Red Bayberry: Botany and Horticulture* Kunsong Chen, Changjie Xu, and Bo Zhang Department of Horticulture Huajiachi Campus, Zhejiang University Hangzhou, 310029, P

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Red Bayberry: Botany and Horticulture* Kunsong Chen, Changjie Xu, and Bo Zhang Department of Horticulture Huajiachi Campus, Zhejiang University Hangzhou, 310029, P. R. China

Ian B. Ferguson The Horticulture and Food Research Institute of New Zealand Private Bag 92 169 Auckland, New Zealand

I. INTRODUCTION A. History B. Distribution C. Commercial Production II. BOTANY A. Taxonomy B. Morphology and Anatomy III. PHYSIOLOGY A. Vegetative Growth B. Flowering and Fruit Set C. Fruit Development IV. ENVIRONMENTAL REQUIREMENTS A. Temperature B. Water C. Soil D. Light E. Elevation and Exposure

*This review was supported by the State Key Basic Research and Development Plan (G2000046806), the National Natural Science Foundation of China (30170660), and Zhe- jiang Natural Science Foundation (ZD0004), and was also a part of a cooperative program between The Horticulture & Food Research Institute of New Zealand and Zhejiang Uni- versity. We thank Dr. Grant Thorp for critically reading the manuscript.

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V. HORTICULTURE A. Propagation B. Field Cultivation C. Pests and Diseases D. Harvest and Handling E. Storage and Transportation F. Processing VI. CONCLUDING REMARKS LITERATURE CITED

1. INTRODUCTION

Red bayberry (Myrica rubra Sieb. & Zucc., Myricaceae) is a subtropical fruit tree native to China and other Asian countries, bearing a delicious, berry-like fruit (Fig. 3.1). Gengmin Wu, founder of modern Chinese horticulture, praised it as a “precious Southern Yangtze fruit of early summer ” (Wu 1995). The fruit ripens in June and early July in the main Chinese production areas of Zhejiang and Jiangsu provinces, earlier than most other local fruits. The rich red colors and appealing flavor make this juicy fruit popular with consumers; it is eaten like a cherry.

Fig. 3.1. Red bayberry (Myrica rubra) fruit and trees. A and B: mature fruit showing (B) the segmented juicy flesh and the hard stone. C: fruit growing on the outer space of the canopy. D: trees growing on hillsides, a common cultivation practice in China. Photos by Jiangguo Xu. 4080 P-03 9/17/03 11:04 AM Page 85

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In addition to being consumed fresh, various products such as juice, canned fruit, jam, wine, sweets and salted fruit are produced. Present- day commercial cultivation is still largely restricted to China. The fruit and roots of red bayberry have been used as important components of traditional Chinese medicines for more than 2000 years (Li 1578), the fruit being beneficial for treating congestion, coughs, diges- tive problems, and diarrhoea. The root also has wound healing properties. In recent years, a number of pharmaceutically active compounds have been identified from the various plant parts (Zhang et al. 1993; Chi et al. 2000; Yi and Liu 2000; Zhong et al. 2000). The evergreen tree has a bushy, round canopy and grows well in soils of low fertility, having an association with the nitrogen-fixing bacterium Actinomyces frankia. The tree is used in China to increase the organic matter content of soil, reduce soil erosion, and to enhance the landscape (Wang and Chen 1989). Red bayberry is often interplanted with existing vegetation such as pine or other natural forest trees (Wang et al. 2001). While the fruit is well known throughout China, where there is a con- siderable body of literature on various aspects of production, it is little known elsewhere. There is a short general review on red bayberry available in English (Li et al. 1992), and a review of research progress in China has recently been published (Li et al. 1999). This review will cover the botany and horticulture of red bayberry, most of it based on Chinese publications.

A. History In China, red bayberry has been known by a variety of names. Yangmei is the most common name in Chinese. Shizheng Li, in Compendium of Materia Medica (1578), wrote: “The shape of the tree is similar to poplar (Yang), and the taste of the fruit is somewhat like mume (Mei), thus it is named Yangmei.” Shumei (strawberry tree) is used in Taiwan. Zhuhong is a common name in Fujian province and, elsewhere in China, names such as Shanyangmei and Zhurong are used. The English names for this fruit include red bayberry, Chinese bayberry, and waxberry. The fruit has a very long history in Chinese civilization. The earliest records come from the Neolithic site at Hemudu, Zhejiang province, indi- cating that the fruit has existed as a foodstuff for more than 7,000 years (Yu 1979; Wu 1984). Red bayberry fruit and stones have also been found in the Mawangdui tumulus of the Western Han Dynasty (206 B.C.E.–25 C.E.) in Hunan province and the Luobowan tumulus in Guangxi Zhuang Autonomous Region (Yu 1979). Nan Fang Cao Mu Zhuang, a book on the properties of various plants from southern China, written by Ji Han during the Jing Dynasty (265–420), recorded the cultivation of red bayberry 4080 P-03 9/17/03 11:04 AM Page 86

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and its use in wine making (Ji 304). By the Song Dynasty (960–1279), the Wu-Yue area (Jiangsu and Zhejiang provinces today) was well known for red bayberry production and the fruit recognized for its quality and quan- tity; locations close to Ningbo and Taizhou in Zhejiang province are still the most important production areas.

B. Distribution Red bayberry originated in southeastern China, where it is still found in the wild and is the source of seed for rootstocks. It is now distributed south of the Yangtze River and north of Hainan Island, approximately 97° to 122°E longitude, and 20° to 31° N latitude. This distribution is similar to that of citrus, loquat, tea, and bamboo, except that red bayberry can withstand lower temperatures (Maio and Wang 1987; Maio et al. 1995). The major commercial production area is concentrated in Zhe- jiang, Fujian, Jiangxi, Jiangsu, Guangdong, and Guizhou provinces. There is some production in Yunnan, Guangxi, Sichuan, Hunan, Shanxi, and Taiwan, from semi- or wholly wild trees (Wang 1995). Outside of China (Yu 1979; Wang 1987) the crop is grown in Thailand, although fruit quality is often poor and the area limited. In Japan, it is grown in Tokushima, Kochi, Ehime and the western part of Honshu. In Europe and America, red bayberry trees are used mainly for ornamen- tal purposes. There are a number of closely related species (described below) that are cultivated. Myrica integrifolia Roxb. is distributed in India, Sri Lanka, Burma, and Vietnam, where it is confined to home gar- dens, producing small and acid fruit, usually used for jam or medicine. Myrica esculenta Buch.-Ham. is found in India, Nepal, and Vietnam as well as in southwest China. Myrica faya Ait. has fruit suitable for fresh consumption and is grown in the Canary Islands.

C. Commercial Production Production of red bayberry has increased dramatically; the cultivated area in China in 1995 was 130,000 ha. The crop has become one of the most important fruit tree crops in south China (Liu 2000; Wang et al. 2001). In Zhejiang province, the cultivated area and production were 4,400 ha and 26,500 tonnes (t) in 1959, 17,500 ha and 46,200 t in 1985, and 38,378 ha and 129,750 t in 2000 (Wang et al. 2001). As a result, red bayberry is second only to citrus among the fruit crops of the province, and the yield is expected to continue to increase. Most production is consumed locally, but an increasing proportion is being exported both within and outside of China. 4080 P-03 9/17/03 11:04 AM Page 87

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II. BOTANY

A. Taxonomy

1. Species. The Myricaceae are widespread in tropical, subtropical, and temperate areas of the world. They consist of two genera, Comptonia and Myrica, both of which are cultivated. The genus Myrica Linn contains more than 50 species of which six are found in China (Yu 1979; Maio and Wang 1987; Qu and Sun 1990; Wang 1995; Li et al. 1999). More recently, RAPD (Random Amplified Polymorphic DNA) markers have been successfully used in classification and identification of Myrica species (Lin et al. 1999). Myrica cerifera L. originating from North Amer- ica was clearly distinguished from three Chinese species (Myrica adenophora Hance, Myrica esculenta Buch. -Ham, and Myrica rubra Sieb. & Zucc.), which clustered together.

