About ricebean (Vigna umbellata (Thunb.) Ohwi and Ohashi
Ricebean (Vigna umbellata ) is a legume grown in Western, Northern and Eastern (WNE) India and Nepal. It is widely grown as an intercrop, particularly of maize (Lawn, 1995), and was widely grown in the past on residual water after rice. It has the potential to play a major role in intercrop systems, and can also be grown on the edges of the terraces or sloping hillsides, as well as on rice bunds and under shifting cultivation on hillsides.
Ricebean grows well on a range of soils. It has rapid establishment, is pest resistant, and has the potential to produce large amounts of nutritious animal fodder and high quality grain, and there is great scope for genetic improvement in this neglected crop.
Although grown in both countries, landraces predominate and there is little or no choice of improved varieties as there has been almost no modern plant breeding in the crop, and seed supply is limited or non-existent. Moreover, when this has been done, little or no attention has been paid to improving grain quality or adaptation. Consequently, ricebean is not grown widely despite its suitability for marginal areas where many poor people live.
Moreover, well-functioning marketing channels for the crop do not exist. The crop has a potentially important role to play in improving food security through increasing the diversity and sustainability of cropping systems and increasing the management options available to the poorer farmers.
Ricebean is not part of any CGIAR mandate, it does not appear in the common fund of commodities or the European catalogue of varieties, and is not mandated by the NARS in India or Nepal. It has been under-researched and should respond well to an integrated approach involving plant breeding, improved agronomic practices and broad market development.
Taxonomy and origin
This section is taken from Lawn (1995) except where stated.
Like other Asiatic Vigna species, ricebean belongs to the subgenus Ceratotropis (Maréchal et al, 1978). Within the various cultivated species in this subgenus there appear to be three more-or-less isolated secondary gene pools: radiata (mungbean, green gram)-mungo (black gram, urd bean), domesticated in India; umbellata (ricebean)-angularis (adzuki bean), domesticated in SE Asia and NE Asia respectively; and aconitifolia (moth bean, mat bean)-tribolata (pillipesara bean, jungle bean), domesticated in S Asia. Vigna glabrens is thought to be a cross between V. radiata and V. umbellata, domesticated in SE Asia. The centre of diversity and presumably of origin of ricebean in Indo-China – it is thought to be derived from the wild species V. umbellata var. gracilis, found naturally from southern China through the north of Vietnam, Laos and Thailand into Burma and India, and which is thought to be cross-fertile (Tomooka et al, 1991).
The species is thought to have become domesticated progressively through accumulating agronomically desirable traits. The wild form is typically fine-stemmed, freely branching and small leaved, with a twining habit, photoperiod sensitivity, indeterminate growth, sporadic and asynchronous flowering, strongly dihescent pods and small, hard seeds.
In many regions, landraces persist which show one or more of the traits of the wild forms, particularly in terms of plant habit, seed characters and photoperiod sensitivity.
Ricebean is most widely grown as an intercrop, particularly with maize, throughout Indo-China and extending into southern China in the east and into NE India, Bangladesh and Nepal in the west. It is grown mainly as a dried pulse, but also used as a fodder crop and a source of green pods.
In the past, it was widely grown as a lowland crop on residual soil water after the harvest of traditional long-season rice varieties. However, it has been substantially displaced where multiple cropping of shorter duration rice varieties has expanded.
Despite their long history, only mungbean has received in-depth research interest. Only three – mungbean, black gram and adzuki bean – are used in mechanised agriculture due to their more upright habit and relatively synchronous flowering.
A major constraint to the use of ricebean and the other Asiatic Vigna species are their low seed yields, photoperiod sensitivity, indeterminate flowering, and susceptibility to pests and diseases.
Ricebean is well adapted to the humid tropics, and does well on a range of soil types. However, it needs substantial attention from plant breeders if it is to become widely adopted.
Most varieties are strongly photoperiod-sensitive, and so tend to be late flowering and produce vigorous vegetative growth when grown under conditions of ample water and warm or high temperature in the subtropics. Their twining habit makes them highly suitable to grow as intercrops with maize, sorghum or millet, but also makes them difficult to harvest mechanically, and in extreme cases the weight of vegetative growth may require additional staking. Present varieties are also shatter-susceptible, and hard-seededness is present: this trait does not appear to be consistent within varieties.