gray’ (15.8) on the final sampling date before harvest. None of the tender cultivars had values exceeding 19.5 °Brix (Table 2).

TABLE 2. Changes in °Brix and titratable acidity (TA) of the juice from 20 grape cultivars during maturation from the last week of August to 17 Oct. 2000

Cultivar and sampling date	SSC (°Brix)								TA (g/L) ^z
	30/08	6/09	13/09	20/09	28/09	5/10	12/10	17/10	30/08	6/09	13/09	20/09	28/09	5/10	12/10	17/10
Sabrevois	8.7	11.1	14.6	16.2	17.4	18.5	18.8	—	29.6	23.0	16.4	14.3	13.7	13.2	13.0	—
Prairie Star	9.8	12.2	14.5	16.1	17.3	18.2	18.9	—	25.9	20.2	16.2	13.7	12.6	12.4	11.9	—
ES 4–7–25	9.3	11.8	15.2	16.7	17.9	18.4	18.8	—	28.3	23.2	14.7	13.4	11.7	11.6	11.0	—
Delisle ^y	9.4	12.1	15.4	17.2	—	—	—	—	18.9	12.4	9.5	7.4	—	—	—	—
Michurinetz	10.0	12.0	15.9	18.3	19.1	22.3	—	—	27.8	22.1	18.1	16.9	16.2	16.2	—	—
St. Croix	6.4	7.9	11.3	13.1	14.6	15.5	15.9	16.9	29.2	23.6	15.6	12.5	10.1	10.1	10.1	10.4
St. Pepin	9.1	11.3	14.7	16.2	17.2	19.0	19.4	—	29.7	23.4	16.6	14.4	12.0	11.8	11.9	—
V. Cliche	7.3	9.2	11.0	12.0	13.6	14.2	14.8	—	28.2	23.1	18.1	15.4	13.2	12.7	12.8	—
ES-6–12–28	—	9.1	11.9	14.3	16.1	17.9	18.1	19.1	—	24.2	18.2	15.1	12.1	11.8	11.9	12.7
Geneva Red	8.9	11.8	15.8	18.0	19.6	22.1	22.6	—	29.9	24.2	16.5	14.8	12.8	13.7	13.6	—
Kay Gray	6.2	8.8	11.6	13.5	15.1	15.8	—	—	31.2	25.1	16.5	12.9	10.1	9.3	—	—
L. Kuhlmann	10.5	13.2	16.5	18.8	20.2	22.3	23.3	—	26.0	19.9	14.7	12.7	11.4	12.2	12.5	—
Chancellor	—	6.5	10.1	12.8	14.0	15.3	16.2	17.0	—	30.7	24.6	20.4	17.2	14.6	13.8	14.2
Hibernal	—	5.3	8.8	12.4	14.3	15.5	15.9	16.5	—	28.4	23.9	19.4	16.3	14.4	14.5	13.2
Ok. Riesling	7.4	9.9	13.6	15.5	16.8	18.5	—	—	35.8	24.5	18.5	15.4	13.1	12.4	—	—
Seyval Blanc	8.5	8.17	13.2	15.2	17.1	19.1	19.2	—	26.8	21.1	16.1	14.0	11.3	11.1	11.4	—
Seyval Noir	7.3	9.1	11.7	14.1	15.5	16.5	17.0	17.6	24.0	19.8	14.5	12.7	11.1	10.7	10.6	11.2
Siegerrebe ^y	11.2	11.9	12.9	—	—	—	—	—	16.5	11.3	7.7	—	—	—	—	—
SV-18307	5.7	7.9	11.8	14.8	16.6	17.7	18.3	18.4	27.3	23.4	16.6	14.2	11.8	11.8	11.5	11.4
Vidal Blanc	—	5.7	9.1	12.2	14.1	15.9	16.1	17.2	—	30.6	25.8	22.2	18.9	17.5	17.5	18.4
lsd 5%	1.0	1.91	1.25	1.21	1.23	1.53	1.16	1.00	1.56	2.12	1.80	1.37	1.08	1.12	1.23	0.84
^zTitratable acidity (TA) expressed in grams tartaric acid per liter.
^yEarly harvest to prevent bird damage.

All the grape cultivars showed decreases in acidity as ripening progressed (Table 2). ‘Seyval Blanc’, ‘St. Pepin’, ‘St. Croix’, and ‘SV-18307’ showed little or no reduction in acidity during the last three sampling dates.

