Seedlings emergence is hypogeal; seed leaves are cordate, long-petioled, and simple. The plant is a bushy, usually erect and slightly pubescent annual that grows from 27 to 90 cm high. Some azuki cultivars exhibit viney growth and can climb from 1 to 3 m. Stem color is normally green but some cultivars are purplish. Branching occurs between the 4th to 9th main stem nodes (Hoshikawa 1985) and secondary branching does not occur under normal planting densities.
Stipules are small, entire or faintly 3-lobed, peltate, lanceolate, acuminate, and have basal appendages. The leaf is pinnately trifoliate with the middle leaflet being broadly ovate and attached to the petiole by a long petiolule; leaflets are 5 to 8 cm wide and 5 to 10 cm long. Some cultivars produce lanceolate-shaped leaflets (Hoshikawa 1985).
Azuki has a taproot type of root system that can extend in a sphere 40 to 50 cm from the point of seed germination; secondary branch development occurs later in the season and can reach 40 cm. Root nodules resulting from cowpea group rhizobium infections are spherical, 4 to 10 mm in diameter, and begin developing when primary leaves start to unfold (Hoshikawa 1985).
Azuki flowers are bright yellow, have hairy styles, flattened stigmas, and an asymmetrical keel that curves to the left and has a hornlike appendage on one side. Inflorescence and flower primordium start developing 23 and 21 days before anthesis, respectively; anthesis normally starts in the morning and can continue for up to 40 days (Hoshikawa 1985). Racemes are axillary, borne on long pedicels on higher parts of the plant and short-subsessile pedicels on the lower parts, and consist of from 6 to 20 flowers. Floral development progresses upward with anthesis beginning on lower main stem nodes and branches first.
Azuki pods are smooth, cylindrical, thin-walled, and green turning white to grey as they mature. Pods hang down and are restricted between seeds when mature. They are 6 to 13 cm long, 0.5 cm in diameter, with 2 to 14 seeds/pod, 2 to 6 pods/pedicel, and 5 to 40 pods/plant. Maturation is indeterminate but, 85% of all pods mature at about the same time. Pod shatter during seed ripening and harvesting is a problem under certain conditions. Components of yield were reported by Nakaseko (1983) to range from 53.4 to 81.2 pods/plant, 1.0 to 1.67 pods/node, 5.1 to 7.5 seeds/pod, and 31.8 to 74.4 g dry seed yield/plant for six cultivars.
Almost all production of azuki occurs in four countries: Japan, China, Taiwan, and South Korea. Other past or present azuki producing countries include Australia, the Philippines, Japan, the Republic of Congo, Thailand, India, Italy, New Zealand, USSR, China, Belgium, United States, Brazil, Argentina, Malaysia, Kenya, Zaire, and Angola.
Japan produces about 90,000 t of azuki each year on about 64,000 ha, of which 60% is on the island prefecture of Hokkaido. Yields average about 1,500 kg/ha in Japan but can vary widely, especially on Hokkaido, depending mostly upon the length of the growing season, accumulated degree days and weather conditions.
The main site of Chinese production occurs in Wuging county, Hebei province, with 4,000 to 5,000 ha annually. Other azuki producing areas are western Jilin province, Tai Lai county of Heilongjiang province, north of the Huaihe River and near Qinling. In Taiwan, azuki is an important winter crop grown in rice paddies, especially in Pingtung and Kaohsiung provinces which account for 98% of all Taiwanese production. Azuki is one of the four most important grain legumes produced in South Korea in terms of planted area and production. Production is scattered throughout the country, usually on hill-side land in rotation with wheat and barley or some in converted paddy fields.
Azuki is believed to have been introduced into the United States by the Perry expedition in 1854. Piper and Morse (1914) provided a list of early introductions of azuki into the United States. The United States has never been a major world producer of azuki although the crop has been grown experimentally and/or on a limited production scale in several states over the past 130 years. Early adaptation experiments were conducted in Kansas, Virginia, and North Carolina, and it was used as a green fodder crop in some southern sections of the country (Hoshikawa 1985; Sacks 1977).
