Journal APS Oct 2017

OCTOBER 2017

Volume 71

Number 4

AMERICAN POMOLOGICAL SOCIETY F ounded in 1848 I ncorporated in 1887 in M assachusetts

2017-2018

PRESIDENT M. WARMUND

FIRST VICE PRESIDENT M. PRITTS

SECOND VICE PRESIDENT N. BASSIL

RESIDENT AGENT MASSACHUSETTS W. R. AUTIO EDITOR R. P. MARINI

SECRETARY T. EINHORN

EXECUTIVE BOARD

P. HIRST Past President

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M. PRITTS 1 st Vice President

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ADVISORY COMMITTEE

2015-2018 L. KALCSITS P. CONNER L. WASKO DEVETTER R. HEEREMA E. HELLMAN 2016-2019 R. MORAN E. GARCIA S. YAO M. EHLENFELDT D. BRYLA 2017-2020 BRENT BLACK GINA FERNANDEZ DAVID KARP IOANNIS MINAS SERA SERRA

CHAIRS OF STANDING COMMITTEES

Editorial R. PERKINS-VEAZIE Wilder Medal Awards J. CLARK

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Membership P. HIRST

Nominations P. HIRST

U. P. Hedrick Award E. FALLAHI

Website M. OLMSTEAD

Registration of New Fruit and Nut Cultivars K. GASIC & J. PREECE

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October 2017

Volume 71 CONTENTS

Number 4

Published by THE AMERICAN POMOLOGICAL SOCIETY Journal of the American Pomological Society (ISSN 1527-3741) is published by the American Pomological Society as an annual volume of 4 issues, in January, April, July and October. Membership in the Society includes a volume of the Journal. Most back issues are available at various rates. Paid renewals not received in the office of the Business Manager by January 1 will be temporarily suspended until payment is received. For current membership rates, please consult the Business Manager. Editorial Office: Manuscripts and correspondence concerning editorial matters should be addressed to the Editor: Richard Marini, 203 Tyson Building, Department of Plant Science, University Park, PA 16802-4200 USA; Email: richmarini1@gmail.com. Manuscripts submitted for publication in Journal of the American Pomological Society are accepted after recommendation of at least two editorial reviewers. Guidelines for manuscript preparation are the same as those outlined in the style manual published by the American Society for Horticultural Science for HortScience, found at http://c.ymcdn.com/sites/www.ashs.org/resource/resmgr/files/style_manual.pdf. Postmaster: Send accepted changes to the Business office. Business Office : Correspondence regarding subscriptions, advertising, back issues, and Society membership should be addressed to the Business Office, C/O Heather Hilko, ASHS, 1018 Duke St., Alexandria, VA 22314; Tel 703-836- 4606; Email: ashs@ashs.org Page Charges : A charge of $50.00 per page for members and $65.00 per page ($32.00 per half page) will be made to authors. In addition to the page charge, there will be a charge of $40.00 per page for tables, figures and photographs. Society Affairs : Matters relating to the general operation of the society, awards, committee activities, and meetings should be addressed to Michele Warmund, 1-31 Agriculture Building, Division of Plant Sciences, University of Missouri, Columbia MO 65211; Email:warmundm@missouri.edu. Society Web Site : http://americanpomological.org Root Architecture, Leaf Nutrient Levels and Photosynthesis of Columnar and Standard Apple Seedlings are different – Shaoxia Guo, Xin Sun, Yuanxia Liu, Jun Zhu, Lu Zhang, Hongyi Dai, and Yugang Zhang.......194 Correction.............................................................................................................................................................202 Thinning of Peach Trees using High-Pressure Water – John A. Cline.................................................................203 ‘Sweetie Pie’ Thornless Semi-Erect Blackberry – Stephen J. Stringer, Barbara J. Smith, Blair J. Sampson, Donna AMarshall-Shaw, and John J. Adamczyk, Jr. ..........................................................................................214 The Relationship Between Environmental Factors and Rootstock Growth Stage with Graft Success in Walnut – Burak Akyüz and Ümit Serdar .........................................................................................................220 Effects of Arbuscular Mycorrhizal Fungi and Phosphate-Solubilizing Fungus on the Rooting, Growth and Rhizosphere Niche of Beach Plum ( Prunus maritima ) Cuttings in a Phosphorus-deficient Soil – Zue M. Zai, Huan S. Zhang, and Zhen P. Hao ..........................................................................................226 ‘BRS RubraMoore’: A Fresh Market peach for Southern Brazil – Maria Do Carmo Bassols Raseira, Rodrigo Cezar Franzon, Ciro Scaranari, Nelson Pires Feldberg, and Marco Antȏnio Dalbó ...........................................236 Table Grape Cultivar Performance in Oregon’s Willamette Valley – Amanda J. Vance, Bernadine C. Strik, and John Clark .....................................................................................................................................................240 About the Cover: ‘Sweetie Pie’ Thornless Semi-Erect Blackberry......................................................................249 Performance of Three Pyrus Pear Rootstocks in Northeastern North America ‒ Jaume Lordan, Suzanne Blatt, Poliana Francescatto, Charles Embree and Terence L. Robinson................................................250 Instructions to Authors.........................................................................................................................................257

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Journal of the American Pomological Society 71(4): 194-202 2017

Root Architecture, Leaf Nutrient Levels and Photosynthesis of Columnar and Standard Apple Seedlings are different S haoxia G uo 1 , X in S un 2 , Y uanxia L iu 2 , J un Z hu 2 , L u Z hang 2 , H ongyi D ai 2 , Y ugang Z hang 2,3 * Additional index words: Columnar apple trees, root architecture, mineral elements, chlorophyll, photosynthetic rate, Malus x domestica Abstract The columnar apple tree is a valuable apple breeding resource, which differs from the standard apple tree in tree architecture. In this study, we used two-year-old F 1 seedlings of columnar and standard apple trees to study their differences in root architectures, nutrient uptake and photosynthesis. The results showed that 1) the numbers of root tips, forks and crossings of the columnar trees were significantly higher than those of the standard trees; 2) F 1 progenies of columnar genotypes had more average root tip numbers, total root lengths and root volumes than those of the two standard genotypes; 3) leaves of the columnar trees had significantly higher (1.77-2.34-fold) Ca, Mg, Fe, Zn and Cu concentrations than the leaves of standard trees, and macronutrient K concentration for standard trees was higher (1.03-1.1-fold) than for columnar trees; 4) leaves of the columnar trees had signifi- cantly higher chlorophyll a, chlorophyll b and chlorophyll a+b concentrations; 5) diurnal variations of both net photosynthetic rate (Pn) and transpiration rate (Tr) showed bimodal curves with a “siesta” phenomenon, and Pn and Tr of the two columnar genotypes were higher than those of the standard trees.

