Arti cial shading reduces the occurrence of double pistils in `Satohnishiki' sweet cherry

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1 Scientia Horticulturae 83 (2000) 241±247 Arti cial shading reduces the occurrence of double pistils in `Satohnishiki' sweet cherry Kenji Beppu 1, Ikuo Kataoka * Faculty of Agriculture, Kagawa University, Miki, Kagawa , Japan Accepted 23 August 1999 Abstract The effect of arti cial shading in summer and early autumn on the occurrence of double pistils in `Satohnishiki' sweet cherry was studied. Potted trees were grown in steel frame structures covered with woven shade cloth made of silvered polyethylene and providing 53% and 78% light reduction, from 23rd July to 4th October in 1995 and from 16th July to 16th September in In 1995, shading levels of 53% and 78% reduced the daily maximum air temperature by 1.88C and 3.28C, respectively, compared to the unshaded control. Forty-seven percent of the buds on nonshaded trees formed double pistil primordia, and 51% of them developed into owers with double pistils the following spring. Reducing light 78% reduced the frequency of double pistils to 24% in buds and 1.5% at anthesis, whereas 53% shade reduced the frequency of double pistils only slightly. Doubling was classi ed into three groups based upon relative length of the two pistils: (1) one pistil much shorter than the other (S), (2) one pistil about half the length of the other (M), and (3) pistils of approximately equal length (L). The frequency of ower primordia with equally developed pistils in autumn buds corresponded to that of owers with double pistils at anthesis. A 78% level of shading markedly reduced the rate of ower primordia with two equally developed pistils. Because of the relatively cool summer in 1997, the frequency of double pistils in autumn buds, even under unshaded conditions, was about half of that in 1995, but shadings still reduced the frequency of double pistils to less than 3%. These results suggest the possibility of applying arti cial shading to reduce the occurrence of double pistils in `Satohnishiki' sweet cherry grown in regions with hot summers. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Prunus avium; Flower morphology; Temperature; Abnormal differentiation * Corresponding author. Tel.: ; fax: addresses: beppuk@ag.kagawa-u.ac.jp (K. Beppu), kataoka@ag.kagawa-u.ac.jp (I. Kataoka). 1 Tel.: ; fax: /00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S (99)

2 242 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241± Introduction Occurrence of double fruits sometimes becomes a serious problem in sweet cherry production in warm regions (Ryugo, 1988). The malformation results from abnormal differentiation of pistil primordia the previous summer (Tucker, 1935; Micke et al., 1983). We demonstrated, under controlled conditions, that the occurrence of double pistils in the `Satohnishiki' cultivar increased markedly when the trees were exposed to temperatures above 308C (Beppu and Kataoka, 1999). In eld-grown trees, double fruits reportedly occur more frequently on the sunny than on the shaded portion of the canopy (Philp, 1933; Tucker, 1934). These facts imply that high solar radiation increases bud temperature which in turn enhances double pistil formation, and that conversely, arti cial shading may prevent the occurrence of the disorder. In this study, we examined the effect of arti cial shading in summer on the occurrence of double pistils in `Satohnishiki' sweet cherry grown in a warm region. 2. Materials and methods 2.1. Experiment 1 (1995) `Satohnishiki' sweet cherry (Prunus avium L.) grafted on `Aobazakura' (Prunus lannesiana Wils.), a common rootstock for sweet cherry in Japan, was used. Five-year-old trees planted in 7 l pots, lled with a two granite soil:one bark compost (v/v) were grown under eld conditions in the experimental eld of Kagawa University prior to the shading treatments. On 23rd July 1996, the trees were placed into steel frame structures covered with woven shade cloth made of silvered polyethylene with two different levels of light transmission. The photosynthetic photon ux density (PPFD) under these shadings, as measured with a LI-190SA quantum sensor (LI-COR, Lincoln, NE, USA) positioned horizontally at the level of the upper leaves, was 53% and 78% of that under full sunlight. Control trees were grown without shading. Three trees were used per treatment. When the soil moisture tension reached 13 kpa, 1 l of water was supplied. During the treatment period, air temperatures in a ventilated case (Fig. 1), and inside and outside the shaded structures (Fig. 2) were measured with thermocouples placed 1.5 m above the ground. Mid-day leaf water potential in each tree was measured using a pressure chamber. On 4th October, ten spur buds per tree were collected, and the occurrence of double pistils was observed microscopically. Flower primordia with double pistils

3 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241± Fig. 1. Daily average, maximum and minimum temperatures in the research eld of Kagawa University in 1995 and Fig. 2. Diurnal time course (1 August 1995) of air temperature under shading and in the eld.

