In sweet cherry orchards, rain protective covers (RPC) are used worldwide to prevent or ... the time when the fruit started to colour (±20 days before harvest).
Vegetative and Reproductive Development of ‘Lapins’ Sweet Cherry Trees under Rain Protective Covering B.N. Wallberg and K.X. Sagredo Facultad de Ciencias Agronómicas Universidad de Chile Santiago Chile Keywords: Prunus avium, fruit firmness, phenology, PAR Abstract A study was carried out to evaluate the effect of rain protective covers on the vegetative and reproductive development and fruit quality of sweet cherry trees. The trial was conducted in the 2010-2011 season in a commercial orchard in Collipulli, Chile, with gabled (Vöen®) crop covers on 10 rows. In half of each row, trees were protected with rain covers from bud-burst, and the other half was protected from first red colour development of the fruit onwards; a treatment without protective rain cover served as control. The following variables were assessed: temperature, relative humidity, rainfall, phenology, intercepted photosynthetically active radiation (IPAR), fruit development, foliar area, flower bud differentiation, fruit set, vegetative growth and fruit quality at harvest and after conventional cold storage were measured. The protective covering filtered approximately 40% of incident PAR. Crop cover at budburst advanced tree phenology and increased shoot length. Fruits of cherry trees protected during the colour development phase showed less colour. Protective covering installed at bud-burst increased fruit size, weight and soluble solids concentration, but with more cracking at the style-end scar of the fruit and with reduced fruit firmness. Flower bud differentiation was advanced by both treatments. INTRODUCTION Growing sweet cherries in the Southernmost commercial production area of Chile (~37°50’S) allow farmers to harvest fruit from late December until the end of January, a period of low fruit offer in the markets of the Northern Hemisphere and, therefore, of high fruit prices and good economic returns. Unfortunately, in this area rain usually falls both at flowering and at harvest, causing severe economic losses and making this the main limiting factor for the expansion of the sweet cherry industry in this area. In ‘Lapins’, one of the cultivars grown in this area, fruit losses can be more than 30%. In sweet cherry orchards, rain protective covers (RPC) are used worldwide to prevent or reduce fruit cracking in rainy areas. However, RPC have other side effects on the vegetative and reproductive growth of the trees. For instance, when RPC are used during the whole season, trees bloom 6 to 13 days earlier, harvest is advanced by 12 to 19 days, and soluble solids concentration increase in comparison with uncovered controls (Blanke and Balmer, 2005). The most susceptible period for cracking is from the start of colour formation to harvest and the use of RPC at this time can increase the percentage of commercial fruit harvested by about 40% (Børve et al., 2003). The aim of this study was to evaluate the effect of RPC on the vegetative growth and on fruit development and quality, either covering the trees during the whole growing season or just from the start of colour development until harvest. MATERIALS AND METHODS The trial was conducted on mature ‘Lapins’ sweet cherry trees in a commercial orchard in the Collipulli area (38°0’4”S, 72°15’32”W) during the 2010-2011 season. Trees were 11-years old, planted at 2 m x 4 m spacing. The RPC was provided by polyethylene covers (Vöen®, Vöhringer GmbH & Co. KG. Berg, Germany) of the gabled type put over 10 rows of 48 trees each. The RPC was Proc. Xth IS on Integrating Canopy, Rootstock and Environmental Physiology in Orchard Systems Ed.: K. Theron Acta Hort. 1058, ISHS 2014
411
