Department of Horticultural Science, Kyungpook National University1
Apple Research Station, National Institute of Horticultural & Herbal Science2
Benzyladenine (BA, 99% purity), MaxCel® (1.9% BA), Fruitone (3.5% NAA), MaxCel® + Fruitone, and simazine were applied postbloom as fruitlet thinning agents to mature ‘Hongro’ and ‘Fuji’ apple (Malus domestica Borkh.) trees. BA and MaxCel® were applied at 100 mg･L-1 a.i. while Fruitone at 0.1 mg･L-1 a.i. and simazine at 400 mg･L-1 a.i. All PGRs were applied at 8 days after full bloom (DAFB, 6 mm fruit diameter) in both cultivars, while simazine was treated twice at 7 and 14 DAFB. In ‘Hongro’, the number of total fruit set per flower cluster in terminal buds was 1.67, 1.84, and 1.81 in MaxCel® + Fruitone, MaxCel®, and simazine applications, respectively, when compared with 2.35 of water control. These reductions in fruit set were mainly attributed to the increased ratio of defruited clusters by the thinning agents. In ‘Fuji’ apple, the number of total fruit set per flower cluster in terminal buds was 1.29, 1.60, and 1.76 in MaxCel® + Fruitone, Fruitone, and MaxCel®, respectively, when compared with 2.56 of water control in ‘Fuji’ apple. The addition of Fruitone to the MaxCel® promoted the thinning efficacy in both cultivars, compared to MaxCel® only. The thinning efficacies were similarly observed with lateral flowers in both cultivars. A significant increase of fruit weight by the postbloom thinning treatments was observed only in the BA application in ‘Hongro’, while the effect was observed in BA and MaxCel® in ‘Fuji’. While the soluble solids content increased in the BA, MaxCel® and MaxCel®+Fruitone treatments in both cultivars, other fruit quality attributes were not affected by the application of post-bloom thinning agents.
1. Batjer, L.P. and H.D. Billingsley. 1964. Apple thinning with chemical sprays. Washington State Expt. Sta. Blu. 651.
2. Black, B.L., M.J. Bukovac, and J. Hull, Jr. 1995. Effect of spray volume and time of NAA application on fruit size and cropping of red chief ‘Delicious’ apple. Sci. Hortic. 64:253-264.
3. Bound, S.A., K.M. Jones, and M.J. Oakford. 1997. Post-bloom thinning with 6-benzyladenine. Acta Hortic. 463:493-499.
4. Bound, S.A., K.M. Jones, T.B. Koen, and M.J. Oakford. 1991. The thinning effect of benzyladenine on red ‘Fuji’ apple trees. J. Hort. Sci. Biotech. 66:789-794.
5. Byers, R.E. and D.H. Carbaugh. 1991. Effect of chemical thinning sprays on apple fruit set. HortTechnology 1:41-48.
6. Dennis, F.G. Jr. 2000. The history of fruit thinning. Plant Growth Regul. 31:1-16.
7. Elfving, D.C. and R.A. Cline. 1993. Benzyladenine and other chemicals for thinning ‘Empire’ apple trees. J. Amer. Soc. Hort. Sci. 118:593-598.
8. Greene, D.W. and W.R. Autio. 1989. Evaluation of benzyladenine as a chemical thinner on ‘McIntosh’ apples. J. Amer. Soc. Hort. Sci. 114:68-73.
9. Greene, D.W. and W.R. Autio. 1994. Combination sprays with benzyladenine to chemically thin spur-type ‘Delicious’ apples. HortScience 29:887-890.
10. Greene, D.W., W.R. Autio, and P. Miller. 1990. Thinning activity of benzyladenine on several apple cultivars. J. Am. Soc. Hort. Sci. 115:394-400.
11. Greene, D.W., W.R. Autio, J.A. Erf, and Y.M. Zhongyuan. 1992. Mode of action of benzyladenine when used as a chemical thinner on apples. J. Amer. Soc. Hort. Sci. 117:775-779.
12. Guak, S., E.J. Kim, J.R. Kook, and D.G. Choi. 2009. MaxCel as a postbloom thinner for ‘Hongro’ and ‘Fuji’ apples. Hort. Environ. Biotechnol. 50:181-187.
13. Guak, S., M. Beulah, N.E. Looney, and L.H. Fuchigami. 2002. Thinning ‘Fuji’ apple blossoms with synthetic auxins (MCPB- ethyl or NAA) and ethephon with or without postbloom thinning with carbaryl. J. Amer. Soc. Hort. Sci. 127:165-170.
14. Jang, H.I., H.J. Wha, H.J. Lee, K.H. Hong, J.J. Choi, and K.Y. Kim. 1998. Evaluation of lime sulfur mixture as a flower thinner for pear trees (Pyrus pyrifolia cv. Niitaka). J. Kor. Soc. Hort. Sci. 39:423-427.
15. Jones, K.M., T.B. Koen, M.J. Oakford, and S.A. Bound. 1989. Thinning ‘Red Fuji’ apples with ethephon or NAA. J. Hort. Sci. 64:527-532.
16. Kook, J.R., E.J. Kim, D.G. Choi, and S. Guak. 2009. Chemical thinning of ‘Hongro’ apple with ammonium thiosulfate and MaxCel. Hort. Environ. Biotechnol. 50:79-83.
17. Moon, B.W. and C.C. Kim. 1986. Effect of NAA and carbaryl on the fruit thinning in apples. J. Kor. Soc. Hort. Sci. 27:239-248.
18. Park, M.Y., J.B. Kim, O.H. Ryu, and J.K. Byun. 1998. Thinning of 'Fuji' apple by simazine. J. Kor. Soc. Hort. Sci. 39:30-34.
19. Robinson, T., A. Lakso, E. Stover, and S. Hoying. 1998. Practical thinning programs for New York. N.Y. State Hort. Soc. Fruit Quarterly Publ. 1:14-18.
20. Schumacher, R., F. Frankhauser, and W. Stadler. 1978. Chemical thinning and natural fruit drop by modifying fruit set. Schweiz. Z. Obst-Weinbau 114:245-258.
21. Schroder, M. and F. Bangerth. 2006. The possible ‘Mode of action’ of thinning bioregulators and its possible contribution to the understanding of ‘Thinning variability’ in apples. Acta Hortic. 727:437-443.
22. Stover, E., M. Fargione, R. Risio, X. Yang, and T. Robinson. 2001. Fruit weight, crop load, and return bloom of ‘Empire’ apple following thinning with 6-benzyladenine and NAA at several physiological stages. HortScience 36:1077-1081.
23. Wismer, P.T., J.T.A. Proctor, and D.C. Elfving. 1995. Benzyladenine affects cell division and cell size during apple fruit thinning. J. Amer. Soc. Hort. Sci. 120:802-807.
24. Wertheim, S.J. 2000. Developments in the chemical thinning of apple and pear. Plant Growth Regul. 31:85-100.
25. Yuan, R. and D.W. Greene. 2000. Benzyladenine as a chemical thinner for ‘McIntosh’ apples. I. Fruit thinning effects and associated relationships with photosynthesis, assimilate translocation, and non-structural carbohydrates. J. Amer. Soc. Hort. Sci. 125:169-176.