Myrica rubra Sieb. & Zucc. Red bayberry (2n = 16) is an evergreen tree growing to a height of 5 to 10 m, distributed in southern China, but also found in Japan, South Korea, and The Philippines. The bark of young trees is smooth and yellow-green, while that of old trees is grey-brown with white spots and narrow cracks. The canopy is uniform and round or slightly flattened. The branches are frail and easily broken, and the leaves alternate and simple, with blades 5–14 cm long and 1–4 cm wide, usually with smooth margins, although sometimes serrated. The upper and lower leaf surfaces are smooth without hairs, the upper lustrous and dark green and the lower light green. The plant is dioecious, although occasionally monoecious, with the inflorescence forming in axillary buds. The staminate inflorescence is a compound catkin, 1–3 cm long, columnar, and yellow-red; the pistillate inflorescence is a simple catkin and shorter and thinner, filaceous, bright red, with two longitudinal grooves along the stigma. The fruit is a small drupe and consists of a fleshy pericarp comprising individual segments and a hard endocarp protecting a single seed. It is red, purple, white, or pink when ripe, depending on the cultivar. Flowers bloom during February to April and fruit ripen during May to July.

Myrica esculenta Buch.-Ham. This is also known as Yangmei Dou in Guizhou. It is mainly distributed in mountains at elevations of 1,500–2,500 m in southwest China (Sichun, Yunnan, Guizhou, Guang- dong, and Guangxi), and in India, Nepal, and Vietnam. The tree is 4–15 m high, with light-colored bark. The shoots are thin and covered with numerous hairs. The leaves are thick, hairless, and oval, 3–12 cm long 4080 P-03 9/17/03 11:04 AM Page 88

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and 1.2–4.5 cm wide, with few or no marginal indentations and sparse yellow glands on the lower surface. The petiole is covered with white hairs. The plant is dioecious and the inflorescences are catkins, the flowers having two bright red, thin stigmas. The fruit are ovoid, about 1 cm long and 0.8 cm in diameter, with an average weight of about 0.5 g, and with red flesh. The edible portion constitutes about 80% of the fruit weight and, when ripe, the soluble solids concentrations are about 12.5% and total acids 1.3%. Flowers bloom during September to October and fruit ripen during the following March to April. There are seven sub- species or variants of this species, which can endure high humidity and temperatures down to –6°C, and which will also grow well in dry areas.

Myrica nana Cheval. This species is variously known as Yunnan Yang- mei and Dian Yangmei and is mainly distributed in subtropical and temperate zones of Yunnan, Guizhou, and Xizhang in China. The plant is a shrub 0.5–1.0 m high, with thick, strong shoots. The bark is rich in tan- nin, and the olive green leaves are narrowly obovate or occasionally elliptic. The upper leaf surface usually has small depressions associated with yellow glands and sunken venation; the lower leaf surface has glands and protruberant venation. Petioles are short and covered with short soft hairs. Fruit are round to oblate, about 2 cm long and 2 cm in diameter, with an average weight of 3.5–5 g. Ripe fruit are red, with an 80% edible proportion and soluble solids levels of 9–10% and total acids of nearly 4%. Flowering may last 1 month from February to March, and fruit normally ripen about 4–6 months after flowering. The species has four variants and two derivatives: M. nana var. integra Cheval., M. nana var. luxurians Cheval., M. nana Cheval, var. humifusa N. Liu et Z. F. Li, var. sp. nov., M. nana Cheval, var. alba N. Liu et Z. F. Liu et Z. F. Li var. sp. nov., M. nana cheval, f. cerea N. Liu et Z. F. Li, f. niv. and M. nana Cheval, f. gracilifolia N. Liu et Z. F. Li, f. onv.

Myrica integrifolia Roxb. This species is mainly distributed in the mountains of South Asia at an elevation of 900–1,400 m in countries such as India, Sri Lanka, Burma, and Vietnam, and also in the western part of Yunnan in China. It is a large evergreen shrub or tree, 8–10 m high with dense shoots covered with dense soft hair. Leaves are lanceolate, bright green, with smooth margins, but sometimes undulate. The plant is dioecious, with oval, red, acid fruit when ripe, weighing about 2.4–3 g, with 10.5% soluble solids and an edible portion of about 85%. Flowers bloom during February to March, and fruit ripen from April to May. The species prefers an acid soil and high humidity, and usually grows in forests together with deciduous plants. 4080 P-03 9/17/03 11:04 AM Page 89

3. RED BAYBERRY: BOTANY AND HORTICULTURE 89

Myrica arborescens. S. R. Liet X. L. Hu, sp. nor. The species is distributed in the south and southwest part of Yunnan in China, and in Burma, growing in the mountains at an elevation of 900–1,400 m. Plants prefer an acid soil and humid climate. It is an evergreen tree, about 15 m in height, with a trunk of more than 300 cm in circumference. Shoots have long white hairs and few glands, and the leaves are larger than for other species, with blades 8–19 cm long and 2–4 cm wide, elongated lanceolate or ellipsoidal in shape, and having obvious sharp sawtooth edges on the abaxial sides. The upper venation of young leaves is covered with white soft hair, while yellow glands cover the lower surface, and the secondary veins are also covered with long white soft hair. Plants are dioecious, with an ovary surrounded by long hairs and the fruit are round or ovoid, 2.5–3 cm in diameter and yellow-white or green-white when ripe. Flowers bloom during February to March, and the fruit ripen from April to May.

Myrica adenophora Hance. Known variously as Xiyeyangmei, Pomei, and Qingmei, it is mainly distributed in Hainan province, the southern part of Guangdong province and southwestern Guangxi province. The variant M. adenophora var. kusanoi Hayata is grown in Taiwan. It is a shrub or small tree, 1–6 m high. The bark is gray and the young thin shoots are covered with short soft hair and yellow glands. Leaves are obovate, both sides with numerous glands. The medial vein has short soft hair, as does the petiole. Staminate and pistillate inflorescences form in axillary buds. The red fruit are oval, small, and less than 1 cm in diameter. Flowers bloom from October to November, and the fruit ripen during February to May.