The most common use of azuki is the sweetened paste form called an. Azuki an, either in a smooth or chunky form, is used in numerous East Asian foods and desserts such as cakes, manju (steamed an-filled buns), yokan (cold gelatinized an slices), taiyaki (an-filled waffle), ice cream, snow cone toppings, and as a base for a beverage served hot from vending machines (Shiruko). About 30% of all an is used by the Japanese and Korea ice cream industries. An can also be flavored with soy sauce or with sweet syrups. A white seeded azuki is also used to make high quality white an for specialty Japanese bakery products (Narikawa 1972).
Azuki an is produced from seed by the following generalized steps: soaking, boiling, rinsing with water to remove antidigestive compounds, crushing, removal of seed coats, drying, and then combined with sugar and various stabilizing ingredients such as agar agar (Duke 1981). Traditional an is composed of equal parts azuki paste and sugar. Rice beans and various common beans are occasionally substituted for azuki in Japanese an production, but azuki is the preferred seed for high quality an (McClary et al. 1989). An can substitute for other traditional Western-style fillings and flavorings in sweet rolls, donuts, and ice cream. Japanese azuki consumption is currently broken down into the following categories: an paste (68.9%), candied seeds (12.8%), boiled seeds (2.4%) and other (15.9%) (Japan Bean Fund Assoc. 1987). In the mid 1970s, 85% of Japanese domestic production and imports of azuki were being used in the production of an.
Most edamame is harvested by hand. When edamame is sold on the stem, plants are hand cut or pulled out with roots intact, unacceptable pods and lower leaves are culled, and branches are tied together in small, aesthetically pleasing bundles. For sale of harvested pods, plants are cut and pods stripped off, sorted, and packaged. In Japan, electrical powered, stationary pod strippers are available and in Taiwan, an Italian single row bean picker is being tested (Konovsky et al. 1992). Initial studies on mechanical harvesting have been conducted in Tennessee (Collins and McCarty 1969) and at INTSOY (1987). For frozen product, standard methods for processing have been described (Liu and Shanmugasundaram 1982).
Japan is the largest commercial producer, nearly 105,000 t in 1988 (MAFF 1990), and the largest importer, over 33,000 t in 1989 (JTA 1989). Taiwan supplies over 99% of those imports as frozen edamame. Almost all Japanese production is consumed as fresh product during the summer months (Kono 1986). Other countries which have produced commercial quantities of edamame include Argentina, Australia, Israel, Mongolia, New Zealand, Taiwan, and Thailand. Home gardeners are known to produce it in Bhutan, Brazil, Britain, Chile, France, Germany, Indonesia, Malaysia, Nepal, Philippines, Singapore, and Sri Lanka (after Wang et al. 1979).
Edamame is consumed mainly as a snack, but is also used as a vegetable, an addition to soups, or processed into sweets. As a snack, the pods are lightly cooked in salted, boiling water and then consumed by pushing the seeds directly from the pods into the mouth with the fingers. As a vegetable, the beans are mixed into salads, stir fried, or combined with mixed vegetables. In soup (gojiru in Japanese), the beans are ground into a paste with miso and is used to form a thick broth. Confectionery products such as sticky rice topped with sweetened edamame paste are occasionally prepared (zunda mochi in Japanese). For marketing, edamame pods are sold fresh on the stem with leaves and roots, or stripped from the stem and packaged fresh or frozen as either pods or beans.
In North America, edamame is usually called vegetable soybean, but also beer bean, edible soybean, fresh green soybean, garden soybean, green soybean, green vegetable soybean, immature soybean, large-seeded soybean, vegetable-type soybean, and the Japanese name, edamame (Shurtleff pers. commun.). The use of the word green is confusing because mature soybean seeds with a green seed coat or cotyledons are also called green soybeans.
