number of fruits tree-1, yield and yield efficiency were determined at harvest. After ... inhibitors on vegetative growth and fruiting of mature 'McIntosh' apple trees.
Vigor control in ‘McIntosh’ apple trees by growth inhibitors L. Rufato1, A.F. Brighenti1, A.D. Rufato2, L.I. Dominguez3 and T.L. Robinson3 1Santa Catarina State University (UDESC), College of Agric. and Life Science, Lages, SC, Brazil; 2Brazilian Agricultural Research Corporation (EMBRAPA), Vacaria, RS, Brazil; 3Dept. of Horticulture, NYSAES, Cornell University, Geneva, NY, USA.
Abstract We evaluated the effects of two gibberellin biosynthesis inhibitors [Prohexadione-Ca (Apogee® 250 ppm) and Trinexapac-ethyl (Moddus® 225 ppm)], on shoot growth of mature ‘McIntosh’/M.9 apple trees. The growth regulators were applied 7 days after bloom, when shoots were 5 cm long. Shoot length was measured every 15 days to determine growth rate. Shoots were measured in the lower, middle and upper portion of tree and according type (terminal and lateral shoots). The number of fruits tree-1, yield and yield efficiency were determined at harvest. After harvest, fruits were classified according to the color. Both growth inhibitors reduced shoot growth rate approximately 30% and reduced the daily growth rate (cm day-1) of all types of shoots and in all positions of tree. Daily growth rate was affected by shoot position. Growth rate of shoots located in lower portion of tree was reduced more than for shoots in the upper part of the tree. Likewise, terminal shoot growth rate was reduced less than lateral shoot growth rate. Trinexapac-ethyl (Moddus® 225 ppm) increased the number of fruits tree-1 and yield efficiency but reduced return bloom about 57% compared to the untreated control and 65% when compared to Apogee®. Both growth inhibitors had a positive effect on fruit color, which was probably due to improved light penetration into the canopy. Keywords: Malus domestica Borkh., Prohexadione-Ca, Apogee®, Trinexapac-ethyl, Moddus®, shoot growth rate INTRODUCTION Excessive vegetative growth in fruit trees is a major concern for the producer because it competes with fruit growth (Byers and Yoder, 1999; Basak and Rademacher, 2000; Costa et al., 2002). This competition is at its strongest during the first 50 days after full bloom when shoot and fruit growth is maximal (Byers and Yoder, 1999; Elfving et al., 2002; Smit et al., 2005). Excessive shoot growth also has a negative effect on fruit quality, yield and pest control (Greene, 1999; Miller and Tworkoski, 2003). In addition, shading caused by excessive shoot growth has a negative effect on flower bud induction and the quality of the return bloom (Greene, 1999; Miller and Tworkoski, 2003). Among the methods to reduce shoot growth is the use of growth regulators based on gibberellins biosynthesis inhibitors (Smit et al., 2005). Trinexapac-ethyl and prohexadionecalcium are growth retardants of the acylcyclohexanedione-type. They block certain dioxygenases catalyzing the late steps of gibberellin metabolism by being structural mimics of 2-oxoglutarate, which is the co-substrate of these enzymes (Rademacher, 2000). Trinexapac-ethyl has been developed primarily as an anti-lodging agent for small grains and for use as a turf growth regulator. Prohexadione-calcium is being commercialized as an anti-lodging agent for rice, cereals, and turf grasses grown for seed production. It is also used to control vegetative growth in fruit trees and ground nuts (Rademacher and Bucci, 2002). The objective of this study was to evaluate the effects of two gibberellin biosynthesis inhibitors on vegetative growth and fruiting of mature ‘McIntosh’ apple trees.
