African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 8, Num. 2, 2000, pp. 137-143

African Crop Science Journal, Vol. 8. No. 2, pp. 137-143

PHENOTYPIC DIVERSITY IN THE ETHIOPIAN NOUG GERMPLASM

Tsige Genet and Ketema Belete¹
Adet Research Centre, P.O. Box 8, Dahir Dar, Ethiopia
¹Alemaya University of Agriculture, P.O. Box, 138, Dire Dawa, Ethiopia

(Received 31 March, 1999; accepted 27 February, 2000)

Code Number: CS00014

INTRODUCTION

Noug (Guizotia abyssinica (L.f.) Cass; 2n = 30) belongs to the family Compositae and the genus Guizotia which is small with only six species, of which five are native to Ethiopia (Baagoe, 1974). Guizotia abyssinica is believed to have originated through disruptive selection from Guizotia scabra, a common weed in Ethiopia (Doggett, 1987). Noug is extensively cultivated in Ethiopia and India. It is also grown in Sudan, Uganda, Zaire, Tanzania, Malawi, Zimbabwe, the West Indies, Nepal, Bangladesh, and Bhutan (Weiss, 1983).

Noug contributes towards 50 - 60% of the Ethiopia’s edible oil needs (Riley and Belayneh, 1989). Noug is grown between 1500 - 2400 m above sea level, in rotation with cereals on poorly drained soils. Gojjam, Shoa, Gonder and Welega are the largest areas of production, accounting for about 90% of the country’s total production (Getinet and Alemayehu, 1997). Noug has a reputation for its ability to grow on marginal soils and to withstand waterlogging because of its tolerance to low oxygen level (Mesfin, 1975). Fertiliser and drainage promotes luxurious vegetative growth but do not increase seed yield (Riley and Belayneh, 1989). Different types of noug are known to be widely cultivated in Ethiopia (Getinet and Sharma, 1996). The predominant type is 'abat' noug grown during the main season from June to December. This type has higher yields, and a high oil content. 'Bungne' noug is adapted to lowland and matures earlier than 'abat', but is lower yielding and bears lighter seed with lower oil content. A third type of noug, 'mesno' is tolerant to frost and grows on residual moisture.

Noug seed yields a pale yellow oil with a pleasant nutty taste. The seed contains about 40% oil with a fatty acid composition of 75 - 80% linoleic acid (Getinet and Tekelewold, 1995), which makes it important in preventing arteriosclerosis in humans (Vaughan, 1970). Noug oil is also used for cooking, as an illuminant, as a lubricant and for manufacturing soap and paints (Simmonds, 1976). It also has potential for cosmetics (Vaughan, 1970).

Noug germplasm has been collected from farmers’ fields and is mostly conserved and documented at the Biodiversity Institute of Ethiopia (the then Plant Genetic Resources Centre for Ethiopia). The distribution and degree of phenotypic diversity of noug in different agro-ecological areas of the country has, however, not yet been studied. Hence, this study was undertaken to estimate the phenotypic diversity in the Ethiopian noug germplasm collections across a wide range of characters.

MATERIALS AND METHODS

The study was conducted at Adet Research Centre (longitude 37° 29’E and latitude 11°16’N and 2240 metres above sea level (masl)) located in north western Ethiopia during the 1993 main cropping season (Keremet). For this study, 157 noug accessions were obtained from the Biodiversity Institute of Ethiopia. These were randomly sampled from varying agro-ecological areas of the country. Forty seeds per accession were planted on vertisols in a single row of 4 m length plot, with a spacing of 1 m between rows, and 10 cm between plants. Fertiliser (both N and P₂O₅) was applied at the rate of 23 kg ha^-1 each at the time of planting. Weeding was carried out 21 days after emergence and 45 days after the first weeding.

Observations on quantitative (days to flowering, days to maturity, and plant height) and qualitative characters (leaf colour, leaf margin, stem colour, stem hairiness, and angle of branching) were recorded following the noug description format of the Biodiversity Institute of Ethiopia (Table 1). Days to 50% flowering is the actual count of the number of days from planting to the date at which about 50% of the plants in a plot have the first flower. Days to maturity is the actual count of the number of days from planting to the date at which 95% of the plants in a plot have reached physiological maturity. Plant height is the actual measurement in cm taken from the ground to upper most leaf at maturity. Leaf colour is the most predominant colour of the leaf during 50% flowering. Allowable states are light green, green, and dark green. Leaf margin is a visual measurement taken at the middle part of the plant at 50% flowering. Allowable states are smooth, pointed, and round. Stem colour is the most predominant colour of the stem recorded at 50% flowering. Allowable states are green and purple. Stem hairiness is a visual measurement at the middle part of the stem during 50% flowering. Allowable states are hairy, intermediate, and very hairy. Angle of branching is a visual measurement taken at 50% flowering at the middle part of the plant. Allowable states are acute and hanged. Days to 50% flowering, days to maturity, and plant height with continuous variation were included in order to examine their value in diversity studies.

