Lablab purpureus L. (Sweet) Usually known as Dolichos bean, Hyacinth bean or Field bean is one of the most ancient crops among cultivated plants. It is a bushy, semi-erect, perennial herb, showing no tendency to climb. It is mainly cultivated either as a pure crop or mixed with finger millet, groundnut, castor, corn, bajra or sorghum in Asia and Africa. It is a multipurpose crop grown for pulse, vegetable and forage. The crop is grown for its green pods, while dry seeds are used in various vegetable food preparations. It is also grown in home gardens as annual crop or on fences as perennial crop. It is one of the major sources of protein in the diets in southern states of India. The consumer preference varies with pod size, shape, colour and aroma (pod fragrance). It is also grown as an ornamental plant, mostly in USA for its beautiful dark-green, purple-veined foliage with large spikes clustered with deep-violet and white pea-like blossoms.
Lablab is remarkably adaptable to wide areas under diverse climatic conditions such as arid, semi-arid, sub-tropical and humid regions where temperatures vary between 22°C–35°C, low lands and uplands and many types of soils and the pH varying from 4.4 to 7.8. Being a legume, it can fix atmospheric nitrogen to the extent of 170 kg/ha besides leaving enough crop residues to enrich the soils with organic matter. It is a drought tolerant crop and grows well in dry lands with limited rainfall. The crop prefers relatively cool seasons (temperature ranging from 14-280C) with the sowing done in July-August. It starts flowering in short days (11-11.5 hour’s day length) and continues indeterminately in spring. Hyacinth bean flowers throughout the growing season.
It is an excellent nitrogen fixer and is sometimes grown as a cover crop or for livestock fodder. Young immature pods are cooked and eaten like green beans (older pods may need to be de-stringed). They have a strong beany flavour and some people like to mix them with other beans or green vegetables. Young leaves are eaten raw in salads and older leaves are cooked like spinach. Flowers are eaten raw or steamed. The large starchy root tubers can be boiled and baked. The immature seeds can be boiled and eaten like any shelly bean. Dried seeds should be boiled in two changes of water before eating since they contain toxins Cyanogenic glucosides. In Asia, the mature seeds are made into tofu and fermented for tempe. They are also used as bean sprouts.
Dry seeds should be well cooked in two changes of water before eating. Raw dry seeds are poisonous and can cause vomiting and even convulsions and unconsciousness.
Unlike the garden bean, the field bean is valued more for its green seeds than for pods. The pods and seeds are also fed to the cattle in addition to vines, which make an excellent fodder when fed with sorghum straw.
In Brazil, Zebu Cattle grazing maize stalks, dry grasses and green Lablab gained 350 g / head / day over 3–month period, while cattle without Lablab lost weight. In subtropical Australia, cattle gains have ranged from 0.09–1.04 kg / head / day depending on the feeding conditions. Trials in Zimbabwe have demonstrated that the use of a Lablab hay supplement resulted in milk yield increase slightly less than those obtained through the use of velvet bean (Mucuna pruriens). Milk quality was also slightly less than that achieved with velvet bean but still very acceptable. Supplementing the diet of goats with Lablab in Zimbabwe has been shown to yield better conditions for does, higher kid birth rates and higher milk yields.
Crop raised through seed. Germination is epigeal and normally takes about 5 days. Seed is reported to remain viable for two to three years. It is generally grown as an intercrop with finger millet (Eleusine coracana) in South India under rainfed conditions with an average rainfall of 600–900 mm per year. Sowing is done in June and July and harvested from November to March. The garden cultivars are sown in pits in July or August and are thinned to four vines per pit after a month. They require support for climbing. They are heavily fertilized and frequently irrigated. They flower in November and the green pods are harvested from December to March. Garden varieties are semi-perennial. Green pods are used as vegetables. The older varieties used to be long duration and photosensitive. Whereas improved varieties are photoinsentive and can be cultivated throughout the year either as pure crop or as mixed crop and they mature in 110–120 days. In pure stands, seed yields are around 12 to 15 q/ha, whereas in intercrop condition, the yields are around 4–5q/ha. In garden types, the green pod yield is 26–45 q/ha.
Lablab has many advantages: It yields 5–10 t/ha of green matter, which can be used as fodder or green manure. It improves the soil condition and is relatively drought tolerant; it is also a good cover crop. As forage, it is very palatable, either as green fodder or as silage.
Dolichos lablab L. has been a novelty garden plant in the U.S. for generaions. This vigorous twining vine is characterized by larger ternate purple-green leaves and purple petioles. The vines produce hundreds of spikes of lavender flowers in late summer followed by long–lasting deep lavendor–purple pods. It is primarily an ornamental annual vine in the US, but it has been used for centuries in India and China as an edible pod and animal forage. The distinctive long–lasting pods are suitable for cut–stems for the cut–flower industry. In addition, the pods are so unique that they could be used for decoration or harvested for Chinese food wholesalers. Some local and regional florists enjoyed the special colour and texture that hyacinth beans offered their arrangements while others had little interest in use of these stems. With yields as 70 cut–stems per linear meter, the potential returns could be quite high– (7 bunch / m x $ 2.50 / bunch). A common minimum wholesale price is $ 17.50 / m for short–term harvest and marketing of this summer / fall crop. But the availability of the established market determines the overall economy of the crop (Anderson, et al., 1996).
Magness, et al., (1971): Food and feed crops of the United States.
The biosystematics of hyacinth bean and its relatives were reviewed and revised. Formerly Lablab was included in the genus Dolichos following Linnaeus. But now it is assigned to the monotypic genus Lablab. Three subspecies are recognized inL. purpureus: ssp. uncinatus: the wild ancestral form distributed mainly in East Africa with small, scimitar-shaped pods of about 40 x 15 mm; ssp. purpureus cultivated as a pulse crop, has larger scimitar-shaped pods, 100 x 40 mm; it includes commercial varieties and ssp. benegalensis, Asiatic origin, has linear oblong-shaped pods, longer than other sub– species, upto 140 mm x 10–25mm. Although pod shape is a significant morphological difference, it is widely believed that ssp. bengalensis and ssp. purpureus are genetically similar. Although most domesticated material is either ssp. purpureus or ssp. bengalensis, ssp. uncinatus has been domesticated in Ethiopia. Studies in Labalab have shown that the perennial types have considerable genetic and morphological diversity. Hybrids between perrenial and forage types have been produced at CSIRO, Australia and have resulted in new cultivars being released.
Labalab is predominantly self- fertilizing. Chromosome number 2n = 22.
Grain maturation on the forage cultivars is not uniform; but landrace types often have more synchronous maturity, high grain yields 1– 2.5 t / ha, depending upon cultivar. But when grown on trellises in small holder systems, the grain yields can be far greater. In mixtures with other crops, grain yields could be about 0.5 t / ha. Late seeding varieties may be affected by early frosts. There is some evidence that Lablab