Acta Hortic. 1177. ISHS 2017. DOI 10.17660/ActaHortic.2017.1177.32 Proc. Int. Symp. on Physiological Principles and Their Application to Fruit Production Ed.: T. Robinson
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MATERIALS AND METHODS At Cornell’s New York State Agricultural Experiment Station - NYSAES (42°52’01”N; 77°02’03”W, 221 m a.s.l.), uniform 17-year-old ‘McIntosh’/M.9 trained to a vertical axis system were used for this experiment. The three treatments were: (1) untreated control; (2) Prohexadione-Ca (Apogee® 250 ppm); (3) Trinexapac-ethyl (Moddus® 225 ppm). Sprays were applied on May 31, 2013, 7 days after bloom, when shoots were 5 cm. Treatments were organized in a randomized complete block design, with 3 plots and 10 replications. Full bloom on ‘McIntosh’ trees occurred on May 24, 2013. Whole trees were sprayed with an airblast Lipco tunnel sprayer. The adjuvant Silwet L77 was used for all treatments. Two guard trees were included between experimental units to minimize cross-contamination of treatments through spray drift during application. Spray applications were conducted during favorable weather conditions where rainfall did not occur for the following 24 h. Ten representative new extension shoots per tree were randomly tagged according to the position (lower, middle and upper portion of tree) and type (terminal and lateral shoots). Their length was measured at the time of the first application and then at 2 weeks intervals until the cessation of shoot growth. Trunk cross-sectional area (TCSA) was calculated from trunk circumference, measured at 30 cm above the soil line in the fall. At harvest, the number and weight of fruit harvested per tree (kg) was recorded and yield efficiency (kg fruit cm-2 TCSA) was calculated. After harvest, fruits were classified according percentage of the skin surface with red color into 5 categories: Utility (0-20% red color). No.1 (20-35% red color), Fancy (40-50% red color), X Fancy (50-75% red color) and XX Fancy (75-100% red color). Data were analyzed by analysis of variance and where significant differences were detected, means were separated by Duncan’s multiple range test (P=0.05). RESULTS AND DISCUSSION The inhibiting effect of both bioregulators on shoot growth was clearly evident 2 week following the application of the chemicals (Figure 1). In the lower portion of the tree Apogee® 250 ppm caused a significant reduction in shoot growth rate compared to the control, while Moddus® 225 ppm had an intermediate effect which did not differ from the control trees or the Apogee trees (Figure 1A). In the middle and upper portions of tree and Apogee® 250 ppm and Moddus® 225 ppm significantly reduced the growth rate compared to the control (Figures 1B, C). With terminal shoots, Apogee® 250 ppm caused the greatest reduction in shoot growth rate, while Moddus® 225 ppm resulted in an intermediate effect but not different from the control trees or the Apogee trees (Figure 1D). With lateral shoots Apogee® 250 ppm and Moddus® 225 ppm significantly reduced the growth rate compared to the control (Figure 1E). Both bioregulators reduced final shoot length in all types and positions of shoots (Table 1). The greatest reduction occurred in the middle portion of tree with mean shoot lengths approximately 40% that of the control (Figure 1B). Both bioregulators applied in the lower and upper portions of tree reduced shoot length from 25 to 30% (Figures 1A, C). Lateral shoot growth rate was reduced 35% compared to the controls (Figure 1E), while terminal shoot growth rate was reduced by 30 and 15% by Apogee® 250 ppm and Moddus® 225 ppm, respectively (Figure 1D). Others (Byers and Yoder, 1999; Unrath, 1999; Miller, 2002) have found greater shoot growth inhibition when Prohexadione-Ca was applied at full bloom. Maxson and Jones (2002) observed that Trinexapac-ethyl reduced apple tree shoot growth beginning 10 to 14 days after application and the inhibition continuing for another 30 days.