2. Cultivars. There is little agreement on cultivar classification. Fruit color and ripening date have been used to identify different groups of cultivars (Yu 1979; Wu 1984; Maio and Wang 1987; Qu and Sun 1990). Guo and Li (1994) sorted the cultivars into five groups and nine types based on physical characters of the stone, fruit, and leaves, while Chen (2000) divided them into two types based on soft and hard fruit flesh. The Chinese Red Bayberry Cooperation Association has established three types based on the fruit ripening date (Chen 2000). Recently, peroxidase isozyme analysis, chromosome banding, and karyotypic analysis have been introduced into varietal classification (Lin et al. 1999). Ripe fruit color is one of the more useful criteria used (Qu and Sun 1990; Li et al. 1992), and this has resulted in four cultivar groups described as follows: 4080 P-03 9/17/03 11:04 AM Page 90

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Wild. This group, also called wild black, is found growing in the wild and is used as rootstocks. The fruit are red and acid, with small flesh segments, and ripen earlier than other types, in Zhe- jiang at about the beginning of June. Red. Fruit of this group are red when ripe, and usually larger and of better quality than other types. Representative cultivars include ‘Shuimei ’, ‘Chise’ , ‘Dongkui’ in Zhejiang, and ‘Dayexidi ’ in Jiangsu. Black. This group has the best fruit quality, with large flesh segments and a stone that can be easily separated from the flesh. The fruit turns from red to red-black during ripening. Representa- tive cultivars include ‘Biqi’ in the Cixi-Yuyao district, ‘Wandao Yangmei’ in Dinghai, ‘Ding-ao Mei’ in Wenzhou, ‘Datanmei’ in Yuhang in Zhejiang, ‘Wumei’ in the Dongting area in Jiangsu, and ‘Shanwu’ and ‘Wuhesu’ in the Chaoyang area in Guangdong. White. The ripe fruit of this group are various shades of white. Yield and fruit quality is less than for fruit of the black or red groups, and it is not so widely planted. ‘Shuijing Yangmei’ (crystal- looking) in Shangyu is the best cultivar of this type grown in Zhe- jiang province. Zhang and Miao (1999) distinguished 268 cultivars in China. Fruit characteristics vary widely among these cultivars, as shown by the percentage of cultivars in different groups on the basis of ripening date, fruit color, and fruit weight (Table 3.1). The cultivars in Zhejiang province can be sorted by ripening date into three groups (Table 3.2).

Table 3.1. Distribution of fruit attributes among different Chinese cultivars of red bayberry. Source: Zhang and Miao (1999).

Ripening Date Flesh Fruit Size

Distribution Distribution Weight Distribution Month (%) Color (%) (g) (%)

April 1.1 White 9.3 <6 6.3 May 6.3 Pink 5.6 6.1–9 25.8 Early June 13.7 Red 17.2 9.1–13 46.6 Mid June 18.7 Deep red 7.8 13.1–15 14.9 Late June 47.8 Purple 37.3 >15 6.3 Early July 12.4 Deep purple 3.4 Purple black 13.8 Jet black 5.6 4080 P-03 9/17/03 11:04 AM Page 91 .7 0.5 .7 0.9 0.6 1 0.90.9 0.6 0.6 .7 .7 .7 .7 8.7 1.1 1 9 9 9.5 1.4 0.8 .7 .7 .7 .7 95 12.8 10 9494 11 11.5 9 95 12 Edible Soluble Total Fruit Characteristics 0 0 .7 .7 Wanqimimei 2.8 2.7 12.5 Zaoqimimei 2.6 2.5 9 Ding-aomei 2.7 2.9 94 11 Wandaoyangmei 2.8 2.7 11.2 Ripe fruit attributes of early-, medium-, and late-maturing cultivars red bayberry grown in Zhejiang. Data are averages Ripening Width Length Weight portion solids sugars Acidity Stone Table 3.2. from unpublished sources. dateEarly (July 5) Dongkui 3.7 3.9 20–25 96 12

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B. Morphology and Anatomy

1. Roots and Nitrogen Fixation. The trees have a shallow, fibrous root system, usually occupying the top 5 to 40 cm of the soil, and typically one- to twofold greater than the diameter of the canopy. The plants form an association with Actinomyces frankia, a nitrogen-fixing bacterium. The nodules are usually greyish yellow, fleshy, and randomly distributed on the roots (Miao and Wang 1987; Wang 1995). In transverse section, the nodules are round and symmetric, and their color changes from oyster white to yellow brown with maturation, and dark brown with senescence (Wang and Huang 1990). Nitrogenase activity of mature nodules is higher than that of the young ones, with two peaks of activity observed in June and October. The lowest activity is found in Janu- ary, and can be inhibited by nitrate (Wang and Huang 1990; Wu and Gu 1994). Measurements by Z. Li et al. (1993) have shown that the average nodulation mass in a 7-year-old red bayberry sapling was 52 g/tree with 460 kg/ha of nitrogen fixed per year. There are clear advantages in this nitrogen-fixing capacity in terms of fertilizer use and soil fertility.

2. Shoots. The bark color varies with development stages, from pale yellow-green in young trees to grey-brown in mature trees. The mature branches, which have very visible lenticels, are weak and easily broken by wind. There are four types of shoots: rapidly growing extension shoots (water shoots), vegetative shoots, bearing shoots, and staminate flowering shoots (Miao and Wang 1987; Wang 1995). Water shoots are usually longer than 30 cm and vegetative shoots shorter than 30 cm, with longer internodes. Well-developed axillary buds on vegetative shoots are the potential fruiting shoots. New leaf and shoot growth generally arises from buds near the shoot apex (Miao and Wang 1987). The season of growth affects leaf size: The spring leaves are the biggest, followed by those produced in the summer, and then the autumn. Leaf color also varies with the season; the spring leaves are deep green, in the summer a lighter green, and autumn leaves are pale green. These characters are also used to estimate nutritional status. Leaves remain on the tree usually for 12–14 months, with a marked peak in abscission just prior to the spring growth flush.

3. Flowers. Flower buds of red bayberry are simple, forming in axillary buds and never in terminal buds, where only vegetative (leaf) buds occur. The flower bud is larger than the leaf bud, and can be distinguished in winter before budbreak. New growth in spring occurs from axillary buds on shoots grown in the previous season. Flower bud differentiation has been well studied, mainly on ‘Xiyeqing ’and ‘White’ cul- 4080 P-03 9/17/03 11:04 AM Page 93

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tivars (Li and Dai 1980). Only apical buds and 4–5 axillary buds can develop into leaf or flower primordia; the other buds remain latent for quite some time and can be stimulated to develop into shoots. This character is useful when replacement of the canopy and fruiting shoots is needed. Leaf buds break about 20 days later than flower buds, and leaf unfurling occurs about 15 days after that. Red bayberry is a typical dioecious fruit tree, but it is difficult to identify sex before flowering. G. Li et al. (1993) established a method based on isozymes patterns and composition of phenolic compounds. The flower is small, unisexual, without perianth, and is wind-pollinated. Each staminate flowering shoot can contain 2–60 inflorescences, normally between 15 and 20, and is part of a compound inflorescence that bears 15–36 catkins, each catkin composed of 4–6 staminate flowers. Staminate inflorescences form in the leaf axil, and are cylindrical or long conical in shape, with the color changing from garnet in young flowers to yellow-red or bright red in mature ones. The distal staminate flowers open first, and the flowering period can be as long as 40–50 days for a whole tree. Staminate flowers are arranged as a corymb, without pedicel or receptacle, and are surrounded by greenish white bracts. Each staminate flower has two stamens, and unequal filament length (Fig. 3.2). The filaments are yellowish red or bright red, and usually bear anthers at the apex. Anthers are kidney-shaped, bright red, fused at the base, and

Fig. 3.2. Morphology of staminate floral structure of red bayberry (from Wang 1995). 1. Staminate flowering shoot. 2. Staminate compound catkin. 3. Individual staminate catkin. 4. Bract for compound catkin. 5. Bract. 6. Stamen. 4080 P-03 9/17/03 11:04 AM Page 94

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release yellow pollen through longitudinal splits. The pollen grains are small (20 µm diameter) and can be carried as far as 1000 m by wind (Miao and Wang 1987). Each anther holds more than 7,000 pollen grains, and each staminate inflorescence contains 200,000–250,000 pollen grains. Each pistillate flower shoot has 2–60 pistillate inflorescences, the average being 15 to 20. The catkins contain 7–26 flowers (average 14). The ovary is unilocular, and the style bright red, 0.5–1 cm in length, with a Y-shaped stigma with 2, sometimes 3–4 sites of dehiscence. Terminal flowers of the pistillate inflorescence usually flower earlier than others (Fig. 3.3), and the flowering period for a whole tree may last for about 30 days. Occasionally, mixed inflorescences occur with pistillate flowers at the top and staminate flowers at the base (Fig. 3.4). Staminate flowers open after 2–3 pistillate flowers have opened in the same inflorescence. However, pistillate flowers in a staminate inflorescence have only been reported once (Miao and Wang 1987).

