- Email: [email protected]
CPPU application on size and quality of hardy kiwifruit
Scientia Horticulturae 110 (2006) 219–222 www.elsevier.com/locate/scihorti
Short communication
CPPU application on size and quality of hardy kiwifruit J.G. Kim a, Y. Takami a, T. Mizugami a, K. Beppu a, T. Fukuda b, I. Kataoka a,* b
a Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan Fuchu Branch, Kagawa Prefectural Agricultural Experiment Station, Sakaide 762-0024, Japan
Received 26 May 2005; received in revised form 28 April 2006; accepted 8 June 2006
Abstract For the purpose of determining the appropriate conditions of application to increase the size of a hardy kiwifruit, Actinidia arguta ‘Mitsuko’, N1-(2-chloro-4-pyridyl)-N3-phenylurea (CPPU) was applied at three different growth stages of the crop: at petal fall, 10 and 25 days after petal fall (DAPF), and three different concentrations: 1, 5 and 10 mg l1. A significant increase in fruit size was obtained by treatment at the concentrations of 5–10 mg l1 and at 10 DAPF. The fruit weight doubled. Although a significant reduction in the concentrations of total soluble solids (TSS), titratable acids (TA) and ascorbic acid (AsA) in the CPPU-treated fruits was recorded, the TSS/TA ratio and AsA content per fruit increased by the treatment. CPPU application at petal fall induced abnormally protruding fruit tip. # 2006 Elsevier B.V. All rights reserved. Keywords: Actinidia arguta; Cytokinin; Fruit growth; Baby kiwi; Forchlorfenuron
1. Introduction Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq., known as hardy kiwifruit, has recently become popular as baby kiwifruit in the market (Kabaluk et al., 1997; Williams et al., 2003). The fruit has an edible smooth skin, contains high amounts of sugar and ascorbic acid and displays an excellent flavor. A. arguta is widely distributed in East Asia and commonly occurs in mountainous areas in Japan (Ohashi, 1989). Although there are many cultivars and recorded selections, the fruit is smaller than that of commercial A. deliciosa kiwifruit, weighing 6–16 g (Williams et al., 2003). Several hexaploid cultivars selected in Japan bear a relatively larger fruit than common tetraploid selections (Okuyama, 2000). However, since the fruit weight remains less than 10 g on an average, increased fruit size should be one of the strategies to increase the yield and marketability of the fruit. Flower and fruit thinning are standard cultural practices performed in fruit crops to increase the fruit size (Lahav et al., 1989). Pescie and Strik (2004) attempted thinning before bloom in ‘Ananasnaya’, a common cultivar of A. arguta grown in Oregon, and showed that thinning increased the average fruit
volume and the volume of the central fruit in a cluster by 18 and 27%, respectively. The use of plant growth substances is another possible method of increasing the fruit size. N1-(2-Chloro-4-pyridyl)N3-phenylurea (CPPU) is known to be effective for enhancing fruit enlargement by stimulating cell division and/or cell expansion in many kinds of fruits including A. deliciosa kiwifruit (Iwahori et al., 1988; Lewis et al., 1996; Cruz-Castillo et al., 2002). As for A. arguta, so far, Jo et al. (2003) have reported that a single application of CPPU at the concentration of 16 mg l1 15 days after pollination was effective for increasing the fruit size of a local selection. As seen in A. deliciosa kiwifruit, the effectiveness of CPPU application on fruit development was largely influenced by the time of application and concentration (Cruz-Castillo et al., 1999). In the present study, the effects of CPPU treatment on the fruit size and quality were examined using a hexaploid cultivar ‘Mitsuko’, to determine the appropriate conditions of application. 2. Materials and methods 2.1. Plant materials
* Corresponding author. Tel.: +81 87 891 3066; fax: +81 87 891 3066. E-mail address: [email protected] (I. Kataoka). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.06.017
Mature vines of A. arguta, cultivar; ‘Mitsuko’ (6), grown at Kagawa Prefectural Agricultural Experiment Station were used. The vines were trained to a pergola system. Male
220
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
