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1 J. Japan. Soc. Hort. Sci. 59 (2) : Differences in Sugar Composition in Prunus persica Fruit and the Classification by the Princi pal Component Analysis Takaya MoRIGucHI, Yuri Division of Breeding, Fruit Tree ISHIZAWA and Research Station, Tetsuro SANADA Tsukuba, Ibaraki 305 Summary Sugars were analyzed in a total of 54 peach cultivars, selections and wild types. Fructose, glucose, sorbitol, inositol and sucrose were detected as the main sugars. In the sugar composition, sucrose was the major sugar and inostitol was the minor one in all the materials, accounting for 74% and 1.1% of the total sugar content, respectively. The percentage of fructose was higher throughout the season in eating peaches than in native and flowering peaches. The distribution of the sugar composition was evaluated by principal component analysis. The scatter diagram of peaches according to scores of 1st and 2nd principal components suggested the existence of 2 groups. These groups corresponded to the different groups for the ratio of fructose to total sugars of peaches. Introduction Peach breeding in Japan was started in the Meiji era ( ) by using peaches introduced from China, Europe and U.S.A. Consequently, the progenies of `Shanhaisuimitsuto' (= Chinese Cling), introduced from eastern China, were adaptable to Japanese conditions (high temperature and moisture in growing season), and have been used as breeding materials (19). Previously, native peaches were grown only on a small scale, because they produced fruits with a commercially unacceptable quality in terms of flavor, color and size. Presently, these peaches have been used as resistant rootstocks to root-knot nematode (19) and as ornamental peaches. Thus, the current commercial cultivars in Japan are entirely different from the native peaches. Many studies on the chemical components during the ripening of fruit (7, 13) and storage (3, 9) were conducted in commercial peach cultivars. However, information for the native peaches is limited (15), and the differences between the current commercial peaches and the native ones, particularly in terms of their chemistry, are not Received for publication October 21, This paper is contribution A-260 of the Fruit Tree Res. Sta. well-documented. In studies on the mechanism of sucrose accumulation in peach (Prunus persica (L.) Batsch) fruits, we observed differences in the sugar composition among peaches. Interspecies differences in the ratio of sucrose/total sugars have also been reported in tomato (4) and melon (5). In addition, differences in the ratio of non-reducing sugars/total sugars and glucose/fructose were also reported in some Japanese pears (11) and in grapes (14), respectively. In this paper, sugar composition was analyzed in peach fruits and the distribution of sugar composition was evaluated by principal component analysis. Materials and Methods Peach fruits grown in the Chiyoda Experimental Orchard of the Fruit Tree Research Station were used for the sugar analysis. The 54 peach materials used are listed in Table 1. Maturity of fruits estimated from the days after full bloom and the easiness of peduncle detachment from the branch. Peach fruits harvested from the same field were used for this experiment, and the amount of each type of sugar was expressed as sugar composition (%) to minimize the year-to-year differences. The amounts and kinds of sugar in the ethanolic extract were determined by HPLC. Soluble sugars were extracted by grinding flesh tissues in 80% 307

2 308 T. MORIGUCHI, Y. ISHIZAWA AND T. SANADA Table 1. Cultivars and selections used in the study'. ethanol, adjusted to ph 7.0 with 0.1 N NaOH and heated for 15 min at 80 C. The extraction was repeated 3 times. The combined extract corresponding to 0.5 g fresh weight was dried up in vacuum, dissolved in water, carried on the ionexchange column (Dowex 50W-X8, Dowex 1-X8) and eluted with water. Aliquot of the eluate was analyzed by using an HPLC (Shimadzu LC-6A) and RI detector (Shimadzu RID-6A) equipped SP1010 (Showa Denko K.K.) column at 70 C with water (0.5 ml/min) as the eluent. Fructose, glucose sorbitol, inositol and sucrose were identified and quantified by comparison with retention and integrated peak areas of external standards. Results and Discussion 1. Analysis of sugar composition Total sugar content and sugar composition (%) in 54 peach cultivars and selections are summarized in Table 2. Sucrose was the major sugar and inositol was the minor one in the sugar composition of all peaches, accounting for % and %, respectively. Peaches after the Meiji era, were characterized by a sugar composition with nearly equal percentages of fructose and glucose. Cultivars bred in other countries such as `Redhaven' and `Rio de Canserva' also showed the same tendency. On the contrary, native and flowering peaches were characterized by a small amount

3 I)IFFERENCES IN SUGAR COMPOSITION IN PEACH FRUIT 309 Table 2. Sugar composition of Prunus persica. of fructose and large amount of glucose. Moreover, these peaches tended to contain higher amounts of sorbitol than the peaches after the Meiji era. It is interesting to note that in the Meiji era, peaches rich in fructose were substituted for peaches with lower amounts of fructose. Seasonal fluctuations of sugar were studied in `Akatsuki', `Elberta', `Naganoyaseito -Early' and `Chichibuyaseito' (Fig. 1). In all the peaches, the sucrose content rapidly increased toward the mature stage while inositol remained at a low level throughout the season. As shown in Table 2, there were differences in the fructose content among these peach fruits. In `Akatsuki' and `Elberta', the content of fructose fluctuated with relatively high values throughout the season, while in `Naganoyaseito-Early' and `Chichibuyaseito', the fructose remained at a low level from the immature to mature stages. It is noteworthy that the content of fructose of these peaches was low throughout the growing season. Fig. 1. Seasonal changes in content of soluble sugars in peach fruit. ( ); Fructose, (Y); Glucose, ( ); Sorbitol, (1); Inositol, ( ); Sucrose. Sugar contents are expressed as mg per g fresh weight.