4. Fruit. The fruit have stones like peach and plum, with an edible part more like a berry (Fig. 3.1). The fruit is usually spherical, and the skin has a waxy coat (Miao and Wang 1987). Fruit size varies among cultivars (Table 3.2), generally being greater than 2 cm in diameter, with some reaching 3 cm or more. Fruit of the wild types are less than 2 cm in diameter, and fruit of Myrica nana Cheval grown in Guizhou, China, are the smallest, measuring less than 1 cm in diameter.

Fig. 3.3. Morphology of pistillate floral structure of red bayberry (from Wang 1995). 1. Pistillate flowering shoot. 2. Pistillate inflorescence. 3. Pistillate flower. 4. Bract for inflorescence. 5. Bract. 6. Pistil. 7. Longitudinal section of fruit. 8. Flesh segment. 4080 P-03 9/17/03 11:04 AM Page 95

3. RED BAYBERRY: BOTANY AND HORTICULTURE 95

Fig. 3.4. Inflorescences of red bayberry (from Liu 2000). 1. Staminate inflorescence. 2. Bisexual inflorescence. 3. Pistillate inflorescence.

The epicarp of the fruit consists of thin-walled parenchyma cells, in which the vascular bundles are arranged like a cup. The parenchyma- tous mesocarp makes up the edible portion. The endocarp consists of a hard stone with small, round, thick-walled sclerenchyma cells, most of which are flattened. The stone includes a seed coat, embryo, and large, soft, waxy cotyledon (Fig. 3.5). The epicarp and mesocarp (flesh segments) develop from the outermost layers of endocarp and usually consist of 1,100–1,300 flesh segments. The length, thickness, pointedness, and hardness of the flesh segments varies with cultivars. Tree age, yield, soil nutrition, humidity, degree of maturation, and position of fruit on the tree influence fruit quality (Li et al. 1992). More mature trees, heavier fruit loads, more abundant nutrition, drier climates, and sun exposure will result in fruit with more pointed flesh segments. In some cultivars, a single fruit may contain both round and pointed segments. The former would be located

Fig. 3.5. Morphology of the fruit of red bayberry (from Miao and Wang 1987). 1. Epicarp. 2. Mesocarp (flesh segment). 3. Endocarp. 4. Seed coat. 5. Seed (cotyledon). 4080 P-03 9/17/03 11:04 AM Page 96

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in the middle of the fruit, with the latter in the outer parts. Fruit with round flesh segments are usually more succulent and taste better, while those with sharper flesh segments tend to have a longer storage life.

III. PHYSIOLOGY

A. Vegetative Growth Root growth usually commences in late February, and the root system has three major growth peaks, in late May, mid-July, and early October (Miao and Wang 1987). Vegetative growth has up to three growth flushes each year. Summer shoots are the most abundant, accounting for 60–70% of the total shoots each year, and these make up most of the bearing shoots in the following season; spring shoots, summer shoots, and sometimes autumn shoots will become flowering branches. Winter shoots can develop into bearing shoots depending on weather and nutrition (Miao and Wang 1987). Spring shoots occur from late March to late June, developing from the spring shoots or summer shoots of the previous year; summer shoots, from June to August, developing from the spring shoots of the same year and bearing shoots of the previous year; autumn shoots, from early August to October, developing mainly from the spring and summer shoots of the same year (Li 2001). Except for the cultivars ‘Biqi’ and ‘Ding-ao’, autumn shoots do not become bearing shoots, as they form too late (Miao and Wang 1987). As might be expected, spring shoots are the longest and autumn shoots the shortest. Leaves unfurl during late March to early April, and develop rapidly in May. Old leaves begin to abscise at the beginning of May, and reach an abscission peak when spring shoots stop growing. Leaf abscission is influenced by both the growing environment and the cultivar. Trees growing on clay soils, attacked by pathogens, or generally weak trees, usually shed leaves earlier, and abscission is postponed in late maturing cultivars such as ‘Wandao Yangmei’.

B. Flowering and Fruit Set Flower-bearing shoots develop from the strong spring and summer shoots of the previous year. Although spring shoots are the best shoots for bearing fruit, they are not sufficient for adequate crop loads, and since summer shoots are the most abundant, they become the most important source of fruit and the key factor influencing yield in the next year (Li 2001). The fruit capacity of a bearing shoot varies with shoot length, and shoots are divided by length in the ‘Biqi’ cultivar into four types: extended, long, 4080 P-03 9/17/03 11:04 AM Page 97

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medium, and short shoots (Miao and Wang 1987). Extended shoots are more than 30-cm long with limited flower buds at the end and most of the buds will be shed after flowering. Long shoots are thin, 20–30 cm in length, with 5–6 flower buds at the end, and a low rate of fruit set. Medium shoots are 10–20 cm long, with a heavy load of flower buds except at the apex; these shoots bear the highest fruit load. Short shoots, 1–10 cm in length, some as short as 1–2 cm, carry many flower buds, with high rates of fruit set. When flowering shoots constitute about 40% of the total shoots, a high, steady yield can be predicted (Chen et al., pers. comm.), but when this ratio is more than 60%, alternate bearing may develop. Flower bud differentiation begins shortly after the cessation of summer shoot growth (Li and Dai 1980). Physiological differentiation of inflorescence primordia of the ‘Xiyeqing’ and ‘White’ cultivars occurs in early or mid-July. During the early stage of flower bud differentiation, abortive pistillate inflorescences emerge and these will be shed rather than open in the next spring. Inflorescences that differentiated after early August normally develop fruit. Morphological differentiation of the primordia of pistillate inflorescences begins in mid-July, and the first small flower primordium forms in late July. The formation of primordia of the staminate inflorescences begins at the end of the same month. Flower bud differentiation stops at the beginning of December. Physio- logical differentiation of the flower buds develops 2–4 weeks earlier than morphological differentiation, and takes about 3 months to complete. Autumn shoots are unable to develop flower primordia in time for the normal flowering period. Flowering date varies according to cultivar and growing conditions (Miao and Wang 1987). Some staminate flowers open in late January, some during February and March, reaching full bloom in March to April. This also happens with pistillate flowers and, as a result, individual pistillate inflorescences commonly carry fruit and opening flowers at the same time. Flowering can be divided into six stages: bud break, inflorescence break, first bloom, full bloom, end of bloom, flower drop (Miao and Wang 1987). Usually, the first bloom stage is when 5% of anthers or stigmas are exposed, full bloom stage is at 75%, and end of bloom when the anther exposes pollen and becomes yellowish-brown or the stigma wilts (Miao and Wang 1987). The period of flowering can span 39 days for staminate flowers and 27 days for pistillate flowers. Though pistillate flowers open later and last for a shorter time than the staminate ones, full bloom stage is longer (13 days) than that of the staminate flowers (5–7 days), and this benefits pollination (Miao and Wang 1987). The highest fruit set occurs in the uppermost five inflorescences on bearing shoots, but the first inflorescence is the predominant one, bearing 4080 P-03 9/17/03 11:04 AM Page 98

98 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

20–45% of the total fruit. The rate of fruit set is only 2–4% for the whole tree (Wang 1995). The main peak in abscission of inflorescences and fruitlets is late April to early May. Additional peaks occur in the middle of May and just prior to harvest in some cultivars such as ‘Shuimei’ and ‘Hunanzhong’, but not in the cultivars ‘Dongkui’ and ‘Wandao Yangmei’ (Miao and Wang 1987).

