Roselle (Hibiscus sabdariffa L.) is an annual shrub that belongs to family Malvaceae (Osman et al., 2011). It is also known by various common names like Karkade, Hibiscus, Rozelle, Red sorrel, Jamaican sorrel, Rosella, Indian sorrel (Mahadevan et al., 2009),(Maganha et al., 2010),(El Naim et al., 2012). Roselle is a tetraploid self-pollinated crops (2n = 4x = 72) which has more related chromosome number with a diploid fiber crop Kenaf (2n = 2x = 36) (Akpan, 2000). The genus hibiscus contains more than 300 known species around the world that are used as ornamental plants (Mohamed et al., 2012).
The exact origin of roselle is debated, but it is believed to be native to tropical Africa and latter distributed to other parts of the world (Morton & others, 1987),(Panchoo & Rhoden, 1990),(Tounkara et al., 2011). Currently, the crop is widely grown in central and west Africa and Southeast Asia(B. H. Ali et al., 2005)(Mohamed et al., 2012). Roselle adapts mainly in areas with altitudinal range of 600–2000 m above sea level and annual rainfall between 400–500 mm with an annual temperature ranging between 18–35ºC (Augstburger et al., 2000). It is drought tolerant, relatively easy to grow and can grow as part of multi-cropping system (Das & Das, 1998).
Roselle is grown mainly in traditional farming methods by small scale-farmers, depending on rainfall and natural soil fertility without using chemical fertilizers or insecticides (El Naim et al., 2012). It is cultivated for its leaves, seeds and calyces. Roselle is consumed as indigenous and traditional leafy vegetables and has been part of the food systems prepared like spinach in West, East and Central Africa for generations (Oguntona, 1998),(Vargas & Lopez, 2003). The fresh swollen calyces are used in soups. Regarding to economical and socioeconomic aspects, roselle is one of the important crops linking smallholder famers to markets. Roselle is economically important beverage and medicinal plant used in several local dishes (Plotto et al., 2004)(Atta et al., 2011). The dried calyces are used for making jelly, jams, food colorants, dyes and beverages (Padmaja et al., 2014).
Globally the demand has steadily increased for roselle over the past decades. Approximately 15,000 metric tons of dry calyx yield enter into world international trades each year and Germany and the United States are the main countries importing roselle for consumption (Nath, 2007). In Ethiopia, two roselle varieties have been registered (WG-Hibiscus-Sudan and WG-Hibiscus-Jamaica) ((MoA), 2020). Accordingly, cultivation of both roselle varieties is profitable in the country (Girma et al., 2015). (Banjaw & Kebede, 2019) reported that WG-hibiscus-Jamaica was found to be superior and produced 0.92 ton ha− 1 calyx yield compared to WG-hibiscus-Sudan, which produced 0.68 ton ha− 1 calyx yield. In contrast, yield production of WG-hibiscus-Sudan by direct sawing on the field can produce more calyx yield (1.2315 ton ha− 1) than Hibiscus-Jamaica (1.10195 ton ha− 1) (Girma et al., 2015).
In order to expand commercial production of roselle in Ethiopia, mainly for kerkede tea and beverage roselle production, Wondogenet Agriculture Research Center, providing basic seed for investors (Girma et al., 2015). The MIDROC Investment Group, agricultural and agro-processing company produces dried calyx, beverages and tea from roselle both for local consumption and export markets. These currently increasing interests in roselle fiber and calyx for commercial cultivation in Ethiopia necessitate collection, evaluation, genetic improvement, and conservation of roselle germplasm. A roselle collection will help to enhance commercial production while conserving the genetic resource bases. In recent years, there are introductions and commercial cultivation of roselle in Ethiopia. However, there is no information on the adaptation and general traits expression of phenotypic and physiological trait behaviors of roselle collection in Ethiopia. The characterization and evaluation of exotic roselle germplasm will provide information for the development of improved cultivars and the preservation of accessions for commercial product development. Hence, the production of these crops is contributing to the countries growth and development by generating foreign currency.
Genetic diversity is a dynamic property of germplasm and its estimation may be based on morphological evaluation, biochemical, or molecular assessment (Bhandari et al., 2017). The nature and magnitude of a crop's diversity for genetic improvement in yield, disease resistance, and quality characteristics is largely dependent on its efficient utilization (Chand et al., 2008). Among the three approaches, morphological characterization is the least expensive and most easily quantifiable to attract breeders for a genetic improvement program.
Morphological evaluation is labour intensive, requires large plant population size, exhibits low rate of polymorphism and is constrained by environmental sensitivity and higher risks of biased estimates (Botha & Venter, 2000). Despite these drawbacks, morphological evaluation provides information on crop characteristics and reveals sources of useful genotypes for trait improvement (Camussi et al., 1985). Genetic diversity studies on roselle are rather scanty and limited to work reported by (Ankrah et al., 2018a) who assessed thirty-six wild roselle accessions in Ghana; characterization of roselle accessions by agro-morphological and RAPD genotyping study in west Africa (Coffie, 2016), and a comparative variability study between kenaf and roselle (Siepe et al., 1997); (Cheng et al., 2004); (Sie et al., 2009). Within-population diversity measures the number of distinct classes in a population as richness and the relative abundance of genotypes within those classes as evenness (Shannon & Weaver, 1949).
In spite of its potential of economic importance, excellent nutritional and phytochemical quality, roselle is still underutilized and has received little attention in Ethiopia, limiting its potential as a food, medicinal, or industrial crop. Ethiopia has an ideal climate for roselle production. However, there are few research findings regarding modern production technologies that increasing productivity in order to link industries or enterprises involved in the production and processing of roselle.
Due to the inadequate number of released varieties and limited demonstration and adoption for farmers outside of the research station, characterization and genetic diversity estimation are needed. Unfortunately, very little research attention by way of breeding has been a focus to the study of genetic diversity and breeding behavior of African accessions in order to facilitate improvement of the crop. Therefore, the objective of this study is to characterize the extent of morpho-agronomic and physiological diversity, genetic variability and to identify high yielding accessions for further breeding work and release in roselle accessions collected from different African countries.