put in place over half of the experimental trees at bud-burst. The other half was covered at the time when the fruit started to colour (±20 days before harvest). The next 10 rows with no RPC, were used as control. Ten trees per treatment were used as the experimental unit. The following variables were measured: air temperature and relative humidity during the whole trial period using a logger (HOBO® V2 temp/RH), rainfall, phenology, intercepted photosynthetically active radiation (IPAR), fruit development, shoot foliar area, floral bud differentiation for next season, fruit set, vegetative growth and fruit quality, at harvest and after 30 days of regular atmosphere cold storage at 0°C. Phenological stages were visually monitored on the lower and upper-middle tree canopy sections using the chart propose by Chapman and Catlin (1976); development of reproductive buds was also quantified on two branches per tree, from the lower and upper canopy position. IPAR was evaluated at harvest time using a ceptometer (AccuPar LP 80, Decagon Devices, Inc. WA, USA) and calculated as a percentage of the total incident PAR. Fruit firmness was measured with a Durofel (DFT 100, Agro-Technologie, France), fruit size was determined by weighing (g) and soluble solids concentration (SSC) (°Brix) by using a hand-held refractometer (Atago modelo ATC-1 c). External fruit defects were quantified in a sample of 100 fruit taken from the lower and upper sections of the tree canopy. Floral bud differentiation was assessed in buds developing at the base of the shoots, following the method described by Engin and Ünal (2007). Data analysis consisted of pairwise comparisons using Student’s t-test (p ≤ 0.05). For those variables expressed as percentages and those that did not meet the assumptions of normality, data were analyzed using the Kruskal-Wallis’s test. RESULTS AND DISCUSSION Intercepted Photosynthetically Active Radiation and Rainfall RPC reduced IPAR by 40%, giving 1,000 to 1,100 µmol·m-2·s-1 under the covers. Trees intercepted approximately 55% of this radiation; trees of the non-covered control treatment intercepted more than 90% of the PAR (Table 1). Rainfall during the growing season (September - January) was about 250 mm, with three rains occurring during the harvest period. Temperature was regulated by the covers, being higher early in the spring and lower at harvest time, compared to the uncovered control (data not shown). Temperature in the tree canopy at harvest time was reduced by the RPC at the three heights (1, 2 and 3 m above the soil level) (Table 1). These results are in disagreement with Meli et al. (1984), who found an increase in temperature when rain covers were installed during fruit ripening. Phenology and Vegetative Growth When RPC was put in place at bud-burst, flowering occurred ca. 15 days earlier compared to the control, reaching full bloom on 30 September, when control trees were only at the early white bud stage (Table 2). Floral bud differentiation was also earlier in RPC treatments, particularly when the RPC was put in place at bud-burst. (Fig. 1a-c). A high incident solar radiation during flower bud induction increases return bloom in apples (Tromp, 1983). Lakso (1980) mentions that 30% of full sun light is the threshold value for flower-bud formation in apple. Our results indicate that a reduction of 40% PAR did not reduce flower bud density (data not shown). The early bud-burst and fruit development induced by the RPC treatments induce an earlier vegetative growth cessation and flower bud development. RPC installed at bud-burst increased shoot length (Table 3) on the upper section of the tree canopy, shoot leaf area and leaf size compared to the control (Fig. 2). This is in agreement with what has been reported in tunnel-covered cherry orchards, where cumulative reduction in PAR was about 25% but shoot growth was 35% more than noncovered trees and leaf size was 20% bigger (Lang et al., 2011). Diffuse light has been shown to increase radiation use efficiency of plants (Healey et al., 1998; Sinclair et al., 412
1992). The composition of incident radiation is known to affects radiation use efficiency (Stamp, 2009), however not enough information is available in relation to light composition under RPC. Fruit Maturity and Quality Fruit developed under RPC installed at bud-burst showed bigger size, mass and SSC (Table 4) than the other treatments, probably as a result of the longer development period. In our experiment, RPC installed at bud-burst increased fruit cracking at the style scar end and reduced fruit firmness, in both the upper and lower tree canopy sections compared to the uncovered control (Fig. 3). The high incidence of cracking under the RPC could be due to the water