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Figure 1. Shoot growth rate of lower shoots (A), middle shoots (B), upper shoots (C), terminal shoots (D) and lateral shoots (E) of ‘McIntosh’ apple trees at Geneva, NY in 2013. Table 1. Growth inhibitors effect on shoot growth and productive aspects of ‘McIntosh’ apple trees at Geneva, NY in 2013. Shoot growth Yield Fruit size Yield efficiency # fruits tree-1 (cm) (kg tree-1) (g) (kg cm-2) Untreated control 10.3 a 194.5 b 35.7 183.5 a 0.25 b ® Moddus 255 ppm 7.2 b 235.8 a 38.2 162.0 b 0.46 a Apogee® 250 ppm 7.2 b 216.4 ab 33.0 152.5 b 0.25 b LSD P≤0.05 1.4 39.5 6.8 17.2 0.18 Significance1 * * NS * * Treatment
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Plants treated with Moddus® 225 ppm produced significantly more fruits tree-1 than the untreated control, but did not differ significantly from trees treated with Apogee® 250 ppm (Table 1). Despite higher fruit numbers, yield was not affected by the application of bioregulators due to smaller fruit size on trees treated with the bioregulatores. The reduction in fruit size due to application of Moddus® and Apogee® was probably a direct effect of higher fruit set. Greene (1999) and Sugar et al. (2002) had similar results where
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growth inhibitor treatments resulted in smaller average fruit size of pears and apple cultivars. Yield efficiency was significantly higher in plants treated with Moddus® 225 ppm. An increased fruit set is an indication that reduced shoot growth early in the season results in increased availability of assimilates to support the early growth of more fruits, however, the greater number of fruits results in reduced carbohydrate supply to each fruit and greater competition for assimilates later in the season with the net result of smaller fruit. This could potentially be managed by more aggressive chemical thinning or with earlier hand thinning (Smit et al., 2005). Plants treated with Moddus® 225 ppm produced more fruits classified as X Fancy, while plants treated with Apogee® 250 ppm produced a higher percentage of fruits classified as XX Fancy category. The untreated control produced higher percentage of poorly colored fruits classified as Utility (Table 2). Table 2. Growth inhibitors effect on fruit quality of ‘McIntosh’ apple trees at Geneva, NY in 2013. Fruit red color (%) Utility N0.1 Fancy X Fancy XX Fancy Treatment (0-20% (20-35% (40-50% (50-75% (75-100% red color) red color) red color) red color) red color) Untreated control 18.7 a 22.0 17.2 22.3 ab 19.8 b Moddus® 255 ppm 9.2 b 15.5 19.6 28.0 a 28.7 ab ® Apogee 250 ppm 7.8 b 17.3 16.6 20.2 b 38.1 a LSD P≤0.05 7.0 9.73 4.2 6.6 15.0 Significance1 * NS NS * * 1NS,
or * indicate the effect of treatment was either non significant or significant at P≤0.05 level.
The percentage of highly colored fruits was higher in plants treated with Moddus® and Apogee® because they reduced shoot growth rate and increased sunlight inside the canopy. Red pigment development in apples requires relatively high light levels within the canopy, and in shaded part of the ‘McIntosh’ apple fruits remains green. High fruit quality comes from combining good light distribution in the canopy and high light interception (Robinson et al., 1991). The spray of Moddus® significantly reduced return bloom about 43% compared to the untreated control while Apogee® reduced return bloom by 12%, which was not significantly different than the control (Table 3). Both gibberellin inhibitors act on GA20 inhibition, but Moddus® probably promotes the liberation of GA20 after its effect wears off. Since it is shorter lived than Apogee® this likely results in worse return bloom the next season than with Apogee®. Table 3. Growth inhibitors effect on percentage of return bloom of ‘McIntosh’ apple trees at Geneva, NY in 2013. Treatment Untreated control Moddus® 255 ppm Apogee® 250 ppm LSD P≤0.05 Significance1 1
Lower 41.1 a 23.6 b 36.6 ab 17.0 *
Return bloom (%) Medium Upper 48.2 a 57.3 a 28.6 b 34.5 b 38.9 ab 50.9 ab 19.3 21.4 * *