C. Fruit Development The time from fruit set to maturation is 60–70 days (Miao and Wang 1987). The fruit of leading cultivars in Guangdong and Fujian ripen during late May to early June, the early-maturing cultivars in Zhejiang and Jiangsu during middle to late June, and the late-maturing cultivars in early July. Fruit on trees in inland areas ripen earlier than in coastal areas because of greater diurnal temperature differences in inland climates. Fruit growth follows a double sigmoid curve in both fruit size (diameter; Fig. 3.6) and fruit weight. For example, ‘Biqi’ and ‘Dongkui’ fruit (Miao and Wang 1987; Gong 1995) develop rapidly and reach the max-

Fig. 3.6. Changes in length, diameter, and ratio of length to diameter during fruit development of ‘Donkui’ red bayberry (from Gong, 1995). 4080 P-03 9/17/03 11:04 AM Page 99

3. RED BAYBERRY: BOTANY AND HORTICULTURE 99

imum of the first growth stage (about 20 days) just after the first peak of fruit abscission in early May. This period of rapid growth is followed by a pit hardening stage (15–20 days) and a second burst in fruit growth, characterized by increases in water content, weight, and color of fruit just prior to fruit ripening on the tree. Fruit size increases synchro- nously with fruit weight and there is a strong correlation between the size of the seed and the fruit. Water content of the fruit increases from the fruitlet to the pit hardening stage, then decreases gradually, before increasing again as the fruit matures (Miao and Wang 1987). The daily increment in fresh weight of the fruit flesh during the maturation stage is three times that at the first rapid growth stage; there is no similar difference in dry weight increase. The length of the pit hardening stage is influenced by fruit size as well as cultivar—the bigger the fruit, the shorter the length of the stage. Total soluble solids (TSS) contents increase with fruit maturation to the point of harvest, with sugars accumulating rapidly during the final 2–3 weeks (Chen et al. 1992). Larger fruit are commonly sweeter than smaller ones, and there is a positive correlation between TSS content and degree of pigmentation. Citric acid is the most abundant of the fruit organic acids, accounting for 97% of the total, with malic, oxalic, succinic, isocitrate, fumaric and other acids making up the remaining 3%. Chen et al. (1992) found that total acidity increased rapidly from about 40 days before harvest, but then decreased as the fruit began to ripen on the tree. Smaller fruit tend to have higher acidity than larger ones (Chen et al. 1992). The pigments responsible for the fruit flesh color (red, and purple to black) are anthocyanins, the levels of which vary with cultivar, fruit development, and environmental factors, especially light. Cyanidin-3- glucoside has been identified as the principal fruit pigment, with pelargonin-3-monoside and delphinidin-3-monoside as minor components (Lin 1984; Ye et al. 1994). Chlorophyll contents decrease during fruit maturation.

IV. ENVIRONMENTAL REQUIREMENTS

A. Temperature The tree performs well in tropical, subtropical, and temperate zones, with optimum temperatures of 15–20°C. It can endure winter freezing with average temperatures of more than 2°C and an absolute minimum 4080 P-03 9/17/03 11:04 AM Page 100

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above –9°C. However, the trees can be damaged and the yield for the following year reduced by more than 20% if the minimum temperature falls below –9°C and a maximum temperature of less than 0°C lasts longer than about three consecutive days. Because the flowering period is quite late, unlike peach and apricot, flower or fruit freezing seldom occurs. To get high yields and quality, the growing conditions should include an annual average temperature >14°C and accumulated temperature (>10°C) of more than 4,500 degree days. Outside these conditions, small, very acid and poor-tasting fruit are likely to be produced. High temperatures during May and June, during the second fast growth phase, also may result in fruit with high acid and low sugar contents. For example, one study has shown that when the mean May–June temperature was 20–22°C, the acid content was 0.7–1.3% and the ratio of soluble solids to acids was 9–16, but when the mean temperature was raised by 2°C, the acid content increased to 1.4–1.9% and the ratio decreased to 6–7 (Miao and Wang 1987). High temperatures (e.g., a mean temperature higher than 28°C) can cause damage, particularly to young, newly transplanted trees, and affect the development of flower buds and fruit-bearing shoots. The optimum temperature for photosynthesis of red bayberry is less than 20°C (Ruan and Wu 1991).

B. Water High humidity and a plentiful water supply assures high cropping and high-quality fruit (Chen et al. 1992). In China, most trees are planted on hills and slopes without artificial irrigation (Fig. 3.1). Annual precipitation and its seasonal distribution are the most important factors influencing tree growth and fruit production. In Zhejiang, precipitation of more than 1000 mm is usually required (Li et al. 1992), and the optimum is between 1300–1700 mm. Low humidity results in poor pollination and reduced yields. Rain- fall of more than 260 mm during February and April favors the growth of the root system, leaf development, blossoming, and fruit set. The period May to June is of particular importance for fruit maturation, warmth and light being needed to enhance fruit color. Rainfall of more than 160 mm is required in June, since less than 100 mm will result in small, poor-quality fruit, and a reduction in yield. Having sunny days during late summer to early autumn is beneficial for the accumulation of carbohydrates and flower bud differentiation. Most of the important commercial areas of red bayberry production in China do not have extremes of temperature and humidity. 4080 P-03 9/17/03 11:04 AM Page 101

3. RED BAYBERRY: BOTANY AND HORTICULTURE 101

C. Soil A deep, fertile, acid soil with a pH of 4–5.5 is the optimum for cultivation. In mountainous areas, successful growth of plants such as Dicra- nopteris pedata (Houtt.) Nakaike, Rhododendron simsii Planch., pines, firs, bamboos, Cyclobalanopsis glauca (Thunb.) Oerst., Quercus acutis- sima Carruth., or Castanopsis sclerophylla (Lindl.) Schott. indicate suitable conditions for bayberry cultivation (Li et al. 1992). Red bayberry is tolerant of shade and can be planted in less-fertile soils and fine sandy loams. Planting in clay or sandy soils can result in weak and/or dwarfed trees. The presence of nitrogen-fixing root nodules allows the trees to perform well on infertile but well-drained slopes. In fertile flat soils, trees may have excess vegetative growth and consequently shed flowers and fruit. The species is susceptible to boron deficiency, which can result in small leaf size.

D. Light Although tolerant of shade, sufficient light is needed for cropping. Ruan and Wu (1991) found that the tree had significant winter photosynthetic –1 –2 rates, although the net rate was usually below 1.5 mg CO2 d m . Fruit of poor quality and small size may be produced on south-facing slopes where direct light and heat is excessive (Li et al. 1992).