 The columnar apple tree is a valuable apple breeding resource and has many characters different from the standard apple tree, such as natural single stem shape, compact structure, dwarf main stem, short internodes and fewer long-branches among other notable features. We previously conducted a series of prelimi- nary experiments on columnar apple breeding (Dai et al., 2003) and studied the anatomical structures of roots, stems and leaves (Zhang et al., 2011b; Zhang et al., 2012a) and expres- sion of genes related to its columnar features (Zhang et al., 2012b; Wang et al., 2014; Han et al., 2012; Bai et al., 2012).  Plant root morphology and architecture are closely related to water absorption and miner- al uptake, and roots influence the tree structure

and mechanical support for the tree (Li et al., 2016; Zhao et al., 2015; Smith et al., 2012). Many scholars have studied the root architec- tures and mineral absorption of maize (Cai et al., 2014), bluegrass (Sullivan et al., 2000) and wheat (Dong et al., 1995). In addition, the root architecture of white clover is also affected by arbuscular mycorrhizal fungi (Wu et al., 2014). The mineral nutrition of apple trees in- fluences fruit quality and growth, and different rootstocks and interstocks have a major effect on nutrient content of apple fruits (Chen et al., 2010; Ma et al., 2010; Xue et al., 2012; Zhang et al., 2011a; Zhang et al., 2014). The colum- nar tree is a type of apple tree with high pho- tosynthetic efficiency and is suitable for high- density planting and orchard mechanization,

1 College of Landscaping and forestry, Qingdao Agricultural University, Qingdao, 266109; 2 College of Horticulture, Qingdao Agricultural University, Qingdao, 266109; 3 Qingdao Key Laboratory of Genetic Improvement and Breeding in Horticultural Plants, Qingdao, 266109; * Corresponding author: Email: ygzhang@qau.edu.cn Foundations: National Natural Sciences Foundation of China (3137203), China Agriculture Research System Foundation (CARS-28), Taishan Scholar Constructive Foundation and Qingdao Scientific Research Foundation (15-9-2-99-nsh).

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mmol·m -2 ·s -1 ), stomatal conductance (Gs, mmol·m -2 ·s -1 ) and intercellular CO 2 concen- tration (Ci, μmol·mol -1 ) were measured using a CIRAS-3 portable photosynthesis meter (PP SYSTEMS). Following gas exchange measurements, half of the marked leaves were used to measure chlorophyll concentra- tion, and the other half were used to measure mineral elements.  Determination of chlorophyll concentra- tion. Pigments were extracted from 0.5 g of marked leaves using 80% acetone and a suit- able amount of CaCO 3 . Chlorophyll a and chlorophyll b concentrations were measured using a UV-2100 spectrophotometer as pre- viously reported (Sun et al., 2010).  Measurement of leaf mineral elements. Af- ter drying at 80 ⁰ C in an oven for three days, 0.5 g of marked leaves was used to measure P, K, Ca, Mg, Fe, Mn, Cu, Zn and Na con- centrations using microwave digestion with HNO 3 / HCIO 4 solution followed by induc- tively coupled plasma atomic emission spec- trometry (ICP-OES) (Wei et al., 2011). To- tal N concentration was measured using the Kjeldahl method (Zhang et al, 2014).  Root architecture analysis. Six seedlings of ACo, ASt, BCo and BSt were selected in mid-June. Three days later after watering, they were harvested with intact root systems using a spade. After washing with distilled water, the intact root images were obtained using the flatbed scanner of V700/WinRHI- ZO analyzer (Seiko Epson Company) and analyzed using WinRHIZO root analysis software to obtain the root architecture pa- rameters including length, area, volume, and number of root tips, number of branches and number of crossings.  Statistical analyses. Statistical analyses were performed using the SAS system soft- ware (SAS 9.3, SAS Institute, Cary, N.C.). Data for most response variables were ana- lyzed with a one-way analysis of variance (ANOVA). Photosynthesis data were ana- lyzed with repeated measures ANOVA with PROC MIXED and LSmeans were com- pared with DIFF.

which is in line with the patterns and trends of high-density planting. In this study, we used two types of hybrid columnar apple seedlings and two types of standard apple seedlings to evaluate differences in root architecture, min- eral uptake and photosynthesis, with the hope of further understanding the relationship be- tween tree architecture and tree physiological metabolism. Materials and Methods  Materials. The experimental materials were 2-year-old hybrid seedlings of ACo, ASt, BCo and BSt, which were planted in the greenhouse of Jiaozhou Experiment Station of Qingdao Agricultural University (JESQAU). Seedlings were grown in 20 cm × 30 cm nutrition pots, spaced 20 cm between pots, and the media was 2 natural soil: 1turfy soil: 1earlite: 1 vermiculite (by volume), and were fertilized with 50-80 g urea fetilizer per tree for three times during the growing season. ACo was the columnar F 1 progeny of ‘Shinsekai’ and ‘94-12’; BCo was the columnar F 1 progeny of ‘Golden De- licious’ and ‘94-12’; ASt was the standard F 1 progeny of ‘Shinsekai’ and ‘94-12’; and BSt was the standard F 1 progeny of ‘Gold- en Delicious’ and ‘94-12’. The ‘94-12’ was a columnar apple strain bred by our group. ‘Shinsekai’ and ‘Golden Delicious’ are stan- dard apple cultivars. After stratification, 1023 hybrid seeds of two combinations (A and B) were sown in the greenhouse. Two years later, when the seedlings could be dis- tinguished as columnar or standard, a total of 6 seedlings per progeny were randomly selected and marked for the study. There- fore the experimental design was considered completely randomized.  Determination of photosynthetic param- eters. Using the selected 24 seedlings, the fifth functional leaf from the top of each seedling was marked and measured every hour from 800 – 1800HR on three sunny days in the mid-June. The photosynthetic parameters including net photosynthetic rate (Pn, μmol·m -2 ·s -1 ), transpiration rate (Tr,

Figure.1 Photographs (top) and scans (bottom) of root systems of four progenies of columnar and standar apple trees

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Fig. 1. Photographs (top) and scans (bottom) of root systems of four progenies of columnar and standard apple trees.