The quantitative characters which are scaled randomly are useful in this study, as the noug accessions show considerable variation within and between regions for these characters. Quantitative characters are in general of more interest to the plant breeder than the discrete or qualitative characters. The phenotypic frequencies of the characters were analysed by the Shannon-Weaver diversity index (H’) as described by Jain et al. (1975) in order to estimate the diversity of each character within each province. For this purpose, the country was divided into four regions: northern Ethiopia (Tigrai, Gonder, and Welo), western Ethiopia (Gojjam, Welega, and Ilubabor), southern Ethiopia (Gamu Gofa, Sidamo, and Bale), and central and eastern Ethiopia (Shewa, Arsi, and Hararghe).

The Shannon-Weaver diversity index described by Jain et al. (1975) was calculated as:

H’=-SP_ilog₂P_i

Where, P_i is the proportion of the accessions in the i^th class of an n class trait in a population. This index has been extensively used to estimate phenotypic diversity in germplasm collections (e.g. Jain et al., 1975; Tolbert et al., 1979). The additivity of the H’ allows characters to be pooled over provinces and over regions (Tolbert et al., 1979). This property permits the use of hierarchical analysis of variance for testing the significance of various components of variation in H’ (regions, provinces, and characters). Each H’ value was standardised by dividing it by its maximum value (log₂ n), which ensured that all scaled H’ values were in the range of 0 to 1.

The minimum value of the index is zero for a monomorphic population. The value of the index increases with the increase in polymorphism and reaches the maximum value when all phenotypic classes have equal frequencies (Yang et al., 1991).

The variance of H’ has not been characterised. However, assuming that the eight characters used in our study represent a random sample of all possible characters of noug plant, an empirical variance was computed from the eight estimates of Shannon-Weaver’s diversity index.

RESULTS AND DISCUSSION

Distribution of phenotypic classes. The phenotypic frequencies for individual characters and provinces as percentage of the number of accessions from each geographic origin are presented in Table 2. The area of origin were grouped into regions and regions into provinces and weighted regional frequencies were computed.

Provinces representing small number sampled showed high monomorphism, namely Gamu Gofa, Sidamo and Hararghe. Thus, variability for the eight characters examined were widely distributed. Individual characters differed in their patterns of distribution and amount of variation.

Leaf colour is widely distributed throughout the collection, i.e., 70% light green, 26% green, and 4% dark green. Except for Gamu Gofa, Sidamo, Bale, and Hararghe, the rest of the provinces have intermediate frequencies in leaf colour. The collection had predominantly pointed type of leaf margin in all provinces.

The accessions were dominated by less hairy stem (56%) and intermediate proportions of hairy stem (42%). Very hairy phenotypes were detected in Tigrai and Shewa provinces only. Gojjam had almost equal proportion of less hairy and intermediate characters, while very hairy phenotypes were not detected.

Although environmentally sensitive, purple stem colour was the dominant colour noted in the accessions. Welega province had the highest frequency of green stem colour. The two phenotypic classes of angle of branching were observed at intermediate frequencies only in Welo province (Table 2). Acute type of branching was a more common phenotype. The continuous metric traits, such as days to flowering, days to maturity and plant height, had intermediate frequencies in their measurement.

Analysis of phenotypic diversity index (H’). Table 3 gives the estimate of H’ individually and pooled over characters and provinces and appropriately weighted by number of accessions. The three highest mean values of H’ were from Gojjam (0.60), Welega (0.57), and Shewa (0.53) provinces. The lowest values of the H’ were from Sidamo and Hararghe (0.00), Gamu Gofa (0.24), and Ilubabor (0.23). One possible reason for these low H’ values could have been the small number of samples for the study from these provinces. On the other hand, there might be greater natural selection for noug in both provinces due to generally low rainfall in the north and high rainfall in the south. Clearly, these results indicate that the amount of variation differ considerably among the provinces.

