Abstract

Argentine rapeseed (Brassica napus) is of recent introduction to Ethiopia about two and a half decades ago. During this period four rapeseed varieties (Target, Tower, Pura and Tower sel.3) were released by a collaborative research with national institutions. Two other varieties (Global No 40619/2 and Consal/1 are also promising for release. Production techniques such as seed rate (12 kg ha-¹), sowing time (three weeks after the commencement of the main rains), fertilizer rate of (46/69, N/P₂O₅) and weed control measures (weeding at 25-30 and 50-60 days after sowing) were determined. The study on relative importance of management factors has revealed that fertilizer was the most critical in the central highlands of Ethiopia followed by early sowing. Further more, important insect pests and diseases of rapeseed were identified of which blackleg disease was found the most limiting factor to production. A possible strategy for increasing the production of the crop was also suggested.

Introduction

Rapeseed and Ethiopian mustard are the third most important oilseeds, after noug (Guizotia abyssinica cass.) and linseed (Linum asitatisimum L.) both in terms of area and production (Table 1). Argentine rapeseed (Brassica napus) is a new Brassica species introduced to Ethiopia in the early 1970s (Hiruy et al., 1983). Research on this crop was started during the same period on materials introduced from Canada and West Germany with main objective of developing high-yielding varieties along with their optimum management practices. The area under Brassica species has increased from 14,000 ha in 1960s to 50,000 ha in 1980s with the release of Pura and Tower varieties. This trend continued for more than 15 consecutive years and rapeseed has been produced mainly on large scale farms almost in a semi-mechanized way (Getinet et al., 1992 and Nigussie A. and Mesfin A. 1994). In 1984, the state farms in south-eastern Ethiopia had 427 ha under rapeseed and increased to 7299 ha in 1988 due to the adoption of new improved varieties and improved management practices (Hiruy and Nigussie 1988).

Productivity of rapeseed under farmers' conditions, however, is very low, in the order of 300-500 kg ha^-1 against the 2000-3000 kg ha^-1 commonly obtained from large research plots (Hiruy and Nigussie 1988). Such low yields of small farmers are largely accounted to lack of resources for using full packages of recommended practices (Nigussie A. and Mesfin A. 1994). The other problems are insect pests and diseases. Aphid is the most serious insect pest which causes heavy damage to rapeseed crop. Similarly a range of diseases like blackleg, alternaria blight, white rust and downy mildew cause yield losses ranging from 10 to 100% in Ethiopia. Parasitic weed, Orobanche, also causes considerable damage to the crop (Badege et al., 1986). Moreover, bird damage and shattering problems have been contributed a lot to the low yield of rapeseed. This paper, therefore, tries to review past research efforts against these production constraints, indicating future prospects.

RESEARCH ACHIEVEMENTS

Breeding/Selection

Over the past 25 years, the rapeseed-breeding program has made a substantial effort in the identification and release of improved varieties. Four varieties (Pura, Target, Tower and Tower sel.3) have been released (Table 2). These improved varieties were found by selecting from exotic materials. Two other varieties (Global No 40619/2 and Consal/1) are also promising for future release as shown in Tables 3 and 4. Results of the multi-location trials showed that the late maturing Ethiopian mustard (B.carinata) outyielded rapeseed (B.napus) under long seasonal conditions of the Ethiopian highlands (Table 5). On the other hand, the mean oil content of rapeseed was greater than that of the Ethiopian mustard as indicated in Table 6.

Agronomy

Improved cropping systems and other agronomic practices have been developed for different agro-climatic conditions of the country. Fertilizer rate of 46/69 kg/ha of N/P₂O₅, respectively Table 7; two hand weeding at 25-30 and 50-60 days after sowing and a seed rate of 12 kg/ha were found with the best return of seed yield (Badege et al., 1986 and Taye B. 1986). Higher yields have generally been obtained when sowing was done not later than three weeks after the commencement of the main rains. Thus, optimum sowing date ranges from late May for the high altitude and cool areas of south-eastern zone to early to late June for the central highlands of Ethiopia. Studies on the effects of various technology packages on seed yield of rapeseed have demonstrated that an increase in seed yield ranging from 20 to 29% can be obtained by adoption of full technology package as indicated in Fig.1 (Nigussie A. and Mesfin A. 1994).

