Postharvest Fruit Quality and Growth of ‘Pacific Gala’ Apple Trees at Different Ages as Influenced by Irrigation and Rootstock

Abstract

The effects of four rootstocks and two irrigation systems on tree growth, and fruit quality after storage in ‘Pacific Gala’ apple [(Malus × domestica) Borkh] were examined. Trees on ‘Budagovsky 9’ (‘B.9’) had a smaller trunk cross sectional area (TCA) and higher yield efficiency, while those on ‘Supporter4’ (‘Sup.4’) had larger TCA and lower yield efficiency than those on other rootstocks. Trees on ‘Nic.29’ (‘RN29’) had higher yield per tree as compared to those on other rootstocks. Trees on ‘RN29’ often had higher fruit weight, while trees on ‘B.9’ had lower fruit weight than did those on other rootstocks. Trees on ‘Sup.4’had lower yields and smaller fruits than those on ‘RN29’ every year. Fruits from trees on ‘B.9’ and ‘Cornell-Geneva30’ (‘CG.30’) often had higher soluble solids concentration (SSC) than other rootstocks at harvest and after storage. Fruits from trees on ‘CG.30’ also had higher fruit spoilage after storage. Trees with full sprinkler (FS) irrigation had higher TCA than those with the full drip (FD) system. ‘Gala’ fruit from trees with FS consistently had better color than those with the FD system every year.

Keywords:

• evapotranspiration
• irrigation scheduling
• Malus domestica
• storage life

INTRODUCTION

The increasing trend in the world population and decreasing trend in the available agricultural land and water mandate a more efficient use of water and orchard land. Using new orchard designs with more efficient irrigation systems and rootstocks can result in lower water consumption (Fallahi et al., 2007a; Neilsen et al., 2006, 2008) while producing higher quality fruit (Autio et al., 1996; Behboudian & Mills, 1997; Behboudian et al., 2005; Fallahi et al., 2007a, 2007b; Naor et al., 2008; Neilsen et al., 2010). Rootstock can influence ripening, color, and shape of the scion fruit. Autio et al. (1996) in the 1984 NC-140 cooperative planting reported that apple fruit ripening was correlated with tree vigor and the most dwarfing rootstocks resulted in the earliest ripening. Rootstock can also influence scion leaf and fruit mineral concentrations and, thus, indirectly affect fruit quality and yield (Fallahi et al., 2001a, 2001b).

Ebel et al. (1993) in a comprehensive study in Washington state applied regulated deficit irrigation (RDI) to ‘Delicious’ apple trees early in the growing season to determine if fruit quality and storage life would be altered compared to well-watered trees. Internal ethylene concentration increased logarithmically earlier in RDI apples. At harvest, RDI fruit were smaller and had a higher soluble solids concentration (SSC) and lower titratable acidity (TA). Starch degradation was delayed in RDI fruit, and their color was not affected. Firmness was not affected when the effect of size on firmness was removed. The SSC of RDI apples remained higher during storage, but starch content, TA, firmness, and color were similar.

Leib et al. (2006) indicated that fruit size and yield of ‘Fuji’ apple in deficit irrigation (DI) were similar to those of partial root zone drying irrigation (PRD) and conventional irrigation (CI) in the semi-arid climate of Washington state. Naor et al. (2008) reported that yield and fruit size decreased as the rate of irrigation was reduced in ‘Golden Delicious’ apple in Israel. Previous reports have indicated that a reduction in water application may result in a reduction in apple firmness, relating this observation to the advanced maturity in fruit with water stress (Drake et al., 1981; Mills et al., 1994). However, other studies have shown that apples from non-irrigated plots were firmer than those from irrigated plots because fruit from non-treated plots had smaller size (Assaf et al., 1975).

Irrigation with a drip system uses lower water volume than sprinkler irrigation (Fallahi et al., 2007a; Proebsting, 1994). However, irrigation through micro-jet sprinkler systems can improve the establishment and maintenance of orchard floor vegetation. Micro-jet sprinklers also create a cooler environment in the orchards under the fruit-growing conditions of Washington and Idaho (E. Fallahi, personal observation).

