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Baye T. and S. Gudeta. 2002. Pest survey of Vernonia galamensis in Ethiopia. p. 219221. In: J. Janick and A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria, VA.
Tesfaye Baye and Sileshi Gudeta*
Recent decades have witnessed an increase in the rate of desertification of agricultural lands. More than one-third of our planets land is now arid. Water for crops and an increasing human population is rapidly becoming a critically short commodity. Yet none of the major crop plants of the world is well adapted to arid lands. Efforts have been made to introduce new crops, which are essentially noncompetitive with the existing crops and possibly provide a new and unique product for industrial use particularly for marginal rainfall areas. Vernonia galamensis (Cass.) Less, Asteraceae is a new industrial crop originating in Ethiopia which combines all the possible merits for the semiarid tropics and subtropics (Baye et al. 2000).
Vernonia galamensis is limited in distribution and endemic to primary East African countries as a weed colonizing disturbed areas and bare agricultural lands. According to the recent taxonomic revision of the complex, this species has six sub-species (nairobensis, gibbosa, lushotoensis, afromontana, mutomonesis, and galamensis). Sub-species galamensis is the most widely distributed; it is highly diverse with four botanical varieties (galamensis, petitiana, australis, and ethiopica) (Gilbert 1986).
Vernonia galamensis ssp. galamensis var. ethiopica is a new annual industrial oilseed. It grows naturally in marginal areas with as little as 200 mm seasonal rainfall and at an elevation ranging from 7002400 m in the southern and southeastern parts of Ethiopia (Gilbert 1986). It was first identified in eastern Ethiopia by R.E. Perdue Jr. in 1964 at 7 km south east of Harar town (9° 14'N and 42° 35'E at 1700 m). It has unique properties which make it interesting both economically and ecologically (Perdue 1988). The oil (35% to 42% of the seed), contains an important epoxy acid called vernolic acid (72% to 80% of the oil). Vernolic (cis-12, 13-epoxy- cis-9-octadecenoic) acid, a naturally occurring epoxidized fatty acid, is primarily present in the oil as the triglyceride trivernolin with unique physical properties in particular low viscosity. Vernolic acid, beside other uses, is a useful raw material for manufacturing paints and coatings. Vernonia oil also contains linoleic acid (12% to 14%), oleic acid (4% to 6%), stearic acid (2% to 3%), palmitic acid (2% to 3%) and a trace amount of arachidic acid (Thompson et al. 1994). Agronomic data shows that the plant requires a well-drained soil and restricted naturally to grow in the region 20° north and south of the equator.
Very recently, the plant was found to be a potential crop for inclusion into the agricultural system in Ethiopia. Among other characters, a seed yield up to 4000 kg/ha and an oil content of 40% using unimproved local materials was obtained which is much higher than found elsewhere (Baye 1996, 1998, 2000; Baye et al. 2001). On the other hand, there is no information on the pests and diseases of Vernonia. Thus, this preliminary survey was conducted to see the associated pests and diseases of V. galamensis spp. galamensis var. ethiopica and design a breeding strategy in a multidisciplinary approach which will help to foster its improvement as a potential new industrial oilseed crop for Ethiopia.
Seeds of Vernonia galamensis were sown at Alemaya, Harar, and Babile, Ethiopia during the 1994/1995 cropping season. Records of pests were made from seedling to harvesting stage of the crop. Vernonia germplasm collection missions were made during NovemberDecember, 1998 and NovemberDecember, 2000 to the various parts of Ethiopia including Hararghe, Arsi, Bale, Sidamo, Gamo Gofa, Shewa, Wollo, and Tigray. Preliminary identification of the causal pathogens and insect pests were made (for both the experimental and collection sites) using different identification keys and pertinent literature at the Alemaya University of Agriculture, Ethiopia.
Vernonia has a number of diseases and pests. Some pathogens have coevolved with this plant and are specific to it. Collection and preliminary identification of the pest species associated with this plant in Ethiopia revealed the presence of various insects (Table 1) and pathogenic fungi/bacteria (Table 2) unlike the reports of various authors including Perdue, who mentioned so far there are no problems with insect, disease or nematodes and the plant appears to have good natural resistance.
Table 1. Insects associated with Vernonia in Ethiopia.
|Common name||Scientific name||Family||Order|
|Aphids||Aphis gossypii (Glover)||Aphidiae||Homoptera|
|Blister beetle||Mylabris sp.||Meloidae||Coleoptra|
|Cluster bugs||Agronoscelis pubescens (Thunb.)||Pentatomidae||Hemiptera|
|Epilachna beetles||Epilachna sp.||Coccinelidae||Coleoptra|
|Green grasshopper||Ornithacris sp.||Acrididae||Orthoptera|
|Green stick bug||Nezara viridula (L.)||Pentatomidae||Hemiptera|
|Harlequin bug||Bagrada sp.||Pentatomidae||Hemiptera|
|Helmet bug||Captosoma sp.||Pentatomidae||Hemiptera|
|Leaf miner||Liriomyza sp.||Agromizidae||Diptra|
|Lygaeus bug||Lygus sp.||Lygaeidae||Hemiptera|
|Spiny boll worm||Earias biplaga (Wkl.)||Noctuidae||Lepidoptera|
|Striped blister||Epileauta sp||Meloidae||Coleoptra|
|Vernonia worm||Indent sp.||Noctuidae||Lepidoptera|
Table 2. Pathogens associated with Vernonia in Ethiopia.
|Common name||Scientific name||Major damaging stage|
|Damping off||Rhizoctonia solani (Kuhn), Fusarium sp.||Seedling|
|Leaf blight||Unknown bacteria||Flowering and maturity|
|Leaf spot||Alternaria sp., Phoma sp.||Flowering and maturity|
|Powdery mildew||Erysiphe sp.||Flowering and maturity|
|Wilt||Fusarium sp.||Seedling, flowering, and maturity|
Damage by the helmet bug and Vernonia worm are very high and they are considered major insect pests of Vernonia. Young shoots and leaves are nibbled off and the growing point is cut off resulting in profuse branching of the stem. Severe wilting was caused by harlequin bugs on a few plants. Variation in pest resistances were also observed in different accessions of Vernonia galamensis. During the seedling stage damping off of seedlings is also serious; over 10% of the seedling were lost at this stage to this disease. Late in the growing period, especially at the flowering stage, severe powdery mildew infestations (in some populations) resulted in drying and shedding of the leaves. The leaves of Vernonia are extremely bitter and livestock do not browse it in open fields.
Preliminary identification of Vernonia diseases revealed the presence of six different fungal pathogens and one bacterial pathogen. Infestation by damping off during the seedling stage across the experimental plots was serious, over 10% of the seedling was lost at this stage to this disease. Late in the growing season severe infestation was caused by powdery mildews. Similar observations were made for the naturally growing Vernonia. Thirteen insect species belonging to seven families and six order were also identified. Infestation and damage by Vernonia worm at early stage and helmet bug (Captosoma spp.) at late stage was very high. Helmet bug alone can cause over 80% damage in Yabello (on wild Vernonia) in southern Ethiopia.
The present preliminary survey indicates that there are major pests that may influence the commercialization effort of Vernonia galamensis as an industrial oilseed crop for Ethiopia, but it is too early to prioritize risks with any degree of certainty. Thus, further evaluation of the wide genetic base of Vernonia, damage and loss assessment due to the major pests, and control options are required.