selection Awaji (4) was planted beside the female plants and additionally, hand pollination was performed at anthesis (12 May 2004). The ploidy of the materials was examined previously (Phivnil et al., 2005). 2.2. CPPU treatments To determine the effect of the time of treatment, CPPU (Fulmet, EC 0.1%; Kyowa, Tokyo, Japan) was applied at the concentration of 5 mg l1 to ‘Mitsuko’ at three growth stages; at petal fall (18 May 2004, 6 days after anthesis and hand pollination), 10 days after petal fall (DAPF) (28 May) and 25 DAPF (12 June). As for the experiment on CPPU concentration, CPPU at the concentrations of 0, 1, 5 and 10 mg l1 was applied to ‘Mitsuko’ singly at 10 DAPF. In all the treatments, the test solution was applied as a 5 s fruit dip to a total of 20 fruits on one shoot. The experimental design was completely random with five single-shoot replications. The control fruits were not subjected to any treatments. 2.3. Evaluation of fruit quality After the CPPU treatment, the diameter and length were measured for 10 fruits per treatment at 2-week intervals until harvest on 17 September. After harvest, 20 fruits were randomly selected and then kept in a plastic box and exposed to ethylene at a concentration of 500 mg l1 for 48 h at 20 8C to
enhance ripening. After ripening, fruit weight, total seed number per fruit, the contents of total soluble solids, titratable acids and ascorbic acid were determined. After pressing a fruit wrapped with cheese cloth, seeds were collected by forceps and counted. Total soluble solids (TSS) and titratable acids (TA) in fruit juice were assayed using a hand refractometer and by titration with 0.05 N NaOH, respectively. Titratable acid content was expressed as citric acid equilibrium. The content of total ascorbic acid (AsA) was measured using the 2,4-dinitro phenyl hydrazine method (Roe et al., 1948). 3. Results In all the treatments, fruit growth was characterized by a sigmoid curve and the most growth occurred within 40 DAPF (Fig. 1). CPPU treatments markedly enhanced the initial fruit growth. Among the treatments, the application at 10 days after petal fall was most effective for enhancing fruit growth, especially in the longitudinal direction. At harvest, fruit weight was significantly increased by the CPPU treatment. Especially, in the treatment of 10 DAPF, the fruit weight doubled (Table 1; Fig. 2). In contrast, the TSS and TA concentration significantly decreased by the CPPU treatments. The degree of reduction was larger for TA than for TSS, while the TSS/TA ratio increased in the CPPU-treated fruits (Tables 1 and 2). The AsA concentration was also significantly decreased by the CPPU
Fig. 1. Effect of time of application of CPPU on fruit growth of A. arguta ‘Mitsuko’ (DAPF, days after petal fall).
Table 1 Effects of time of application of CPPU on fruit quality at harvest CPPUa
Fruit weight (g)
Seed numberb
TSS (%)
Titratable acids (%)
TSS/TA ratio
Ascorbic acid (mg/100 g)
(g/fruit)
Control Petal fall 10 DAPFd 25 DAPF
7.4 11.7 16.0 13.9
140 131 138 132
15.4 15.5 13.9 14.6
1.4 1.1 1.0 0.7
10.7 15.0 14.8 22.0
165.9 124.2 99.4 105.6
1.2 1.5 1.6 1.5
a b c d
a b c c
a a a a
c c a b
c b b a
CPPU concentration, 5 mg l1. Seed number, total seed number per fruit. Means followed by same letter in each column were not significantly different by Tukey’s test at P 0.05. DAPF, days after petal fall.
a b b c
b a a a
ac ab b ab
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
221
At increasing concentrations of CPPU up to 5 mg l1, the fruit growth was markedly enhanced. At a rate of 1 mg l1, the promoting effect of CPPU was less pronounced than at higher concentrations (Fig. 3). The weight and size of the harvested fruit was significantly higher in the CPPU treatment than in the control (Table 2; Fig. 4). The TSS concentration was significantly reduced by CPPU application at concentrations of 1 and 5 mg l1. CPPU-treated fruits contained a lower level of TA than that in the control fruits. AsA concentration was also decreased by CPPU application even at a low concentration such as 1 mg l1. The AsA content per fruit was increased by CPPU application. No adverse effect of the CPPU treatment even at high concentration was observed in the appearance of sinuses at stylar end, or in flesh texture of the fruit, except the fading of green color in the pericarp (Fig. 4). 4. Discussion
Fig. 2. Fruit size in A. arguta ‘Mitsuko’ at different application times of CPPU (DAPF, days after petal fall).
treatment, regardless of the time of application. However, the AsA content per fruit increased by the CPPU treatment (Tables 1 and 2). On the other hand, earlier application of CPPU at petal fall induced abnormally protruding fruit tip (Fig. 2).
