Effects of Pruning on Light Interception, Specific Leaf ... - Science Direct

Scientia Horticulturae, 41 (1989) 55-61 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

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Effects of P r u n i n g on Light Interception, Specific Leaf Density and Leaf Chlorophyll Content of Mango* BRUCE SCHAFFER and G.O. GAYE** University of Florida, Institute of Food and Agricultural Sciences, Tropical Research and Education Center, 18905 S. W. 280 Street, Homestead, FL 33031 (U.S.A.) (Accepted for publication 1 May 1989)

ABSTRACT Schaffer, B. and Gaye, G.O., 1989. Effects of pruning on light interception, specific leaf density and leaf chlorophyll content of mango. Scientia Hortic., 41: 55-61. Photosynthetic photon flux (PPF), specific leaf density (Wa), and total leaf chlorophyll concentration (Chl) were determined at several positions in pruned and non-pruned mango (Mangifera indica L. cultivar 'Tommy Atkins') canopies during April, July and November. Pruned trees had approximately one-fourth of the center of the canopy removed during March. Penetration of PPF was generally greater in canopies of pruned trees than in non-pruned trees during each season. There was no difference in W~ between pruned and non-pruned trees at any measurement period. Total leaf chlorophyll content was greatest for pruned trees during November, but similar for pruned and non-pruned trees during April and July. During the year that the pruning treatment was imposed, there was no significant effect of pruning on fruit color. Keywords: Mangifera indica L.; photosynthetic photon flux. Abbreviations: Chl-- chlorophyll concentration; LSD = least PPF = photosynthetic photon flux; Wa= specific leaf density.

significant

difference;

INTRODUCTION L i g h t i n t e r c e p t i o n b y fruit tree c a n o p i e s has b e e n s t u d i e d for several fruit species ( G r e e n e a n d Gerber, 1967; Cain, 1971; B a r d e n , 1974; J a c k s o n , 1980; Porpiglia a n d B a r d e n , 1981; K a p p e l a n d Flore, 1983; M a r i n i a n d Marini, 1983). H o w e v e r , v e r y little r e s e a r c h in t h i s a r e a h a s b e e n c o n d u c t e d w i t h t r o p i c a l fruit crops, especially m a n g o , w h i c h is o n e o f t h e m o s t widely p l a n t e d fruit c r o p s in t h e w o r l d ( B o n d a d , 1980). D i f f e r e n t i a l light i n t e r c e p t i o n w i t h i n tree c a n o p i e s m a y i n f l u e n c e v e g e t a t i v e *Florida Agricultural Experiment Station Journal Series No. 9633. **On leave from: Horticulture Unit, Yundum Agricultural Station, The Gambia.

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B. SCHAFFER AND G.O. GAYE

growth, flower initiation, fruit set, fruit color, fruit size and fruit quality (Jackson, 1980; Marini and Marini, 1983; Robinson et al., 1983). Light intensity during leaf development can also influence specific leaf density, leaf anatomy, photosynthetic efficiency, and leaf chlorophyll and nitrogen content (Barden, 1974; Kappel and Flore, 1983; Marini and Marini, 1983; Syvertsen, 1984; Syvertsen and Smith, 1984; Schaffer and Gaye, 1989). Mango trees are rarely selectively pruned commercially (Young and Sauls, 1981 ), but previous studies have shown that pruning mangoes may result in increased yield and fruit color (Whiley, 1984). Determination of the effects of pruning on light interception and utilization within mango trees may enable the canopy to be designed for optimum fruit yield and quality. The objectives of the present study were to determine seasonal light interception, total leaf chlorophyll content (Chl), specific leaf density (Wa) and fruit color in pruned and non-pruned mango tree canopies during overcast days. MATERIALS AND METHODS