The decline in acidity and the increase in °Brix was greater in ‘Lucie Kuhlmann’ and ‘Geneva Red’ than in the other cultivars, as illustrated in Fig. 2. The lowest values were obtained for ‘Vidal Blanc’ and ‘Vandal Cliche’. ‘Delisle’ and ‘Sigerrebe’ had the lowest acidity on all sampling dates. ‘Vidal Blanc’, ‘Michurinetz’, and ‘Hibernal’ had the highest acidity (>15 g/L), followed by ‘Chancellor’ (14.2 g/L) and ‘Geneva Red’ (13.6 g/L). The TA levels of the remaining cultivars on the harvest date ranged from 10.4 to 13 g/L.

FIGURE 2. Changes in soluble solids concentration (SSC) and titratable acidity (TA) in ‘Lucie Kuhlmann’, ‘Geneva Red’, ‘Vandal Cliche’, and ‘Vidal Blanc’ cultivars during fruit maturation.

Most of the cultivars showed lower SSC and higher TA values than those reported previously (Plocher and Parke, 2001; Reisch and Luce, 2002; Wolf and Warren, 2000), because of the short season and the premature harvest, which was necessary in order to control bird damage (Khanizadeh et al., 2005). However, comparable values were reported (Kaps and Odneal, 2001) in the Missouri Ozark region, where winter low temperatures regularly reach −29°C, with average °Brix values of 19.7, 19.8, and 18.2 for ‘Chancellor’, ‘Seyval Blanc’, and ‘Vidal Blanc’ over six seasons. TA values were higher than is ideal but they were in the same range as those reported at harvest in cooler regions (Gallander, 1983).

In the 2000 season, temperatures were cooler than usual, with mean maximum and minimum August temperatures of about 24.0 and 14.6°C, respectively. Heat unit accumulation (10°C base) ranged from 987 for the early ripening cultivar Delisle to 1031 for late maturing ones, such as ‘Chancellor’, ‘Hibernal’, ‘St. Croix’, ‘ES-6–12–28’, and ‘Vidal Blanc.’

Under the climatic conditions observed in this study, some cultivars did not produce fully matured berries at harvest; however, some cultivars, namely Prairie Star, ES-4–7–25, Geneva Red, St. Pepin, Delisle, ES-6–12–28, Vandal Cliche, Kay Gray, Lucie Kuhlmann, Okanagan Riesling, and SV-18–307 had acceptable SSC and TA values.

Plocher and Parke (2001) reported that ‘Kay Gray’ and ‘Vandal Cliche’ produced excellent wine when harvested at low sugar content to avoid an undesirable flavor caused by fully matured fruit, whereas a sugar content of 19 °Brix in ‘Seyval Blanc’ was insufficient for full development of its varietal flavor. Sugar accumulation in berries during maturation is a complex process that depends on the interaction of many factors such as cultivar, microclimate, crop load, and length of the growing season. All of these factors must be taken into consideration by grape growers (Boubals, 2000).

Effect of Winter Protection Systems on Fruit Distribution

Significant cultivar and winter protection effects were observed for fruit distribution. No clusters were observed at wire level 5 (L5)—that is, above 175 cm—in any of the winter protection systems (data not shown). The data for the M4 method are not presented since only one cultivar was subjected to severe pruning to protect it from the cold and it did not have all of the wire levels tested in the M1, M2, and M3 systems.

In the M1 and M2 treatments, almost all the cultivars produced the highest proportion of clusters (>50%) at level 3 (Table 3). The minimum fruit rate (<30%) was found closer to the ground, at level 1, except in the case of ‘ES-4–7–25’ for both M1 and M2 and ‘St. Pepin’ for the M2 method. In these cases, the minimum fruit rate was found at level 4. ‘Prairie Star’ and ‘Michurinetz’ showed a comparable fruit distribution with few clusters (<20%) at L1 and L4 with the M2 method (Table 3). Interestingly, these results indicated that clusters on the grapevine were grouped in the middle, well above the ground but not too high in the plant, a situation that should make harvesting easier.