In the present study, it was found that A. arguta ‘Mitsuko’ responded significantly to the CPPU treatment and the fruit size enlarged. Jo et al. (2003) compared the sensitivity to CPPU at a concentration of 16 mg l1 for fruit growth among several Actinidia species, and observed that A. arguta was highly sensitive as well as A. deliciosa. In the case of ‘Mitsuko’, an adequate fruit enlargement was obtained even at the lower concentration of 5 mg l1. As for the time of application, treatment at 10 days after petal fall was most effective for fruit enlargement in A. arguta ‘Mitsuko’. Practically, in kiwifruit, application of CPPU from
Table 2 Effect of CPPU treatment on fruit quality at different concentrations CPPU (mg l1)
0 1 5 10 a b
Fruit weight (g)
7.4 11.7 16.0 17.7
a b c c
Seed numbera
140 134 138 132
a a a a
TSS (%)
15.4 12.6 13.9 14.9
c a b c
Titratable acids (%)
1.4 0.7 1.0 0.7
c a b a
TSS/TA ratio
10.7 18.2 14.8 20.1
a c b c
Seed number, total seed number per fruit. Means followed by the same letter in each column are not significantly different by Tukey’s test at P 0.05.
Fig. 3. Changes in fruit growth in A. arguta ‘Mitsuko’ at different CPPU concentrations.
Ascorbic acid (mg/100 g)
(g/fruit)
165.9 98.4 99.4 93.7
1.2 1.2 1.6 1.7
b a a a
ab a b b
222
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
Although the CPPU treatment reduced the AsA concentration (fresh weight basis), the content per fruit increased because of the large size. In conclusion, CPPU should be applied at concentrations of 5–10 mg l1 at 10 DAPF to obtain a sufficiently enlarged fruit in A. arguta ‘Mitsuko’, without any practical adverse effects on the fruit shape and quality. The effect on the storability of the fruit and the cumulative effect of continuous CPPU treatment on the productivity of the vines should be further examined. References
Fig. 4. Fruit size of A. arguta ‘Mitsuko’ at different CPPU concentrations (CPPU was applied 10 days after petal fall).
20 to 30 days after flowering was recommended for obtaining a stable effect on fruit enlargement and avoiding adverse sideeffects. Ninomiya (2001) reported that the early application of CPPU at 10 days after full bloom induced abnormally protruding fruit tip or cracking of the skin around the pedicel. In the present experiment, very early treatment at petal fall caused a protruding of fruit in A. arguta ‘Mitsuko’. The growth pattern of the fruits with early treatment with CPPU was characterized by a larger increase in length than in diameter (Fig. 3). The insufficient transverse growth in the distal part of the fruits may result in the occurrence of protruding fruit tip. With increasing fruit size by CPPU application, a small but significant reduction in the TSS content occurred in A. arguta ‘Mitsuko’. In A. deliciosa, however, the CPPU treatment did not affect (Iwahori et al., 1988; Cruz-Castillo et al., 1999) or rather increased the TSS content (Antognozzi et al., 1996, 1997). The larger extent of fruit enlargement obtained in A. arguta may exert a diluting effect on TSS in a fruit or caused a competition for carbohydrates among the fruits. A significant reduction in the TA and AsA contents was also observed in CPPU-treated fruits of A. arguta ‘Mitsuko’. Similar reduction in the TA and AsA contents was reported in A. deliciosa (Iwahori et al., 1988; Antognozzi et al., 1997). The reduction in the TA content may be induced not only by the diluting effect but also by the influence of CPPU on the maturation process. Due to the larger reduction in the TA content than in that of the TSS content, the TSS/TA ratio increased in the CPPU-treated fruits resulting in the slightly sweeter taste of the fruit. This suggests that the CPPU treatment did not adversely affect the fruit taste, actually. AsA is one of the important nutritional components in A. arguta fruit (Nishiyama et al., 2004).