Although there has been some progress in the understanding of micro-irrigation systems (Chun et al., 2001; Fallahi et al., 2007a; Neilsen et al., 1994, 2010; Yao et al., 2001; Zydlik & Pacholak, 2001), information on tree growth, yield, and fruit quality for new apple cultivars and rootstocks under various regimes of drip or micro-jet sprinkler irrigation systems in the Pacific Northwestern United States is lacking. Thus, the objective of this long-term experiment was to study the effect of four rootstocks and two irrigation treatments consisting of micro-jet sprinkler and drip systems, using ET _c -based water scheduling, on water use, tree growth, yield, and postharvest fruit quality attributes in ‘Pacific Gala’ apple trees at different ages during 2004–07.

MATERIALS AND METHODS

Orchard Establishment

The experimental orchard was established at the University of Idaho Parma Research and Extension Center in spring and early summer of 2002. ‘Pacific Gala’ trees on four rootstocks were planted at 1.52 × 4.27 m spacing with an east-west row orientation. The rootstocks were: ‘Budagovsky 9’ (‘B.9’), ‘Nic.29’ (‘RN29’), ‘Cornell-Geneva30’ (‘CG.30’), and ‘Supporter4’ (‘Sup.4’). ‘Manchurian’ crab apple [(Malus baccata) mandshurica] on ‘RN29’ rootstock (C & O Nursery, Wenatchee, WA, USA) was planted in each row as a pollinizer between every 10 ‘Pacific Gala’ trees. Trees were trained into a vertical axis central leader system during the dormant season in early March every year. Tree leaders were maintained at about 3.7 m height.

The experimental site had a semi-arid climate, with an annual precipitation of about 297 mm and a sandy loam soil of pH ∼7.3. Crested wheatgrass [Agropyron cristatum (L.) Gaertn.], which is a drought tolerant grass, was planted as the orchard floor cover in all treatments. Weeds were controlled chemically to maintain a 5-ft weed-free herbicide strip under trees.

Trees in all treatments were blossom-thinned at about 80% bloom with 5% lime sulfur, followed by one or two applications of post-bloom thinners. The first post-bloom thinner was a mixture of carbaryl (44.1% by weight a.i.; Sevin XLR; 1-naphthyl N-methylcarbamate; Bayer Crop Science; Research Triangle Park, NC, USA) and Ethephon (21.7% a.i.; Ethrel [(2-chloroethyl) phosphonic acid]; Bayer Crop Science; Research Triangle Park, NC, USA) at a rate of 0.125% to 0.156% of formulation and was applied at petal-fall. The second post-bloom thinner (when applied, depending on the crop load) was carbaryl (Sevin XLR) at 0.125% formulation that was applied when fruitlet diameter was about 7 mm. Fruits were subsequently hand-thinned when fruits were about 18 mm in diameter (around mid-June) to maintain a space of at least 12.5 to 15 cm between fruits. Kaolin (95% a.i.; Surround; Englehard; Iselin, NJ, USA) was sprayed for sunburn protection at the rate of 56.8 kg^.ha⁻¹ in early July, followed by three 1-week interval applications, each at 28.4 kg^.ha⁻¹ every year. Cultural practices other than irrigation and rootstocks were similar to those recommended for commercial orchards in the Pacific Northwest (Washington State University, 2012).

Irrigation Regimes

We applied two irrigation regimes, Full Sprinkler (FS) and Full Drip (FD). Each irrigation regime was applied in one row, consisting of four rootstocks as described earlier. A row of guard trees was used between every two experimental rows. These trees received only drip irrigation to prevent any possible over-spray from the sprinkler systems in the experimental rows. Trees from the guard rows were not used for any part of the study. The two irrigation regimes (FS and FD) in this study were as follows:

1.