E. Elevation and Exposure Flowering and fruiting have been shown to be delayed by up to 20 days with an increase in elevation from 50 to 600 m (Chen et al. 1989). Trees grown at between 200 and 400 m produce fruit of high quality, with soluble solids levels of 9.9–10.1% and acidity 1.8–1.55% (Chen et al. 1992). Elevations greater than 500 m are unsuitable for cultivation since annual temperatures are usually below 15°C. The trees are not tolerant of strong winds because of a shallow root system, dense branches and leaves, large canopy, and brittle shoots.

V. HORTICULTURE

A. Propagation The most widely used methods for propagation include seeds, grafting, and layering (Wang 1995). Propagation from seed has been the traditional practice in many areas in China, especially for rootstocks. Seeds need to 4080 P-03 9/17/03 11:04 AM Page 102

102 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

be stratified, and are generally sown in November. The soil should be deep, well drained, and with reasonable organic matter. Soils previ- ously used for citrus, peach, pine, cypress and red bayberry itself are usually unsuitable for sowing, probably because of nutrient depletion, with soils used for annual crops such as rice, vegetables and leguminous plants being preferred. The seeds are sown at a density of about 1.2–1.5 kg⋅m–2, and they germinate in the following spring. In April, seedlings can be transplanted to nurseries when about 7 cm high. By the time of the next spring after transplanting, the saplings are suitable for grafting. Seedlings with a stem diameter over 0.5 cm can be used as rootstocks for grafting. For scions, one- to two-year-old shoots are cut from trees over 10 years old with a history of good yields, and these are cut into several 7-cm segments after removing the leaves. The optimum time for grafting is between late March and early April in Zhejiang. A survival rate of over 70% can be achieved with cleft grafting. The growers in Xiaoshan and Lanxi in Zhejiang province often prop- agate red bayberry by layering, which is usually performed before bud break in spring. This method speeds up the time to production of a fruiting tree. However, the root systems of such plants are often shallow, and the growth weak.

B. Field Cultivation Red bayberry is a long-lived tree and can remain productive for more than 30 years (Wang 1995). The optimum time for planting varies with regions. To avoid freezing injury in winter, planting takes place during late February to mid-March in Zhejiang, Jiangsu, Hunan, and Jiangxi. In regions with a relatively warm winter, such as in Guangdong, Fujian, Yunnan, Guizhou, and Sichuan, planting is carried out during early October to early December or from mid-February to mid-March. Plant- ing density is about 600 trees/ha. Since the tree is dioecious, it is necessary to interplant staminate trees, at a frequency of about 1–2% (Wang 1995). Pollen grains are small and can be carried some distance by wind, and if an orchard has staminate plantings nearby, then interplanting is not always necessary. Organic fertilizer applications are commonly made in October, and green manure crops, usually leguminous plants, are often interplanted with young trees to improve soil structure and provide another source of income. For plantings on slopes, mounding up can prevent exposure of roots and promote root growth. According to Zhang (1999), a tonne of ‘Dongkui’ fruit contains 1.4 kg N, 0.07 kg P, 1.8 kg K, 0.06 kg Ca, and 0.28 kg Mg, with a ratio of N: P: 4080 P-03 9/17/03 11:04 AM Page 103

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K=20:1:26. The nutrient contents of fruit (Table 3.3) are generally lower than in many fruit crops, especially levels of P and Ca. Since nodulated roots supply part of the N requirements of the tree, K is the most important major nutrient that must be supplied from the soil. Excess P application can be harmful because of possible boron, zinc, and molybdenum deficiencies. The kinds of fertilizers used and application rates are related to plant age and soil nutrient status. For example, at a density of 270 trees/ha, fertilizers applied annually to young trees (5 years old) should contain 3.5 kg N, 0.9 kg P, and 3.0 kg K, and for adult trees (12 years old) 9.2–10.6 kg N, 2.3 kg P, and 12.3 kg K. Fertilizers should be applied three times a year: during February or March to promote spring flush growth, blossoming, and fruit set; late May for promoting fruit development; and a further application just after harvest. The trees are upright and will grow too tall if not trained, and the rec- ommended practice throughout China is to create a tree with a low canopy and open center (Fig. 3.1). Pruning is carried out in February to March (spring) and September to October (autumn). Unwanted branches are removed or cut back to allow light penetration into the canopy to promote fruit set and increase fruit quality. For example, training of ‘Dongkui’ trees involves establishing a trunk with 3–4 primary scaffold limbs, with angles between the trunk and the limbs greater than 45°, and the height of the canopy less than 2.5–3.0 m. Groups of fruiting branches, rather than secondary scaffold limbs, should be allowed to develop on the main limbs, and these should be replaced by new groups about every 4 years (Wang 1999).

Table 3.3. The content of mineral elements in different organs of red bayberry trees (data from Zhang 1999).

Fruit Nutrient Content (% dry weight)

Tree age Organs N P K Ca Mg

Non-bearing (5 year old) Leaves 1.33 0.08 0.95 0.46 0.14 Shoots 0.31–0.67 0.03–0.04 0.24–0.76 0.12–0.31 0.02–0.08 Roots 0.57 0.03 0.53 0.15 0.07 Bearing (12 year old) Leaves 1.27 0.07 1.02 0.38 0.13 Fruit 1.01 0.02 1.10 0.03 0.12 Shoots 0.24–0.82 0.02–0.03 0.25–0.08 0.11–0.28 0.02–0.09 Roots 0.55 0.03 0.57 0.17 0.06 4080 P-03 9/17/03 11:04 AM Page 104

104 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

Alternate bearing has been the target of recent research. Li et al. (2001)

showed that spraying bayberry trees with 250 g/L GA3 in June and July inhibited the activities of PAL, POD, and PPO, and hence slowed down the biosynthesis of lignin, suppressed the differentiation of flower buds, and as a result, greatly reduced flowers in the following year. These results confirm those of Lavee (1989), who found that phenylalanine ammonia lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO),

and lignin were related to formation of flower buds. GA3 treatment pro- moted the emergence of spring shoots by 133%, increased the size of flower buds on spring shoots, and increased fruit weight by 3.8 g, soluble solids by 3.4%, and advanced maturity by 3 days (Liang et al. 2000).

Paclobutrazol (PP333), an inhibitor of GA biosynthesis, applied in autumn or spring to arrest the vigorous growth of young trees, accelerates the formation of flower buds. However, Luo and Huang (1997) reported that

spraying trees with PP333 at 500 mg/L in spring decreased fruit size and sugar content while increasing acid levels. Trunk spiral girdling also effectively promotes flower formation (Luo et al. 1999). In China, growing red bayberry in greenhouses was first carried out in Wenzhou, Zhejiang in 1999–2000 with ‘Ding-ao’ (Huang and Zhao 2001). The system has proved to be profitable, with fruit in the market early in the season realizing higher prices. The plastic house, 20 m × 10 m × 4.5 m, resulted in average temperatures being increased by 4.5°C, humidity by 7.5%, the ripening date being advanced by 14–16 days, and yields being increased by 11.5%. However, the time from fruit set to full maturation did not change, remaining at about 106 days.