condensation that usually occurred on the fruit surface, particularly in the early mornings. More wetness under umbrella covering system has been reported by Børve et al. (2003). Lang et al. (2011) found prevalent fruit cracking under tunnels when rain was significant, but lower than the uncover trees. Fruit cracking might not be absent under orchard conditions. Rain water lead to high root pressure, and more water can be taken up by the tree and thereby go into the fruit flesh enhancing formation of microcracks (Peschel and Knoche, 2005). When the RPC was installed once fruit started colour formation, fruit colouring was affected and a higher proportion of fruits showed a low percentage of over-colour in both the upper and lower tree canopy sections (data not shown). Meli et al. (1984) claimed that high temperature inhibited fruit colour development. In our study we speculate that the sudden reduction in PAR when the RPC was installed could induce a low-light stress that delayed fruit colouring. CONCLUSIONS In conclusion, under the conditions of this study the use of RPC installed on ‘Lapins’ either at bud-burst or at the start of fruit colour development affected the quality of sweet cherries. Fruit mass, size and SSC increased, but fruit firmness was reduced and bruising and cracking increased. RPC installed at bud-burst affected the phenology of the trees, by advancing full bloom and fruit ripening, and also time of flower bud differentiation, which already occurred at the time of fruit ripening. The use of RPC installed later at the start of colour development (20 days before harvest) shows more benefits that when the RPC was installed at bud-burst or when no RPC is used. ACKNOWLEDGEMENTS We are grateful for financial support from FONDEF – CONICYT, Chile. Literature Cited Blanke, M. and Balmer, M. 2005. Forced cultivation of sweet cherry under rain covers. Acta Hort. 795:479-484. Børve, J., Skaar, E., Sekse, L., Meland, M. and Vangdal, E. 2003. Rain protective covering of sweet cherry trees: Effects of different covering methods on fruit quality and microclimate. Hort. Technol. 13:143-148. Chapman, P.J. and Catlin, G.A. 1976. Growth stages in fruit trees-from dormant to fruit set. N. Y. Food Life Sci. 58(11):10. Engin, H. and Ünal, A. 2007. Examination of Flower Bud Initiation and Differentiation in Sweet Cherry and Peach by Scanning Electron Microscope. Turk. J. Agric. For. 31: 373-379. Healey, K.D., Rickert, K.G., Hammer, G.L. and Bange, M.P. 1998. Radiation use efficiency increases when the diffuse component of incident radiation is enhanced under shade. Aust. J. Agr. Res. 49:665-672.
413
Lakso, A.N. 1980. Correlation of fisheye photographs to canopy structure, light climate, and biological responses to light in apple trees. J. Amer. Soc. Hort. Sci. 105:43-46. Lang, G., Valentino, T., Demirsoy, H. and Demirsoy, L. 2011. High tunnel sweet cherry studies: innovative integration of precision canopies, precocious rootstocks, and environmental physiology. Acta Hort. 903:717-723. Meli, T., Riesen, W. and Widmer, A. 1984. Protection of sweet cherry hedgerows with polyethylene films. Acta Hort. 155:463-467. Peschel, S. and Knoche, M. 2005. Characterization of microcracks in the cuticle of developing sweet cherry fruit. J. Amer. Soc. Hort. Sci. 130:487-653. Sinclair, T.R., Shiraiwa, T. and Hammer, G.L. 1992. Variation in crop radiation-use efficiency with increased diffuse radiation. Crop Sci. 32:1281-1284. Stamps, R.H. 2009. Use of Colored Shade Netting in Horticulture. HortScience 44:239241. Tromp, J. 1983. Flower-bud formation in apple as affected by air and root temperature, air humidity, light intensity and daylength. Acta Hort. 149:13-23. Tables Table 1. Fraction of PAR intercepted measured at harvest (3 Jan. 2011) below east and west canopy section and temperature at different canopy heights of ‘Lapins’ sweet cherry trees. Rain protective covering
Non-covered From bud-burst From SCF z z SCF:
PAR intercepted on PAR intercepted on Temperature in the canopy the eastern tree the western tree at different heights section section (°C) (%) (%) 1m 2m 3m y 92,26 a 95,02 a 23,2 a 23,7 a 23,8 a 55,38 b 56,91 b 21,4 b 21,7 b 21,9 b 55,89 b 56,12 b 21,9 b 22,3 b 22,6 b
start of colour formation. separation at 5% level.