Antognozzi, E., Battistelli, A., Famiani, F., Moscatello, S., Stanica, F., Tombesi, A., 1996. Influence of CPPU on carbohydrate accumulation and metabolism in fruits of Actinidia deliciosa (A Chev.). Sci. Hort. 65, 37–47. Antognozzi, E., Famiani, F., Proietti, P., Ferranti, F., Frenguelli, G., 1997. Effect of CPPU (Cytokinin) treatments on fruit anatomical structure and quality in Actinidia deliciosa. Acta Hort. 444, 459–465. Cruz-Castillo, J.G., Woolley, D.J., Lawes, G.S., 1999. Effect of CPPU and other plant growth regulators on fruit development in kiwifruit. Acta Hort. 498, 173–178. Cruz-Castillo, J.G., Woolley, D.J., Lawes, G.S., 2002. Kiwifruit size and CPPU response are influenced by the time of anthesis. Sci. Hort. 95, 23– 30. Iwahori, S., Tominaga, S., Yamasaki, T., 1988. Stimulation of fruit growth of kiwifruit, Actinidia chinensis Planch., by N-(2-chloro-4-pyridyl)-N0 -phenylurea, a diphenylurea-derivative cytokinin. Sci. Hort. 35, 109–115. Jo, Y.S., Cho, M.Y., Park, J.O., Park, T.D., Shim, K.K., 2003. Comparison of CPPU effect on fruit development in several Actinidia species. Acta Hort. 610, 539–543. Kabaluk, A.K., Kempler, C., Toivonen, P.M.A., 1997. Actinidia arguta— characteristics relevant to commercial production. Fruit Var. J. 51, 117– 122. Lahav, W., Korkin, A., Adar, G., 1989. Thinning stage influences fruit size and yield of kiwifruit. HortScience 24, 438–440. Lewis, D.H., Burge, G.K., Hopping, M.E., Jameson, P.E., 1996. Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa) II. Effects of reduced pollination and CPPU application. Physiol. Plant. 98, 187–195. Ninomiya, T., 2001. Promotion of fruit enlargement by plant growth substance. In: Encyclopedia of Fruit Tree, vol. 12. Kiwifruit, Rural Culture Association, Tokyo, pp. 48–51 (in Japanese). Nishiyama, I., Yamashita, Y., Yamanaka, M., Shimohashi, A., Fukuda, T., Oota, T., 2004. Varietal difference in Vitamin C content in the fruit of kiwifruit and other Actinidia species. J. Agric. Food Chem. 52, 5472–5475. Ohashi, H., 1989. Actinidiaceae. In: Satake, Y., Hara, H., Watari, S., Tominari, T. (Eds.), Wild Flowers of Japan. Woody plants. Heibonsha Ltd., Tokyo, (in Japanese), pp. 135–137. Okuyama, J., 2000. Sarunashi. In: Encyclopedia of Fruit Growing, vol. 16. Special crops of deciduous fruit trees, Rural Culture Association, Tokyo, pp.171–188 (in Japanese). Pescie, M.A., Strik, B.C., 2004. Thinning before bloom affects fruit size and yield of hardy kiwifruit. HortScience 39, 1243–1245. Phivnil, K., Beppu, K., Takamura, T., Fukuda, T., Kataoka, I., 2005. Flow cytometric assessment of ploidy in native resources of Actinidia in Japan. J. Am. Pom. Soc. 59, 44–49. Roe, J.H., Mary, B.M., Oesterling, M.J., Charlotle, M.D., 1948. The determination of diketo-gluconic acid, dehydro-L-ascorbic acid, and L-ascorbic acid in the same tissues extract by 2,4-dinitrophenyl hydrazine method. J. Biol. Chem. 174, 201–208. Williams, M.H., Boyd, L.M., McNeilage, M.A., MacRae, E.A., Ferguson, A.R., Beatson, R.A., Martin, P.J., 2003. Development and commercialization of ‘Baby Kiwi’ (Actinidia arguta Planch). Acta Hort. 610, 81–86.