Results  Root architecture appearance. Root im- ages clearly show differences in the root ar- chitectures between the standard and colum- nar apple trees (Fig.1). The two columnar F 1 progenies ACo and BCo (Figure 1-A, 1-C) had obviously more lateral roots and fibrous roots than the standard F 1 progenies ASt and BSt (Figure. 1-B, 1-D), although their tap- roots were not different. These phenomena in the fibrous roots were more clear in the scan

images of root system (Figures A-2, B-2, C-2 and D-2), indicating that columnar apple trees had more developed fibrous roots than the standard apple trees.  Root architecture parameters. The two co- lumnar F 1 progenies had significantly more root tips, forks and crossings than the two standard F 1 progenies (Table 1). The aver- age numbers of root tips of the two columnar F 1 progenies ACo and BCo were 1.22- and 2.52-fold greater than those of the two stan-

1

Table 1. Numbers of the root tips, forks and crossings of roots for four progenies of columnar and standard apple trees. Combination of Root tip Root fork Root crossing F 1 progeny F 1 progeny type number number number ‘Shinsekai’ Columnar (ACo) 3873.7b z 9072.5b 1389.2b × ‘94-12’ Standard (ASt) 3175.8d 6671.5d 1039.0d ‘Golden Delicious’ Columnar (BCo) 5477.0a 13018.0a 2034.4a × ‘94-12’ Standard (BSt) 3598.1c 8429.2c 1277.2c Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD.

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dard F 1 progenies ASt and BSt, respectively. The number of root tips was highest for BCo (5477.0), and lowest for ASt (3175.80). The numbers of forks and crossings were propor- tional to the number of root tips among the same type of apple trees, and BCo had the highest number of forks and crossings among the four types.  The total root length also differed signifi- cantly for columnar and standard trees (Fig. 2). The total root lengths of the two colum- nar progenies ACo and BCo were 1.18- and 1.59-fold greater than the two standard F 1 progenies ASt and BSt, respectively. The to- tal root length was highest for BCo, (1833.76 cm), and lowest for ASt (1020.11cm). Of the four types of seedlings, the length of roots with diameter of 0-0.5 mm accounted for 73.8%, 73.9%, 75.7% and 75.1% of the total root length for ACo, ASt, BCo and BSt, re- spectively, whereas the length of roots with diameter greater than 4.5 mm accounted for only 1.0-2.1% of the total root length.

The root surface areas of columnar and stan- dard apple trees were significantly different (Fig. 3). The root surface areas of the two columnar progenies ACo and BCo were 1.16- and 1.45-fold greater than the two stan- dard progenies ASt and BSt, respectively. The root surface area of BCo was the largest (290.04 cm 2 ), and that of ASt was the small- est (188.79 cm 2 ). Although the four types of seedlings had varied root surface areas in dif- ferent ranges of root diameter, their perfor- mance was similar. In other words, the sur- face of roots with diameters of 0-0.5 mm was the largest, followed in turn by the roots with diameter of greater than 4.5 mm, 0.5-1.0 mm and 4.0-4.5 mm.  Root volume was larger for columnar trees than for standard trees (Fig. 4). The root vol- umes of the two columnar progeniesACo and BCo were 1.16- and 1.46-fold higher than for the two standard progenies ASt and BSt. BCo had the greatest root volume (18.10 cm 3 ), and BSt had the least root volume (12.39 cm 3 ).

Figure.2 Length of roots with different diameters for four progenies of columnar and standard apple trees.

Fig. 2. Length of roots with different diameters for four progenies of columnar and standard apple trees.

Figure.3 Surface area of roots with different diameters for four progenies of columnar and standard apple trees.

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Fig. 3. Surface area of roots with different diameters for four progenies of columnar and standard apple trees. Figure.4 Volume of different diameter roots of four progenies of columnar and standard apple trees.

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Fig. 4. Volume of different diameter roots of four progenies of columnar and standard apple trees.

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Table 2. Leaf mineral concentrations for four progenies of columnar and standard trees F1 N P K Ca Mg Fe Mn Zn Cu progeny (g·Kg -1 ) (mg·Kg -1 ) type ACo 4.70b z 1.00b 1.47b 5.31b 0.57a

Na

65.27b 27.40c 16.57a 6.60b 35.04bc 60.03c 23.17d 14.45c 5.71c 30.33c 70.44a 49.59a 16.67a 7.90a 36.33b 61.07c 46.71b 14.79bc 6.29bc 41.48a

ASt

3.83c 1.43a 1.51a 2.27d 0.41b

BCo 4.96b 1.43a 1.34c 6.88a 0.56a

BSt

5.71a 1.43a 1.47b 3.89c 0.38b

Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD.

Leaf chlorophyll concentrations. Chloro- phyll concentrations were significantly in- fluenced by tree architecture type (Table 3). The two columnar progenies had much higher chlorophyll a, chlorophyll b and chlo- rophyll a+b concentrations than the two stan- dard progenies. In addition, the external leaf morphology and color also reflect the differ- ences between columnar and standard trees. The average leaf mass and thickness were greater for columnar trees than for standard trees (data not shown) and the leaves were also darker green for columnar trees than for standard trees.  Diurnal variation of net photosynthetic rate (Pn) and transpiration rate (Tr). During the growing season, the diurnal net photo- synthesis of new leaves showed similar bi- modal curves with a “siesta” phenomenon at noon in all progeny (Table 4). Pn first peaked at1100HR, then declined until 1300-1400HR, and started to increase again, reaching a sec- ond peak at 1500HR. In the diurnal variation of the day, the two columnar progenies had significantly higher Pn than the two standard

The volume of roots with diameter greater than 4.5 mm accounted for 67.6%, 69.2%, 58.8% and 52.5% of the total root volume of ACo, ASt, BCo and BSt, respectively. In addition, the root volume of columnar trees of the same diameter was 0.02-0.63 times greater than that of the standard trees.  Leaf mineral concentrations. The leaf mineral concentrations varied significantly between different types of apple trees (Table 2). The trends of macronutrients Ca and Mg as well as trace elements Fe and Cu were similar, with significantly higher concentra- tions in columnar leaves than in standard leaves. Ca concentration in columnar leaves was 1.77-2.34 times greater than in standard leaves. Mn and Zn concentrations were also higher in columnar leaves than in standard leaves. By contrast, the K concentration in standard leaves was 1.03-1.1-fold higher than in columnar leaves. The concentrations of N, P and Na were not significantly influenced by tree type. The order of N concentration was BSt> BCo> ACo> ASt whereas the order of P content was ASt = BCo = BSt> ACo.