C. Pests and Diseases There are important disease and pest problems in red bayberry (listed in Table 3.4), and although studies on these are generally limited, there is some information available in the literature. Pseudomonas syringae pv. myrigae is one of the most widely distributed pathogens, infecting 2- to 3-year-old shoots and resulting in a tumor-like growth known as red bayberry ulcer or sore (Li 2002). Smooth, milky tubercles arise at the infected sites, and then develop into larger, rough, brown or black tumors, 1.5–2 cm in diameter. The symptoms become apparent about 30 days after infection. The disease develops in late April to May, and protective methods involve removal and burning of infected shoots followed by a 0.5% Bordeaux spray. Brown leaf spot results from infection of Mycosphaerella myricae Saw. The round or irregular spots are 4–8 mm in diameter, with brown 4080 P-03 9/17/03 11:04 AM Page 105

3. RED BAYBERRY: BOTANY AND HORTICULTURE 105

Table 3.4. Major pathogens and pests of red bayberry (data from Chen 1994; Cai 2000; Rao et al. 2001).

Disease Production or pest Binomial Affected tissue area

Disease Brown leaf Mycosphaerella myricae Leaves Zhejiang spot Root rot Botryosphaeria dothidea Roots Zhejiang Rust Caeoma makinoi Kusano Leaves Fujian Tumor-like Pseudomonas syringae Shoots, trunk Zhejiang, growth pv. myricae Japan Red mould Corticium saimonicolor Branches Zhejiang Stem blight Myxosporium corticola Trunk All producing areas Shoot rot Valsa coronata Cortex of shoot Zhejiang Nematode Root-knot Meloidogyne spp. Roots Fujian

Insect Leaf wilt moth Lebeda nobilis Leaves Jiangsu, Zhejiang, Fujian Scale insect Lepidosphes cupressi Spring leaves Zhejiang Leaf rolling Homona spp. Young leaves Zhejiang moth Scale insect Fiorinia myricae Fruit Japan Fruit fly Drosophila melanogaster Fruit Japan White ant Odontotermes formosanus Trunk, root Zhejiang White ant Macrotermes barneyi Trunk, root Zhejiang

or greyish-brown borders and reddish-brown or greyish-white centers. The spots can coalesce and may result in leaf wilting and abscission. Control is through use of fungicides such as a 0.5% Bordeaux spray, and 70% thiophanate methyl and 50% carbendazol wettable powders, sprayed onto foliage one month before full fruit ripening, two weeks prior to harvest, and after harvest (Li 2002). Root rot is an important disease in Zhoushan Island of Zhejiang Province. The pathogen has been identified as Botryosphaeria dothidea (Moung ex Fr.) Ces. & de. Not. (Li et al. 1995), with infection spreading through the root system, resulting in wilting and tree death. Control is through soil applications of carbendazol at 0.25–0.5 kg/tree or thiophanate at 0.25–0.5 kg/tree (Ren et al. 2000). 4080 P-03 9/17/03 11:04 AM Page 106

106 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

Scale insects are common and important pests resulting in severe yield losses and decline in fruit quality; they include Lepidosaphes cupressi Borchsenius in Zhejiang and Jiangsu areas of China, and Fior- inia myricae Targioni in Japan (Xu et al. 1995; Mao 2000). Lepidos- aphes cupressi feed on foliage and have two reproductive cycles per year, egg-laying being in mid-April and late July. Insecticides such as buprofezin are used for control, in combination with agriculture prac- tices and native predators such as Chilocorus kuwanae Silvestri and Prospaltella spp. (Xu et al. 1995).

D. Harvest and Handling Bayberry fruit are picked when eating ripe. Fruit maturation and time of ripening on the tree varies greatly with growing region. The fruit ripen in early April in Guizhou, from mid- to late May in Fujian, Guangdong, and Sichuan, and from early June to mid-July in Zhejiang, Anhui, Jiangsu, Hunan, and Jiangxi. In most regions, high temperatures and rain are common at the time of fruit ripening, making them susceptible to preharvest drop and rots, resulting in a comparatively short harvest time (Liu 2000). Fruit maturation also varies with cultivars, and since unripe fruit are excessively acid, estimation of maturity and the appropriate harvest time is important. Flesh color is a useful indicator of ripeness and is used as a harvest index. For example, color changing from red to purple or black indicates ripeness for the black type, from bluish green to white for the white type, and from green to deep red for the red type. The soluble solids contents increase in the fruit with ripening, while total acid levels decrease. The optimum acid content for harvest is between 1–1.2% for ‘Biqi’ fruit (Miao and Wang 1987). Individual fruit on a tree ripen at different times, and fruit often have to be picked as frequently as every day. Since the fruit are susceptible to mechanical injury, careful handling is necessary. The optimum times for picking are early morning and evening, when the field heat is least. The flesh is susceptible to damage from pickers, and current recom- mendations are that fruit should be picked with stalk attached, and packed in 3–5 kg bamboo baskets with leaves or weeds to reduce damage. Fruit shaken from the trees can only be used for processing.

E. Storage and Transportation Red bayberry is a delicate fruit and has a short storage life, made shorter by enhanced flesh softness resulting from high temperatures and rain at harvest. The storage life of the fruit is 9–12 days at 0–2°C, 5–7 days at 4080 P-03 9/17/03 11:04 AM Page 107

3. RED BAYBERRY: BOTANY AND HORTICULTURE 107

10–12°C, and 3 days at 20–22°C (Xi et al. 1993). There is a need for more research on extending the storage and shelf life of the fruit, particularly if it is to be used more widely as an export crop. As the fruit ripens, the total soluble solids (TSS) contents increase and acid levels decrease, resulting in higher ratios of TSS to acids. Sugars are the main constituents of TSS, and sucrose is the principal sugar, accounting for about 60% of the total. Citric acid is the predominant acid, with oxalic acid as the next most abundant; acetic and malic acids are minor components. Fruit quality declines rapidly during storage. For example, after storage at 0–2°C for 12 days, fruit TSS decreased by 10.5%, total acids by 41.4%, sucrose by 49.1%, and vitamin C by 36%, from 432 µmol/L to 277 µmol/L (Xi et al. 1993). These decreases can be retarded by treatment with salicylic acid, an inhibitor of plant senescence (Gao et al. 1989). Cell membrane permeability, measured by changes in electrical con- ductivity of tissue, increases during fruit storage, and is greater at higher temperatures (Xi et al. 1994). These permeability changes, along with increased respiration and ethylene production, increase under vibrational stress, such as may occur during postharvest handling and trans- port (Ying et al. 1993; Zheng et al. 1996). There are different views on the respiration pattern of ripening red bayberry fruit. Xi et al. (1994) classified it as nonclimacteric, whereas Hu et al. (2001) regarded it as climacteric because they detected a small ethylene production peak both at 21°C and 1°C. Ethylene production during storage may be dependent on fruit maturity at harvest, since less mature ‘Biqi’ fruit (picked at the pink stage) showed some increase in ethylene production after harvest (Fig. 3.7; K. Chen et al., unpublished data). The activity of superoxide dismutase (SOD), a free radical scavenger and thus a protectant against oxidative stress, gradually increases in the fruit during the first 6 days after harvest, and then decreases rapidly, following a pattern familiar in senescing tissues. High storage temperatures and vibration stress accelerate this decline in SOD activity (Xi et al. 1994; Zheng et al. 1996). The levels of SOD in vibration-stressed fruit were less than those in control fruit, supporting the observation that such stress can promote fruit senescence (Zheng et al. 1996). Malondiadehyde (MDA), a product of membrane peroxidation, which itself can further damage membrane structure and function, has been followed during storage. Fruit stored at 1°C or under high nitrogen (85%) had substantially lower contents of MDA and a longer storage life (Xi et al. 2001). Another group of metabolites, polyamines including spermidine, spermine, and putrescine, share the same precursor as ethylene in their biosynthetic pathway. In a study of vibration stress on bayberry 4080 P-03 9/17/03 11:04 AM Page 108