4 244 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241±247 Fig. 3. Classi cation of ower primordia by the relative size of pistils. Normal ower primordia (a) and abnormal ones with double pistils classi ed into three groups: (S) one pistil much shorter than the other (b), (M) one pistil about half the length of the other (c), and (L) pistils of approximately equal length (d). Bars: 200 mm. (sample data on 4 October 1995). were classi ed into three groups based upon relative length of the two pistils: (1) one pistil much shorter than the other (S) (Fig. 3b), (2) one pistil about half the length of the other (M) (Fig. 3c), and (3) pistils of approximately equal length (L) (Fig. 3d). Then all the trees were transferred to the eld. At anthesis in the spring of 1996, the percentage of owers with double pistils was determined Experiment 2 (1997) Nine-year-old `Satohnishiki' trees on `Aobazakura' rootstock in 36 l containers lled with the same medium as in Experiment 1 were grown under eld conditions. The trees were subjected to the same levels of arti cial shading as in Experiment 1 from 16th July to 16th September Control trees were grown without shading. Three trees were used per treatment. When the soil moisture tension reached 13 kpa, 2 l of water was supplied. Field temperatures were recorded during the treatment period (Fig. 1). After the termination of the treatment, all the trees were transferred to the eld. On 13th October, 20 spur

5 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241± buds per tree were collected and the occurrence of double pistils was evaluated based on the same classi cation as that described in Experiment 1. In the spring of 1998, the percentage of owers with double pistils was determined. 3. Results 3.1. Experiment 1 (1995) Daily maximum temperature from mid-july to August averaged 33.68C, and daily maximum temperature reached 358C for 14 days (Fig. 1). Shading lowered the average daily maximum air temperatures between 23 July and 31 August in the structures by 1.88C (53% shade) and 3.28C (78% shade), and the average temperature during the day (0600±1800 h) by 1.28C and 2.18C, respectively. Shading had little effect on mid-day leaf water potential (data not shown). In the control, a total of 47% of the ower buds contained double pistils (Table 1), and the percentage was not affected by 53% shading. A 78% level of shading tended to reduce the total rate of double pistils, but not signi cantly. Twenty- ve percent of the control ower buds had equally developed double pistils. Although a 53% level of shading did not change the rate signi cantly, a 78% level of shading markedly reduced it. Table 1 Effect of shading on the occurrence of double pistils in `Satohnishiki' sweet cherry Shading Percentage of flowers with double pistils SE In the bud Total S a M L At anthesis Experiment 1 Control % % Significance NS b NS NS * c * c Experiment 2 Control % % Significance * c NS * c * c NS a One pistil much shorter than the other (S), one pistil about half the length of the other (M), and pistils of approximately equal length (L). b Nonsigni cant. c Signi cant at P < 0.05 by ANOVA.