Table 3. Leaf chlorophyll concentrations for four progenies of columnar and standard apple trees Combination of F 1 F 1 progeny type Chlorophyll a Chlorophyll b Chlorophyll a+b progeny conc. (mg . g -1 ) conc. (mg . g-1) conc. (mg·g -1 ) ‘Shinsekai’ Columnar (ACo) 1.352±0.069b z 0.447±0.016a 1.886±0.065b × ‘94-12’ Standard (ASt) 0.987±0.122d 0.301±0.048c 1.272±0.213d ‘Golden Delicious’ Columnar (BCo) 1.401±0.148a 0.481±0.035a 1.911±0.183a × ‘94-12’ Standard (BSt) 1.190±0.138c 0.373±0.045b 1.591±0.165c Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD.

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Table 4. Hourly photosynthetic rates (Pn, μmol·m -2 ·s -1 ) of four progenies of columnar and standard apple trees F1 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 progeny ACo 7.9±0.59b z 9.8±0.68c 14.4±0.84b 15.7±1.47b 13.8±1.08b 8.3±0.63b 6.8±0.48c 10.8±0.978c 7.7±0.57b 6.2±0.72b 4.8±0.38a ASt 5.3±0.33d 8.6±0.86d 11.3±0.63c 12.9±1.09c 11.9±1.19c 6.8±0.78c 6.4±0.54c 9.5±0.95d 6.6±0.46c 5.1±0.51c 3.3±0.33bc BCo 9.1±0.53a 12.8±0.74a 15.3±1.49a 18.6±1.38a 15.3±0.89a 12±1.40a 10.6±0.61a 15±1.37a 8.9±0.52a 7.6±0.44a 3.8±0.22b BSt 6.2±0.36c 11.1±0.64b 14.2±0.82b 15.2±0.98b 13.9±0.81b 8.2±1.78b 7.6±0.54b 11±1.64bc 8.5±0.49a 7.4±0.43a 2.9±0.17c Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD. Table 5. Hourly transpiration rates (Tr, mmol·m -2 ·s -1 ) of leaves of four progenies of columnar and standard apple trees F1 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 progeny 2.8±0.26a 2.1±0.19b 1.5±0.11c ASt 2.4±0.23c 2.9±0.19c 3.2±0.27c 3.5±0.25d 3.1±0.22b 2.4±0.21c 2.1±0.17d 3.0±0.20c 2.1±0.14bc 2.1±0.18b 1.4±0.10c BCo 3.1±0.27a 3.6±0.35a 4.0±0.18a 4.6±0.35a 3.6±0.16a 3.0±0.23a 2.9±0.26a 3.6±0.26a 2.8±0.25a 2.2±0.20a 1.8±0.15b BSt 2.9±0.28ab 3.0±0.20c 3.5±0.22 b 3.9±0.29bc 2.7±0.26c 2.6±0.27b 2.4±0.18bc 3.2±0.26bc 2.3±0.20b 2.0±0.16b 2.0±0.17a Z Means within columns followed by common letters do not differ at the 5% level of significance, by LSD. ACo 2.7±0.28b z 3.3±0.13b 3.7±0.35b 4.2±0.20b 3.6±0.24a 2.8±0.19ab 2.6±0.22b 3.3±0.23b

progenies. In addition, the decrease of Pn from the first peak to the “siesta” at noon was slower for columnar trees than for standard trees, and most obvious in BCo.  Net photosynthetic rate is usually positive- ly related to transpiration rate. The diurnal Tr followed a similar pattern as Pn for both columnar and standard apple trees, showing bimodal curves with a “siesta” phenomenon (Table 5). In the diurnal variation of the day, the two columnar progenies had higher Tr than the two standard progenies. Discussion  The columnar apple tree is a valuable re- source for genetic improvement of new ap- ple cultivars due to its special architecture, which is important for crop yield, quality, and cultivation. Tree architecture also affects root architecture, mineral uptake and pho- tosynthesis of apple trees. Compared with standard trees, columnar trees had more fi- brous roots. The average number of root tips and total root length of columnar trees were 1.22-1.52-fold and 1.18-1.59-fold greater than those of standard apple trees, respec- tively. The root tips contain a large amount

of root hairs and are important for absorp- tion of water and mineral elements. The fact that columnar trees had more root tips provides a foundation for its high efficient absorption of mineral elements. Analyses of root and stem architecture showed that the diameters of root and stem xylem vessels of the columnar trees were greater than those of the standard apple trees. In addition, co- lumnar trees had normal stem xylem vessel morphology, whereas the standard trees had more deformed stem xylem vessels (Zhang et al., 2012a). Stem xylem vessels with larger diameter provide a basis for efficient trans- port of mineral elements in columnar trees (Zhang et al., 2011b). Many factors affect the absorption and uptake of mineral nutri- tion in plants (Zouar, et al., 2016; Quirantes, et al., 2016; Li et al., 2016). The leaf min- eral Ca, Mg, Fe, Cu, Mn and Zn concentra- tions in the columnar trees were significantly higher than those in the standard trees, which might be related to the root architectures as well as the root and stem xylem vessels. In addition, relatively wider xylem vessels in columnar trees may have also enhanced the upward transportation ability, thus result-

