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Genetic enhancement of indigenous vegetables in Kenya

James A. Chweya
University of Nairobi, Nairobi, Kenya

Introduction

Indigenous vegetables form a substantial proportion of the diets of most low- and middle-class Kenyans. For rural Kenyans, the vegetables are inexpensive, easily accessible and excellent sources of micronutrients. Sale of the vegetables in rural and urban areas is a source of income for the producers, who are mainly women. Some of the vegetables are partially domesticated, but most are weeds and/or wild. The more important species have been described (Chweya 1985; Juma 1989; Mwajuma et al. 1991; Opole et al. 1991).

There is a general feeling by Kenyans that the use of indigenous vegetables is declining. The attributed reasons for this include the inability of these species to compete with exotic types and their reputation as low-status food items, especially in urban areas and by the youth. The yield potential of the indigenous vegetables is considerable but has not yet been exploited. Efforts to make the vegetables competitive with exotic ones are therefore required, as essential components of a strategy of conservation through utilization.

There is, therefore, a need to improve yields and nutritive value of the vegetables by genetic enhancement through selection and/or breeding and to develop efficient agromanagement systems with minimum but appropriate input application. To achieve this, both genetic stocks and biological/botanical, ethnobotanical and agronomic information are necessary.

Unfortunately, no comprehensive, systematic germplasm collections of indigenous vegetables have been made and very little research on agronomic problems has been carried out. However, since 1985 a programme has been underway at Kabete Field Station, Faculty of Agriculture, University of Nairobi, on some of the more important Kenyan species: Gynandropsis gynandra, Solanum nigrum, Cucurbita spp. and Crotalaria brevidens. This paper reports on some of the findings so far.

Gynandropsis gynandra

Genetic variation

Studies were conducted between 1985 and 1989 (Chweya 1990) on seed samples collected from farmers' fields in Kakamega, Siaya, South Nyanza, Kisii, Kericho and Machakos districts in Kenya to determine whether there were any differences in plant characteristics and nutritive quality among populations from different geographical areas. The plant characteristics considered included morphology of roots, stems, leaves and flowers, colour of stems, petioles and flowers, plant height and leaf yield. Nutritive quality was evaluated through determination of the amounts of dry matter, ascorbic acid, beta-carotene, calcium, sodium, iron and crude protein and fibre contained in the leaves.

Seeds from the various areas were grown on plots measuring 6 x 3 m in a randomized complete block design experiment with three replicates. Results indicated that there were no significant differences in plant characteristics, leaf yield and nutritive quality of plants from seeds collected from the different areas in Kenya. However, there was variation in stem and petiole colouration, number of leaflets and length of petioles. Based on pigmentation, four different plant types were recognized:

· green stems, green petioles
· green stems, purple petioles
· purple stems, green petioles
· purple stems, purple petioles.
Leaves that were palmate had lengths ranging from 2 to 23 cm with 3 to 7 leaflets. Lengths of leaflets also varied from 2 to 10 cm, while the width ranged between 2 and 4 cm.

Another study (Omondi 1990) was conducted at the same time to investigate the presence of heritable variation in the samples collected and to assess the utility of yield components in the improvement of yield and duration of harvesting through the component breeding approach. Families from each population were planted in a three-replicate compact family block design at two sites (Thika Horticultural Research Station and Kabete Field Station) in two different agro-ecological zones. Data collected included days to flowering, plant height, number of primary leaves, leaf length, leaf breadth, fresh leaf weight and dry leaf weight. The results indicated that there was significant variation among populations for leaf length and dry leaf weight at Thika and number of primary leaves at Kabete. This reflected a variation within populations for days to flowering and fresh and dry leaf yields. Yield prediction studies revealed that duration of harvesting could be prolonged by selecting late-flowering genotypes and that leaf yields could be improved by direct selection.

