Conservation and use of genetic resources of traditional vegetables in Tanzania

R.E.A. Swai
Tengeru Horticultural Research & Training Institute, Arusha, Tanzania

Abstract

Tanzania has accorded high priority to the development of traditional vegetables (TVs) and other nutrient-rich local foods as a strategy to overcome malnutrition. Many TVs are still collected from the wild and only a few have been domesticated. This paper describes efforts in Tanzania to conserve, characterize, evaluate and document TVs, and also to produce seeds to facilitate germplasm exchange and promote the use of these species.

Introduction

Traditional vegetables (TVs) are adapted to local agro-ecological conditions, require a minimum of cultivation, can be grown in home gardens, give high yields within a short period, and are easy to harvest and preserve. They are widely consumed by different communities (Manyafu 1971; Reuben and Minjas 1991; Mnzava 1993). Tanzania has accorded high priority to the development of these plants in an attempt to overcome malnutrition. Vitamin A deficiency is one of the most prevalent and potentially serious forms of malnutrition in Tanzania after nutritional anemia and goiter, especially in the low-rainfall areas (Mganza 1980). It is especially pronounced in children and pregnant and lactating mothers. Such malnutrition can be partially alleviated by consumption of dark green leafy vegetables, which are excellent sources of proteins, vitamins and minerals (Swai 1989). Traditional vegetables are nutritionally higher in vitamins A and C, folic acid and minerals than many exotic vegetables (Table 1). However, traditional vegetables are abundant only during rainy seasons, when they are found growing in the wild, often on fallow land, or as weeds in cultivated areas. During the dry seasons, they are scarce or available only in limited amounts as dried, preserved material.

Status of traditional vegetables

Information on traditional vegetables in Tanzania is scanty and dispersed (Mnzava 1993). Early studies by Manyafu (1971), Fleuret (1979) and Gerson (1989) are exploratory in nature. Despite the wide range of TVs found and consumed in Tanzania, only a few species have been scientifically documented (Table 2). On the other hand, indigenous knowledge of the nutritive values, methods of production, preservation and utilization of TVs is disappearing, as, with the young moving to urban centres, systematic transmission of the information from the old generation breaks down. There is also evidence that some wild plant species which have been used as vegetables are on the verge of disappearance in some areas owing to:

· changes in the ecology of many areas due to prolonged drought, overgrazing, bush fires, deforestation, etc.

· introduction of exotic vegetables, resulting in a gradual decline in the use of wild and weedy species.

Vegetable	Ca (mg)	Fe (mg)	Vit. A (µg)	Vit. C (mg)	Protein (g)	Fibre (mg)
African eggplant	523	6.0	?	67	4.8	24
Amaranthus	410	8.9	2300	50	5.0	24
Cassava (lvs)†	300	7.6	3000	310	6.1	20
Cowpea (lvs)	255	5.7	700	56	4.7	20
Hare's lettuce	130	3.1	1430	0	?	20
Pumpkin (lvs)	475	0.8	1000	70	4.0	20
Sweet potato (lvs)	160	6.2	2620	70	3.2	20
Taro (lvs)	98	2.1	1530	11	4.1	12

^† lvs = leaves.
Source: West et al. 1988. The Composition of Food Tables.

Scientific name	Botanical family
Amaranthus spp.	Amaranthaceae
Basella spp.	Basellaceae
Bidens pilosa	Astercaeae
Brassica carinata	Brassicaceae
Chenopodium spp.	Chenopodiaceae
Corchorus spp.	Tiliaceae
Cucurbita pepo	Cucubitaceae
Galinsoga parviflora	Compositae
Gynandropsis gynandra	Capparidaceae
Hibiscus sabdariffa	Malvaceae
Ipomoea batatas	Convolvulaceae
Manihot esculenta	Euphorbiaceae
Nasturtium officinale	Cruciferae
Portulaca oleracea	Portulacaceae
Sesbania aegyptica	Fabaceae
Solanum aethiopicum	Solanaceae
Solanum macrocarpon	Solanaceae
Solanum nigrum	Solanaceae
Solarum pseudonigrum	Solanaceae
Sonchus spp.	Compositae
Telfairia occidentalis	Cucubitaceae
Vigna unguiculata	Leguminosae
Xanthosoma brasiliense	Araceae

Sources: Swai 1991 and Mnzava 1993.

