Canopy Position Influences CIELAB Coordinates of Peach Color
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HORTSCIENCE 28(10):992–993. 1993, The tagged fruit L* a* b* values were measured at the midpoint between the stem and the stylar end. Measurements were made Canopy Position Influences CIELAB at about the same marked location on each fruit at intervals between 17 July and harvest. Coordinates of Peach Color The calorimeter was calibrated at illuminant C with a white standard. We calculated other Bernard B. Bible and Suman Singha CIELAB coordinates from the L* a* b* val- Department of Plant Science, University of Connecticut, Storrs, ues, including hue angle (tan-1b*/a*) and chroma (Ö a*2+b*2). Color differences (DE* ) CT 06269-4067 ab and hue differences (D H*ab) between pairs of Additional index words. Prunus persica, fruit color, calorimeter peach samples were computed as DE* ab = 2 2 2 ÖD L* + D a* + D b* , and D H*ab = 2Ö (C*1 × Abstract. Differences in color development between exposed and shaded fruit during the C*2) × sin (D H/2) (Sève, 1991), where C* 1 growing season were determined for ‘Loring’ and ‘Raritan Rose’ peach (Prunus persica and C*2 represent the chromas of pair mem- L. Batsch). The surface color of fruit exposed to sunlight in the upper canopy, and in the bers, and DH is the hue angle difference be- shade in the lower canopy, was measured with a tristimulus calorimeter, and L* a* b* tween the pair members. values were recorded for each fruit from 17 July through harvest. Color changes (DE* ab) Photosynthetic photon flux (PPF) near the during maturation for both cultivars at either canopy position were characterized by large exposed fruit cheek was measured in the upper changes in hue (D H*ab) and lesser changes in lightness (D L*ab) and chroma (D C*ab). Upper and lower canopies between 1100 and 1200 HR canopy fruit of both cultivars were redder and darker than the lower canopy fruit initially on clear, sunny days ( 17 July and 5 and 7 Aug.) and at harvest. Flesh firmness for ‘Loring’ and ‘Raritan Rose’ tended to correlate with with a Lambda LI-905 quantum sensor with a color change from initial sampling to harvest. LI-COR LI 185A quantum/radiometer/pho- tometer (LI-COR, Lincoln, Neb.). Information is meager on peach fruit color ‘Loring’ and ‘Raritan Rose’ fruit were Based on ground color, fruit was harvested development during maturation at different sampled from 8-year-old trees (height 3.4 m) from the upper and lower canopies on 12 and canopy positions, although this may be an at the university orchard. Trees trained to a 19 Aug., respectively, for ‘Loring’; and on 5 important consideration in designing peach modified central leader were spaced 4.9 × 3.1 and 9 Aug., respectively, for ‘Raritan Rose’. orchards for efficient light use. This study m with rows oriented east–west. CIELAB Following harvest, flesh firmness was mea- determined the differences in peach fruit color coordinates were measured with a Minolta sured on both sides of each fruit using a pen- development at two canopy positions. CR-200b colorimeter (Minolta, Ramsey, N.J.) etrometer equipped with an 8-mm plunger. for 10 tagged fruit on each of three trees of Soluble solids concentration (SSC) was deter- Received for publication 28 Sept. 1992. Accepted mined with a hand-held refractometer. The for publication 8 June 1993. Storrs Agricultural each cultivar. Of the 10 fruit, five were ex- Experiment Station scientific contribution 1457. posed to sunlight in the upper canopy (height relationship of CIELAB coordinates to flesh The cost of publishing this paper was defrayed in >2.2 m), and five were in the shade in the lower firmness and SSC at harvest was tested for a part by the payment of page charges. Under postal canopy. There were three single-tree repli- linear model. regulations, this paper therefore must be hereby cates per canopy position and per cultivar in a During maturation, color changes (DE* ab) marked advertisement solely to indicate this fact. randomized complete block design. for fruit of both cultivars at both canopy posi- 992 HORTSCIENCE, VOL. 28(10), OCTOBER 1993 The PPF values in our orchard’s upper canopy ranged from 1360 to 1580 µmol·s-l compared to 23 to 58 µmol·s-1 in the lower canopy. Erez and Flore (1986) reported that exposure to full sunlight is essential for maxi- mum red pigment development in peach fruit. Our results are consistent with the proposition that shading reduces red pigmentation in peach fruit because of reduced anthocyanin synthe- sis. For both cultivars, flesh firmness tended to correlate with color change from initial sam- pling to harvest (DE* ab, DH* ab, D L*) (Table 2). The SSC correlated with color at harvest (hue angle, L*, C*ab), especially for ‘Loring’. Hue angle of the fruit surface at harvest correlated with flesh firmness for both cultivars in the lower canopy, but for neither cultivar in the upper canopy (data not shown). Perhaps dif- ferences in the surface color of the fruit cannot be ascribed to differences in skin pigmenta- tion only, particularly for shaded fruit. Shaded fruit have less red pigmentation at the fruit surface, which may allow underlying flesh color or ground color to come through. Our results show the extent to which lack of unifor- mity of maturity in peach is exacerbated by canopy position. Literature Cited Erez, A. and J. Flore. 1986. The quantitative effect of solar radiation on ‘Redhaven’ peach fruit skin color. HortScience 21:1424-1426. Sève, R. 1991. New formula for the computation of tions were characterized by large changes in change is consistent with decreasing chloro- CIE 1976 hue difference. Color Res. Applica- hue (DH* ab) and lesser changes in lightness phyll and increasing anthocyanin. Singha and tions 16:217–218. Singha, S., T. Baugher, E. Townsend, and M. (D L*) and chroma (D C*ab) (Table 1). Initially Townsend (1989) reported that differences in and at harvest, upper canopy fruit of both the CIELAB coordinates of leaf color could be D’Souza. 1991. Anthocyanin distribution in cultivars were redder (– DH* ) and darker ascribed largely to differences in chlorophyll ‘Delicious’ apples and the relationship between ab anthocyanin concentration and chromaticity (- D L*) than lower canopy fruit. Interestingly, concentration. The lower L* readings for up- values. J. Amer. Soc. Hort. Sci. 116:487–499. much of this color difference between fruit in per canopy fruit vs. lower canopy fruit at Singha, S. and E. Townsend. 1989. Relationship the upper and lower canopies had already harvest could be explained by higher levels of between chromaticity values and chlorophyll developed by the initial reading on 17 July. anthocyanin in the upper canopy fruit (Singha concentration in apple, grape, and peach leaves. During maturation, fruit surface hue angle et al., 1991). HortScience 24:1034. HORTSCIENCE, VOL. 28(10), OCTOBER 1993 993.