Full Sprinklers (FS). 30-cm micro-jet sprinklers (Olson Ultra-jet, Santee, CA, USA) were connected to a lateral polyethylene line installed in a 14-cm deep trench (subsurface), 30 cm away from and parallel to the tree row. Each micro-jet sprinkler was installed mid-way between two adjacent trees and covered a complete circle with a radius of 2.1 m. In this treatment, trees were irrigated once a week at the full rate of evapotranspiration (ETc) for apple starting in 2002 (see calculation for water application below).

2.

Full Drip (FD). One 16-mm drip line (Rain Bird Corporation, Azusa, CA, USA) was installed in a 10-cm deep trench (subsurface), 30 cm away from and parallel to the tree row on each of the north and south sides of the tree row. Each of these lines was connected to a pressure regulator to keep the water pressure constant at 1.41 kg·cm−2. Pressure compensating emitters were spaced at 45 cm on each line, and each emitter delivered 2.27 L·hr−1 of water. Pressure compensation ensured consistent flow from each inline emitter throughout the entire length of tubing and the emitter design prevented debris from clogging emitters for maximum performance. The drip line on the north side of the tree was “off-centered” with the line in the south side to provide better water coverage. Trees in this system were irrigated twice a week at 100% of daily ETc (as described below), but adjusted for the ground shading area (GS). Therefore, in this treatment, liters of water applied per tree = (ETc in mm/percent drip efficiency factor) × 1.52 × 4.27 m spacing × %GS.

Irrigation treatments were initiated in about mid-May and terminated in mid-October every year. Shortly before the first irrigation of the year, soil moisture was measured using AquaPro sensors (AquaPro Sensors, Decor, CA, USA), and trees were watered to the soil saturation point. After this general irrigation, water requirements were calculated based on ETc where Etc = ETr × Kc with ETr (Penman-Monteith reference evapotranspiration) (Allen et al., 1998) being calculated from the Agri-Met Parma Weather Station data and Kc being the crop coefficient. Each year starting in 2002, the crop water use coefficient was calculated as: Kc = K_c base + % M × (mature K_c – K_c base). Percent canopy maturity (%M) was a measurement of tree canopy size and was calculated as: % M = 3.05 + 2.558 × (%GS) – 0.016 × (%GS)². Kc base was the base coefficient, calculated as the percentage area between the rows that was occupied by a cover crop. In this experiment, spacing between rows was 4.27 m and the herbicide strip extended 0.61 m on either side of the row. Thus, Kc base was [4.27 - (0.61 × 2)]/4.27 = 0.71]. Percentage of ground shading (%GS) was estimated as the area of orchard shaded by the tree canopy at different stages of growth. Ground shading reached 62% and tree maturity reached 100% in early August 2005. Thus, Kc values for mature trees were used after August 1, 2005. Since crested wheatgrass was planted as the orchard floor cover plant, value for mature Kc for each month was adopted from Proebsting (1994) for apple with cover crop, i.e., 0.71 in May, 0.96 in June, 1.04 in July and August, 1.0 in September, and 0.79 in October.

Several random checks were made to test the accuracy of water delivery in both irrigation systems every year. Based on the precision in designing the irrigation systems and these random checks, an efficiency factor of 100% was assumed for all irrigation treatments. Rainfall during the growing seasons was generally low and when it rained, this amount was subtracted from the ETc value to calculate the actual amount of irrigation needed in each application.

Tree Growth, Yield, and Quality Attributes

For monitoring tree growth, trunk cross sectional area (TCA) was calculated by measuring trunk diameter at approximately 20 cm above the bud union (about 12 cm above the soil line) in early March every year. For this purpose, two measurements were made, one from the east-west and the other one from the north-south directions and the diameter values were averaged and the radius was computed. Tree TCA (cm²) was calculated every year from 2004 through 2007. Yield per tree was recorded at harvest time and yield efficiency was calculated as (total yield per tree in kg)/TCA.