Short communication
CPPU application on size and quality of hardy kiwifruit J.G. Kim a, Y. Takami a, T. Mizugami a, K. Beppu a, T. Fukuda b, I. Kataoka a,* b
a Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan Fuchu Branch, Kagawa Prefectural Agricultural Experiment Station, Sakaide 762-0024, Japan
Received 26 May 2005; received in revised form 28 April 2006; accepted 8 June 2006
Abstract For the purpose of determining the appropriate conditions of application to increase the size of a hardy kiwifruit, Actinidia arguta ‘Mitsuko’, N1-(2-chloro-4-pyridyl)-N3-phenylurea (CPPU) was applied at three different growth stages of the crop: at petal fall, 10 and 25 days after petal fall (DAPF), and three different concentrations: 1, 5 and 10 mg l1. A significant increase in fruit size was obtained by treatment at the concentrations of 5–10 mg l1 and at 10 DAPF. The fruit weight doubled. Although a significant reduction in the concentrations of total soluble solids (TSS), titratable acids (TA) and ascorbic acid (AsA) in the CPPU-treated fruits was recorded, the TSS/TA ratio and AsA content per fruit increased by the treatment. CPPU application at petal fall induced abnormally protruding fruit tip. # 2006 Elsevier B.V. All rights reserved. Keywords: Actinidia arguta; Cytokinin; Fruit growth; Baby kiwi; Forchlorfenuron
1. Introduction Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq., known as hardy kiwifruit, has recently become popular as baby kiwifruit in the market (Kabaluk et al., 1997; Williams et al., 2003). The fruit has an edible smooth skin, contains high amounts of sugar and ascorbic acid and displays an excellent flavor. A. arguta is widely distributed in East Asia and commonly occurs in mountainous areas in Japan (Ohashi, 1989). Although there are many cultivars and recorded selections, the fruit is smaller than that of commercial A. deliciosa kiwifruit, weighing 6–16 g (Williams et al., 2003). Several hexaploid cultivars selected in Japan bear a relatively larger fruit than common tetraploid selections (Okuyama, 2000). However, since the fruit weight remains less than 10 g on an average, increased fruit size should be one of the strategies to increase the yield and marketability of the fruit. Flower and fruit thinning are standard cultural practices performed in fruit crops to increase the fruit size (Lahav et al., 1989). Pescie and Strik (2004) attempted thinning before bloom in ‘Ananasnaya’, a common cultivar of A. arguta grown in Oregon, and showed that thinning increased the average fruit
volume and the volume of the central fruit in a cluster by 18 and 27%, respectively. The use of plant growth substances is another possible method of increasing the fruit size. N1-(2-Chloro-4-pyridyl)N3-phenylurea (CPPU) is known to be effective for enhancing fruit enlargement by stimulating cell division and/or cell expansion in many kinds of fruits including A. deliciosa kiwifruit (Iwahori et al., 1988; Lewis et al., 1996; Cruz-Castillo et al., 2002). As for A. arguta, so far, Jo et al. (2003) have reported that a single application of CPPU at the concentration of 16 mg l1 15 days after pollination was effective for increasing the fruit size of a local selection. As seen in A. deliciosa kiwifruit, the effectiveness of CPPU application on fruit development was largely influenced by the time of application and concentration (Cruz-Castillo et al., 1999). In the present study, the effects of CPPU treatment on the fruit size and quality were examined using a hexaploid cultivar ‘Mitsuko’, to determine the appropriate conditions of application. 2. Materials and methods 2.1. Plant materials
* Corresponding author. Tel.: +81 87 891 3066; fax: +81 87 891 3066. E-mail address: [email protected] (I. Kataoka). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.06.017
Mature vines of A. arguta, cultivar; ‘Mitsuko’ (6), grown at Kagawa Prefectural Agricultural Experiment Station were used. The vines were trained to a pergola system. Male
220
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