Total tree 50.2 a 28.8 b 44.2 ab 15.7 **
** or * indicate the effect of treatment was significant at P≤0.005 or P≤0.05 levels.
CONCLUSIONS Both growth inhibitors reduced shoot growth rate approximately 30% and reduced the daily growth rate of all types of shoots and in all positions of tree. 226
Shoot position affected daily growth rate. Growth rate of shoots located in the lower portion of tree was reduced more than for shoots in the upper part of the tree. Likewise, terminal shoot growth rate was reduced less than lateral shoot growth rate. Both growth inhibitors had also a increased the number of fruits tree-1, which resulted in smaller fruit size but had a positive effect on fruit color, which was probably due to improved light penetration into the canopy. Trinexapac-ethyl (Moddus® 225 ppm) reduced return bloom considerably which makes it a less desirable growth inhibitor than Apogee® for apple. Literature cited Basak, A., and Rademacher, W. (2000). Growth regulation of pome and stone fruit trees by use of prohexadioneCa. Acta Hortic. 514, 41–50 https://doi.org/10.17660/ActaHortic.2000.514.4. Byers, R.E., and Yoder, K.S. (1999). Prohexadione-calcium inhibits apple, but not peach tree growth, but has little influence on apple fruit thinning or quality. HortScience 34, 1205–1209. Costa, G., Andreotti, C., Sabatini, E., Bregoli, A.M., Bucchi, F., Spada, G., and Mazzini, F. (2002). The effect of prohexadione-Ca on vegetative and cropping performance and fire blight control of pear trees. Acta Hortic. 596, 531–534 https://doi.org/10.17660/ActaHortic.2002.596.89. Elfving, D.C., Sugar, D., and Faubion, D. (2002). Pear tree shoot growth patterns in relation to chemical control of vegetative growth with prohexadione-Ca (Apogee). Acta Hortic. 596, 711–716 https://doi.org/10.17660/ ActaHortic.2002.596.122. Greene, D.W. (1999). Tree growth management and fruit quality of apple trees treated with prohexadionecalcium (BAS 125). HortScience 34, 1209–1212. Maxson, K.L., and Jones, A.L. (2002). Management of fire blight with gibberellin inhibitors and sar inducers. Acta Hortic. 590, 217–223 https://doi.org/10.17660/ActaHortic.2002.590.31. Miller, S.S. (2002). Prohexadione–calcium control vegetative shoot growth in apple. J. Tree Fruit Prod. 3 (1), 11– 28 https://doi.org/10.1300/J072v03n01_02. Miller, S.S., and Tworkoski, T. (2003). Regulating vegetative growth in deciduous fruit trees. PGRSA Q. 31, 8–46. Rademacher, W. (2000). Growth retardants: effects on gibberellin biosynthesis and other metabolic pathways. Annu. Rev. Plant Physiol. Plant Mol. Biol. 51 (1), 501–531 https://doi.org/10.1146/annurev.arplant.51.1.501. PubMed Rademacher, W., and Bucci, T. (2002). New plant growth regulators: high risk investment? Horttechnology 12, 64–67. Robinson, T.L., Lakso, A.N., and Carpenter, S.G. (1991). Canopy development, yield, and fruit quality of ‘Empire’ and ‘Delicious’ apple trees grown in four orchard production systems for ten years. J. Am. Soc. Hortic. Sci. 116, 179–187. Smit, M., Meintjes, J.J., Jacobs, G., Stassen, P.J.C., and Theron, K.I. (2005). Shoot growth control of pear trees (Pyrus communis L.) with prohexadione-calcium. Sci. Hortic. (Amsterdam) 106 (4), 515–529 https://doi.org/10.1016/ j.scienta.2005.05.003. Sugar, D., Elfving, D.C., and Mielke, E.A. (2002). Effects of prohexadione-Ca (ApogeeTM) on blossoming, production and fruit quality in pear. Acta Hortic. 596, 757–760 https://doi.org/10.17660/ActaHortic.2002.596. 130. Unrath, C.R. (1999). Prohexadione–Ca: a promising chemical for controlling vegetative growth of apples. HortScience 34, 1197–1200.
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