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Literature Cited Bai, T.H., Y.D. Zhu, F. Fern á ndez-Fern á ndez, J. Keule- mans, S. Brown, and K.N. Xu. 2012. Fine genetic mapping of the Co locus controlling columnar growth habit in apple. Mol. Genet. and Genomics . 287: 437-450. Cai, H.G., J.Z. Liu, X.Z. Zhang, X.G. Yan, H.X. Zhang, J.C. Yuan, J.H. Gai, and J. Ren. 2014. Root morphology and its response to planting density in different genotypes with root architecture. J. Maize Sci. . 22: 81-85. Chen, X.S., M.Y. Han, G.L. Su, F.Z. Liu, and H.R. Su. 2010. Discussion on today’s world apple industry trends and the suggestions on sustainable and ef- ficient development of apple industry in China. J. Fruit Sci. 27: 598-604. Dai, H.Y., C.H. Wang, B. Chi, J. Zhu, R. Wang, G.X. Li, and L.L. Zhuang. 2003. Report on breeding co- lumnar apple varieties. J. Fruit Sci. 20: 79-83. Dong, B., Z. Rengel, and R.D. Graham. 1995. Root morphology of wheat genotypes differing in zinc ef- ficiency. J. of Plant Nutr. 18: 2761-2773. Fan, W.G. and H.Q. Yang. 2014. Response of root architecture, nutrients uptake and shoot growth of Malus hupehensis seedling to the shape of root zone. Scientia Agr. Sinica 47: 3907-3913. Han, F.,H.Y. Dai, and Y.G. Zhang. 2012. Cloning and bioinformatic analysis of MdSCR gene of GRAS gene family in columnar apple. J. of Qingdao Agr. Univ.. 29: 196-200, 2012. Li, X.X., Z.S. Zeng, and H. Liao. 2016. Improving crop nutrient efficiency through root architecture modifications. Journal of Integrative Plant Biol. 3:193-202. Ma, B.K., J.Z. Xu, and J.S. Sun. 2010. Consideration for high density planting with dwarf rootstocks in apple in China. J. Fruit Sci. 27: 105-109. Quirantes, M., F. Calvo, E. Romero, and R. Nogales. 2016. Soil-nutrient availability affected by dif- ferent biomass-ash applications. J. Soil Sci. Plant Nutr.1:159-163. Smith, S. and I.D. Smet. 2012. Root system architec- ture, insights from Arabidopsis and cereal crops. Philosophical Trans. Royal Soc. B . 367: 1441-1452. Sullivan, W.M., Z.C. Jiang, and R.J. Hull. 2000. Root morphology and its relationship with nitrate uptake in Kentucky bluegrass. Crop Sci. 40: 765-772. Sun, S., Z. Zhang, M. Lu, and G.M. Xing. 2010. Effects of cadmium stress on photosynthesis and active oxy- gen metabolism in the leaves of small watermelon seedlings. J. Nuclear Agr. Sci. . 24: 389-393. Wang, C.H., M.D. Bai, Y.K. Tian, and W. Tian. 2014. Characterization of two genes encoding cytochrome P450 mono-oxygenases involved in gibberellin bio- synthesis in apple ( Malus × domestica Borkh.). J.

ing in increased concentrations of leaf Ca, Mg, Fe, Cu and other mineral elements. By contrast, leaf K concentration in the colum- nar trees was significantly lower than that in the standard apple trees, which was possibly related to its own regulation. The detailed underlying mechanisms need to be further studied. The concentrations of N and P were similar for both tree types in this study. Xiao et al. (2014) showed that root architecture of young peach trees was significantly associ- ated with nitrogen metabolism. Sullivan et al. (2000) showed that the blue-grass roots with larger surface area can absorb more nitrogen. Fan and Yang (2014) showed that Malus hu- pehensis seedlings with more lateral roots could absorb more P and K. Our results were inconsistent with the above-mentioned stud- ies, presumably because of the difference in the test materials.  Chlorophyll concentrations were closely related to photosynthesis. The concentra- tions of chlorophyll a, chlorophyll b as well as chlorophyll a+b were significantly higher in columnar leaves than in standard leaves, in agreement with higher Pn and Tr rates in columnar leaves than in standard leaves. Co- lumnar trees have higher luminous efficiency and leaf area index than standard trees (Zhang et al., 2011b). Higher Pn and Tr not only in- creased the transpiration force of columnar leaves, but also enhanced the absorption of water and mineral elements. Mg, Fe, Zn, Cu, Mn and other elements were closely related to photosynthesis. Deficiencies of these ele- ments can significantly inhibit photosynthe- sis, which was also proved by the correlation between the concentrations of Mg, Fe, Zn, Cu, and Mn with chlorophyll concentrations (data not shown).  Different types of apple trees have differ- ent root architectures, which affect mineral uptake and leaf photosynthesis. The root sys- tem and leaves in columnar apple trees leads to more efficient photosynthesis as well as higher absorption and utilization of mineral elements than those of the standard apple trees.

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eral contents and fruit qualities of Fuji apple. J. Plant Nutr. and Fert. 20: 414-420. Zhang, Y.G. and H.Y. Dai. 2011b. Comparison of pho- tosynthetic and morphological characteristics, and microstructure of roots and shoots, between colum- nar apple and standard apple trees of hybrid seed- lings. Phyton Intl. J. Ext. Bot. 80: 119-125. Zhang, Y.G. and H.Y. Dai. 2012a. Morphological dif- ferences of the vessel in secondary xylem of colum- nar and standard apple trees. Phyton Intl. J. Expt. Bot. 81: 229-232. Zhang, Y.G., J. Zhu, and H.Y. Dai. 2012b. Character- ization of transcriptional differences between co- lumnar and standard apple trees using RNA-Seq. Plant Mol. Biol. Rep. 30: 957-965. Zhao, Y.Y., Z.H. Lu, J.B. Xia, and J.T. Liu. 2015. Root architecture and adaptive strategy of 3 shrubs in Shell Bay in Yellow River Delta. Acta Ecologica Sinica. 3:602-603. Zouar, M., N. Elloumi, C.B. Ahmed, D. Delmail, B.B. Rouina, F.B. Abdallah, and P. Labrousse. 2016. Ex- ogenous proline enhances growth, mineral uptake, antioxidant defense, and reduces cadmium-induced oxidative damage in young date palm ( Phoenix dac- tylifera L.). Ecol. Eng. 86:202-209.