6 246 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241±247 The percentage of owers with double pistils observed at anthesis the following spring coincided with the rate of ower buds with equally developed pistils, but not with the total rate including the buds with unequally developed pistils (Table 1) Experiment 2 (1997) The average of the daily maximum temperature from mid-july to August was 31.28C, and the daily maximum temperature reached 358C for only two days (Fig. 1). Generally, the frequency of occurrence of double pistils in Experiment 2 was considerably lower than in Experiment 1 in 1995 (Table 1). In the control buds, the total rate of double pistils was 21%, and half of the buds showed equally developed pistils. Shading reduced the rate, only 2.4% of the buds had double pistils even under a 53% level of shade. The percentage of owers with double pistils the following spring was as low as 5.5% in the control. Shading tended to reduce the rate, but not signi cantly. 4. Discussion In both experiments in this study, the frequency of double pistils was considerably higher in the autumn buds than in the owers at anthesis. We obtained similar results in our previous study when we examined the effect of the temperature on doubling (Beppu and Kataoka, 1999). The present study showed that most of the owers with double pistils developed from ower primordia with equally developed pistils. This nding suggests that the weakest of the two pistils degenerates during bud break, probably because of competition with the stronger one. Shading treatments markedly reduced the percentage of owers with equally developed pistils, and hence reduced the percentage with double pistils. The shading treatments reduced maximum air temperature by 1.8±3.28C. In a previous study under controlled environment, we showed that the formation of double pistils occurred in `Satohnishiki' when trees were exposed to a high day temperature (>308C) during ower initiation (Beppu and Kataoka, 1999). We did not monitor bud temperature in this experiment, but shading should have reduced bud temperature as shown in banana pseudostem (Eckstein et al., 1997) and in leaves of grape (Klenert, 1974) and lily (Sorrentino et al., 1997). These results suggest that reduced formation of double pistils by shading is mainly due to reduced temperature, especially in the bud. This also explains why doubling is generally less serious in the northern and shaded parts of the canopy than in the southern parts (Philp, 1933; Tucker, 1934).

7 K. Beppu, I. Kataoka / Scientia Horticulturae 83 (2000) 241± The reason for the reduction in the percentage of ower buds with equally developed double pistils by shading remains unclear. Shading may delay the initiation of pistils, possibly through nutritional or hormonal factors. Our data suggest that arti cial shading could be a practical method for reducing the occurrence of double pistils, especially in unusually hot summers. In `Bing' and `Mazzard', the light saturation for photosynthesis is as low as 500 mmol m 2 s 1 (DeJong, 1983; Roper and Kennedy, 1986). The reduction of PPFD by 1400 mmol m 2 s 1 caused by the 78% shading level in this experiment would have little effect on the photosynthetic rate, at least in the outer leaves of the canopy. Considering the cost of materials and labor, the suitability of shading treatment for commercial production should be examined in detail. References Beppu, K., Kataoka, I., High temperature rather than drought stress is responsible for the occurrence of double pistils in `Satohnishiki' sweet cherry. Sci. Hort. 81, 125±134. DeJong, T.M., CO 2 assimilation characteristics of ve Prunus tree fruit species. J. Am. Soc. Hort. Sci. 108, 303±307. Eckstein, K., Robinson, J.C., Fraser, C., Physiological responses of banana (Musa AAA; Cavendish sub-group) in the sub-tropics. VII. Effects of windbreak shading on phenology, physiology and yield. J. Hort. Sci. 72, 389±396. Klenert, M., KuÈnstliche VeraÈnderung der meteorologischen VerhaÈltnisse im Rebbestand und ihre Auswirkungen auf das GroÈssen wachstum der Traubenbeeren. Vitis 13, 8±22. Micke, W.C., Doyle, J.F., Yeager, J.T., Doubling potential of sweet cherry cultivars. California Agric. 37, 24±25. Philp, G.L., Abnormality in sweet cherry blossoms and fruit. Bot. Gaz. 94, 815±820. Roper, T.R., Kennedy, R.A., Photosynthetic characteristics during leaf development in `Bing' sweet cherry. J. Am. Soc. Hort. Sci. 111, 938±941. Ryugo, K., Fruit Culture Ð Its Science and Art. Wiley, New York. Sorrentino, G., Cerio, L., Alvino, A., Effect of shading and air temperature on leaf photosynthesis and growth in lily plant. Sci. Hort. 69, 259±273. Tucker, L.R., Notes on sweet cherry doubling. Proc. Am. Soc. Hort. Sci. 32, 300±302. Tucker, L.R., Additional notes on sweet cherry doubling. Proc. Am. Soc. Hort. Sci. 33, 237± 239.