Ekai Thabi - An aquatic vegetable cash crop in Manipur

Dr N Irabanta Singh *

Introduction:

Ekai Thabi (Manipuri)/ Water mimosa (English) is an aquatic floating perennial herb that attaches to the bank at the water edges and sends down a tap root. The North Eastern region of India particularly Manipur provide a favourable condition for mass propagation of water mimosa (Neptunia prostrata) owing to its ample rainfall, humidity and moderate range of temperature.

Moreover, about 70% of the total population of four districts( Imphal East, Imphal West, Bishnupur and Thoubal) of the state practised with paddy cultivation as the major source of income and 20% of this population are poor and marginal farmers.

In this article the author wishes to describe the taxonomy, preservation methods, propagation through seed, ecology, nutritional and medicinal values, cost benefit analysis of water mimosa cultivation in Manipur as well as suggestions for cultivation of water mimosa in their inundated paddy fields.

Description and taxonomy:

Botanically, water mimosa is known as Neptunia prostrata (Lam.) Baill. (Syn. N. oleracea Lour.). It is an aquatic legume (Order -Fables and Family- Leguminoceae) and native to several continents of the humid tropics and is used for both human consumption and as green manures for rice cultivation in India and some Asiatic countries (Subha Rao et. al., 1995).

N. prostrata stems ranges 1 to 1.5 m long, prostrate at the water edge, rarely branched, becoming detached from the primary root system, forming a spongy-fibrous indument between the nodes and producing fibrous adventitious roots at the nodes when growing in water. Leaves have leaflets, 8-20 pairs per pinna. The leaflets are very sensitive to touch and close quickly.

Flowers, yellow 30-50 per spike and each flower is 7.0-16.0 mm long, 0.5-1.0 mm broad. Seeds are oval and brown, 4-8 per legume. Each seed is, 4.0-5.1 mm long, 2.7-3.5 mm broad. Water mimosa can grow from seeds and from sections of stem that break free from the parent plant. Flowering begins in early summer.

Preservation methods:

Old stock plants could be preserved for supply of plantlets to the growers for the following season. The selected plants for preservation could be skipped off from harvesting at least one (1) month before the end of the season. In Manipur, three different indigenous methods are practised for preservation of water mimosa during off-season. They are i) Shallow water method, ii) Floating method and iii) Mud method.

Propagation through seed:
Water mimosa seeds could be collected from different sites of Manipur. For aseptic germination, water mimosa seeds could be scarified and surface sterilized for 5-10 min in 0.01% HgCl2 solution followed by repeated rinsing with sterile distilled water.

The seeds could be placed on sterile moistened double layered paper towels in petri dish and allowed to germinate at 25 degree +1 or -1 degree Celsius for 24 hrs in continuous dark. The germinated seeds could be transplanted aseptically in culture pot containing sterile soils and culture under control condition for 14 hr light/10hr dark at 25 degree Celsius for 30 days.

Ecology:

In Manipur, N prostrata grows in warm, stagnant ponds, slowly moving streams during rainy season (May-September). The plant flowers at the third month of its growth cycle (i.e. June-July). Whereas in the Manipur Valley, the growth of the plant is found poor, flowering also takes place abnormally and nodulation is hardly seen.

This variation in behaviour of N. prostrata is due to its different sensitivity to photoperiod, temperature, humidity, soil nature. The humidity plays a major role in nodulation due to infection of Rhizobiium. The plant prefers to very bright light intensity and short day (<12 hours) photoperiod. 25-30 degree Celsius is the optimum temperature of their growth. Studies on the soil habitat of the plant revealed that it prefers to slightly acidic soil (pH 5-6.5), soil depth (20-50 cm shallow) and high soil fertility.

Nutritional and medicinal values:

Water mimosa is nutritionally high in Calcium. A serving of 100g contains as much as 387 mg of Niacin. Niacin plays an essential part in the metabolic process of living cells and is involved in both DNA repair and production of steroid hormones in the adrenal glands. Moreover, water mimosa contains upto 5.3 g of fibre for every serving of 100g.

Juice of the stem and roots are used for medicinal purposes. Whole plant extract exhibited cytotoxic activity on neoplastic cell lines. Extract of the herb exhibited hepatoprotective activity.

Cost benefit analysis between water mimosa cultivation and paddy cultivation:
The cost benefit analysis for water mimosa (N. prostrata) cultivation and paddy cultivation revealed that more income could be earned from water mimosa cultivation (=Rs. 46,419/- approx. per year per 0.46 acre of cultivable land) than paddy cultivation (=Rs. 11,605/- approx. per year per 0.46 acre of cultivable land).

Discussion:

Water mimosa is cultivated as a vegetable in South-East Asia (leaves and shoots have cabbage-like flavour). Young ends of stems and pods are edible and usually eaten raw as a vegetable in Thailand and Cambodia which is cultivated much like rice. The young leaves, shoot tips and young pods are usually eaten raw or in stir-fries and curries.

On the other hand, water mimosa poses an extreme threat to Queensland’s (Australia) waterways and wetlands. It establishes from small plant pieces in water and from seed. Under favourable conditions, water mimosa grows out from the banks to form floating rafts of dense interwoven stems. These can be dislodged by water movement (especially during floods) and are soon replaced by more water mimosa.

These floating rafts can restrict water flow in creeks, channels and drains. It can impede recreational water sports and boating access. These rafts are so dense they can reduce water quality by preventing light penetration and reducing oxygenation of water. This creates favourable habitat for mosquitoes and reduce fish activity, causing the death of native, submerged water plants and fish.

Thus, water mimosa comes under legal requirements in Australia. Water mimosa are restricted invasive plants under the Biosecurity Act 2014. The Act requires that all sightings of water mimosa plants must be reported to Biosecurity Queensland within 24 hours of sighting.

By law, everyone has a general biosecurity obligation (GBO) to take all reasonable and practical steps to minimise the risk of spread of water mimosa until they receive advice from an authorised officer. It must not be kept, moved, given away, sold or released into the environment without permit.

Recommendation:

In Manipur, large areas of cultivable land surrounding the Loktak lake has been left unused due to seasonal inundation caused by Ithai barrage being constructed for generating Loktak Hydro Electric Project, commissioned in 1983 under National Hydro Power Corporation. This barrage has brought a great hardship to thousand of peasants in Southern Manipur Valley.

The cost benefit analysis of cultivating water mimosa with paddy cultivation in the same area revealed that more income could be generated from water mimosa cultivation than paddy cultivation. This suggests that the farmers could start plantation of water mimosa in their unused inundated lands in order to generate sustainable income.

Conclusion:

The technology for mass propagation/ cultivation of water mimosa is an effective income generating enterprises for the poor and marginal farmers of Manipur in their unused inundated paddy fields.