selection Awaji (4) was planted beside the female plants and additionally, hand pollination was performed at anthesis (12 May 2004). The ploidy of the materials was examined previously (Phivnil et al., 2005). 2.2. CPPU treatments To determine the effect of the time of treatment, CPPU (Fulmet, EC 0.1%; Kyowa, Tokyo, Japan) was applied at the concentration of 5 mg l1 to ‘Mitsuko’ at three growth stages; at petal fall (18 May 2004, 6 days after anthesis and hand pollination), 10 days after petal fall (DAPF) (28 May) and 25 DAPF (12 June). As for the experiment on CPPU concentration, CPPU at the concentrations of 0, 1, 5 and 10 mg l1 was applied to ‘Mitsuko’ singly at 10 DAPF. In all the treatments, the test solution was applied as a 5 s fruit dip to a total of 20 fruits on one shoot. The experimental design was completely random with five single-shoot replications. The control fruits were not subjected to any treatments. 2.3. Evaluation of fruit quality After the CPPU treatment, the diameter and length were measured for 10 fruits per treatment at 2-week intervals until harvest on 17 September. After harvest, 20 fruits were randomly selected and then kept in a plastic box and exposed to ethylene at a concentration of 500 mg l1 for 48 h at 20 8C to
enhance ripening. After ripening, fruit weight, total seed number per fruit, the contents of total soluble solids, titratable acids and ascorbic acid were determined. After pressing a fruit wrapped with cheese cloth, seeds were collected by forceps and counted. Total soluble solids (TSS) and titratable acids (TA) in fruit juice were assayed using a hand refractometer and by titration with 0.05 N NaOH, respectively. Titratable acid content was expressed as citric acid equilibrium. The content of total ascorbic acid (AsA) was measured using the 2,4-dinitro phenyl hydrazine method (Roe et al., 1948). 3. Results In all the treatments, fruit growth was characterized by a sigmoid curve and the most growth occurred within 40 DAPF (Fig. 1). CPPU treatments markedly enhanced the initial fruit growth. Among the treatments, the application at 10 days after petal fall was most effective for enhancing fruit growth, especially in the longitudinal direction. At harvest, fruit weight was significantly increased by the CPPU treatment. Especially, in the treatment of 10 DAPF, the fruit weight doubled (Table 1; Fig. 2). In contrast, the TSS and TA concentration significantly decreased by the CPPU treatments. The degree of reduction was larger for TA than for TSS, while the TSS/TA ratio increased in the CPPU-treated fruits (Tables 1 and 2). The AsA concentration was also significantly decreased by the CPPU
Fig. 1. Effect of time of application of CPPU on fruit growth of A. arguta ‘Mitsuko’ (DAPF, days after petal fall).
Table 1 Effects of time of application of CPPU on fruit quality at harvest CPPUa
Fruit weight (g)
Seed numberb
TSS (%)
Titratable acids (%)
TSS/TA ratio
Ascorbic acid (mg/100 g)
(g/fruit)
Control Petal fall 10 DAPFd 25 DAPF
7.4 11.7 16.0 13.9
140 131 138 132
15.4 15.5 13.9 14.6
1.4 1.1 1.0 0.7
10.7 15.0 14.8 22.0
165.9 124.2 99.4 105.6
1.2 1.5 1.6 1.5
a b c d
a b c c
a a a a
c c a b
c b b a
CPPU concentration, 5 mg l1. Seed number, total seed number per fruit. Means followed by same letter in each column were not significantly different by Tukey’s test at P 0.05. DAPF, days after petal fall.
a b b c
b a a a
ac ab b ab
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
221
At increasing concentrations of CPPU up to 5 mg l1, the fruit growth was markedly enhanced. At a rate of 1 mg l1, the promoting effect of CPPU was less pronounced than at higher concentrations (Fig. 3). The weight and size of the harvested fruit was significantly higher in the CPPU treatment than in the control (Table 2; Fig. 4). The TSS concentration was significantly reduced by CPPU application at concentrations of 1 and 5 mg l1. CPPU-treated fruits contained a lower level of TA than that in the control fruits. AsA concentration was also decreased by CPPU application even at a low concentration such as 1 mg l1. The AsA content per fruit was increased by CPPU application. No adverse effect of the CPPU treatment even at high concentration was observed in the appearance of sinuses at stylar end, or in flesh texture of the fruit, except the fading of green color in the pericarp (Fig. 4). 4. Discussion
Fig. 2. Fruit size in A. arguta ‘Mitsuko’ at different application times of CPPU (DAPF, days after petal fall).
treatment, regardless of the time of application. However, the AsA content per fruit increased by the CPPU treatment (Tables 1 and 2). On the other hand, earlier application of CPPU at petal fall induced abnormally protruding fruit tip (Fig. 2).