Crop protection

Pathological research on rapeseed has revealed 13 fungi, one virus and one bacterium diseases. Of these, leaf and pod-spot (Alternaria brassicae), and blackleg (Leptosphaeria maculans) are most widely distributed. Blackleg, which was observed in the Mid 1970s in some experiment stations, is becoming one of the production limiting factors of rapeseed in Ethiopia.

Future prospects

The increasingly growing demands of oil crops for local consumption, agro-industrial plants and export markets implies the need for stronger research and development efforts towards the improvement of rapeseed in Ethiopia. Hence, due emphasis should be given to select varieties with stable and high yield, better oil content and resistant to diseases and insect pests. Development of low-input technology to serve the need of small scale farmers are also necessary besides the adoption of suitable crop protection measures in response to the rapeseed farming conditions and constraints of farmers.

Table 1. Estimated Area, production and yield of highland oil crops in Ethiopia 1995-97.

Source: CSA, 1997

Table 2. Seed yield (kg ha^{-1) and} agronomic characteristics of rapeseed genotypes in the national yield trial 1985-1990.

Table 3. Mean seed yield (kg ha^-1) of all rapeseed varieties tested at five locations from 1994-1996 in Ethiopia

Table 4. Location mean seed yield (kg ha^-1) of 11 rapeseed varieties tested at five locations from 1994-1996 in Ethiopia.

LSD 0.05

Location 271.2 295.8 532.6

Genotype 207.6 NS NS

Location x Genotype 464.2 463.8 388.9

CV% 17.72 15.0 13.96

Table 5. Summary of seed yields (kg/ha) of the released and local varieties in the rapeseed national and extension variety trials grown at 10 sites in four agricultural development zones (ADZ) with 46/69 kg/ha of N and P₂O₅ fertiliser (F1) or without (F0) 1984-86 in Ethiopia.

Table 6. Seed oil content of the rapeseed and local varieties in the rapeseed national variety trials grown at four sites in two (ADZ) in Ethiopia.

Table 7. Effect of NP on the seed yield of rapeseed at Sinana combined over two years (1988-1989) in Ethiopia.

Fig.1. Relative contribution (%) of mean effects (kg ha^-1 ) of early sowing (SD1), fertiliser (F+) weeding (W+) and broadcasting (BBR) on seed yield of rapeseed at Holetta and Klumsa (1988-1989).

REFERENCES

1. Badege Gebre, Rezene Fissehaie and A.Stroud. 1986. Preliminary weed research findings on two Ethiopia highland oilseed crops, rapeseed (Brassica napus) and higher (Guizotia abyssinica). PP. 58-65. In: proc. of the third oilcrops network workshop. A.Omran (ed.) Addis Ababa, Ethiopia, 6-10 October, 1986. IDRC, MR 153 (ed) Ottawa, Canada.

2. CSA, Central Statistics authority. 1997. Time series data on area, production and yield of major crops. Addis Ababa, Ethiopia.

3. Getinet A., Adefris T/W., Mengistu N. and Tesfaye G. 1992 Rapeseed and Gomenzer breeding in Ethiopia. In: proc. of the 1st National oil seeds workshop Dec. 3-5/1991 Addis Ababa pp. 31- 40.

4. Hiruy Belayneh, K.W. Riley, Nigatu Tadesse and Getinet Alemaw.1983. the response of three oilseed Brassica spp. to different planting dates and seed rates in the highlands of Ethiopia. Ethiopian J.Agric.Sci. 5: 22-31.

5. Hiruy Belayneh and Nigussie A. 1988. Comperative performance of Ethiopian mustard (Brassica carinata A.Brau) and Argentine rapeseed (Brassica napus L.) under improved and traditional farming practices. Presented at the 7^th International Rapeseed Congress, 11-14 May Poznan Poland.

6. Nigussie Alemayehu and Mesfin A. 1994. Relative importance of some management factors in seed and oil yields of Ethiopian mustard (Brassica carinata Braun.) and rapeseed (B. napus L.). Ethiopian J. Agric. Sci. 14 (1/2) 27-36.

7. Taye Bekele. 1986 Response of oil seed brassica to fertilizers. PP. 40-45. In proc. of the third oil crops network workshop. A. Omran (ed.) Addis Ababa, Ethiopia, 6-10 October, 1986 IDRC, MR 153e, Ottawa, Canada.