An orchard in Homestead, FL, consisting of 7-year-old Mangifera indica cultivar 'Tommy Atkins' mango trees on cultivar 'Turpentine' rootstocks was selected for this study. Trees were spaced 7.6 X 6.1 m and had never been selectively pruned. Uniform trees with an average height of ~ 6.2 m and an average canopy height and width of 5.8 and 5.4 m, respectively, were used. Tree rows were oriented in a N-S direction and were divided into two treatments: (1) pruned trees which retained a central leader, but had approximately one-fourth of the interior of the canopy removed during March 1988, leaving a modified open center, and (2) trees which were not pruned. Each treatment consisted of five single-tree replicates in a completely randomized design. String lines were placed in N W - S E and NE-SW directions through the canopy of each tree at 1 m above the bottom and 1 m below the top of the canopy. Each line was marked at 1-m intervals from the trunk to the outside of the canopy. Thus, there were two positions from the tree center outward, on each of four sides and at two heights for each tree. Photosynthetic photon flux (PPF) was measured outside the canopy and between marks on each line with an LI-191SA line quantum sensor and an LI1000 light meter/data logger (LI-COR Instruments, Inc., Lincoln, NE). Cloudiness increases the amount of diffuse light available to the tree, thus allowing greater efficiency for the estimation of available light within canopies (Lakso and Musselman, 1976). Therefore, all measurements were taken on uniformly overcast days between 10.00 and 12.00 h in April, July and November 1988. Total Chl and Wa were determined for leaves on current-season shoots which were closest to the marks in the canopy. Total leaf Chl was determined as described by Marini and Marini (1983). Eight 0.32-cm leaf discs were removed from each leaf, brought into the laboratory, placed in 10 ml of 80% methanol

EFFECTS OF MANGOPRUNING

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and held in darkness at room temperature for 48 h. Total Chl was calculated from absorption values obtained at 642 and 664 nm with a Bausch and Lomb Spectronic 21 spectrophotometer. For Wa determinations, four 0.32-cm 2 leaf discs were sampled, dried at 70 ° C and weighed. During June 1988 (at the time of the first commercial harvest ), all fruit were harvested from all trees in both treatments and fruit color was determined for each fruit by estimating the percentage of fruit with 0, 1-25, 26-50, 51-75 and 76-100% red color for each treatment. RESULTS AND DISCUSSION

During July-September, there was a regrowth of new shoots near most of the pruned surfaces which averaged ~ 61 cm by the end of the summer. These were easily removed by hand from all trees. There were no significant interactions between canopy position and canopy height with regard to the percentages of available PPF, Chl or Wa during any measurement period (P > 0.05 ). Therefore, measurements taken in the upper and lower canopy were combined at each canopy orientation. During April, PPF was greater for pruned trees than for non-pruned trees on the NW and SW sides and outer NE side of the canopy (Fig. 1). During July, the percentage of PPF was greater for pruned trees than non-pruned trees on the NW and SW sides of the canopy. In November, the percentage of available PPF was greater for pruned trees than non-pruned trees at all but the outer SE position of the canopy (Fig. 1). The mean percentage of available PPF within the canopy was greatest for pruned trees during each season (see Fig. 3). Light penetration within pruned canopies averaged > 25% during each measurement period, whereas light penetration in non-pruned canopies averaged 10-15% in April and July, and 5% in November. Reduced light penetration within non-pruned canopies in November was presumably because of the increased shading by the new growth. The pattern of light interception by mango trees was different from that of apple trees trained to a central leader, or peach trees trained to an open center. In apple trees, PPF increased exponentially from the trunk outward (Porpiglia and Barden, 1981 ). In peach trees, PPF was greatest in the center of the canopy (Kappel and Flore, 1983; Marini and Marini, 1983 ). Although pruned mango trees in our study had approximately one-fourth of the center branches removed, a central leader still remained. Thus, light penetration into the center of the tree was partially blocked by this main stem. Ideally, light interception by mango canopies may be maximized if, as is often done with peach trees, trees are trained to an open center at an early stage of development. There were no significant differences in Wa between pruned and nonpruned trees (data not shown), regardless of the position in the canopy or the month that the measurements were taken. Thus, even though pruned trees had greater

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B. SCHAFFER AND G.O. GAYE

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Fig. 1. Percentage o f available P P F w i t h i n p r u n e d ( © © ) and non-pruned (• - - • ) 'Tommy A t k i n s ' m a n g o canopies m e a s u r e d o n t h r e e o v e r c a s t days. E a c h p o i n t r e p r e s e n t s t h e m e a n o f five single-tree replicates. Vertical b a r s r e p r e s e n t L S D s .