Edamame research as been conducted in the United States for over 50 years. Dorsett and Morse collected extensive germplasm from 1929 to 1931, and Morse used it to develop 49 cultivars of edamame (Hymowitz 1984). Research flourished during the 1930s and 1940s because of a protein shortage (Smith and Van Duyne 1951). A second surge of research began with the interest in organic farming in the 1970s. The Rodale Research Center focused edamame research on adaptability and quality (Hass et al. 1982). Basic agronomic research was begun at Cornell (Kline 1980) and seed companies developed new cultivars, e.g. `Butterbeans'. Today, some home gardeners grow edamame, but there is little commercial production. Asian-Americans seeking edamame are usually limited to frozen imports in specialty supermarkets.
Plants have several stems which grow to a height of 1.5 to 2.0 m, and are covered with compound pinnate leaves having T-shaped soft hairs. The primary root is thick and long with many lateral roots. The secondary root system begins 20 to 30 cm below the soil surface and can attain 150 cm in width. Rhizobium nodules develop on the upper portions of the roots near the soil surface.
Seedlings grow slowly, averaging 0.5 cm daily, the first year. Once established, its growth exceeds that of competing weeds. Rapid growth continues from the second to fourth year, primarily in May and June (1 cm daily). Plants will reach a height of 70+ cm and tiller during July and August, reaching a final height of 105 to 110 cm with 20 to 25 tillers.
Flowers bloom throughout August. Some racemes are apical, but most are axillary. Inflorescences are indeterminate and have 17 to 79 small blue, purple or blue-purple papilionaceous flowers. Pod development is evident 2 or 3 days following bloom and pods are square in cross-section, consisting of two chambers with 10 dark brown seeds per chamber and are 6 to 13 mm long with a bent beak-shaped top. Seed development begins 7 days post-anthesis (Barneby 1964).
Studies on forage yield and quality, along with seed production have shown that A. adsurgens is capable of producing 75 t/ha of coarse, fresh fodder. The crop can be harvested 2 or 3 times yearly beginning the second year. Crude protein values range from 12 to 14% and crude fiber range from 27 to 30%. Profuse seed production continued even under semi-arid growing conditions. The A. adsurgens planted at Pullman, Washington has been growing successfully for five years under 500 mm mean annual rainfall.
A superior Rhizobium strain, CA 8116, was identified for A. adsurgens (Ning et al. 1984a,b). Plants inoculated with CA 8116 increased nodulation from 27 to 47% at the first leaf stage, while, total biomass increased by 81%.
Edamame and azuki each face other issues related to quality. Japanese consumers show a strong preference for the taste and other qualities of Japanese cultivars of edamame over those from Taiwan or the United States. The edamame germplasm collection of 600 accessions at Washington State University (WSU) will be used to develop cultivars well suited to the Pacific Northwest climate with the qualities the Japanese desire.
For azuki, there are no industry standards for the quality of an paste in the United States and a very poor understanding of Japanese quality standards. While a rudimentary understanding of the general process and technology required for paste production was obtained on a tour of azuki facilities, quality issues are being studied at WSU to find quantifiable characters. Future United States an paste production will depend upon our understanding and meeting Japanese quality standards.
The introduction of two new crops to the Pacific Northwest will further diversify United States agricultural exports away from surplus commodities. With proper research, the potential exists for United States producers to capture a large share of the Japanese and Korean market for imported azuki and edamame. Market analyses for both commodities indicate a consistent opportunity for export of high quality raw and processed products to Japan (Cook 1988). A market study by our research group on azuki has just been completed and is available from the IMPACT Center at Washington State University (McClary et al. 1989). Several East Asian countries cannot meet their own needs for many niche crops and the long-term demand in the marketplace is stable, thus the United States has the opportunity to export products needed in foreign markets if they are of higher quality and more competitively priced than current imported.
New East Asian crops should also be considered for solving environmental problems within the United States Chinese selections of A. adsurgens were recently introduced into the United States. Although limited research has been conducted within the United States thus far, the plant holds great potential for restoration and conservation in cold arid regions where soil erosion is a problem.