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The role of the National Genebank of Kenya in the collecting, characterization and conservation of traditional vegetables

J.K. Kemei, R.K. Wataaru and E.N. Seme
National Gene Bank of Kenya, Kikuyu, Kenya

Introduction

The National Gene Bank of Kenya (GBK) was established in 1988 by the Kenyan Government as the national institution for coordination and implementation of all activities concerned with crop plant and forage genetic resources. These activities include: collecting, seed processing and conservation, multiplication, regeneration, characterization, preliminary evaluation and documentation. Among the priority species for action are the leafy vegetables threatened by genetic erosion or required for improvement programmes.

Genetic erosion of leafy vegetables

Kenya has many wild and weedy species of edible leafy vegetables. They contribute significantly to the nutritional well-being of the rural population (Chweya 1994). While a few of these species have been domesticated or are semi-domesticated, most grow as weeds or wild in virgin, disturbed and/or cultivated areas.

With increasing pressure on both wild habitats and agricultural land, due to demographic and socioeconomic changes, the ecological niches of many leafy vegetables are fast disappearing, and genetic erosion is therefore rapid. At the same time, the cultural status of these valuable food plants has declined as official policy has given priority to growing crops that suit urban tastes, or that offer a potential for export (FAO 1988). An example of this is the introduction of exotic vegetables, which have become more prestigious than local vegetables, slowly causing the latter to disappear (Ford-Lloyd and Jackson 1986). Furthermore, modern agricultural approaches in Kenya, as in much of Africa, often discourage farmers from growing their indigenous crops and cultivars. As a result, the genetic resources base of food security is gradually being undermined (Juma 1989; Kabuye 1993).

In view of the above, an urgent need has been perceived in Kenya to safeguard the genetic basis of traditional vegetables. Programmes for collecting, characterization and conservation were therefore initiated and implemented by the GBK.

Collecting

The GBK, together with the University of Nairobi (Department of Crop Science) and Ben Gurion University in Israel, has organized and implemented various collecting missions for local vegetables and their wild/weedy relatives (Table 1), covering a wide range of ecological zones and climatic conditions.

The objectives of this collaborative programme were both to undertake systematic countrywide collecting and to assess genetic erosion. The target groups were Cucurbita, Crotalaria, Gynandropsis, Corchorus, Lagenaria, Cucumis, Luffa, Solanum and Vigna. Areas selected for collecting were the ones where consumption of these traditional vegetables was believed to be still important culturally, and where species and genetic diversity were likely to be highest. These areas ranged from high-rainfall areas to semi-arid, from well-drained to swampy habitats and from hot lowlands (coastal region) to cool highlands (Rift Valley highlands and the Mt Kenya region). Collecting sites ranged from natural habitats to farmers' fields, backyards or home gardens, and occasionally included marketplaces. Mature fruits and seeds were targeted for collecting.

Table 1. Some of the valuable cultivated and wild/weedy relatives of vegetables collected by NGBK and collaborating institutions (1987-94).

Genus

Altitude (m asl)

Regions

No. accessions

Amaranthus

60-2200

Coast, Eastern, Central, Rift Valley, Western, Nyanza

landrace (40); weedy (33); wild (18); ? (7)

Citrullus

450-1025

Rift Valley, Eastern

landrace (1); weedy (2); wild (11)

Coccinia

686-1550

Eastern, Rift Valley, Coast

weedy (2); wild (13)

Corchorus

620-1350

Nyanza, Rift Valley, Western, Eastern

landrace (5); weedy (25); wild (5); IJO (116)

Crotalaria brevidens

540-2200

Rift Valley, Western

landrace (18)

Cucumis

180-2130

Coast, Eastern, Rift Valley, Nyanza, Central

landrace (6); weedy (4); wild (62); ? (13)

Cucurbita

20-2270

Coast, Eastern, Rift Valley, Central Nyanza, Western,

landrace (160); wild (15)

Lagenaria

140-2440

Eastern, Rift Valley

landrace (25); ? (17)

Luffa

5-1680

Coast, Eastern, Rift Valley, Nyanza

landrace (14); weedy (3); wild (3); ? (3)

Gynandropsis gynandra

700-2300

Eastern, Nyanza, Rift Valley, Coast, Western

landrace (28); weedy (7); wild (9); ? (1)

Solanum nigrum

620-2200

Nairobi, Nyanza, Western, Rift Valley, Eastern, Coast

landrace (12); weedy (13); wild (9); ? (9)

Vigna

560-2050

Nyanza, Eastern, Central, Coast, Western, Rift Valley

1312

IJO = International Jute Organization.
Local people in the collecting regions were from a wide variety of ethnic groups and were very knowledgeable on the vernacular names, characteristics and uses of the different species. Elders and women in these communities were the main sources of indigenous knowledge on the crops and other species that are used for food. Information on the various valuable cultivated and wild/weedy vegetables which were collected is summarized below.