light interception, Wa was not increased. This contrasts with observations on Citrus (Syvertsen, 1984), apple (Barden, 1974) and peach (Kappel and Flore, 1983; Marini and Marini, 1983), which had greater Wa as a result of increased light intensity. However, in a previous greenhouse study with mango, the percentage of shade during leaf development did not affect W~ (Schaffer and Gaye, 1989). Total leaf Chl was determined on a dry-weight basis. However, it has previously been determined that the effect of light intensity on Chl of mango is the same when expressed on a leaf area or dry-weight basis (Schaffer and Gaye,

EFFECTS OF MANGOPRUNING

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1989). During April and July, there were no significant differences in Chl between leaves of pruned and non-pruned canopies (Fig. 2). However, during November, leaves of non-pruned trees had a higher Chl (Fig. 3) at every canopy position except in the outer NE portion of the canopy. There was no significant difference in fruit color between treatments (data not shown), although the pruned trees had significantly greater light interception by the canopies. The pattern of light penetration within mango canopies observed during this study may be useful for designing orchards to maximize productivity. Our results indicate that pruning mango trees by removing approximately one-fourth 70

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of the center portion of the canopy can increase light interception into the canopy considerably. Increased light interception, however, did not improve fruit color during the same year that the treatments were imposed. Additional work is needed to assess the effect of pruning on fruit quality, as well as yield and fruit color, over a period of several years before mango trees can be designed for maximum light utilization.

REFERENCES Barden, J.A., 1974. Net photosynthesis, dark respiration, specific leaf weight, and growth of young apple trees as influenced by light regime. J. Am. Soc. Hortic. Sci., 99: 547-551. Bondad, N.D., 1980. World mango production and trade. World Crops, 32: 160-168. Cain, J.C., 1971. Effects of mechanical pruning of apple hedgerows with a slotting saw on light penetration and fruiting. J. Am. Soc. Hortic. Sci., 96: 664-667. Greene, B.A. and Gerber, J.F., 1967. Radiant energy distribution in Citrus trees. Proc. Am. Soc. Hortic. Sci., 90: 77-85. Jackson, J.E., 1980. Light interception by orchard systems. Hortic Rev., 2: 208-267. Kappel, F. and Flore, J.A., 1983. Effect of shade on photosynthesis, specific leaf weight, leaf chlo-

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rophyll content of leaves and morphology of young peach trees. J. Am. Soc. Hortic. Sci., 108: 541-544. Lakso, A.N. and Musselman, R.C., 1976. Effects of cloudiness on interior diffuse light in apple trees. J. Am. Soc. Hortic. Sci., 101: 642-644. Marini, R.P. and Marini, M.C., 1983. Seasonal changes in specific leaf weight, net photosynthesis, and chlorophyll content of peach leaves as affected by light penetration. J. Am. Soc. Hortic. Sci., 108: 600-605. Porpiglia, P.J. and Barden, J.A., 1981. Effects of pruning on penetration of photosynthetically active radiation and leaf physiology in apple trees. J. Am. Soc. Hortic. Sci., 106: 752-754. Robinson, T.L., Seeley, E.J. and Barritt, B.H., 1983. Effect of light environment and spur age on 'Delicious' apple fruit size and quality. J. Am. Soc. Hortic. Sci., 108: 855-861. Schaffer, B. and Gaye, G.O., 1989. Gas exchange chlorophyll and nitrogen content of mango leaves as influenced by developmental light environment. HortScience, 24: 507-509. Syvertsen, J.P., 1984. Light acclimatization in citrus leaves. II. CO2 assimilation and light, water, and nitrogen use efficiency. J. Am. Hortic. Sci., 109: 812-817. Syvertsen, J.P. and Smith, M.L., 1984. Light acclimatization in citrus leaves. I. Changes in physical characteristics, chlorophyll, and nitrogen content. J. Am. Soc. Hortic. Sci., 109: 807-812. Whiley, A.W., 1984. Crop management - a review. Proceedings of the First Australian Mango Research Workshop, Cairns, Queensland, CSIRO, Melbourne, pp. 196-201. Young, T.W. and Sauls, J.W., 1981. The mango industry in Florida. Fla. Coop. Ext. Serv., Univ. of Florida, Gainesville, FL, 70 pp.