TABLE 3. Effect of winter protection methods on fruit distribution in selected grape cultivars

Winter Protection	M1				M2				M3
Cultivar	L1	L2	L3	L4	L1	L2	L3	L4	L1	L2	L3	L4
Sabrevois	0.8	1.5	3	1	0.8	2.0	3.0	1.5	1.0	2.0	3.0	1.3
Prairie Star	0.5	2.0	3	1.0	1.5	2.5	2.5	1.5	0.8	1.8	3.0	1.5
ES-4–7–25	1.3	3.0	3	0.3	2.0	2.8	2.3	1.3	1.8	3.0	2.5	1.5
Delisle	0.8	2.0	3	1.0	1.0	2.0	3.0	1.8	0.8	2.3	2.3	1.3
Michurinetz	0.8	1.5	3	1.0	1.0	2.3	3.0	1.0	0.8	1.8	3.0	1.0
St. Croix	0.8	2.8	3	1.3	0.8	1.8	3.0	2.3	1.0	2.3	2.8	1.5
St. Pepin	0.8	2.0	2.8	1.3	1.8	2.8	2.5	1.3	1.3	2.3	2.8	1.5
Vandal Cliche	1.0	2.0	3	1.3	1.3	2.5	2.8	1.8	1.5	2.5	3.0	1.0
Kay Gray	0.8	1.5	3	0.8	1.0	2.0	3.0	1.5	0.5	1.8	3.0	1.5
ES-6–12–28	1.0	2.5	3	2.3	1.3	2.5	2.3	2.0	1.5	2.3	3.0	1.8
Geneva Red	0.5	1.3	3	1.8	0.5	2.5	3.0	1.5	0.8	2.0	3.0	1.8
L. Kuhlmann	0.3	1.3	3	1.8	0.8	1.8	3.0	1.3	1.3	2.0	3.0	1.8
Chancellor	—	—	—	—	—	—	—	—	1.5	2.5	2.5	0.8
Hibernal	—	—	—	—	—	—	—	—	1.5	2.3	2.8	1.0
Ok. Riesling	—	—	—	—	—	—	—	—	1.5	1.8	3.0	1.0
Seyval Blanc	—	—	—	—	—	—	—	—	1.3	2.8	2.5	1.3
Seyval Noir	—	—	—	—	—	—	—	—	1.3	2.8	2.5	1.3
Siegerrebe	—	—	—	—	—	—	—	—	1.5	2.3	2.0	0.3
SV-18–307	—	—	—	—	—	—	—	—	2.0	2.0	1.3	0.3
Vidal Blanc	—	—	—	—	—	—	—	—	1.3	1.3	1.5	0.5
F value	1.17	1.78	0.97	2.60	0.97	0.89	0.60	1.03	1.98	1.92	3.19	1.49
lsd 5%	0.69	0.86	0.21	0.98	1.74	1.36	2.21	0.96	1.03	0.74	0.76	0.95
Data represent average fruit distribution in 4 replicates of 5 vines/replicate scored as follows: 0 = no cluster: (0%), 1 = very few clusters: (10–20%), 2 = a small proportion of clusters (20–40%), and 3 = the majority of clusters: (>50%). L1, L2, L3, and L4 are the wire placement levels measured in centimeters above the ground (L1 = 0–45 cm, L2 = 46–80 cm, L3 = 81–125 cm, L4 = 125–175 cm, and L5 > 175 cm).
Winter protection: M1 = no winter protection, M2 = 50% of canes on ground covered by snow and 50% of canes without protection, M3 = vine under geotextile fabric.
—Not planted, using an incomplete, randomized block design (split plots).

In the geotextile fabric system, a significant between-cultivar difference was found at each wire level. Unlike the M1 and M2 methods, the M3 winter protection approach produced a wide distribution of fruit in the canopy. Hardy and semi-hardy cultivars showed similar trends of fruit distribution with the highest percentage of clusters (>50%) at L3. By contrast, tender cultivars had scattered fruits, with overall fruit distribution concentrated within the first three levels, up to a height of 125 cm. This difference between hardy, semi-hardy, and tender cultivars within the M3 method can be attributed to the training system used. The few fruit clusters obtained for the cultivars Siegerrebe, SV-18–307, and Vidal Blanc probably relate to their susceptibility to cold injury. In fact, although these cultivars were covered with geotextile fabric, they suffered the most injury, with mortality rates of >50% (Khanizadeh et al., 2005).

Snow cover protection of ‘Seyval Blanc’ resulted in fruit distribution with few clusters, which were concentrated between L2 and L3, with less than 20% of clusters found at the lowest and highest wire levels. The low canopy density was attributed to the high bud mortality (58%) that occurred during the year (Khanizadeh et al., 2005).