Hort. Sci. and Biotechnol. 89: 329-337. Wei, Y.S., J.G. Ning, and M.Y. Zheng. 2011. Determi- nation of mineral elements of Rhodiola Kirilowii by the method of microwave digestion and ICP-OES. Appl. Chem. Ind . 40: 728-730. Wu, Q.S., F.Y. Yuan, Y.J. Fei, L. Li, Y.M. Huang, and C.Y. Liu. 2014. Effects of arbuscular mycorrhizal fungi on root system architecture and sugar contents of white clover. Acta Prataculturae Sinica 23: 199- 204. Xiao, Y.S., F.T. Peng, Y.F. Zhang, Y.J. Qi, G.F. Wang, X.L. Wang, and H.R. Shu. 2014. Effects of aera- tion cultivation on root architecture and nitrogen metabolism of young peach trees. Sci. Agr. Sinica 47: 995-2002. Xue, X.M., C. Lu, J.Z. Wang, G.H. Yu, and P.G. Wang. 2012. Impacts of dwarf interstocks on growth and fruit quality of apple trees. Deciduous Fruits. 44: 5-7. Zhang, Q., Q.P. Wei, R.S. Jiang, X.D. Liu, H.P. Liu, and X.W. Wang. 2011a. Correlation analysis of fruit mineral nutrition contents with several key quality indicators in “Fuji” apple. Acta Hort. Sinica 38: 1963-1968. Zhang, X.Z., J.Y. Guo, Y.Z. Wang, C.L. Liu, and Y.B. Yuan. 2014. Effects of different rootstocks on min-

Correction In volume 71(2), in the article by Do Su Park, Shimeles Tilahun, Jae Yun Heo, Kyong Cheul Park and Cheon Soon Jeong “Effect of 1-MCP on persimmon fruit quality and expression of ethylene response genes during ripening”, the temperature at which persimmon fruit were ripened is incorrect in the captions for Figures 1 – 6. The ripening temperature was 25°C.

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Journal of the American Pomological Society 71(4): 203-213 2017

Thinning of Peach Trees Using High-Pressure Water J ohn A. C line 1 Additional index words: Prunus persica, crop load management, hand thinning Abstract Peach trees ( Prunus persica [L.] Batsch) annually produce an over-abundance of flowers that often set to pro- duce an excessive number of unmarketable, small fruit. Hand-thinning fruits following natural fruit abscission in June is a costly but essential management practice growers undertake to ensure remaining fruits are marketable at harvest. Past thinning methods have focused on chemical and mechanical approaches to removing flowers or fruitlets. The focus of this two-year study was to outline a method using high-pressure water and demonstrate its proof of concept to thin peach trees non-chemically at bloom. ‘Harrow Beauty’ and ‘Harrow Diamond’ peach trees trained using a central leader spindle system were subjected to one of three high-pressure water spray treatments at full bloom based on amount of time spraying each tree: 1) ‘LOW’- 45 s tree -1 (5.7 L water tree -1 ); 2) ”MED” - 60 s tree -1 (7.6 L water tree -1 ), and; 3) “HIGH” -75 s tree -1 (9.5 L water . tree -1 ). An unsprayed hand- thinned (“HAND”) treatment served as a control. All treatments, including HAND, were hand-thinned after ‘June’ drop. In year one, high-pressure water treatments reduced fruit set, the requirement for hand-thinning, crop load, total fruit per tree and yield at harvest and increased fruit weight of ‘Harrow Beauty’ by 27%. In year two, treatments reduced fruit set, the total number of fruit per tree and increased the fruit weight of ‘Harrow Beauty’ at harvest. Effects on the early ripening cultivar ‘Harrow Diamond’ were less pronounced; although, there was an increase in fruit weight at harvest in response to high-pressure sprays. Overall, increasing the duration of spray- ing resulted in greater treatment effects compared with the HAND treatment. High-pressure water treatments increased the percentage of fruit in the 2.25” (57 mm) and larger fruit diameter categories. In comparison with HAND and based on final crop load, the ideal rate of thinning using high-pressure water was in the range of 60- 70s per tree requiring 7.6 – 9.5 L water per tree. The merits of this novel thinning approach and design factors for commercialization are discussed.

 Apple, peach, nectarine, plum and pear producers often hand thin immature fruit (fruitlets) four to six weeks after bloom fol- lowing natural fruit abscission (Havis 1962; Byers and Lyons 1984; Webster and An- drews 1986; Byers 1989a). Fruit thinning by hand has become a standard cultural practice to enhance fruit size and quality at harvest, to increase return bloom of biennially bearing species (eg. Malus ), and to prevent scaffold limbs from breaking under the weight of ex- cess fruit. Hand thinning is most effective when performed as early as reasonably pos- sible (Day and DeJong, 1999; Jiménez and Díaz, 2002). Thinning of peaches at bloom has several advantages over hand thinning, including reduced labour costs, increased flowering the following season by up to sixty

percent and a greater number of shoots per tree (Byers, 1989a).  Labour costs for hand-thinning peaches in Ontario are approximately $C 1,729/ha based on 124 trees/ha labour and 2010 labour rates (OMAFRA, 2010). While bloom thin- ning may increase peach fruit size and yields by 20-30% compared to hand thinning 40-50 days later (Byers, 1989a), hand-thinning re- mains the most effective method to regulate peach crop load. Alternative thinning meth- ods have been sought, including robotics (Lyons et al, 2015) and mechanical thinning at bloom using a ‘string’ thinner (Schupp et al, 2008; Sauerteig and Cline, 2013) in order to offset this time-consuming and expensive practice. Chemical thinning sprays, such as carbaryl, 1-naphthalene acetic acid or 6-ben-

1 University of Guelph, OntarioAgricultural College, Department of Plant Agriculture Simcoe, Ontario N3Y 4N5, Canada; Tel: +1-519-426-7127; Email address: jcline@uoguelph.ca