4 310 T. MORIGUCHI, Y. ISHIZAWA AND T. SANADA Table 3. Year-to-year changes in sugar composition (%) of peach fruit. It is known that the amount of total sugar in pear (6) and apple (1) varies readily depending on the area of cultivation, year and developmental stage of the fruits, while the percentage of each sugar in mature pear fruits does not change appreciably (8). The results of the 2 year trials of sugar analysis in peach fruit are shown in Table 3. Although the total amounts of sugar changed with the year, the sugar composition (%) did not change appreciably. In the Rosaceae family including peach, sorbitol is the principal photosynthate and translocating sugar (2,16). In apple (17), pear (18), and peach (13), loaded sorbitol appears to be converted to fructose or glucose by NAD+-dependent sorbitol dehydrogenase and sorbitol oxidase, respectively. Resultant fructose and glucose are further metabolized, and accumulate in fruit. It was suggested that sucrose accumulated in peach fruit due to the activity of sucrose synthase (12). A small amount fructose and large amount of sorbitol were present in native and flowering peaches, suggesting the existence of an inhibitor or a weak enzyme activity in the metabolic process into fructose. These 2 types, which differed in the sugar composition could be a good material for studies on the mechanism of sugar accumulation in peach.

5 DIFFERENCES IN SUGAR COMPOSITION IN PEACH FRUIT Classification of peaches by principal component analysis Correlation of content of five sugars is shown in Table 4. A high negative correlation was found between the sucrose and glucose content. The eigen vector, eigen value and contribution of 1st, 2nd, 3rd, 4th and 5th principal components obtained by the analysis are shown in Table 5. A scatter diagram of the 54 peach cultivars and selections in a Z1-Z2 plane obtained by the analysis is shown in Fig. 2. Contribution of the 1st principal component was 52% and cumulative contribution of the 1st and 2nd principal components was 78% (Table 5). The scatter diagram suggested that the closer the genetic position of peaches, the more similar their sugar composition. Peaches were mainly classified into 2 groups. One group included eating peaches, `Shanhaisuimitsuto' and its progenies (Group I), and the other group included native and flowering peaches (Group II). Peaches of the European group tended to stand between Group I and II. It is interesting to note that the differentiation of cultivars in terms of sugar composition was observed in the Meiji era. `Hijoto', an eating peach cultivar belonging to the Northern group in China, showed a similar sugar composition to that of native and flowering peaches (Group II). This finding suggests that the native and flowering peaches introduced to Japan in the Yayoi era (about B.C A.D. 300), may have been derived from peaches of the Northern group with a low fructose content such as `Hijoto'. Then, where did the cultivars with a high content of fructose such as `Shanhaisuimitsuto' arise from? Further studies will be needed to elucidate this point. Recently released cultivars and selections were placed in the 4th quadrant. The sugar composition of the progenies of cultivars and selections seemed to be similar to that of the parents and these materials were close in the scatter diagram. For example, selection 197 was placed near the parental cultivar `Akatsuki' and selection was also placed near the parent `Yuzora'. Kikuchi also (10) demonstrated that open-pollinated seeddlings of peach tended to show characters similar to those of their mother parents and did not exhibit large variations genetically due to their selfpollination ability. G-29-2 (flowering peach `Zansetsushidare' x eating peach `Akatsuki') which was selected as intermediate mother plant showed a low fructose percentage. Moreover, G-46-2 (self-pollination of G-29-2) contained a high percentage of fructose (data not shown). This finding suggests that if native and flowering peaches as parent were used for crossing to eating peaches, the F1 may require further crossing to attain a sugar composition similar to that of the eating peaches. Acknowledgments We are grateful to Dr. M. Yoshida, Mr. H. Kyotani, Mr. K. Nishimura (Fruit Tree Research Station), Mr. M. Yamaguchi (Yamagata Prefectural Horticultural Experiment Station) and Dr. S. Yamaki (Nagoya Univ.) for their suggestions and for critically reading the manuscript. We are also grateful to Mrs. S. Hayashi for her technical assistance. Literature Cited 1. ARDHBOLD, H. K Chemical studies in the physiology of apples. IX. The chemical composition of mature and developing apples, and its relationship to environment and to the rate of chemical changes in store. Ann. Bot. 42: BIELESKI, R.L Accumulation and translocation of sorbitol in apple phloem. Austral. J. Biol. Sci. 22: CRAFT, C.C Polyphenolic compounds in Elberta peaches during storage and ripening. Proc. Amer. Soc. Hort. Sci. 78:

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