Amaranthus spp.

This genus includes several vegetable species widely distributed in Kenya, usually occurring as weeds in cultivation, and eaten by various communities. The nutritional level is good, with high levels of vitamin C, iron and proteins (Schmidt 1971; Grubben 1977; Chweya 1994).

Citrullus lanatus

The watermelon has wild, weedy and cultivated types reported to be growing in East and Southern Africa (Grubben 1977). It produces both edible fruits and seeds.

Corchorus spp.

Africa is the primary centre of diversity of this genus, which occurs throughout the continent. The largest number of species is found in the eastern and southern parts, with the greatest diversity in South Africa (Edmonds 1990). Thirteen species are said to be indigenous to Kenya. Among the species conserved at GBK are C. aestauns, C. capsularis, C. olitorius and C. trilocularis. Most of the accessions were collected in collaboration with the International Jute Organization (IJO) in 1987. Most species are found as weeds in cultivated farmland. A few are cultivated as leafy vegetables, e.g. C. olitorius, which is widely used by various communities in Kenya. Some of the wild and weedy species are also used as vegetables, but their major future potential is in fibre improvement programmes.

Cucumis spp.

Various wild species were targeted for collection, including C. dipsaceus and C. prophetarum. Species differed in fruit size, shape, colour and spininess. Various species have potential uses as leafy vegetables and for their fruits, but there has been relatively little research on nutritional quality of fruits and leaves and agronomy (Benzioni et al. 1989).

Cucurbita moschata

The pumpkin has long been widely grown in Kenya and other parts of Africa for home consumption or, to a limited extent, for sale at local markets. Both the fruit and leaves are eaten in Kenya. Pumpkins have an advantage over other vegetables in that the fruits can be stored for up to 6 months before being consumed and can play an important role in maintenance of nutritional levels during the long dry seasons, when few fresh vegetables are available (Mendlinger et al. 1991). Little research has been conducted on the extent of genetic variation, but this is believed to be high (Mendlinger et al. 1991).

Lagenaria siceraria

The bottle gourd or dodhee is widely grown in Kenya, especially in the semi-arid and arid regions. Its principal use is as a storage container for liquids, but it is sometimes eaten in the immature stage as marrow. Relatively little modern research has been conducted on the species (Mendlinger et al. 1990).

Luffa spp.

Two species were collected:

· L. acutangula, which is grown by Kenyan farmers for the local and export market. The fruits are cooked and eaten as summer marrow.

· L. cylindrica, which is widely grown in Kenya, usually along fences or the sides of huts. It is mainly grown to be used as a sponge for washing, but sometimes the immature fruit is eaten as a marrow. It can be crossed with L. acutangula, and has excellent resistance to powdery and downy mildews (Mendlinger et al. 1991).

Solarium nigrum

The black nightshade is known by various names by different ethnic communities in Kenya: mnavu (Kiswahili), managu (Kikuyu), kitulu (Kamba), momoi (Maasai). It is commonly found as a weed in a cultivated fields. Two forms are easily recognized in Kenya, a densely hairy type (form B) and the more common sparsely hairy type (form A). Both are used as leafy vegetables (Maundu 1990). The orange fruits are edible and its leaves are used to treat a wide range of ailments in various parts of the world.

Vigna spp.

Vigna unguiculata, the cowpea, is an important subsistence pulse in the drier areas. The wild/weedy species are found in various parts of the country, along the edges of fields, roadsides and in bushy areas. The fresh young shoots and leaves and the immature pods are eaten as vegetables (Purseglove 1968). It is also used as a fodder (hay), silage, pasture and green manure or cover crop.

Conservation

The GBK has facilities for seed processing and drying, viability testing, sealing, packaging and long-term storage. Seeds for base collection (-20°C) are dried to 3-7% moisture content. This is done in a drying room (cool drying system) running at 20°C and 15% relative humidity, until the correct moisture content is achieved. Then the seeds are sealed in airtight aluminium foil containers. Seed viability testing is done after drying, just before storage. The recommended viability standard is 85% and above. Subsamples for regeneration/multiplication, distribution, characterization and monitoring viability are kept at +5°C and/or -20°C.