Twenty fruits were randomly sampled from each tree between August 10 and August 25, 2004–2007. Ten of these fruits were used for evaluation of quality attributes at harvest time and the other 10 were kept in perforated polyethylene bags at 0°C regular storage atmospheres for 5 months and then for quality analyses. For quality evaluation at harvest, fruits were weighed and skin color was visually ranked on a scale of 1 to 5, with 1 = 20% red, progressively to 5 = 100% red. Soluble solids concentration (SSC) was measured at harvest and after storage, using a temperature-compensated refractometer (Atago N1, Tokyo, Japan) and fruit firmness was measured, using an 11-mm probe, with a Fruit Texture Analyzer (Guss, Strand, Western Cape, South Africa). Percentage of fruit spoilage (rot) was determined after storage. Starch degradation pattern (SDP) was determined according to the charts reported by Bartram et al. (1993).

Experimental Designs and Statistics

The experimental design was a randomized complete block split-plot with two irrigation treatments as main plots and four rootstocks as sub-plots and five blocks (replicates). Each block contained 10 trees per plot of each irrigation-rootstock combination, five of which in the center of the plot were used for measurements (i.e., a total of 50 trees per treatment, of which 25 were used for measurements). Data were collected during 2004 through 2007. Computing univariate analyses for all tree responses in this study checked the assumption of normal data distribution. Analyses of variance were conducted by using SAS (SAS Institute, Cary, NC, USA), with PROC GLM and means were compared by least significant difference (LSD) at P ≤ 0.05.

RESULTS AND DISCUSSION

Interaction

There was no significant interaction between year and water or rootstock treatments for any amount of applied water, tree growth, yield, or fruit quality attributes at harvest or after storage in this study. Thus, in addition to the results in each year, results of overall years from 2004 through 2007 are reported for each of the postharvest quality attributes.

TABLE 1 Precipitation, Evapotranspiration, Depth of Applied Water, and Total Volume of Applied Water per Tree in ‘Gala’ Apple from 2004 to 2007^zy

Parameter	Avg. 2004–05	Avg. 2006–07
Precipitation (mm)	66.0	55.1
ET r (mm)	941.0	1106.7
ET c (mm)	888.7	1050.3
Water applied by sprinkler (mm)	872.3	994.0
Water applied by drip (mm)	448.9	614.1
Applied by sprinkler (L/tree)	5616.8	6461.7
Applied by drip (L/tree)	2921.1	3996.0
^zAbbreviations: ETr = Penman Monteith; ETc = Evapotranspiration coefficient for crop (apple).
^yPrecipitation data covers the period of first irrigation (about mid-May) to last irrigations (about mid-October) in each year.

Water Application

Trees with FS treatment received a considerably greater volume of water than those with the drip system (Table 1). Trees with a FS system received 872.3 mm (5616.8 L/tree), while those with FD received 448.9 mm (2921.1 L/tree) when trees were young (averaging over 2004 and 2005). However, when trees were mature (averaging over 2006 and 2007), trees with a FS system received 994 mm (6461.7 L/tree), while trees with a FD received 614.1 mm (3996 L/tree) of irrigation water per growing season (Table 1).

Leib et al. (2006) compared three micro-sprinkler irrigation systems in mature ‘Fuji’ trees in Washington State. In that study, the soil water content in the conventional irrigation (CI) was maintained close to field capacity, which was only 60–70% of estimated ETc for apple without cover crop. They estimated that irrigation scheduling based on soil-water measurements required 26% less water than what was predicted by the ETc model for an apple orchard without a cover crop. They found that the 3-year average potential evapotranspiration (ETo) was 991 mm, ETc was about 790 mm, and irrigation amounts applied were 707 mm for CI irrigation regimes. In our study when trees were mature (2006 and 2007), the 2-year average for ETr was 1106.7 mm and for ETc was 1050.3 mm (Table 2), and thus, these values were about 11% and 25% higher than similar measurements in Washington, respectively. During 2006 and 2007, we applied an average of 994 mm of water to the FS trees, which was about 287 mm (about 29%) higher than the levels applied to the CI treatment in Washington State (Leib et al., 2006). This difference is perhaps largely due the higher ETr and ETc values in Idaho than Washington. The difference could also be in part due to the fact that trees receiving FS were applied with water at full ETc level in our study (Table 1), while CI trees in their experiment received water at about 70% of ETc. Rainfall in both experiments was somewhat comparable.