In the present study, it was found that A. arguta ‘Mitsuko’ responded significantly to the CPPU treatment and the fruit size enlarged. Jo et al. (2003) compared the sensitivity to CPPU at a concentration of 16 mg l1 for fruit growth among several Actinidia species, and observed that A. arguta was highly sensitive as well as A. deliciosa. In the case of ‘Mitsuko’, an adequate fruit enlargement was obtained even at the lower concentration of 5 mg l1. As for the time of application, treatment at 10 days after petal fall was most effective for fruit enlargement in A. arguta ‘Mitsuko’. Practically, in kiwifruit, application of CPPU from
Table 2 Effect of CPPU treatment on fruit quality at different concentrations CPPU (mg l1)
0 1 5 10 a b
Fruit weight (g)
7.4 11.7 16.0 17.7
a b c c
Seed numbera
140 134 138 132
a a a a
TSS (%)
15.4 12.6 13.9 14.9
c a b c
Titratable acids (%)
1.4 0.7 1.0 0.7
c a b a
TSS/TA ratio
10.7 18.2 14.8 20.1
a c b c
Seed number, total seed number per fruit. Means followed by the same letter in each column are not significantly different by Tukey’s test at P 0.05.
Fig. 3. Changes in fruit growth in A. arguta ‘Mitsuko’ at different CPPU concentrations.
Ascorbic acid (mg/100 g)
(g/fruit)
165.9 98.4 99.4 93.7
1.2 1.2 1.6 1.7
b a a a
ab a b b
222
J.G. Kim et al. / Scientia Horticulturae 110 (2006) 219–222
Although the CPPU treatment reduced the AsA concentration (fresh weight basis), the content per fruit increased because of the large size. In conclusion, CPPU should be applied at concentrations of 5–10 mg l1 at 10 DAPF to obtain a sufficiently enlarged fruit in A. arguta ‘Mitsuko’, without any practical adverse effects on the fruit shape and quality. The effect on the storability of the fruit and the cumulative effect of continuous CPPU treatment on the productivity of the vines should be further examined. References
Fig. 4. Fruit size of A. arguta ‘Mitsuko’ at different CPPU concentrations (CPPU was applied 10 days after petal fall).
20 to 30 days after flowering was recommended for obtaining a stable effect on fruit enlargement and avoiding adverse sideeffects. Ninomiya (2001) reported that the early application of CPPU at 10 days after full bloom induced abnormally protruding fruit tip or cracking of the skin around the pedicel. In the present experiment, very early treatment at petal fall caused a protruding of fruit in A. arguta ‘Mitsuko’. The growth pattern of the fruits with early treatment with CPPU was characterized by a larger increase in length than in diameter (Fig. 3). The insufficient transverse growth in the distal part of the fruits may result in the occurrence of protruding fruit tip. With increasing fruit size by CPPU application, a small but significant reduction in the TSS content occurred in A. arguta ‘Mitsuko’. In A. deliciosa, however, the CPPU treatment did not affect (Iwahori et al., 1988; Cruz-Castillo et al., 1999) or rather increased the TSS content (Antognozzi et al., 1996, 1997). The larger extent of fruit enlargement obtained in A. arguta may exert a diluting effect on TSS in a fruit or caused a competition for carbohydrates among the fruits. A significant reduction in the TA and AsA contents was also observed in CPPU-treated fruits of A. arguta ‘Mitsuko’. Similar reduction in the TA and AsA contents was reported in A. deliciosa (Iwahori et al., 1988; Antognozzi et al., 1997). The reduction in the TA content may be induced not only by the diluting effect but also by the influence of CPPU on the maturation process. Due to the larger reduction in the TA content than in that of the TSS content, the TSS/TA ratio increased in the CPPU-treated fruits resulting in the slightly sweeter taste of the fruit. This suggests that the CPPU treatment did not adversely affect the fruit taste, actually. AsA is one of the important nutritional components in A. arguta fruit (Nishiyama et al., 2004).