Previous findings based on field observations showed that the relative cold hardiness of grapevines affects crop load and hence yield and fruit composition (Hummel and Ferree, 1998; Smart, 1985). Although absolute hardiness is critical to cultivar choice for cold viticultural regions like Quebec, cultural and geographical factors can have a considerable influence on a vine's ability to acclimate prior to potential cold events. Examples of such factors are location/aspect, local microclimate, vine age, pruning, thinning, crop load, shoot exposure to sunlight, and node position on a given shoot (Ahmedullah and Himelrick, 1989; Howell et al., 1991; Reynolds et al., 1994, 1995).

Resistance of Grape Cultivars to Fungal Diseases

The study results showed that most of the cultivars tested were infected by powdery mildew, with ‘Michurinetz’ appearing to have the highest susceptibility. ‘Siegerrebe’ and ‘Lucie Kuhlmann’ exhibited moderate susceptibility to powdery mildew, whereas ‘Prairie Star’, ‘ES 4–7–25’, ‘St. Croix’, ‘St. Pepin’, ‘Vandal Cliche’, ‘Hibernal’, ‘Okanagan Riesling’, and ‘Seyval Noir’ had low susceptibility. No powdery mildew symptoms were noted in ‘Sabrevois’, ‘Delisle’, ‘Kay Gray’, ‘ES-6–12–28’, ‘Chancellor’, ‘SV-18307’, or ‘Seyval Blanc’ (Table 4). Although not affected by powdery mildew, ‘SV-18307’ and ‘Chancellor’ showed moderate susceptibility to downy mildew, with leaves, clusters, and canes being the most infected. ‘Vidal Blanc’ was slightly susceptible, while the other cultivars were ranked as having a relatively low susceptibility to downy mildew in this trial.

TABLE 4. Relative disease susceptibility of grape cultivars

Cultivar	Powdery mildew	Downy mildew
Sabrevois	−	−
Prairie Star	+ ^z	−
ES 4–7–25	+ ^z	−
Delisle	−	−
Michurinetz	+++ ^z	−
St. Croix	+ ^z	−
St. Pepin	+ ^z	−
V. Cliche	+ ^z,y,x,w,v	−
ES-6–12–28	−	−
Geneva Red	−	−
Kay Gray	−	−
L. Kuhlmann	++ ^z,y,w,v	−
Chancellor	−	++ ^z,w
Hibernal	+ ^z,v	−
Ok. Riesling	+ ^z,v	−
Seyval Blanc	−	−
Seyval Noir	+	−
Siegerrebe	++	−
SV-18307	−	++ ^z,w,v
Vidal Blanc	++ ^v	+ ^z,w,v
Key: += slightly susceptible or sensitive. ++= moderately susceptible or sensitive, +++= highly susceptible or sensitive, −= relatively low susceptibility or sensitivity not seen.
The letters represent each area observed to have symptoms: ^zleaf, ^ypetiole, ^xshoot, ^wcluster, ^vcane.

Of the most common grape diseases, powdery mildew and downy mildew were the only ones for which we observed symptoms, despite the fact that some of the cultivars studied are reported to be susceptible to some or all of the major grape diseases (Bordelon, 2001). According to Plocher and Parke (2001), different cold climate regions where grapes are grown have different disease problems. These authors reported that the kind of susceptibility to downy mildew that is seen in certain grape varieties in Minnesota is nonexistent in Latvia and Estonia, because the cold temperatures there prevent the growth of fungi. Boubals (2000) reported that there are very few countries (i.e., Sinkiang in northwestern China, Chile, Argentina, and Iran) where grapevines can be cultivated without chemical treatments. Powdery mildew is the only disease of significance that occurs in these countries. In addition to cultivar susceptibility, many other factors can affect disease incidence, such as site selection, vine vigor, and canopy density (Bordelon, 2001). Consistent differences in ripening were observed among the grapevine cultivars. These differences could be harnessed to extend harvest time and make better use of processing capacity. In Quebec's climatic conditions, the decision of when to harvest should be based on the type of wine that is to be produced. For example, early harvesting should be done when a low soluble solids concentration is desired; these grapevine cultivars are well suited to the production of low-alcohol wine. For a higher alcohol content, SSC and TA should be carefully monitored during ripening in order to ensure optimum grape quality. Late-maturing cultivars can also produce acceptable wine, despite their high TA level. However, even if SSC and TA seem to be good criteria for assessing grape maturity, pH remains an important indicator of wine quality and stability. In addition, aroma/flavor and phenol content, which may have a greater influence and contribute to greater varietal character, warrant further investigation in northern climates.