Vernonia (Vernonia galamensis (Cass.) Less.) (2n = 18) is an annual herb, about 13–500 cm tall, erect plant in the sunflower family, known for its use as an oilseed [1]. It is often called ironweed, and it is the largest source of vernonia oil, which is rich in a useful epoxy fatty acid known as vernolic acid which is used to make plastics, rubbery coatings, and drying agents. The polymerizing characteristics and low viscosity of vernonia oil make it very important as a solvent in paints and industrial coatings replacing the traditional additives that are complained to be hazardous and less ecofriendly [2]. The oil extract from Vernonia is useful for the production of degradable lubricants/additives, epoxy resins, insecticides or insect repellants, crop oil concentrates, and the formulation of carriers for slow release pesticides [3].
Vernonia is native to Africa, and over 300 species occurred in countries such as Ethiopia, Madagascar, Cape Verde, Eritrea, Mozambique, Kenya and northern Tanzania [4]. Nowadays, vernonia grows across the world in North America, South America, Africa, and Southeast Asia. But, its highest diversity occurs in Ethiopia and Kenya [5]. In Ethiopia, V. galamensis was first reported by Perdue in 1964 at 7 km southeast of Harar town, 9 ° 14' N and 42° 35' E. It is frequently found in Eastern and Southeastern part of the country in farmlands, in the forests, and in the compounds of mosques and churches. It grows well in areas with well-drained soil, relatively warm climate, and annual rainfall of as low as 250 mm [4].
Plant oils need chemical modification like adding epoxy group before used in the synthesis of oleochemicals such as plasticizers, adhesives, soaps, coatings, paints, lubricants and polymers [6]. However, the chemically artificial production of epoxy group from soybean and linseed oils is considered to be expensive, accompanied by emission of volatile organic compounds, which causes secondary pollution [7]. In this regard, natural epoxy oils extracted from plants represent economical, environmental-friendly and renewable feedstocks that could replace petrochemicals (Sun et al., 2022). Vernonia galamensis is one of the major source of natural epoxy oil used for the manufacturing of polyvinylchloride (PVC plastic), paints, adhesives, insecticides, and structural polymers [8, 9]. Vernonia seeds contain up to 40% epoxy oil and this oil has up to 80% vernolic acid (cis-12,13-epoxyoleic acid).
Vernonia oil is rich in important fatty acids including vernolic acid (above 74%), linoleic acid (13.02–14.05%), oleic acid (3.77–5.28%), palmitic acid (2.48–2.98%) and stearic acid (2.26–2.75%). The oil extracted from Vernonia seed has unique physical and chemical properties that will permit its use in the formulation of reactive diluents, products to serve as solvents that become part of the dry paint surface and do not evaporate to pollute the air [5]. These days, due to the high oil and vernolic acid content and its relatively low shattering nature, var. ethiopica has been the focus of research and at present its production in some parts of the world reaches semi-commercial scale [10, 11]. Some vernonia species like V. amygdalina (Bitterleaf) are also useful as traditional herbal medicine to treat fevers, diarrhea, malaria, hepatitis, regular coughs, scabies, stomach-aches, headaches, and gastrointestinal problems. Moreover, Veronial leaves also serve as good source of food in western Africa particularly in Nigeria and Cameroon.
In spite of its potential economic significances, V. galamensis is a research neglected crop, and limited information is available in Ethiopia. The potential of Vernonia species in Ethiopia has not been well studied. It is only considered as a wild weed and colonizing disturbed areas with bare agricultural lands. Even its production and management system is restricted; its potential value for industries has been underutilized and under exploited [4]. Limited attempts to study the naturally existing variability in Ethiopian V. galamensis have been made since 1990 [11]. Angelini et al. [12] and Thompson et al.[13] reported Vernonia seed yields of up to 4,000 kg/ha and an oil content of 40% in unimproved local materials, which was higher than found elsewhere. Lack of improved genotypes, limited awareness about the significance of the crop, biotic and abiotic factors are the major factors affecting the production and productivity of the crop.
Genetic variability offers opportunity for breeders to develop new and improved cultivars with desirable characteristics, including both farmer-preferred traits (large seed and yield potential, etc.) and breeders preferred traits such as pest and disease resistance and photosensitivity [14]. In this regard, Baye and Becker [8] confirmed existence of considerable genetic variability among Ethiopian vernonia accessions collected from various parts of the country. The studied accession showed significant differences in terms of maturity time, plant structure, flower color, and branching patterns as well as fatty acid composition. The vernolic acid content of the seed oil of the accessions ranged from 34–87% with overall mean of 74%, indicating presence of promising possibility to improve the seed oil composition by exploiting the available genetic variations through breeding. Assessing the extent and patterns of genetic diversity of crops is a preliminary and most important step for its improvement and conservation [10, 15].
Studying genetic variability is vital in plant genetic resource management programs as the information it provides make possible to identify genotypes of interest and use them in the establishment of effective conservation strategies. Various approaches such as morphological, protein and DNA markers are sued to explore the extent and patterns of genetic variation between individuals in a population or between populations in a species. However, morphological markers such as seed shape, colour, length, tast etc are considered to be less powerful to explain the true genetic variability in populations. Moreover, protein markers are highly environmental influenced, developmental stage dependent and tissue specific, and hence, provide limited insight into the actual genetic diversity among study population. In this regard, DNA marker systems, which were introduced to genetic analysis in the 1980s, have many advantages over the traditional morphological and protein markers based genetic and ecological analyses of plant populations. So far, various DNA marker systems such as Restriction Fragment Length Polymorphism (RFLP), Random Amplified Polymorphic DNA (RAPD), Amplified Fragment Length Polymorphism (AFLP), microsatellite, Diversity Arrays Technology, (DArT), Inter simple sequence repeats (ISSR), Simple sequence repeats, and single nucleotide polymorphism (SNP) have been used to investigate the extent and patters of genetic diversity various crops. ISSRs are found to be useful to elucidate the genetic diversity and population structure of various crops [16].