Response to fertilizer application

Several preliminary experiments have been conducted to study the effects of nitrogen, phosphorus and farmyard manure application on crop stand and leaf yield and quality. The fertilizers were applied singly or in combination in randomized complete block or split-plot experimental designs replicated three times. The experiments were carried out between 1987 and 1988 (Chweya 1990) and between 1990 and 1991 (Maumba 1993). Harvesting was done once, 8-9 weeks after seedling emergence.

Results (Tables 1, 2, 3 and 4) indicated that fertilizer application significantly improved field crop establishment and increased leaf yield. However, increased soil fertility significantly decreased harvest index. The results clearly show that G. gynandra plants respond to fertilizer (inorganic or organic) application. Fertilizer application increases crude protein content, decreases beta-carotene, ascorbic acid and iron, and has no effect on phenolic compounds and calcium and sodium contents of the leaves.

Deflowering

In flowering plants, there is competition between reproductive and vegetative organs. Once flowering begins, vegetative growth declines. In 1991, a study was conducted (Maumba 1993) to show the effect of deflowering on vegetative growth and leaf yield and quality. Designated plants were deflowered as soon as the plants had flowered and this continued until final harvest, which was done 8 weeks after seedling emergence. The results (Table 5) showed that deflowering significantly decreased plant height, significantly increased number of branches per plant, leaf yield and leaf ascorbic acid content and had no effect on petiole length, beta-carotene and total phenolics contents.

Table 1. Effect of phosphorus application on crop stand and leaf yield of Gynandropsis gynandra.

P2O5 (kg/ha)

Crop stand (%)

Leaf yield (kg/m2)

Harvest index (%)

0

45c

0.11c

18a

46

73b

0.22b

18a

92

86b

0.25b

21b

184

95a

0.31 a

21b

Values followed by same letter within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Table 2. Effect of nitrogen application on plant growth and leaf yield and quality of Gynandropsis gynandra

Nitrogen (kg N/ha)

Final plant height (cm)

Petiole length (cm)

Number of branches

Leaf yield (t/ha)

Ascorbic acid (mg/100 g DM)

0

62b

8.0b

12b

7.0d

1063a

13

67ab

8.0b

12b

10.4c

1039ab

26

75a

9.0a

13a

14.6b

986bc

52

76a

9.0a

13a

17.0a

913c

Values followed by the same letter(s) within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Table 3. Effect of nitrogen and phosphorus application on crop stand and leaf yield and quality of Gynandropsis gynandra.

N:P2O5 (kg/ha)

Crop stand (%)

Leaf yield (kg/ha)

Harvest index (%)

Crude protein (% DM)

Beta-carotene (mg/100 g DM)

Iron
(% FW)

0:0

55d

0.3c

21a

33.8b

12a

0.4a

40:40

78c

0.5b

21a

34.8ab

9b

0.1c

80:80

91a

0.5b

18b

36.2ab

9b

0.3b

160:160

96a

0.7a

16c

37.1 a

8b

0.2b

Values followed by the same letter(s) within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Table 4. Effect of diammonium phosphate (DAP) (18%N:46%P2O5) and farmyard (FYM) application on crop stand and leaf yield of Gynandropsis gynandra.

Fertilizer

Crop stand (%)

Leaf yield (kg/m2)

Harvest index (%)

0 DAP, FYM

44c

0.06c

40a

10 t/ha FYM

75b

0.26b

36b

200 kg/ha DAP

93a

0.33b

32c

20 t/ha FYM

96a

0.46a

28d

Values followed by the same letter within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Table 5. Effect of deflowering on vegetative growth and leaf yield and quality of Gynandropsis gynandra.


Not deflowered

Deflowered

Plant height (cm)

75a

65b

Petiole length (cm)

9a

9a

Number of branches per plant

13b

14a

Leaf yield (t/ha)

7.2a

9.5a

Ascorbic acid (mg/100 g DM)

1056b

1152a

Beta-carotene (mg/100 g DM)

44.3a

42.2a

Total phenolics (mg/100 g DM)

5000a

4966a

Values followed by the same letter across rows are not significantly different according to a t-test at 5% probability level.
Plant age

Leaves of G. gynandra plants are harvested over time. Plant age may, therefore, have an influence on leaf yield and quality. A study was conducted in 1991 (Maumba 1993) to show the effect of plant age on leaf yield and quality. After field establishment, plants were harvested weekly starting 4 weeks after seedling emergence for 5 weeks and weekly leaf yields were recorded. Leaf samples were taken at 7 and 10 weeks after seedling emergence for determination of ascorbic acid, beta-carotene and total phenolics contents.