y Means
Table 2. Effect of rain covering on ‘Lapins’ sweet cherry trees on the developmental stages during flowering expressed as percentages of buds. 30 Sept. 2010 Rain protective z 4a 4b 5 6 covering From bud-burst 51.0 36.6 12.4*y --x Non-covered 22.0 34.0 46.0 -From bud-burst 50.0 33.0 17.0 -Non-covered 34.0 40.0 26.0 --
4 Oct. 2010 4a
4b 5 6 Lower branch 35.0* 32.0 33.0* 0.0 9.7 28.3 61.5 0.5 Upper branch 39.5* 37.0 23.5* 0.0 14.8 27.7 57.0 0.5
15 Oct. 2010 4a
4b
5
6
---
-- 44.5* 55.5* -- 19.2 80.8
---
-- 54.5* 45.5* -- 25.4 74.6
Growth stages according to Chapman and Catlin (1976): 4a: early white bud, 4b: white bud, 5: bloom, 6: petal fall. y * indicates significant difference (p< 0.05). x The stage was not present. z
414
Table 3. Effect of protective rain covering on shoot growth expressed as the total length of shoot per branch cross-sectional area. Rain protective covering Non-covered From bud-burst From SCF z
Lower branch Upper branch Shoot length per branch (cm cm-2) 73.91 n.s. y 55.56 b y 58.53 94.89 a 70.87 80.32 ab
z SCF: y n.s.:
start of colour formation. no significant differences. Means separation at 5% level.
Table 4. Effect of rain protective covering on maturity and size in a sample mahogany-red coloured fruit from the upper a lower tree canopy sections. Treatments Medium-low Non-covered From bud-burst From SCF z Upper-middle Non-covered From bud-burst From SCF z y x
Diameter (mm)
Mass (g)
Firmness Soluble solids (UD 0-100) x (%)
29.3 b y 32.3 a 31.2 a
10.4 c 13.0 a 11.7 b
76.3 a 70.2 b 77.4 a
15.9 b 16.5 a 17.0a
28.5 c 32.3 a 30.7 b
10.1 c 13.0 a 11.3 b
74.4 ab 71.7 b 76.9 a
16.6 17.3 16.7
SCF: start of colour formation. Means separation at 5% level. Durofel index: resistance to pressure from 0 to 100; 0 = No resistance.
415
Figurese
100%
a
n.s z
b 100%
80%
a
80%
60%
b
60%
40%
40%
a a
20%
b n.s
20%
b
n.s
0%
0% A
A
B
B
C
100%
c
90% 80%
a
70%
a
n.s
60%
Non-covered
50% b
40%
Covered from bud-burst Covered from SCF
30% 20%
n.s
10% 0% A
B
C
D
E
Development stages of flower bud
Fig. 1. Differentiation of floral buds developed at the base of current season’s shoots evaluated five days before harvest (a), and seven (b) and thirty (c) days after harvest. Capital letters are used for the bud stages: bract primordia forming (A), primordia enlarged and rounded (B), sepal primordial (C), petal primordia differentiate (D) and all floral organs differentiated (E). SCF: start of colour formation. Lower case letters are used to separate means (p=0.05).
416
a) b
a
b Non-covered Covered from bud-burst Covered from SCF
cm2
cm2
100 90 80 70 60 50 40 30 20 10 0
b
100 90 80 70 60 50 40 30 20 10 0
a
b
b
Treatments
Treatment
Fig. 2. Effect of rain covering treatments on average leaf area per shoot (a) and leaf size (b). SCF: start of colour formation. Different letters indicate significant differences at p=0.05.
35 30 25 20 15 10 5 0
b b a
a b
b
a b
b b
SE-C
SSE-C
Bruising
b
b
Pitting
Fig. 3. Incidence of defects in mature fruits picked from the upper (left) and lower (right) tree section. SCF: start of colour formation. SE-C: stem-end cracking, SSE-C: style-scar end cracking.
417
418