Antognozzi, E., Battistelli, A., Famiani, F., Moscatello, S., Stanica, F., Tombesi, A., 1996. Influence of CPPU on carbohydrate accumulation and metabolism in fruits of Actinidia deliciosa (A Chev.). Sci. Hort. 65, 37–47. Antognozzi, E., Famiani, F., Proietti, P., Ferranti, F., Frenguelli, G., 1997. Effect of CPPU (Cytokinin) treatments on fruit anatomical structure and quality in Actinidia deliciosa. Acta Hort. 444, 459–465. Cruz-Castillo, J.G., Woolley, D.J., Lawes, G.S., 1999. Effect of CPPU and other plant growth regulators on fruit development in kiwifruit. Acta Hort. 498, 173–178. Cruz-Castillo, J.G., Woolley, D.J., Lawes, G.S., 2002. Kiwifruit size and CPPU response are influenced by the time of anthesis. Sci. Hort. 95, 23– 30. Iwahori, S., Tominaga, S., Yamasaki, T., 1988. Stimulation of fruit growth of kiwifruit, Actinidia chinensis Planch., by N-(2-chloro-4-pyridyl)-N0 -phenylurea, a diphenylurea-derivative cytokinin. Sci. Hort. 35, 109–115. Jo, Y.S., Cho, M.Y., Park, J.O., Park, T.D., Shim, K.K., 2003. Comparison of CPPU effect on fruit development in several Actinidia species. Acta Hort. 610, 539–543. Kabaluk, A.K., Kempler, C., Toivonen, P.M.A., 1997. Actinidia arguta— characteristics relevant to commercial production. Fruit Var. J. 51, 117– 122. Lahav, W., Korkin, A., Adar, G., 1989. Thinning stage influences fruit size and yield of kiwifruit. HortScience 24, 438–440. Lewis, D.H., Burge, G.K., Hopping, M.E., Jameson, P.E., 1996. Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa) II. Effects of reduced pollination and CPPU application. Physiol. Plant. 98, 187–195. Ninomiya, T., 2001. Promotion of fruit enlargement by plant growth substance. In: Encyclopedia of Fruit Tree, vol. 12. Kiwifruit, Rural Culture Association, Tokyo, pp. 48–51 (in Japanese). Nishiyama, I., Yamashita, Y., Yamanaka, M., Shimohashi, A., Fukuda, T., Oota, T., 2004. Varietal difference in Vitamin C content in the fruit of kiwifruit and other Actinidia species. J. Agric. Food Chem. 52, 5472–5475. Ohashi, H., 1989. Actinidiaceae. In: Satake, Y., Hara, H., Watari, S., Tominari, T. (Eds.), Wild Flowers of Japan. Woody plants. Heibonsha Ltd., Tokyo, (in Japanese), pp. 135–137. Okuyama, J., 2000. Sarunashi. In: Encyclopedia of Fruit Growing, vol. 16. Special crops of deciduous fruit trees, Rural Culture Association, Tokyo, pp.171–188 (in Japanese). Pescie, M.A., Strik, B.C., 2004. Thinning before bloom affects fruit size and yield of hardy kiwifruit. HortScience 39, 1243–1245. Phivnil, K., Beppu, K., Takamura, T., Fukuda, T., Kataoka, I., 2005. Flow cytometric assessment of ploidy in native resources of Actinidia in Japan. J. Am. Pom. Soc. 59, 44–49. Roe, J.H., Mary, B.M., Oesterling, M.J., Charlotle, M.D., 1948. The determination of diketo-gluconic acid, dehydro-L-ascorbic acid, and L-ascorbic acid in the same tissues extract by 2,4-dinitrophenyl hydrazine method. J. Biol. Chem. 174, 201–208. Williams, M.H., Boyd, L.M., McNeilage, M.A., MacRae, E.A., Ferguson, A.R., Beatson, R.A., Martin, P.J., 2003. Development and commercialization of ‘Baby Kiwi’ (Actinidia arguta Planch). Acta Hort. 610, 81–86.