Adzuki bean
The adzuki bean, or red mung bean, is an annual vine widely cultivated throughout East Asia for its small bean. The cultivars most familiar in East Asia have a uniform red color, but white, black, gray, and variously mottled varieties also are known.
Scientists presume Vigna angularis var. nipponensis is the progenitor.
Origin and diversity
Speciation and domestication
The wild ancestor of cultivated adzuki bean is probably Vigna angularis var. nipponensis, which is distributed across Japan, Korea, China, Nepal and Bhutan. Speciation between Vigna angularis var. nipponensis and Vigna angularis var. angularis occurred around years ago. Archaeologists estimate it was domesticated around 3000 BC. However, adzuki beans dating from 3000 BC to 2000 BC are indicated to still be largely within the wild size range. Enlarged seeds occurred during the later Bronze Age or Iron Age, periods with plough use. Domestication of adzuki beans resulted in a trade-off between yield and seed size. Cultivated adzuki beans have fewer but longer pods, fewer but larger seeds, a shorter stature, and also a smaller overall seed yield than wild forms. The exact place of domestication is not known; multiple domestication origins in East Asia have been suggested.Breeding
In Japan, the adzuki bean was one of the first crops subjected to scientific plant breeding. Important breeding traits are yield, pureness of the bean colour, and the maturing time. Separate cultivars with smaller seeds and higher biomass are bred for fodder production and as green manure. Locally adapted cultivars are available in China, Japan, Korea, and Taiwan. More than 300 cultivars/landraces/breeding lines are registered in Japan. Moreover, China and Japan accommodate large germplasm collections of adzuki bean.Weed forms
forms of adzuki bean frequently occur in Japan. The wide spread of weed forms is due to adaptation to human-disturbed habitats, escapes of old cultivars, and natural establishment from derivatives of hybrids between cultivars and wild forms. In contrast to wild forms, the weed forms of adzuki bean are used as a substitute for the cultivated form and consumed as sweet beans, especially if cultivated adzuki beans are attacked by pests. However, in cultivated gardens the weed form is recognized as contamination and lowers the seed quality of adzuki cultivars.Names
The name adzuki is a transliteration of the native Japanese name. Japanese also has a Chinese loanword,, which means "small bean", its counterpart "large bean" being the soybean. It is common to write 小豆 in kanji but pronounce it as azuki ', an example of jukujikun. In China, the corresponding name still is used in botanical or agricultural parlance, however, in everyday Chinese, the more common terms are hongdou and chidou, both meaning "red bean'", because almost all Chinese cultivars are uniformly red. In English-language discussions of Chinese topics, the term "red bean" often is used, but in other contexts this usage may cause confusion with other beans that also are red. In normal contexts, "red cowpeas" have been used to refer to this bean. In Korean, adzuki beans are called pat and it contrasts with kong, rather than being considered a type of it. Kong without qualifiers usually means soybeans. In Vietnamese it is called đậu đỏ. In some parts of India, they are referred to as "red chori". In Punjabi it is called ravaa'n and is a common ingredient of chaat. In Marathi, it is known as lal chavali, literally meaning 'red cowpea'. In Iraq its name is lūbyā ḥamrāˈ'' meaning "red cowpeas".Cultivation
Area and yield
The adzuki bean is mainly cultivated in China, Japan, South Korea, and Taiwan . The bean is also grown commercially in the US, South America, and India, as well as New Zealand, Kongo, and Angola. In Japan, the adzuki bean is the second most important legume after the soy bean; its 1998 annual yield of this crop was around 100,000 tons. With a consumption of about 140,000 t/year, Japan is also the most important importer of adzuki beans. The imports are received from China, Korea, Colombia, Taiwan, US, Thailand, and Canada.The bean yields per area spread over a broad range due to differing cultivation intensity. Amounts of 4 to 8 dt/ha are reported, but in Japan and China yields between 20 and 30 dt/ha are reached.