The results showed that weekly leaf yields increased with plant age until about the seventh week of growth, when yields (2.8 t/ha) started declining. By the tenth week of growth, leaf yields had declined to 0.5 t/ha, a decrease of about 90%. The results further indicated that leaf ascorbic acid content significantly increased while leaf total phenolics significantly decreased with plant age (Table 6). Beta-carotene increased and then decreased with plant age.

Table 6. Effect of plant age on leaf ascorbic acid, carotene and total phenolics contents of Gynandropsis gynandra.

Weeks after seedling emergence

Ascorbic acid (mg/100 g DM)

Beta-carotene (mg/100 g DM)

Total phenolics (mg/100 g DM)

4

680c

42b

5790a

7

1069b

49a

5403a

10

1251 a

44a

4966b

Values followed by same letter within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Intercropping

A study conducted in 1991 in which G. gynandra plants were intercropped with maize (Zea mays) showed that intercropping significantly reduced leaf yield of the plants. The yield reduction was more than 50%. However, the land equivalent ratio was more than one.

Solarium nigrum

Genetic variation

Mtotomwema (1987) identified variants within S. nigrum. The variants differ in terms of colour of mature fruits (blackish purple, orange or green) and leaf serration (serrated or entire). Studies were conducted (Mwafusi 1992; Onyango 1993) to determine whether there were any plant growth, leaf yield and nutritive quality differences between the various variants (orange fruits, serrated leaves; orange fruits, non-serrated leaves; purple fruits; green fruits). The results indicated that there were significant differences in most of the parameters measured except for plant canopy spread and beta-carotene and protein contents (Table 7).

Propagation

Solanum nigrum is commonly propagated by seed. However, it has been observed that some growers use shoot cuttings, especially during the rainy season. There is hardly any information in the literature on the effect of asexual propagation on leaf yield and quality of S. nigrum. A study was therefore conducted in 1990/91 (Mwafusi 1992) to investigate the effect of propagation method on vegetative growth and leaf yield and quality. Shoot cuttings, 15 cm long, were obtained from 4-month-old plants, rooted in vermiculite and allowed to grow for 4 weeks. During growth the plants were deflowered. The plants were set out in the field and their performance compared with that of 4-week-old seedlings which had been raised in the nursery.

Table 7. Plant growth, leaf yield and nutritive quality differences of Solarium nigrum variants.


Orange fruits, serrated leaves

Orange fruits, entire leaves

Purple fruits

Green fruits

Plant height (cm)

50a

57a

33b

-

Number of branches

16ab

20a

13c

-

Canopy spread (cm)

78a

92a

90a

-

Leaf yield (kg/ha)

2010b

2860a

1370c

-

Dry matter (%)

14.5a

13.4ab

13.3b

12.2b

Total phenolics (mg/100 g DM)

2940a

2840b

2740c

-

Total glycoalkaloids (mg/100 g FW)

110b

132a

131a

-

Beta-carotene (mg/100 g DM)

26.8a

28.6a

31.7a

31.9a

Crude protein (% DW)

35.7a

35.7a

36.7a

36.5a

Crude fibre (% DW)

10.1a

10.1a

9.2b

9.6b

Total ash (% DW)

17.4b

18.7b

17.9b

20.9a

Iron (mg/100 g DW)

56.9c

80.8b

63.4bc

106.3a

Calcium (mg/100 g DW)

294.9c

357.7b

275.8c

432.2a

Values followed by the same letter(s) across rows are not significantly different according to Duncan's Multiple Range Test at 5% probability.
Vegetatively propagated plants branched, spread and yielded significantly less than those raised from seed (Table 8). Furthermore, plants that were vegetatively propagated gave leaves which had significantly less total phenolics and significantly more glycoalkaloids than those raised from seeds. However, the results show that S. nigrum could be propagated vegetatively using shoot cuttings.