Germplasm of traditional vegetables has been distributed to various institutions collaborating with the genebank, for research and improvement programmes.

Characterization and evaluation

A number of accessions of indigenous vegetables conserved at GBK have been characterized and evaluated. Most of the characters described show diversity within each species. In most cases, characteristics of the edible part of the plant have been recorded, such as leaf shape, length, peristence and total foliage cover in leafy vegetables. For those whose fruit is the edible part, emphasis has been on fruit size, texture, colour, length and weight. Some examples of the characters recorded for different species are shown in Appendix I. These data show fairly wide variation within each species for most characters.

Not all species held at the genebank have been characterized and the work is continuing. It is envisaged to include more characters in future, particularly those relating to the nutritive aspects of each species. It is also anticipated to include plant characteristics related to duration of production of the edible parts of the plant. Attributes related to storability of the harvested part for consumption need to be investigated.

Further characterization and evaluation have been conducted in collaboration with the universities of Nairobi and Ben Gurion. The species targeted for this study were the Cucurbitaceae. The material was examined for vegetative and yield characters and the extent and structure of genetic variation (pumpkins). The results of the evaluation studies carried out on the fruits of Cucurbita moschata showed that major differences between lines exist (Mendlinger et al. 1991; Chweya 1994), which implies that there is scope for selecting for higher yields and better fruit quality. However, it is likely that there is genetic erosion occurring in Kenya as a result of new introductions, especially in the area between Nairobi and Mombasa and the region west of Nairobi.

Conclusion

The GBK is a modern ex situ conservation facility which meets the required standards established by the international community. While considerable work has been carried out during the last several years on collecting, characterization and conservation of various species of traditional vegetables, much remains to be done in the following areas:

1. Collecting. To date, the semi-arid and arid parts of the country (Marsabit, Wajir, Mandera, Garissa and Tana River) have not been surveyed. Genetic erosion should be assessed in these areas.

2. Characterization and evaluation. Morphological and agronomic description will continue, in collaboration with other institutions as necessary, to add value to conserved germplasm. Biochemical and molecular techniques will become increasingly important.

3. Complementary conservation strategies. GBK will start pilot on-farm conservation activities. Selection of farmers in strategic zones will be the first priority. The genetic changes which arise in on-farm maintenance is an area which needs particular attention.

4. Regional collaboration. As many species of traditional vegetables are widely used, there is a need for African genebanks to establish collaborative activities in germplasm collecting, evaluation and duplicate storage. Exchange of germplasm and information for research purposes is also important.

References

Benzioni, A., S. Mendlinger, J. Chweya, S. Huyskens and M. Ventura. 1989. Optimization of agromanagement in the cultivation of new vegetables for the local and export market. BGUN-ARI-57-89. Annual report 1988-89 on AID-CDR programme.

Chweya, J. 1994. Potential for agronomic improvement of indigenous plant germplasm in African Agriculture: A case study of indigenous vegetables in Kenya. Pp. 105-113 in Safeguarding the Genetic Basis of Africa's Traditional Crops (A. Putter, ed.). Proceedings of a CTA/IPGRI/KARI/UNEP seminar, 5-9 October 1992, Nairobi, Kenya. CTA, The Netherlands/IPGRI, Rome, Italy.

Edmonds, J.M. 1990. Herbarium survey of African Corchorus L. species. IBPGR/IJO, Rome.

FAO. 1988. Traditional food plants feed the rural poor. In Ecoafrica, an Environment and Development Magazine for Africa NGOs 2(4).

Ford-Lloyd, B. and M. Jackson. 1986. Vegetables, industrial crops, medicinal and forage plants. In Plant Genetic Resources - An Introduction to their Conservation and Use. Edward Arnold (Publishers) Ltd., London WCIB 3DQ, England.

Grubben, G.J.H. 1977. Tropical Vegetables and their Resources. IBPGR, Rome, Italy.

Juma, C. 1989. Biological Diversity and Innovation: Conserving and Utilizing Genetic Resources in Kenya. African Centre for Technology Studies (ACTS), Nairobi, Kenya.

Kabuye, C.H.S. 1993. Indigenous Food Plants. In Proceedings of the Indigenous Food Plants Workshop, held at National Museums of Kenya. Compiled at NMK, Nairobi, Kenya.