Ecological requirements
Optimal temperature range for adzuki bean growth is between 15 °C and 30 °C. The crop is not frost-hardy and needs soil temperatures above 6-10 °C for germination. Hot temperatures stimulate vegetative growth and are therefore less favorable for pea production. The adzuki bean is usually not irrigated. Annual rainfall ranges from 500–1750 mm in areas where the bean is grown. The plant can withstand drought but severe reduction in yield is expected. The cultivation of the adzuki bean is possible on preferably well drained soils with pH 5-7.5. Fertilizer application differs widely depending on expected yield but is generally similar to soybean. Due to nodulation with rhizobia nitrogen fixation of up to 100 kg/ha is possible.Production
The sowing of the peas is in 2–3 cm depth in rows 30–90 cm apart and 10–45 cm within the row. Rarely seeds are sown by broadcast. The amount of seeds ranges between 8–70 kg/ha. Growth of the crop is slow, therefore weed control is crucial mainly between germination and flowering. Cultivation systems differ largely among different countries. In China adzuki bean is often grown in intercrops with maize, sorghum and millet while in Japan the bean is grown in crop rotations. Harvest of the peas should not be done as long as moisture content of the seed is higher than 16%.Pests and diseases
Fungal and bacterial diseases of the adzuki bean are powdery mildew, brown stem rot, and bacterial blight. Furthermore, pests such as the adzuki pod worm, Japanese butterbur borer, and cutworm attack the crop. The bean weevil is an important storage pest.Botany
The description of the adzuki bean can vary between authors because there are both wild and cultivated forms of the plant.The adzuki bean is an annual, rarely biennial bushy erect or twining herb usually between 30 and 90 centimeters high. There exist climbing or prostrate forms of the plant. The stem is normally green and sparsely pilose.
Roots
The adzuki bean has a taproot type of root system that can reach a depth of 40–50 cm from the point of seed germination.Leaves
The leaves of the adzuki bean are trifoliate, pinnate and arranged alternately along the stem on a long petiole. Leaflets are ovate and about 5–10 cm long and 5–8 cm wide.Flowers
Adzuki flowers are papilionaceous and bright yellow. The inflorescence is an axillary false raceme consisting of six to ten flowers.Fruits
Adzuki pods are smooth, cylindrical and thin-walled. The colour of the pods is green turning white to grey as they mature. The size is between 5–13 cm x 0.5 cm with 2 to 14 seeds per pod. Pod shatter during seed ripening and harvesting might be a difficulty under certain conditions.Seeds
The seeds are smooth and subcylindric with a length of 5.0-9.1 mm, width of 4.0-6.3 mm, thickness of 4.1-6.0 mm. The thousand kernel weight is between 50 and 200 g. There are many different seed colours from maroon to blue-black mottled with straw.Physiology
The emergence of the seedlings is hypogeal and takes 7–20 days. Compared to other pulses the growth of the plant is slow. Normally the adzuki plant reaches maturity between 80 and 120 days depending on the cultivar and the environmental conditions. Flowering lasts 30–40 days. Commonly the plant self-pollinates but cross-pollination also exists.Uses
In East Asian cuisine, the adzuki bean is commonly sweetened before eating. In particular, it often is boiled with sugar, resulting in red bean paste, a very common ingredient in all of these cuisines. It also is common to add flavoring to the bean paste, such as chestnut.Red bean paste is used in many Chinese dishes, such as tangyuan, zongzi, mooncakes, baozi, and red bean ice. It also serves as a filling in Japanese sweets such as anpan, dorayaki, imagawayaki, manjū, monaka, anmitsu, taiyaki, and daifuku. A more liquid version, using adzuki beans boiled with sugar and a pinch of salt, produces a sweet dish called hong dou tang. Adzuki beans are commonly eaten sprouted or boiled in a hot, tea-like drink. Some East Asian cultures enjoy red bean paste as a filling or topping for various kinds of waffles, pastries, baked buns, or biscuits.
Traditionally in Japan, rice with adzuki beans is cooked for auspicious occasions. Adzuki beans are used in amanattō and ice cream with the whole bean or as paste.