TABLE 2 Effects of Rootstock on Tree Growth, Yield, Fruit Weight, Color, and Firmness at Harvest and Fruit Firmness after 5 Months of Regular Atmosphere Storage at 0°C over 2004–07^zy

						Firmness after storage (kg)
Rootstock	TCSA 2006 (cm^2)	Cum. yield 2004–07 (kg/tree)	Avg. 2004–07 yield efficiency (kg/TCSA cm^2)	Avg. fruit weight at harvest 2004–07	Avg. fruit color 2004–07	2004	2005	2006	2007	Avg. 2004–07	Firmness at harvest avg. 2004–07 (kg)	Percent firmness reduction in storage
B.9	14.36 c	64.00 b	1.25 a	193.2 c	3.5 ab	6.34 a	6.76 ab	7.07 b	6.40 ab	6.65 a	8.33 bc	20
RN29	31.33 b	93.08 a	0.86 b	214.5 a	3.4 ab	6.36 a	6.61 b	7.20 b	6.22 ab	6.66 a	8.50 b	22
CG.30	33.17 b	75.44 b	0.67 c	200.8 b	3.6 a	6.27 a	7.03 a	7.30 ab	6.16 b	6.78 a	8.18 c	17
Sup. 4	39.94 a	33.85 c	0.26 d	200.0 b	3.3 b	6.29 a	6.97 ab	7.52 a	6.82 a	6.84 a	8.72 a	22
^zAbbreviations: B.9 = ‘Budagovsky 9’, RN29 = ‘RN29’; CG.30 = ‘Cornell-Geneva’; and ‘Sup.4’ = ‘Supporter4’; TCS = trunk cross sectional area.
^yMean separation within columns by least significant difference at the 5% level. Each value represents the average of two irrigation systems; each irrigation–rootstock combination has five blocks, each block with five trees per year.

Effects of Rootstock on Tree Growth and Yield

‘Gala’ trees on ‘B.9’ had significantly smaller TCA while those on ‘Sup.4’ had larger TCA than those on other rootstocks (Table 2). Judging based on the foliage density after tree canopy reached 100% maturity (about 67% Ground Shading as described before), it seemed that 1.52 m spacing between trees was too far for trees on ‘B.9’ and that could have been as close as 0.9 to 1.2 m spacing for this rootstock. Both ‘CG.30’ and ‘Sup.4’ are too large for planting under tree spacing of this study.

Trees on ‘RN29’ had higher cumulative yield over the 2004–07 seasons (Table 2). Trees on ‘B.9’ and ‘RN29’ had higher yield per tree and yield efficiency than those on ‘Sup.4’ in 2004 and 2005 (data not shown). Thus, both ‘B.9’ and ‘RN29’ rootstocks can be recommended for their yield under closed-space conditions of this study. ‘Sup.4’ was not a suitable rootstock for ‘Pacific Gala’ in this study as trees were too large and low in yield efficiency.

Effects of Rootstock on Fruit quality Attributes

Trees on ‘RN29’ often had higher, but trees on ‘B.9’ had lower fruit weight than did those on other rootstocks (Table 2). Smaller fruits in trees on‘B.9’ is perhaps due to a lower leaf/fruit ratio and smaller leaf size in these trees (data not shown). Fruit in trees on all rootstocks was kept at about 15-cm spacing at the time of thinning, leading to a lower leaf/fruit ration in ‘B.9’ rootstock because these trees had smaller canopy (Table 2) and lower foliage density (data not shown). Usually lower yield is associated with larger fruit size. However, trees on ‘Sup.4’ had rather small fruits in spite of their low yield and thus not suitable for planting. Trees on ‘Sup.4’ had slightly less red color and that could be due to the larger canopy size and thus more shading of trees on ‘Sup.4’ rootstock (Table 2).