Maundu, P. 1990. Indigenous food plant programme (IFPP). Newsletter 5, May.

Mendlinger, S., J. Chweya, A. Benzioni, E.N. Seme and M. Ventura. 1990. Collection, Evaluation and Breeding of African Edible Vegetables. BGUN-ARI-25-92. Annual report 1990 on AID-CDR programme.

Mendlinger, S., J. Chweya, A. Benzioni, E.N. Seme, M. Ventura, C. Lungaho and V. Okoko. 1991. Collection, evaluation and breeding of African edible vegetables. BGUN-ARI-25-92. Annual report 1991 on AID-CDR programme.

Purseglove, J.W. 1968. Tropical Crops: Dicotyledons. Longman Group Ltd., Essex CM 20 2JE, England.

Schmidt, D.R. 1971. Comparative yields and composition of eight tropical leafy vegetables grown at two fertility levels. Agron. J. 63:546-550.

Appendix I. Variation in some vegetables

Character

Range

Amaranthus

Growth habit

erect - prostrate

Plant height (cm)

20.0-122.1

Branching index

No branches - branches all along the skin

Stem pubescence

none - conspicuous

Leaf length (cm)

2.34 - 15.86

Leaf width (cm)

0.92 - 11.10

Leaf pubescence

none - conspicuous

Leaf shape

lanceolate - oval

Leaf margin

entire - undulate

Inflorescence colour

yellow - red

Seed colour

brown - black

Seed shape

round - ovoid

Days to 50% flowering

149 - 174

Shattering tendency

low - high

1000-seed wt (g)

0.2-1.1

Lodging

none - high

Pest and disease susceptibility

very resistant - susceptible

Crotalaria brevidens

Days to emergence (days)

4 - 8

Seedling vigour

1 - 5

Days to 50% flowering

21 - 300

Flower colour

brown - yellow

Plant type

erect - semi-erect

Plant height

36 - 16

Stem colour

green - purple

Stem pubescence

glabrous - abundant

Stem diameter (cm)

2.0 - 8.5

Branching habit

upright - spreading

No. of basal tillers

0-5

No. of primary branches

1 - 50

No. of secondary branches

2 - 192

Number of nodes

2 - 44

Internode length (cm)

0.5 - 5

Leaf pubescence

glabrous - abundant

Leaf length (cm)

5.5 - 16.8

Leaf width (cm)

3.5 - 16.0

Leaf senescence

few - most

Flowering tendency

low - high

Fruit colour

brown - black

Fruit length (cm)

2.5 - 8

Fruit width (cm)

2-5

Seed colour

white - brown

Seasonality

annual - biennial

Gynandropsis gynandra

Days to emergence

4-8

Seedling vigour

very strong - very weak

Days to 50% flowering

17 - 35

Plant type

erect - semi-erect

Plant height (cm)

25-71

Stem colour

green - red

Stem pubescence

glabrous - abundant

Stem diameter (cm)

1.0 - 3.8

Branching habit

upright - spreading

Primary branches (no.)

2-7

Leaf colour

green - brown

Leaf pubescence

glabrous - abundant

Leaf length (cm)

1.7 - 6.6

Leaf width (cm)

0.8 - 2.2

Disease susceptibility

medium - resistant

Pest susceptibility

medium - resistant

Lodging

none - nearly 100%

Flowering tendency

low - high

Position of fruit

top - throughout

Fruit length (cm)

6.4-11.1

Solarium nigrum

Plant growth habit

prostrate - erect

Stem pubescence

glabrous - abundant

Stem colour

green - purple

Leaf pubescence

glabrous - abundant

Corolla colour

all white

Fruit position

declining - intermediate

Fruit size

small - very large

Fruit shape

all round

Ripe fruit colour

yellow - black

Plant height (cm)

45 - 120

Plant width (cm)

3 - 7.5

Foliage cover

fair - good

Leaf attitude

semi-erect - drooping

Vigna

Twinning tendency

none - pronounced

Days to 50% flowering

40 - 60

Pod length (cm)

11.0 - 22.0

Seed shape

round - drum shaped

Leaflet length (cm)

7.4 - 15.3

Leaflet width (cm)

3.4 - 11.0

Number of branches

3-8

Flower colour

light yellow - purple

Pods per penducle

1 -3

Pod width (cm)

0.4 - 1.3

100-seed weight (g)

8.4 - 23.7

Growth habit

erect - semi-erect



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