108 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

Fig. 3.7. Changes in ethylene production of ‘Biqi’ red bayberry fruit of different maturity (K. Chen et al., unpublished data).

fruit, synthesis of spermidine increased whereas ethylene production decreased during the initial post-vibration storage period, suggesting a possible protective metabolic system (Zheng et al. 1996). At a later stage, spermine content decreased while ethylene was produced at a higher rate than in control fruit, suggesting that vibrational stress ultimately accelerated the overall senescence process. Putrescine accumulated during the final storage period, and may be detrimental to fruit storage. Storage life of the fruit can be extended up to two weeks if fruit are stored at 0–1°C, with a relative humidity of 85–90% (Xiao et al. 1999; Xi et al. 2001). Postharvest treatments such as sodium sorbate, 1% sal-

icylic acid, or 0.5% CaCl2 together with 7.5 mg/L NAA (Liu 2000) increased storage life, although 1-MCP (the inhibitor of ethylene recep- tion) had little effect (K. Chen et al., unpublished data). Modified atmos- phere packaging and controlled atmospheres have not been studied to any great extent. 4080 P-03 9/17/03 11:04 AM Page 109

3. RED BAYBERRY: BOTANY AND HORTICULTURE 109

In China, red bayberry is traditionally picked from the tree directly into bamboo baskets, and then transported to the market. Because of the increasing commercial production and value of the crop, packaging of the fruit has greatly improved. Fruit are graded by size and color to provide uniform packs. In Yuyao, Zhejiang province, high-quality ‘Biqi’ fruit are selected and packed in 500-g plastic boxes, then in 3-kg cartons, and shipped to Hong Kong. ‘Dongkui’ fruit, being larger and of higher quality, are packed 10 to a plastic box. Good results have also been achieved with other cultivars by changing the number of fruit in a box (Lu et al. 1999). In Japan, red bayberry are packed in 400-g polyethyl- ene bags and then into 1.6-kg wooden or plastic boxes (Miao and Wang 1987). Because they are susceptible to rots, fruit should be precooled before packing and transported carefully to avoid vibration and high temperatures. Since the short storage life limits the period of supply to the market, there are benefits in freezing. Fresh fruit can be blast-frozen at –25 to –30°C for 15 minutes, and then stored and transported at –18°C.

F. Processing Red bayberry fruit can be processed into jam, juice, wine, or as candied products, and canned red bayberry fruit is exported from China, particularly to Southeast Asian countries. Recent annual production of the canned product in Zhejiang has reached 1,800 t, about a third of which is exported. Ye and Zhang (2000) have shown that the fruit pigments can be used as food additives, although they are readily affected by pH, ultraviolet light, and reducing agents. Rapid and simple carbon dioxide supercrit- ical extraction technology is needed for pigment extraction. The pigments have good potential uses so long as stability can be assured. Juice can be extracted with 2% saline at 70–80°C, and the preferred product contains 40% original extract, 10.5% sugar, and 0.45% acid (Zheng and Chen 2000). Red bayberry wine is also an important product of the fruit. Relatively high pectin and cellulose contents are largely responsible for the existence of methanol in the wine, and this needs to be kept at levels less than 0.08 mg/100 ml (Huang 1999). The composition of red bayberry fruit is summarized in Table 3.5. In addition, three flavonoids have been isolated from the fruit stone and identified by spectral analysis as quercetin, myricetin, and quercetin-3-O-α- D-glucopyranosyl-(6→1)-α-α-L-rhamnopyranoside (Zou 1995). These compounds, especially quercetin and myricetin, are active antioxidants. 4080 P-03 9/17/03 11:04 AM Page 110

110 K. CHEN, C. XU, B. ZHANG, AND I. FERGUSON

Table 3.5. Chemical composition of ripe red bayberry fruit.

Content Component (fresh weight basis) Reference

Total soluble solids 11.6–13.4% Wang et al. 2001 Total sugars 9.8–11.7% Wang et al. 2001 Sucrose 46.6 mg/g Zhang et al. 1991 Glucose 13.5 mg/g Zhang et al. 1991 Fructose 13.8 mg/g Zhang et al. 1991 Total acids 0.42–1.28% Wang et al. 2001 Citric acid 0–10.3 mg/g Zhang et al. 1991; Wang et al. 2001 Tartaric acid 1.2–4.5 mg/g Wang et al. 2001 Malic acid 1.3–1.7 mg/g Wang et al. 2001 Succinic acid 1.2–3.1 mg/g Wang et al. 2001 Acetic acid 0.5–2.0 mg/g Wang et al. 2001 Oxalic acid 1.9 mg/g Zhang et al. 1991 Minerals Potassium 1.41 mg/g Wang et al. 2001 Trace elements (Fe, Mn, Zn, 0.075 mg/g Miao and Wang 1987 Cu, Mg) Vitamins Vitamin C 0.11–1.14 mg/g Wang et al. 2001 (ascorbic acid) Vitamin B1 0.054 mg/g Wang et al. 2001 Vitamin B6 0.008–0.016 mg/g Wang et al. 2001 Vitamin E 0.0007–0.0016 mg/g Wang et al. 2001 Vitamin A 0.00004–0.0005 mg/g Wang et al. 2001 Protein 0.33% Zhang et al. 1991

There are also some unknown compounds in the stones that can arrest the growth of cancer cells or induce cell death (Zhang et al. 1993).

VI. CONCLUDING REMARKS

China has a rich genetic resource in red bayberry, with a wide range of cropping and fruit properties that should be exploited for breeding purposes. Some wild species fruit early, resist high temperature, are dwarfing, and have excellent postharvest properties. Many contain compounds of medical importance. These resources are in danger of being destroyed; species such as Myrica esculenta Buch are on the edge of extinction. 4080 P-03 9/17/03 11:04 AM Page 111

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There are 268 cultivars planted in China, of which about two-thirds ripen in mid- to late June (Zhang and Miao 1999). There are some early- maturing cultivars such as ‘Zaoxingmei’ grown in Huangyan and Wen- ling, Zhejiang province, that ripen in May, but the fruit is small and acid. The storage life of almost all cultivars is very limited, resulting in severe losses each season. It is imperative that further breeding work be carried out to create new early-maturing cultivars of high fruit quality and longer storage potential. Only 9.3% of total cultivars are white fleshed (Miao and Wang 1987), and only one, ‘Shuijingyangmei’ or ‘Crystal’, has been commercially planted, in Shangyu, Zhejiang province, its place of origin. There is a need for more effort in breeding new white-fleshed cultivars adapted to different climates. Alternate bearing has a major impact on production; in years of high yield, the price of fruit may be low, while in low years there may be insufficient fruit to meet consumer demand. Furthermore, compared with other fruit crops, the yield of red bayberry is quite low. This means that there is a need to increase yield and reduce cropping variability. The short storage life, together with other cultivation, harvesting, and handling problems has inhibited the development of the crop. Red bayberry is a candidate for international markets provided that storage and shelf life of the fruit can be extended. The crop has potential outside of China in warm-temperate and sub-tropical growing conditions. With current limitations on storage life, production would need to be aligned with easily accessible markets.

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