On average, fruits from trees on ‘CG.30’ had lower firmness at harvest, but there were no significant differences among rootstocks after storage over 2004 and 2007 (Table 2). Fruits from trees on ‘CG.30’ also had the lowest post-storage firmness reduction among all rootstocks (Table 2). The presence of significant differences in the ‘Pacific Gala’ fruit firmness at harvest and lack of them after storage could be due to enzymatic or mineral content differences between rootstocks and this field deserves further study.

Fruit from trees on ‘B.9’ and ‘CG.30’ had higher SDP at harvest and SSC at harvest and after storage than those on other rootstocks (Table 3). Fruits from trees on ‘CG.30’ also had a significantly higher percentage of fruit spoilage (rotten fruit) after storage (Table 3). The high trends in SSC, SDP, and stem-end cracking and low firmness at harvest and the high percentage of post-storage spoilage in the fruit from trees on ‘CG.30’ suggest that this rootstock advances fruit maturity of ‘Pacific Gala’. Based on the trends in SSC and SDP in the fruits from trees on ‘B.9’, this rootstock should also advance fruit maturity.

TABLE 3 Effects of Rootstock on Fruit Starch Degradation Pattern at Harvest and Soluble Solids Concentration, and Firmness at Harvest and Fruit Firmness after 5 Months of Regular Atmosphere Storage at 0°C over 2004–07^zy

		Soluble solids concentration (SSC) after storage (°Brix)							Fruit spoilage after storage (%)
Rootstock	SDP at harvest (1–6)	2004	2005	2006	2007	Avg. 2004–07	SSC at harvest avg. 2004–07 (°Brix)	SSC change in storage (%)	2005	2006	2007	Avg. 2005–07
B.9	4.39 a	14.0 a	15.0 a	14.4 a	13.7 a	14.4 a	14.3 a	0.7	9.9 a	6.3 b	0.4 a	6.25 b
RN29	3.80 b	14.1 a	14.1 b	14.2 a	13.6 a	14.1 ab	13.9 bc	1.4	4.2 ab	10.9 b	1.2 a	6.40 b
CG.30	4.29 a	13.7 b	14.4 b	14.6 a	13.5 a	14.2 ab	14.1 ab	0.7	5.3 ab	28.0 a	1.6 a	13.97 a
Sup. 4	3.77 b	13.7 b	14.1 b	14.2 a	13.7 a	13.8 b	13.8 c	0.0	1.9 b	8.9 b	2.9 a	5.59 b
^zAbbreviations: B.9 = ‘Budagovsky 9’, RN29 = ‘RN29’; CG.30 = ‘Cornell-Geneva’; and ‘Sup.4’ = ‘Supporter4’; SDP = Starch degradation pattern ranging from 1 = immature, progressively to 6 = mature; SSC = Soluble solids concentration.
^yMean separation within columns by least significant difference at the 5% level. Each value represents the average of two irrigation systems; each irrigation–rootstock combination has five blocks, each block with five trees per year.

Effects of Irrigation on Tree Growth and Yield

Trees with FS irrigation had higher TCA and lower yield efficiency than those with FD when trees were young but differences became insignificant as trees matured (data not shown). We suggest that FD is a preferred method of irrigation over a FS system for ‘Gala’ apples.

Effect of Irrigation on Fruit Quality Attributes

Averaging over all years, fruit from trees with a FD system had heavier fruit and higher SDP but less red color than those with a FS system (Table 4) and the differences were more significant when trees were younger (data not shown). Larger fruit size in FD during early years after planting (2004 and 2005) is because roots in these trees were mostly concentrated where the irrigation was applied and thus causing larger fruits. In 2006 and 2007, tree roots in FS were expanded and thus, trees were able to uptake more of the water that was applied to a distance from the tree roots.