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ty’ and ‘Harrow Diamond’ in 2009.  A6-yr old research orchard of ‘Harrow Di- amond’/Bailey and ‘Harrow Beauty’/Bailey ( Prunus persica ) (different trees from those used in 2008) located at the University of Guelph, Vineland (lat. 43 o 10’55.1” N, long. 79 o 23’ 23.1” W) and planted at a spacing of 2.5 m x 5.0 m was used for this study.  ‘Harrow Diamond’ is an early maturing cultivar with a ripening date around 27 July in Southern Ontario. Because the fruit is small-to-medium sized, this cultivar must be thinned early and adequately to obtain suit- able size, making it a good candidate cultivar for early bloom thinning.  Both cultivars were planted in individual rows and trained using an ‘Italian Fusetto’ (central leader) spindle system with indi- vidual tree supports and fastened to wire trel- lis (Caruso et al., 1989; Miles et al., 1999). Trees and pests were managed according to conventional practices for Ontario (Anony- mous, 2012).  Experiments 1 and 2. On 12 May 2008, and 6 May 2009 at full bloom, treatments were applied using a commercial gasoline- powered pressure washer (Model PE2055- HWSCOM, BE Pressure, Inc., Cambridge, ON) equipped with a 0 o nozzle (direct spray) on a hand-wand at a working pressure of 1 378 KPa and discharge rate of 7.6 l per min (Fig. 1-3). The stream of high-pressure water was directed at individual limbs (Fig. 2) at a distance of ~1.5 m. If the stream was within 1 m of the limb, removal of bark was possible (Fig. 3); although, this occurred infrequently. Fresh, clean municipal water was supplied to the pressure washer via a 10 mm (i.d.) high- pressure rubber hose connected to commer- cial air blast sprayer (GB Irrorazione Diser- bo, Model Laser P7, Italy) acting as a ‘nurse’ tank and operating with a supply pressure of 500 KPa.  For experiment one, a randomized com- plete block (RCBD) with four treatments and ten replications was used as the experimental design. For experiment two, a RCBD with four treatments and nine replications for the

zyl adenine, are for use on apple; however, there are no chemical thinners currently reg- istered for many stone fruit crops including peaches and cherries.  Our previous research at the University of Guelph investigated three approaches to reduce the requirement for hand-thinning peach trees: flower inhibition, blossom thin- ning, and chemical fruitlet thinning. All three approaches were successful with ‘Red- haven’, ‘Harrow Diamond’, and ‘Harrow Beauty’ and further studies are ongoing to re- fine the methodology for other cultivars and to ensure the results are repeatable annually (Coneva and Cline, 2006).  The primary objective of this study was to investigate a non-chemical approach to thinning peaches at bloom. Thinning early offers a distinct advantage in comparison with fruitlet thinning by providing earlier allocation of limited photosynthates and assimilates to fewer sinks. Although blos- som thinning peaches with various chemical products has been studied extensively since the 1940s (Larsen, 1947), an approach that does not rely on chemicals and that is con- sistent across cultivars, weather conditions, and phenological stages of flower develop- ment would be ideal. A high-pressure water stream, directed at the peach inflorescence at or near full bloom, may reduce fruit set and result in less hand-thinning at ‘June’ drop. Furthermore, thinning at this early stage would result in larger fruit at harvest and in contrast to hand-thinning would also provide more predictable results. Material and Methods  Experiment 1: Thinning of ‘Harrow Beau- ty’ in 2008. A 5-yr old research orchard of ’‘Harrow Beauty’ ( Prunus persica ) located at the University of Guelph, Vineland (lat. 43 o 10’55.1” N, long. 79 o 23’ 23.1” W) planted at a spacing of 2.5 m x 5.0 m (500 trees ha -1 ) was used for this study. ‘Harrow Beauty’ rip- ens around 2 Sept. in the Niagara Peninsula of Southern Ontario.  Experiment 2: Thinning of ‘Harrow Beau-

432

CLINE – THINNING PEACHES WITH HIGH-PRESSURE WATER

P each

205

2

‘Harrow Beauty’ and five replications for the ‘Harrow Diamond’ was used as the experimental design. To minimize treatment interference, experimental units were separated by at least one ‘guard’ tree in the orchard. Treatments consisted of three levels of thinning based on amount of time spraying each tree: ‘LOW’- 45 s per tree (5.7 L water per tree); ”MED” - 60 s per tree (7.6 L water per tree), and;) “HIGH” - 75 s per tree (9.5 L water per tree); and a hand- thinned control (‘HAND’).  In early June after flowering, five pri- mary scaffold limbs per tree were select- ed randomly between 1.0 – 2.0 m above the ground to determine initial fruit set after treatment application but before ‘June drop’. Shoot length of 1-yr-old wood and the number of flower buds were recorded to evaluate flower density. The number of fruitlets were counted on these shoots after ‘June drop’ but before hand-thinning. All treatments, including hand-thinned control treatments, were hand-thinned between 3-5 July 2008 (52-54 DAFB) and 29 June-4 July 2009 (54-59 DAFB) to approximately 15-20 cm between fruits (5-7 fruits per mshoot length). The total number of fruit thinned per tree was counted and weighed (2008 only).  ‘Harrow Beauty’ fruit were harvested on 9 Sept. 2008 and 1 Sept. 2009 while ‘Harrow Diamond’ were harvested over a period of 5 days beginning 31 Jul 2009, all based on uniform background colour and full suture swelling. The yield and total number of fruit harvested per tree was recorded. All fruit were then graded into one of the following six size catego- ries based on minimum diameter: <57 mm, 57-62 mm; 63-69 mm; 70-75 mm; 76-81 mm and > 81 mm. A diameter greater than 57 mm is the commercial target for marketable fruit, hence, the category “> 57” mm (which combined all but the fruit with a 57 mm minimum

Fig. 1. Treatments being applied on May 12, 2008 to ‘Harrow Beauty’ peach trees in full bloom. Approximately only 5% of flowers are required to set a commercial crop. [J. Cline photo] 3 Figure 1. Treatments being applied on May 12 2008 to ‘Harrow Beauty’ peach 4 trees in full bloom. Approximately only 5% of flowers are required to set a 5 commercial crop [J. Cline photo] 6 . 433 Figure 1. Treatments being applied on May 12 2008 to ‘Harrow Beauty’ peach 434 trees in full bloom. Approximately only 5% of flowers are required to set a 435 commercial crop [J. Cline photo] 436 . 437 438 439

7 8 9

Figure 2. It was necessary to direct the high-pressure water at the shoot limbs at a set distance to avoid damaging the tree bark whilst also dislodging the flower. [J. Cline photo] Figure 2. It was necessary to direct the high-pressure water at the shoot limbs at a set distance to avoid damaging the tree bark whilst also dislodging the flower. [J. Cline photo] Fig. 2. It was necessary to direct the high-pressure water at the shoot limbs at a set distance to avoid damaging the tree bark whilst also dislodging the flower. [J. Cline photo] CLINE – THINNING PEACHES WITH HIGH-PRESSURE WATER