Plant density

Optimum plant density reduces competition between plants, resulting in maximum yield. A study was conducted in 1990/91 (Onyango 1993) to show the effect of plant density on number of harvestable shoots and fresh shoot and leaf weights of S. nigrum plants. The results showed that plant density significantly affected yield of S. nigrum (Table 9) and that the optimum density could be above 66 660 plants/ha.

Table 8. Effect of propagation on plant growth and leaf yield and quality of Solarium nigrum.


Seed propagation

Vegetative propagation

Plant height (cm)

39.0a

37.5a

Number of branches

10.4a

8.5

Canopy spread (cm)

57.5a

48.0b

Leaf yield (kg/ha)

521.0a

381.0b

Total phenolics (mg/100 g DM)

5275a

5225a

Total glycoalkaloids (mg/100 g FW)

108a

144.0a

Values followed by the same letter across rows are not significantly different according to a t-test at 5% probability level.
Table 9. Effect of plant density on cumulative number of harvested shoots and fresh shoot and leaf weights of Solanum nigrum plants grown for 11 weeks and harvested weekly.

Plant density/m2

No. harvested shoots/m2

Fresh shoot (g/m2)

Fresh leaf weight (g/m2)

2.2

312b

1004c

707c

3.3

381b

1337b

909b

6.7

675a

2646a

1844a

Values followed by the same letter within columns are not significantly different according to Duncan's Multiple Range Test at 5% probability level.
Response to fertilizer application

An experiment was carried out in 1988/89 (Murage 1990) to study the effect of nitrogen fertilizer (CAN-26%N) application on plant growth, leaf yield and nutritive quality of S. nigrum. Four nitrogen rates (0, 5, 10 and 15 g N/plant) were used in a randomized complete block design experiment with three replicates. Plants were spaced at 30 cm between and within rows and top-dressed with various nitrogen rates 2 weeks after transplanting (done 6 weeks after seedling emergence). Plants were harvested once (6 weeks after top-dressing) and the following parameters determined: plant height, number of branches, leaf number and fresh weight, dry matter, crude protein, crude fibre, beta-carotene, ascorbic acid, total phenolics, nitrates and oxalates.

Plant growth was significantly increased by nitrogen application; application of 5 g N/plant (19 g CAN/plant) was optimum (Table 10). Beta-carotene, crude protein, nitrates and phenolic leaf contents were significantly increased while ascorbic acid, crude fibre and oxalate leaf contents were significantly reduced by nitrogen application. Thus, although nitrogen application improved leaf yield and nutritive quality of S. nigrum, it led to increased phenolic compounds and accumulation of nitrates in the leaves.

Table 10. Effect of nitrogen fertilizer application on plant growth, leaf yield and nutritive quality of Solanum nigrum plants harvested 12 weeks after seedling emergence.


Nitrogen rates (g N/plant)

0

5

10

15

Plant height (cm)

36b

56a

45b

40b

Number of branches per plant

25c

47a

37b

40b

Number of leaves per plant

360c

540a

527a

467b

Leaf yield (t/ha)

20c

51a

27b

20c

Leaf dry matter (%)

12.3a

9.2c

10.1b

10.1b

Leaf crude protein (g/100 g DM)

16.0d

30.8c

32.0b

34.4a

Leaf crude fibre (g/100 g DM)

18.5a

16.3b

14.9bc

14.6c

Leaf beta-carotene (mg/100 g DM)

163a

103c

93bc

110b

Leaf ascorbic acid (mg/100 g DM)

191d

435a

301b

246c

Leaf nitrate-N (mg/100 g DM)

382b

2500a

2550a

2544a

Leaf oxalate (mg/100 g DM)