Conservation activities

Until 1990, conservation of genetic resources of traditional vegetables was the responsibility of research institutions located in zones of high potential for horticultural crops production. Ex situ collections are maintained at:

· HORTI (Horticultural Research & Training Institute), Tengeru for the northern highlands areas

· Sokoine University of Agriculture (SUA) and CASRC, Dakawa for humid lowlands and coastal areas

· MARTI (Ministry of Agricultural Research Training Institute), Uyole for the southern highlands areas.

Following the establishment of the National Plant Genetic Resources Centre (NPGRC) at the Tropical Pesticides Research Institute (TPRI), Arusha in 1990, conservation activities of traditional crops and other crops have been strengthened and coordinated. At NPGRC, accessions are maintained in cabinet freezers at temperature of -18°C and moisture content below 7%. Seeds are packed and sealed in aluminium foil packets.

Uses of genetic resources of traditional vegetables

Programmes to improve the traditional vegetables have been limited to a few species, i.e. Amaranthus spp., Brassica carrinata, Solanum nigrum and S. aethiopicum. Purification of populations of these vegetables over time has resulted in uniform and stable varieties which have been evaluated for their potential yield and other agronomic attributes. Some detailed studies on their nutritive values and preparation and preservation methods have been done in collaboration with the Tanzania Food and Nutrition Centre (TFNC). Improvement programmes for TVs have been limited in scope because of a shortage of specialized plant breeders.

Documentation of TVs and other horticultural crops maintained in various working collections in the country has been carried out by NPGRC in collaboration with IPGRI. This has greatly promoted exchange of TV germplasm within the country and to other SADC member states. With the establishment of vegetable seed-processing facilities at Tengeru and Dakawa, multiplication and availability of seeds of commonly grown and consumed traditional vegetables have been greatly facilitated.

Future plans

The capacities of research institutions in terms of finance, staff and facilities, as well as national coordination, will need to improve if the activities necessary to ensure continued conservation and use of genetic resources of TVs are to be implemented. These include:

· specialized ecogeographic surveys and collecting missions to investigate the whole available range of genetic diversity

· socioeconomic surveys on production and consumption of TVs

· promotion of home gardening of TVs.

Fleuret, A. 1979. The role of wild foliage plant in diet: A case study from Lushoto, Tanzania. Ecol. Food Nutrition 8:87-93.

Gerson, R. 1989. Exploratory Survey on Indigenous Vegetables. HORTI Tengeru Annual Research Report 1989.

Manyafu, J.L. 1971. The role of wild fruits and vegetables in Tanzania. Acta Hort. 21:93-96.

Mganza, O.S. 1980. Nutritional Problems and Policy in Tanzania. Cornell International Nutrition, Monograph series No. 7. Cornell Univ., USA.

Mnzava, N.A. 1993. Traditional vegetables in Tanzania. Paper presented at the First National Vegetable Crops Research and Planning Workshop, 26-27 July 1993, Arusha.

Reuben, S.O.W.M. and A.N. Minjas. 1991. Genetic resources on underexploited indigenous plants in Tanzania. Pp. 251-266 in Proceedings of the First National Workshop on Plant Genetic Resources and Biotechnology; held at Arusha, Tanzania, 16-20 January 1990 (F.M. Shao, F.S.S. Magingo, A.N. Minjas, H.F. Bitanyi and R. Mahunnah, eds.). Benedictine Publications, Ndanda, Peramiho Tanzania.

Swai R.E.A. 1991. Genetic resources of horticultural crops in Tanzania. Pp. 251-266 in Proceedings of the First National Workshop on Plant Genetic Resources and Biotechnology; held at Arusha, Tanzania, 16-20 January 1990 (F.M. Shao, F.S.S. Magingo, A.N. Minjas, H.F. Bitanyi and R. Mahunnah, eds.). Benedictine Publications, Ndanda, Peramiho Tanzania.

Swai, R.E.A. 1989. The role of horticultural crops in alleviating Vitamin A. Paper presented at the Deficiency and Xerophhthalmia Workshop held at Muhumbili Medical Centre, Dar Es Salaam, 24-28 October 1989.