440 Figure 3. Bark injury as a result of excessive water pressure on the peach shoot. 441 Generally, a distance of 1.5 m or greater from the branch was maintained to 442 prevent injury. [J. Cline photo] Fig. 3. Bark injury as a result of excessive water pressure on the pe ch shoot. Gen rally, a distance of 1.5 m r greater f om the branch was maintained prevent injury. [J. Cline photo]

443 444

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Results and Discussion  In 2008, high-pressure water thinning treatments reduced fruit set, the requirement for follow-up hand-thinning, crop load, to- tal number of fruit per tree and mean fruit weight at harvest of ‘Harrow Beauty’ com- pared to the hand thinned control (Table 1). Overall, the LOW and MED treatments re- duced fruit set and there was little additional benefit from the HIGH treatment. Treatments reduced yield per tree based on the Tukey’s HSD test, but not based on the ANOVAF test (P=0.058). When mean fruit weight was ad- justed for crop-load (Marini et al, 2002) us- ing ANCOVA, treatments were similar. Fruit set was unaffected by the amount of time applying the thinning treatments (from 45 to 75 seconds per tree). The LOW, MED, and HIGH treatments resulted in 26, 58 and 57% (252, 143, and 146 fruits removed) reductions in the amount of hand-thinning required after ‘June drop’, respectively compared with the untreated hand-thinned trees (343 fruits re- moved) (P<0.0001). Similar levels of hand- thinning were needed for MED and HIGH treatments (P>0.05). At the time of thinning, not only was there a greater number of fruit thinned per tree for the ‘HAND’ treatments, but the fruitlet size at thinning was 16-25% smaller than the MED and LOW treatments, respectively (data not shown). These data are consistent with studies by Redman (1952)

fruit diameter) was also chosen for analyses of fruit size distribution. Fruit were counted and weighed in each category.  Tree trunk circumference 30 cm above the soil line was measured and recorded in Sept. of each year to calculate trunk cross- sectional area.  Data were analyzed by ANOVA using PROC MIXED (version 9.4, SAS Institute, Inc., Cary, NC) and Tukey’s HSD was used to separate means with treatments as the fixed effect, and blocks as the random ef- fect. To investigate the relationship between the response variables and thinning timing (rate), linear regression was conducted on the LOW, MED, and HIGH treatments only; the HAND treatment was excluded because it was not an untreated control. Linear regres- sion of yield and crop load was conducted us- ing Sigma Plot (ver. 13.0, Systat Software, Chicago, IL). A Shapiro-Wilk test was used to test the assumption that the residuals were normally distributed. Scatterplots of studen- tized residuals were visually observed to test the assumption that the errors were not het- erogeneous. Lund’s test of outliers with stu- dentized residuals indicated whether outliers were present and, if so, they were removed from the analysis (Bowley, 2008). In cases where there were large deviations from the assumptions, data were corrected by log- or square root-transformation prior to analysis.

CLINE – THINNING PEACHES WITH HIGH-PRESSURE WATER CLINE – THINNING PEACHES WITH HIGH-PRESSURE WATER

Table 1. The effect of thinning treatments on follow-up hand thinning, fruit set, weight of thinned fruit, crop load, tree yield and mean fruit weight at harvest. ‘Harrow Beauty’/Bailey. University of Guelph, Vineland, Ontario. 2008 data. Table 1. The effect of thinning treatments on follow-up hand thinning, fruit set, weight of thinned fruit, crop load, tree yield and mean fruit weight at harvest. 'Harrow Beauty'/Bailey. University of Guelph, Vineland, Ontario. 2008 data. Table 1. The effect o thinning treatments on foll w-up hand thin ing, fruit set, weight of thinned fruit, crop load, tree yield and me fruit weight at harvest. 'Harrow Beauty'/B iley. University of Guelph, Vineland, Ontario. 2008 data.

Initial set (number of fruit/m shoot length) y

Initial set (number of fruit/m shoot length) y

Crop load adjusted mean fruit weight (g)

Crop load adjusted mean fruit weight (g)

Final crop load at harvest (frt/cm 2 tcsa)

Final crop load at harvest (frt/cm 2 tcsa)

Number of fruit thinned per tree

Total fruit per tree (number)

Total fruit weight (kg/tree)

Number of fruit thinned per tree

Total frui per tree (number)

Total frui weight (kg/tree)

Mean fruit weight (g)

Mean fruit weight (g)

Treatment Hand thinned control

Treatment Hand thin ed co trol

343 252 143 146

a b c c

35 19 20 17

a b b b

11.5

a b b b

337 221 247 193

a b b b

40.6 31.8 34.2 29.7

a b 138.1 144.7 ab 144.1 150.1 0.445 b

138.1 144.7 144.1 150.1 0.445

125.3 148.1 143.8 159.9 c b b a 0.0006

c b b a

343 252 143 146

a b c c

35 19 20 17

a b b b

11.5

a b b b

337 221 247 193

a b b b

40.6 31.8 34.2 29.7

a b

125.3 148.1 143.8 159.9

Low

Low

7.9 8.7 6.5

7.9 8.7 6.5

Medium

Medium

ab

High

High

b

P value

P value

<0.0001

<0.0001

0.0008

0.0017

0.0577

<0.0001

<0.0001

0.0008

0.0017

0.0577

0.0006

Regression of Low, Med, High z

Regression of Low, Med, High z

L*

ns

ns

ns

ns

ns

ns

L*

ns

ns

ns

ns

ns

ns

y set was determined on June 17, prior to hand thinning in early July. y Values within columns not followed by common letters differ at the 5% level of significance, by Tukey's HSD z ns, *, **, ***, indicates not significant, and significant differences at P = 0.06, P = 0.01 respectively s n prior to hand thi ning in early July. y alues ithin colu ns not follo ed by co on letters differ at the 5 level of significance, by Tukey's S z ns, *, **, ***, indicates not significant, and significant differences at P= 0.05, P=0.01 and P=0.001 respectively. y set wa determined on June 17, prior to hand t i ing early July. y Values within columns not followed by common letters diff at th 5% level of significance, by Tuke 's HSD z ns, *, **, ***, indicates not sig ificant, and significant d fferences at P= 0.05, P= .01 and P=0.001 respectively.

459 460

59 60