1281a

1265a

1208b

1108b

Leaf total phenolics (mg/100 g DM)

888c

1027a

1010a

910b

Values followed by the same letter(s) across rows are not significantly different according to protected LSD-test at 5% probability level.
Harvesting

Harvesting frequency

Leaves of S. nigrum plants are frequently harvested repeatedly as required. The plants could also be harvested once, but it has been observed that continuous harvesting could result in higher leaf yields than harvesting once. Defoliation may lead to decreased growth and productivity of the plants. It is important to determine the optimum harvesting frequency for maximum yield from plants that are frequently defoliated. An experiment was therefore conducted in 1990/91 (Onyango 1993) to study the effect of harvesting frequency on the yield of S. nigrum plants. Plants, at plant density of 66 660 plants/ha, were harvested either weekly or fortnightly for 11 weeks after seedling emergence. The results (Table 11) show that although fortnightly harvesting resulted in significantly fewer harvested shoots, it gave significantly higher leaf yields than weekly harvesting.

Table 11. Effect of harvesting frequency on cumulative yield of Solarium nigrum plants grown for 11 weeks.


Harvesting

Weekly

Fortnightly

Number of harvested shoots/m2

675a

564b

Average shoot length (cm)

16.6a

13.5b

Marketable fresh shoot weight (g/m2)

2646b

3355a

Edible fresh leaf weight (g/m2)

1844b

2071 a

Wastage from harvested shoots (%)

30b

38a

Values with same letter across rows are not significantly according to a t-test at 5% probability level.
Harvesting height

Some farmers harvest S. nigrum plants by cutting off all vegetative parts above a certain height. An experiment was carried out in 1991 to show the effect of harvesting heights on leaf yield of S. nigrum plants. Plants, at a plant density of 17 plants/m2, were harvested at 15, 20, 25 and 30 cm above the ground starting 4 weeks after seedling emergence at fortnightly intervals for 6 weeks. Results indicated that the higher the harvesting height, the lower the cumulative leaf yield. Cumulative yields for the various heights were 1200, 820, 960 and 730 g/m2 for cutting heights of 15, 20, 25 and 30 cm, respectively. The best harvesting height was 15 cm.

Deflowering

Solanum nigrum flowers 5-8 weeks after seedling emergence. Because there is competition between reproductive and vegetative plant organs, once flowering begins, vegetative growth declines and flowering may, therefore, lead to reduced leaf yield. An experiment was conducted in 1990/91 (Mwafusi 1992) to determine the effect of deflowering on vegetative growth and leaf yield and nutritive quality of S. nigrum. Plants spaced at 60 and 40 cm between and within rows, respectively, were either deflowered or not deflowered starting immediately at flowering and continuing until final harvest at 12 weeks after transplanting (done 6 weeks after seedling emergence). The results showed that deflowering did not significantly affect plant height, plant canopy spread and number of branches per plant. However, it increased leaf yield by 40%, the deflowered plants yielding 2154 kg/ha of leaf. The results further indicated that deflowering did not have any significant effect on total phenolics and glycoalkaloids in the leaves.

Plant age

As has been reported elsewhere, S. nigrum plants are harvested frequently over time. Experiments have indicated that fortnightly harvesting gives higher yields than weekly harvesting. Experiments were conducted in 1990/91 (Mwafusi 1992; Onyango 1993) to investigate leaf nutritive changes during the various harvests. Results (Table 12) indicated that yields and leaf nutritive quality are significantly affected by plant age. Yield increases and then declines as expected; leaf dry matter, crude fibre, total ash, iron and calcium increase; beta-carotene and phenolic compounds increase and then decrease, whereas crude protein seems to be unaffected by increasing plant age.

Intercropping

A study was conducted in 1991 to investigate the suitability of S. nigrum as an intercrop in a maize crop. The results indicated that leaf yield of S. nigrum could be reduced by less than 40% and that land equivalent ratio was more than 1. The indication, therefore, is that S. nigrum could be successfully intercropped with maize.