The estimate of diversity index for individual characters pooled over provinces and regions showed considerable variation among characters (Table 3). For example, the index varied from 0.98 for leaf margin to 0.53 for angle of branching country-wide. The average diversity across 8 characters from all the regions or the overall diversity for Ethiopia was H’ = 0.40. Based on the average diversity calculated from the individual regions across all characters, the most diverse region was western Ethiopia H’ = 0.61 and the least diverse was central and eastern Ethiopia H’ 0.51. Generally, northern Ethiopia is considered to be the centre of origin and diversity of noug (Baagoe, 1974), but in this analysis northern Ethiopia had estimates of H’ = 0.56. This might be due to natural selection in the areas of northern Ethiopia which are frequently affected by drought and/or it could also be due to sampling effect.

Hierarchical analysis of variance in H’ values for individual characters (Table 4) shows that diversity among regions was not significantly different (P>0.05), whereas greater variance was obtained among provinces within different characters (P<0.05).

In conclusion, based on limited characters studied and small collections evaluated, the centres of diversity for noug appears to be in Gojjam, Welega, and Shewa. Further exploration should be undertaken in these regions.

The utility of germplasm collection to research programmes designed to locate genes depends on adequate sampling procedures. The Ethiopian collection presently has a large number of accessions representing a valuable reservoir of genetic resources. However, several important areas in Ethiopia are not still adequately represented. Hence, several noug collection missions representing diverse agro-ecological areas of the country should be organised for carrying out diversity analysis to derive some guidelines for conservation activities.

ACKNOWLEDGEMENTS

This work was supported by the International Development Research Centre (IDRC) of Canada. The authors acknowledge the help of Dr. Getinet Alemaw and Dr. P.A. Chadhokar in reviewing the manuscript, and thank Alamine Atanaw, Melkie Nibret, and Menychel Alameneh for their assistance in the fieldwork.

REFERENCES

1. Baagoe, J. 1974. The genus Guizotia (Compositae). A taxonomic revision. Botanssk Tidsskrift 69:1-39.
2. Doggett, H. 1987. Niger/Noug research methodology. In: Oil Crops: Niger and Rapeseed/Mustard. Proceedings of the Third Oil crops Network Workshop held in Addis Ababa, Ethiopia, 6-10 October. Omran, A. (Ed.), pp. 210 - 219. IDRC-MR 153e.
3. Getinet, Alemaw and Nigussie Alemayehu. 1997. Highland oil crops: a two-decade research experience in Ethiopia. Research Report No. 30. Institute of Agricultural Research, Addis Ababa, Ethiopia.
4. Getinet, Alemaw and Sharma, S.M. 1996. Niger. Guizotia abyssinica (L.f.) Cass. Promoting the conservation and use of underutilized and neglected crops. 5. Institute of Plant Genetics and Crop Plant Research, Gatersleben International Plant Genetic Resources Institute, Rome.
5. Getinet, Alemaw and Adefris Tekelewold. 1995. An agronomic and seed-quality evaluation of noug (Guizotia abyssinica Cass.) germplasm in Ethiopia. Plant Breeding 114:375- 376.
6. Jain, S.K., Qualset, C.O., Bhatt, G.M. and Wu, K.K. 1975. Geographic patterns of phenotypic diversity in a world collection of durum wheats. Crop Science 15:700-704.
7. Mesfin, Abebe. 1975. Ecophysiology of Noug (Guizotia abyssinica Cass.). Ph.D. Dissertation, Univ. of California, Riverside, USA.
8. Riley, K.W. and Hiruy Belayneh. 1989. Niger seed (Guizotia abyssinica Cass.). In: Oil Crops of the World, Their Breeding and Utilization. Robbelen, G., Downey, R.K. and Ashri, A. (Eds.), pp. 394 - 404. McGraw-Hill, New York.
9. Simmonds, N.W. 1976. Evolution of Crop Plants. Longman Group Ltd., London.
10. Tolbert, D.M., Qualset, C.O., Jain, S.K. and Craddock, J.C. 1979. A diversity analysis of a world collection of barley. Crop Science 19:789 - 794.
11. Vaughn, J.G. 1970. The Structure and Utilization of Oilseeds. Chapman and Hall, London.
12. Weiss, E.A. 1983. Oilseed Crops. Tropical Agriculture Series, Longman, London.
13. Yang, R.C., Jana, S. and Clarke, J.M. 1991. Phenotypic diversity and associations of some potentially drought-responsive characters in durum wheat. Crop Science 31:1484 - 1491.