TABLE 4 Effects of Irrigation System on Fruit Weight, Color, and Starch Degradation Pattern at Harvest and Soluble Solids and Firmness at Harvest and after Storage, and Percentage Spoilage after 5 Months of Regular Atmosphere Storage at 0°C over 2004–07^zy

	Avg. 2004–07 at harvest			Avg. 2004–07 soluble solids (°Brix)			Firmness after storage (kg)
Irrigation	Weight (g)	Color (1–5)^y	SDP (1–6)^y	Harvest	Storage	SSC dif.^y (%)	2004	2005	2006	2007	2004–07	Harvest firmness (kg)	Firmness dif.^y (%)	Storage spoilage (%)
Sprinkler	198.5 b	3.69 a	3.99 b	14.0 a	14.1 a	0.7	6.35 a	7.15 a	7.28 a	6.31 a	6.81 a	8.55 a	20	7.0 a
Drip	205.7 a	3.27 b	4.13 a	14.0 a	14.1 a	0.7	6.28 a	6.55 b	7.26 a	6.48 a	6.66 a	8.32 b	20	9.2 a
^zMean separation within columns by least significant difference at the 5% level. Each value represents the average of four rootstocks. Each irrigation–rootstock combination has five blocks, each block with five trees per year.
^yFruit skin color: 1 = green skin color progressively to 5 = uniform red; SDP = Starch degradation patter ranging from 1 = immature, progressively to 6 = mature; SSC = Soluble solids concentration; dif. = difference between the value at harvest and after storage.

The irrigation system did not have any effect on post-storage fruit soluble solids concentration, firmness, or percentage of fruit spoilage (Table 4).

Ebel et al. (1993) reported that ‘Delicious’ apple fruits from tree receiving early season RDI treatment were smaller and had a higher soluble solids concentration (SSC) and slower starch degradation that those from well-water trees. However, they did not observe any difference in the color or firmness of fruits from RDI and well-watered trees. Leib et al. (2006) showed that SSC in fruit from trees receiving DI was higher than in fruit from trees receiving CI. A 2-year study by O'Connell and Goodwin (2007) on ‘Pink Lady’ in Victoria, Australia showed that SSC tended to be higher in DI fruit than CI fruit for each of the 2 years. In contrast, Talluto et al. (2008) reported that ‘Pink Lady’ fruits from DI and CI treatments had similar SSC. Differences in the volume of water applied in deficit irrigation treatments and method of calculation for water requirement (ETc versus soil moisture content) could partially explain these contradictory reports.

CONCLUSIONS

A significantly greater volume of water is required for trees under full micro-jet sprinkler systems than those with drip systems. Application of water through a drip system, based on full ETc rate and adjusted by percentage of ground shade, can result in major water savings and often improves yield and fruit quality. Considering yield and fruit attributes, ‘B.9’ and‘RN29’ seem to be excellent rootstocks for ‘Pacific Gala’ while ‘Sup.4’ is not desirable under the conditions of this study. ‘B.9’ and ‘CG.30’ rootstocks advanced the maturity of ‘Pacific Gala’ apple. Fruits from trees on ‘CG.30’ rootstocks had a significantly higher percentage of spoilage after storage.

With an increasing demand for new cultivars, higher orchard tree density, and different canopy architectures, the impact of various irrigation systems and newer rootstocks on postharvest fruit quality and yield of apples needs to be further studied.

ACKNOWLEDGMENTS

We wish to thank the Idaho Apple Commission, International Fruit Tree Association, Washington Tree Fruit Research Commission, and the Idaho Agricultural Experiment Station for their financial support of this project. We are also thankful to the Columbia Basin, Van Well, and C & O Nurseries in Washington State for providing the experimental trees and to Mr. Richard L. Bronson, Pipeco, Fruitland, Idaho for his invaluable contribution and assistance in designing the irrigation layout and providing the irrigation materials for this project.