Table 12. Effect of Solanum nigrum plant age on shoot yield and leaf nutritive quality of plants harvested for 11 weeks after transplanting (done 6 weeks after seedling emergence).


Weeks after transplanting

3

5

7

9

11

Harvested yield (t/ha)

4.1

12.7

13.7

8.3

10.0

Dry matter (%)

11.3

12.1

12.0

15.5

16.0

Crude protein (% DM)

37.8

32.6

37.5

37.8

35.1

Crude fibre (% DM)

9.5

9.2

10.0

10.0

10.3

Total ash (% DM)

17.8

18.1

18.1

18.4

21.2

Iron (mg/100 g DM)

54.4

47.6

46.4

80.6

161.7

Calcium (mg/100 g DM)

245.3

347.0

323.1

336.9

446.7

Beta-carotene (mg/100 g FW)

3.1

4.1

4.8

4.2

3.7

Phenolic compounds (mg/100 g FW)

-

2600

2850

3250

2300

Cucurbita species

Germplasm collecting

In collaboration with Ben Gurion University of the Negev, Beer-Sheva, Israel and the Gene Bank of Kenya, systematic collecting of pumpkin germplasm has been done in several parts of Kenya. Over 100 seed accessions are now stored at the Gene Bank of Kenya (Mendligner et al. 1992).

Genetic variation

Between 1990 and 1992, experiments were carried out to evaluate agronomic and nutritive parameters of some of the collected pumpkin accessions. The evaluation was done both in Israel and Kenya. Table 13 shows that there is great variability between the accessions and there is, therefore, scope for breeding for higher yields and better fruit quality.

Table 13. Agronomic and nutritional evaluation of pumpkin germplasm collected in Kenya.

Character

Range of values

Main stem length (cm)

3.69 - 9.37

Cotyledonous length (cm)

2.67 - 6.09

Cotyledonous diameter (cm)

1.72 - 3.88

First leaf length (cm)

3.20 - 5.34

First leaf diameter (cm)

2.40 - 3.73

Peduncle length (cm)

8.25 - 16.83

Days to first flower

49.7 - 69.0

Days to first female flower

57.3 - 88.3

Number of female flowers per plant

1.0 - 33.3

Fruit number per plant

1.7 - 27.7

Fruit circumference (cm)

33.75 - 71.50

Average fruit weight (kg)

0.84 - 13.70

Fruit dry weight (%)

0.9 - 20.0

Acidity

17.7 - 33.0

TSS (%)

4.0 - 13.7

Reducing sugars (mg/g fresh weight)

3.1 - 14.5


Crotalaria brevidens L.

Plant density

An experiment was carried out in 1991 to study the effect of plant density on leaf yield of C. brevidens. Three plant densities (11, 17 and 33 plants/m2) were investigated in a randomized complete block design replicated three times. Results indicated that plant density of 17 plants/m2 gave higher leaf yields (683 g/m2) than 11 and 33 plants/m2 which gave leaf yields of 510 and 563 g/m2, respectively.

Harvesting heights

Shoots of C. brevidens are also harvested repeatedly as required. A study was conducted in 1991 to investigate the effect of cutting heights on leaf yield. Plants at a density of 17 plants/m2 were harvested at heights of 15, 20, 25 and 30 cm above the ground. Harvesting at 15 cm gave the highest yield; harvesting at the other heights significantly reduced leaf yields. Harvesting at 15, 20, 25 and 30 cm above ground gave leaf yields of 960, 600, 530 and 640 g/m2, respectively.

