Assessing the Effect of Spotted Tentiform Leafminer Injury to Apples- An oral presentation for the Centennial Conference of the American Society for Horticultural Science October 2003, Providence, Rhode Island, USA(2.8MB)

Carbon Balance Dynamics to Intergrate Whole Tree Physiology and Cultural Practices- An oral presentation for the Department of Horticulture at National Taiwan University May 27, 2002 (4MB)

Physiological Effect of Summer Pruning in Apple Trees-An oral presentation for Great Lakes Fruit Workers Conference November 30, 2000, Ithaca, New York, USA (250KB)

Summer Pruning and Re-exposure Effects on Leaf and Whole Canopy Gas Exchange in Apple Trees-An oral presentation for the 7th International Symposium on Orchard and Plantation Systems February 2000, Nelson, New Zealand (presented by Dr. Alan N. Lakso)

Summer Pruning Effects on Leaf and Whole Canopy Gas Exchange in Apple Trees-An oral presentation for the 96th International Conference of the American Society for Horticultural Science June 1999, Minneapolis, Minnesota, USA

Summer Pruning Effects on Canopy, Root System, and Integral Carbohydrate Balance in Apple Trees-A grant proposal submitted to the Arthur Boller Apple Research Grants 1999

Summer Pruning Effects on Canopy, Root System, and Integral Carbohydrate Balance in Apple Trees

Summer pruning is commonly used in the modern apple culture system in New York State to control tree size and increase the light penetration into inner canopy to improve fruit color. However, summer pruning may reduce fruit size, yield and the consequently commercial profit. This effect is probably due to the decrease in carbohydrate supply after sizable quantities of leaf area are removed by summer pruning. Our prior studies showed that a significant decrease in whole-canopy net carbon dioxide exchange rate can be induced by a commercial pruning severity. However, the inconsistent influence on fruit growth in our studies suggested that the reproductive growth did not response immediately to the decrease in carbon supply. Based on the concept of carbohydrate balance we hypothesize that other carbohydrate sinks such as root system, trunk, and carbon reserves may be more sensitive to summer pruning but may require successive years of summer pruning to reduce tree vigor and productivity. Therefore, it is necessary to exam many components of carbohydrate supply/demand to get a integrated overview of summer pruning effects. This proposed research will examine the influences of summer pruning on root system growth, canopy photosynthesis, and whole-plant respiration to estimate the short and long term effects of summer pruning . Our goal is to develop a simulation model to integrate and quantify the effects of this pruning practice into the production system to maintain sustainability and profitability of commercial apple management.

Objectives

The objectives of this proposed research are:
1) To evaluate the effect of summer pruning on each component of carbohydrate supply and demand including whole-canopy photosynthesis, whole-plant respiration, carbohydrate reserve, fruit growth and quality, and the growth of root system.
2) To provide information for estimating the long-term effects of summer pruning on integral carbohydrate balance and productivity
3) To develop a simulation model for regulating annual summer pruning practice based on the tree vigor and cropping level to maintain a higher sustainability and profitability.

Rationale and Significance

Fig. 2. The decreases in whole-canopy net carbon exchange rate (NCER) were approximately proportional to pruning severity and percentage leaf removal. (1998 summer pruning experiment result)

Summer pruning has become a routine practice in modern apple orchard management to improve fruit color and control tree size. This is especially important for varieties grown where the weather is not ideal for color development, such as New York State (Fig.1). Because exposure to sun light is important for fruit color development, by removing extension shoots from the outer canopy, summer pruning increases light penetration into the canopy and to the fruit, hence increases the fruit color and percentage of well-colored fruit number. On the other hand, the removal of extension shoots with large vigorous and well exposed leaves is expected to reduce the overall carbon dioxide assimilation by the tree. This would be a disadvantage for fruit growth if the carbohydrate demand is high, i.e. when the crop load is high, resulting in smaller fruit size or yield reduction. Our previous studies in 1998 have shown that the re-exposure of shading leaves after summer pruning did not functionally compensate for the reduction in carbohydrate supply lost from the removal of extension shoots and leaves. The decreases in whole-canopy net carbon exchange rate (NCER) were approximately proportional to pruning severity and percentage leaf removal (Fig. 2). However, data from our studies show the influence of summer pruning on fruit growth in the same year is somewhat ambiguous and did not fully reflect the decrease in NCER. Based on the carbohydrate balance concept, this result suggests that not only fruit but other carbohydrate sinks should also be affected by the reduction in carbon supply after summer pruning. Therefore, we hypothesize that the removal of extension shoots and leaves by summer pruning reduces the whole-tree respiration, carbon reserves, trunk and root system growth. In consequence, although summer pruning may not affect fruit growth in the same growing season, its influence on vegetative growth and flower bud development are probably additive after successive summer pruning practices. Summer pruning that reduces canopy NCER will likely become significant on next year or long-term tree vigor and productivity. Maintaining a constant annual cropping and stable fruit quality is a important issue for sustainable management of a modern commercial orchard. By analyzing each component in the carbohydrate supply/demand the proposal will provide information for integrating the influences of summer pruning and optimizing this practice.

