The mung bean or green gram (Vigna radiata) is a plant species in the legume family. It is mainly cultivated in East, Southeast, and in South Asia and used as an ingredient in both savoury and sweet dishes.
Names The English names "mung" or "mungo" originated from the Hindi word mūṅg (मूंग), which is derived from the Sanskrit word mudga (मुद्ग). It is also known in Philippine English as "mongo bean". Other less common English names include "golden gram" and "Jerusalem pea".
Description The green gram is an annual vine with yellow flowers and fuzzy brown pods. It has a height of about 15–125 cm (6–49 in). Mung bean has a well-developed root system. The lateral roots are many and slender, with root nodules grown. Stems are much branched, sometimes twining at the tips. Young stems are purple or green, and mature stems are grayish-yellow or brown. They can be divided into erect cespitose, semi-trailing and trailing types. Wild types tend to be prostrate while cultivated types are more erect. Leaves are ovoid or broad-ovoid, cotyledons die after emergence, and ternate leaves are produced on two single leaves. The leaves are 6–12 cm long and 5–10 cm wide. Racemes with yellow flowers are borne in the axils and tips of the leaves, with 10–25 flowers per pedicel, self-pollinated. The fruits are elongated cylindrical or flat cylindrical pods, usually 30–50 per plant. The pods are 5–10 cm long and 0.4–0.6 cm wide and contain 12–14 septum-separated seeds, which can be either cylindrical or spherical in shape, and green, yellow, brown, or blue in color. Seed colors and presence or absence of a rough layer are used to distinguish different types of mung bean.
Growth stages Germination is typically within 4–5 days, but the actual rate varies according to the amount of moisture introduced during the germination stage. It is epigeal, with the stem and cotyledons emerging from the seedbed. After germination, the seed splits, and a soft, whitish root grows. Mung bean sprouts are harvested during this stage. If not harvested, it develops a root system, then a green stem which contains two leaves and shoots up from the soil. After that, seed pods begin to form on its branches, with 10–15 seeds contained in each pod. The maturation can take up to 60 days. It can reach up to 76 cm (30 in) tall, with multiple branches with seed pods. Most of the seed pods become darker, while some remain green.
Similar species Vigna radiata is sometimes confused with Vigna mungo (black gram) due to their similar morphology.
Taxonomy Mung beans are one of many species moved from the genus Phaseolus to Vigna in the 1970s. The previous names were Phaseolus aureus or P. radiatus. It is a species of Fabaceae and is also known as green gram. There are three subgroups, including one cultivated (V. radiata subsp. radiata) and two wild ones (V. radiata subsp. sublobata and V. radiata subsp. glabra).
Ecology
Nitrogen fixation and cover crop As a legume plant, mung bean is in symbiotic association with Rhizobia, which enables it to fix atmospheric nitrogen (58–109 kg per ha mung bean). It can provide large amounts of biomass (7.16 t biomass/ha) and nitrogen to the soil (ranging from 30 to 251 kg/ha). The nitrogen fixation ability not only enables it to meet its own nitrogen requirement, but also benefits the succeeding crops. It can be used as a cover crop before or after cereal crops in rotation, which makes a good green manure.
Domestication
The mung bean was domesticated in India, where its progenitor (Vigna radiata subspecies sublobata) occurs wild. 2nd millennium BCE scripture Yajurveda in its 4th chapter refers to mudga (मुद्ग) as one of the important grains and asks Rudra to bless with its good harvest (मु॒द्गाश्च॑ मे॒ खल्वा॑श्च मे) in Rudradhyaya. The mung bean is listed as one of the nine auspicious grains (navdhānya) in Vedic astrology and associated with planet Budha (Mercury). Carbonized mung beans have been discovered in many archeological sites in India. Areas with early finds include the eastern zone of the Harappan civilisation in modern-day Pakistan and western and northwestern India, where finds date back about 4,500 years, and South India in the modern state of Karnataka where finds date back more than 4,000 years. Some scholars, therefore, infer two separate domestications in the northwest and south of India. On the other hand, a recent study suggested a single genetic origin likely contributing to the loss of pod shattering, the key domestication trait in legumes. In South India, there is evidence for the evolution of larger-seeded mung beans 3,500 to 3,000 years ago. By about 3,500 years ago mung beans were widely cultivated throughout India. Cultivated mung beans later spread from India to China and Southeast Asia. Archaeobotanical research at the site of Khao Sam Kaeo in southern Thailand indicates that mung beans had arrived in Thailand by at least 2,200 years ago. A genetic study demonstrated that, following its domestication in South Asia, mung bean spread sequentially to Southeast Asia and East Asia and eventually to Central Asia, despite the geographic proximity of South and Central Asia. The study suggests that the short and dry growing seasons in the northern regions of Asia were not suitable for southern cultivars, which had been bred for extended life cycles to maximize yield. This highlights the critical role of ecological factors, such as climate, in shaping crops evolution.
Cultivation
Varieties The mung bean varieties now are mainly targeted in resistance to pests and diseases, particularly the bean weevil and mung bean yellow mosaic virus (MYMV). For now, the main varieties include Samrat, IPM2-3, SML 668 and Meha in India; Crystal, Jade-AU, Celera-AU，Satin II，Regur in Australia; Zhonglv No. 1, Zhonglv No. 2, Jilv No. 2, Jilv No. 7, Weilv No. 4, Jihong 9218, Jihong 8937, Bao 876-16, Bao 8824-17 in China. Also, with the help of the World Vegetable Center, the traits of mung bean have been considerably improved. 'Summer Moong' is a short-duration mung bean pulse crop grown in northern India. Due to its short duration, it can fit well in-between of many cropping systems. It is mainly cultivated in East and Southeast Asia and the Indian subcontinent. It is considered to be the hardiest of all pulse crops and requires a hot climate for germination and growth.
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