Intercropping

Crotalaria brevidens is a shrubby legume. Cereal/legume intercrop performance has received considerable attention from several researchers who have shown substantial advantages in terms of yield and soil fertility improvement. Finger millet (Eleusine coracana) is a small grain popular in Western Kenya, where C. brevidens is also used as an indigenous leafy green vegetable. A randomized complete block design experiment was conducted in 1993/94 (Akuja 1995) to investigate the effect of C. brevidens intercrop on growth and yield of finger millet. For both crops, in alternate rows, seeds were drilled in rows spaced 30 cm apart. Three weeks after seedling emergence, plants were thinned to leave 10 cm within rows. The results showed that the grain and leaf yields of finger millet and C. brevidens were not significantly affected by intercropping. Leaf yields of C. brevidens and grain yield of finger millet were depressed by 15 and 26%, respectively. However, the calculated land equivalent ratio was more than 1, indicating that it was advantageous to grow the two crops in an intercropping system.

In the season following the above experiment, finger millet was grown on plots that had had either sole finger millet or finger millet intercropped with C. brevidens. Results indicated that grain yield from finger millet growing in previously intercropped plots was 2.10 t/ha, which was 27% more than that from the previously monocropped plots, which gave 1.55 t/ha. These results indicate that C. brevidens has a residual effect on soil fertility.

Conclusion

From the results reported here, it is evident that improvement of indigenous vegetable production is possible. This could be done through breeding and selection aimed at genetic enhancement. However, there is also scope for improving cultural practices, in particular by bringing into cultivation some of the vegetable species which are currently semi-cultivated or regarded as weeds.

References

Akuja, T.E. 1995. Effect of legume intercrop management practices and inorganic nitrogen application on growth and yield of finger millet (Eleusine coracana L.). M.Sc. Thesis, University of Nairobi.

Chweya, J.A. 1985. Identification and nutritional importance of indigenous green leaf vegetables in Kenya. Acta Hort. 153:99-108.

Chweya, J.A. 1990. Nutrient evaluation and production of Gynandropsis gynandra (L.) Briq: An indigenous leaf vegetable in Kenya. Final Scientific Project Report submitted to National Council for Research Science and Technology, Ministry of Research Science and Technology, Government of Kenya.

Juma, C. 1989. Biological diversity and innovation: conserving and utilizing genetic resources in Kenya. ACTS Research Series No. 3:35-40.

Maumba, M.K. 1993. The effect of nitrogen application and deflowering on vegetative growth, yield and quality, and postharvest storage stability of Gynandropsis gynandra (L) Briq. M.Sc Thesis, University of Nairobi.

Mendlinger, S., J. Chweya, A. Benzioni, N. Seme, M. Ventura, C. Lungaho and V. Okoko. 1992. Collections, evaluations and breeding of African edible vegetables. BGUN-ARI-25-92. Annual report. AID-CDR programme, Beer-Sheva, Israel.

Mtotomwema, K. 1987. Horticultural techniques in wild leafy vegetables with special reference to Solanum nigrum L. Paper presented at IFS Seminar on Horticultural Techniques, Tunis, Tunisia.

Murage, E.N. 1990. The effect of nitrogen rates on the growth, leaf yield and nutritive quality of the black nightshade (Solanum nigrum L.). M.Sc Thesis, University of Nairobi.

Mwafusi, C.N. 1992. Effects of propagation method and deflowering on vegetative growth, leaf yield, phenolic and glycoalkaloid contents of three black nightshade selections used as vegetable in Kenya. M.Sc Thesis, University of Nairobi.

Mwajumwa, L.B.S., E.M. Kahangi and J.K. Imungi. 1991. The prevalence and nutritional value of some Kenyan indigenous leafy vegetables from three locations of Machakos District. Ecol. Food Nutrition 26:275-280.

Omondi, C.O. 1990. Variation and yield prediction analyses of some morphological traits in six Kenyan landrace populations of spider-flower (Gynandropsis gynandra (L.). Briq). M.Sc Thesis, University of Nairobi.

Onyango, M.A. 1993. Effect of plant density and harvesting frequency on the yield and vegetable quality of four variants of black nightshade (Solanum nigrum L.). M.Sc. Thesis, University of Nairobi.

Opole, M., J.A. Chweya and J.K. Imungi. 1991. Indigenous vegetables in Kenya. Field and Laboratory Experience Report. KENGO, Nairobi.


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