Literature Review

Light exposure is a essential factor for red color development of apple fruit. Increasing light penetration into the canopy has been shown to increase red coloring (Preston and Perring, 1974; Taylor and Ferree, 1984). Early studies on summer pruning have been reviewed by Marini and Barden (1987) and Saure (1987). The major functions of summer pruning have been reported to control tree size and to increase canopy openness, thus increase penetration of sunlight into the tree canopy (Ferree, 1979; Taylor and Ferree, 1984). However, it can also reduced orchard leaf are index (LAI) and whole-canopy light interception (Palmer et al., 1992) . Re-exposure of shading leaves did not functionally substitute for the extension shoots and leaves removed by summer pruning (Lakso et al., 1989). As a result, carbohydrate reserves are thought to be reduced by summer pruning, thus suppressing root, shoot, trunk growth, fruit size and final yield (Taylor, 1978; Marini and Barden, 1982; Taylor and Ferree, 1984) . However, the results maintained unclear, and some conflicting results have been reported. Studies on yield/quality and stress responses in apples suggest that the carbohydrate supply/demand balance may provide the best indicator of tree response to summer pruning (Francesconi et al., 1996 a, b; Lakso et al., 1996). If the carbohydrate demand of fruit growth can not be satisfied by the supply after summer pruning, reduction in fruit size and yield may occur. The sensitivities of each component in carbohydrate demand may depend on their sink strength and the competition between each component. Summer pruning has also been found to affect fruit quality. Several reports indicated that soluble solids content was depressed following summer pruning (Greene and Lord, 1983, Morgan et al., 1984). In other studies, fruit storage quality was increased by summer pruning (Preston and Perring, 1974; Boon, 1980). Young tree experiments show root dry weight was decreased by summer pruning (Myers and Ferree, 1983). Decrease in root growth by a high crop load from container-grown trees studies (Ebert, 1992; Ebert and Lenz, 1991) indicating that root system is relatively a weak carbohydrate sink provides the evidence that root may be more sensitive and significant in response to summer pruning. The restriction on the root system may became a feedback limitation on return cropping, although this has not been determined on mature cropping trees in the field where tree size may provide some buffering of these effects.

Methodology

Fig. 3. Minizhizotron and video system for root growth observation.

Material and pre-summer pruning easurements-twenty-year-old, slender spindle 'Empire' trees with similar bloom density and vigor will be selected in May, 1999. Crop load of each tree will be hand-regulated after fruit set to maintain a final target range. Twenty fruits at different canopy location on each tree will be labeled for monitoring fruit growth. Total leaf area of each tree will be estimated when the canopies are fully expanded before summer pruning. Four clear root observation tubes will be mounted around the rhizosphere of each tree before new roots start growing in the early season for observing root growth (Fig. 3; Caldwell and Virginia, 1991; McMichael and Taylor, 1987). In early August right before summer pruning is applied, light interception of each tree will be measured by a ceptometer line light sensor. Fish-eye photography will be used for analyzing light penetration into different canopy locations. Whole-canopy photosynthesis and dark respiration will be measured by whole-canopy balloons and a automated gas exchange system (Fig. 4; Lakso et al., 1999). Root growth will be monitored by a video periscopy. Root/soil respiration will be measured by inverted chambers and gas exchange system.

Fig. 4. NCER is measured with whole-canopy balloon gas exchange system before and after pruning treatments.

Pruning treatments-Trees will be randomly assigned to different pruning severity treatments in early August when the extension shoots reach maximum length and the leaves are fully expanded. The pruning severity is determined by the proportion of extension shoots thinned out from the canopy. Removed shoots and leaves from each tree will be collected to measure the percentage of total leaf area reduced by summer pruning

Post-summer pruning measurements-Measurements mentioned earlier will be repeated right after summer pruning and later in the growing season to monitor the change and response of each component to the pruning treatment. Fruit quality analysis-Fruits will be harvested on early or October for fruit number and total yield. Twenty fruits will be randomly sampled right after harvest for quality analysis including fruit weight, color, firmness, starch and soluble solids content. Twenty other fruits will be cold stored at least 4 months to exam the internal browning and the other storage characteristics.

Return cropping and root growth-The number of flower clusters and final cropping on each tree will be recorded in May to June, 2000. Re-growth of the root system will also be measured in the early growing season. Development of a simulation model-Information collected from this year and previous experiments will be integrated into the simplified dry matter production model developed by Lakso and Johnson (1990) with "Stella" dynamic simulation automatic programming language to exam the feasibility of quantifying and predicting summer pruning effects and with the simulation model.

Budget does not include costs of the extensive equipment used in this study or the labor of the lab supervisor supporting this complex study).

Literature Cited

Boon, J. van der. 1980. Prediction and control of bitter pit in apples. II. Control by summer pruning, fruit thinning, delayed harvesting and soil calcium dressings. J. Hort. Sci. 55:313-321.

Caldwell, M.M. and R.A. Virginia. 1991. Root systems. p. 367-398. In: R. W. Pearcy, J. Ehleringer, H. A. Mooney and P. W. Rundel. Plant physiological ecology, field methods and instrumentation. Chapman and Hall, London.

Ebert, G. 1992. The root respiration of apple trees. II. Influence of endogenous factors. Erwerbsobstbau 34:165-168. (in German).

Ebert, G., and F. Lenz. 1991. Annual course of root respiration of apple trees and its contribution to the CO2 balance. Gartenbauwissenschaft 56:130-133. (in German).

Ferree, D.C. 1979. Current experiences with summer pruning. Proc. N.Y. State Hort. Soc. 124:77-79.

Francesconi, A.H.D., A.N. Lakso, J.P. Nyrop, J.Barnard, and S.S. Denning. 1996a. Carbon balance as a physiological basis for the interactions of European red mite and crop load on 'Starkrimson Delicious' apple trees. J. Amer. Soc. Hort. Sci. 121:959-966.

Francesconi, A.H.D., C.B. Watkins, A.N. Lakso, J.P. Nyrop, J. Barnard, and S.S. Denning. 1996. Interaction of European red mite and crop load on maturity and quality, mineral concentration, and economic value of 'Starkrimson Delicious' apples. J. Amer. Soc. Hort. Sci. 121:967-972.

Greene, D.W., and W.J. Lord. 1983. Effect of dormant pruning, summer pruning, scoring, and growth regulators on growth, yield, and fruit quality of 'Delicious' and 'Cortland' apple trees. J. Amer. Soc. Hort. Sci. 108:590-595.

Lakso, A. N., S.S. Denning, R.M. Piccioni, F. Sottile and J.Costa Tura. 1999. An automated "balloon" chamber system for continuous measurement of gas exchange of apple trees. Acta Hort. (in press).

Lakso, A.N., and R.S. Johnson. 1990. A simplified dry matter production model for apple using automatic programming simulation software. Acta Hort. 276:141-148.

Lakso, A.N., G.B. Mattii, J.P. Nyrop, and S.S. Denning. 1996. Influence of European red mite on leaf and whole-canopy carbon dioxide exchange, yield, fruit size, quality, and return cropping in 'Starkrimson Delicious' apple trees. J. Amer. Soc. Hort. Sci. 121:954-958.

Lakso, A.N., T.L. Robinson, and S.G. Carpenter. 1989. The palmette leader: a tree design for improved light distribution. HortSciecne 24:271-275.

Marini, R.P., and J.A. Barden. 1982. Effects of summer v.s. dormant pruning and NAA treatment on growth of one and two year old apple trees. J. Amer. Soc. Hort. Sci. 107:604-607.

Marini, R.P. and J.A. Barden. 1987. Summer pruning of apple and peach trees. Hort. Reviews 9:351-375.

McMichael, B.L. and H.M. Taylor. 1987. Applications and limitation of rhizotrons and minirhizotrons. p. 1-13. In: H. M. Taylor. Minirhizotron observation tubes: methods and applications for measuring rhizosphere dynamics. Amer. Soc. Agron. Spec. Publ. 50, Madison, WI.

Morgan, D.C., C.J. Stanley, R. Volz, and I.J. Warrington. 1984. Summer pruning of 'Gala' apple: the relationships between pruning time, radiation penetration, and fruit quality. J. Amer. Soc. Hort. Sci. 109:637-642.

Myers, S.C., and D.C. Ferree. 1983. Influence of summer pruning and tree orientation on net photosynthesis, transpiration, shoot growth, and dry-weight distribution in young apple trees. J. Amer. Soc. Hort. Sci. 108:4-9.

Palmer, J.W., D.J. Avery, and S.J. Wertheim. 1992. Effect of apple tree spacing and summer pruning on leaf area distribution and light interception. Sci. Hort. 52:303-312.

Preston, A.P., and M.A. Perring, 1974. The effect of summer pruning and nitrogen on growth, cropping, and storage quality of Cox's Orange Pippin apple. J. Amer. Soc. Hort. Sci. 106:752-754.

Saure, M.C. 1987. Summer pruning effects in apple - a review. Scientia Hort. 30:253-282.

Taylor, B.H. 1978. The influence of summer pruning on photosynthesis, transpiration dry weight and leaf area of young Delicious apple trees. MS Thesis, Ohio State Univ., Columbus.

Taylor, B.H., and D.C. Ferree. 1984. The influence of summer pruning and cropping on growth and fruiting of apple. J. Amer. Soc. Hort. Sci. 108:19-24.

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