Abstract: Sorghum bicolour is one of the most important cereal crops around the world, particularly in Africa which is highly cultivated for dietary staple. For this reason, a good knowledge and usage of this genetic resource in sorghum accessions are very vital for improving the crop quality. Analysis of genetic variability among the accessions will enable accurate results in breeding. The research design used was augmented design, which is common in many gene banks. This research finding would be used later by plant breeders to select best performers for further evaluation of the crop and obtain a new variety of sorghum.
Keywords: Genetic Diversity, Genetic Variability
1. Introduction
Sorghum is ranked the fifth most produced food crop in the world, and it is a dietary staple for over half a billion people in over thirty countries, where most of them are found in developing countries [1][2]. It is also the second most cultivated cereal crop in Africa, where cultivation of farmer’s variety of sorghum is the predominant form of agriculture next to maize [3]. Sorghum was domesticated in the African continent, particularly in east Africa, Ethiopia, from where it was believed to be introduced to other regions of the world with a wide agro-ecology [4]. It is one of most vital crop cultivated over a wide extreme ecological habitat in Ethiopia, in the range of low to high altitude (400-3000 meter above sea level) [5]. It is well adapted to the range of environmental conditions in semi-arid Africa, with high variability [1][6][7]. Sorghum is the single most important cereal in the lowland areas because of its extreme resistance to water stress [8]. Sorghum bicolor contains both cultivated and wild relative races and provides a substantial amount of genetic diversity for traits of agronomic importance so as to develop the different variety of interest of the crop for plant breeders [9].
Ethiopia is known to be one of the Vavilovian centers of origin or diversity for many cultivated and wild species of crops including sorghum [10][11]. Sorghum is one of the cereal crops for which Ethiopia has been credited as being a center of origin and/or diversity [10] [12]. In the high altitude areas, the landrace sorghum germplasm has often been the only well-adapted materials that are easily accessible for use. There is a higher probability of genetic material exchange to occur between the wild (Sorghum bicolor subsp. arundinaceum) and the cultivated sorghum since both types mostly grow in sympathy with the wild and weedy relatives in most of sorghum growing parts of Ethiopia, mainly in south-eastern and south-western part of the country [1]. The greater extent of genetic diversity existed within a species, often used as a measure of its ability to adapt its new environment. Hence, biodiversity is like a wealth for coping with environmental fluctuations. Sorghum has one of the largest crop germplasm collections, consisting of more than 42,000 accessions worldwide [13][14].The largest diversity of the crop germplasm provides a greater opportunities for improvement to its environmental adaptation ability and getting a better agronomic traits from the crop species. Identifying and selecting best varieties meeting specific local food and industrial requirements from this great biodiversity is of high importance for food security assurance of any given country [14].
Having a good understanding knowledge of the genetic diversity of a crop often enables the plant Geneticist in selecting the desirable family for the breeding program and gene introgression from distantly related germplasm. The more variable genotypes or accessions can be crossed to produce better varieties that can tolerate a range of environmental changes to abiotic and biotic-stresses. Therefore, a better understanding knowledge of the genetic diversity in sorghum crop species, it will definitely facilitate the further improvement of this cereal crop for its genetic architecture [15].
Genetic diversity in the crop species is one of the precious present of nature to us and it arises due to geographical isolation or genetic boundary to gene flow. Phenotypic traits are conventional tools to analyze the genetic diversity since studies of this type generally do not require complicated types of equipments and methodology. They are very simple and easy to score. These simple observable morphological characters are the useful tool for primary genetic diversity study as they provide a quick and useful approach for assessing the range of diversity in the crop species. Over the years, a number of studies have dealt with estimating genetic diversity in cultivated sorghum using morphological traits [16–22].
The use of phenotypic characters is the most advisable method usually used to estimate relationships between genotypes. The genetic variability of cultivated crops and their wild relatives together forms a potential and continued source for breeding new and better crop varieties. A better understanding of the genetic diversity in sorghum would contribute a lot to the crop improvement for food quality and the other important agronomic traits. Therefore, there is a need to evaluate the available accessions for genetic diversity and identifying the best accessions according to their performance.
There are around 11,353 sorghum accessions collected and conserved in Ethiopian Biodiversity Institute gene bank, of these number 8913 accessions were characterized used by plant breeders and other researchers and another 2440 accessions of sorghum accessions that are yet to be screened for their potentially useful characters. For this reason, the main objective of this research was to determine the range of variation among sorghum accessions in general and to classify them into clusters based on their similarity features for the traits of the study (quantitative characters) and also to generate data on their performance for plant breeders for further evaluation of the crop in particular.
2. Materials and Methods
The study on sorghum was conducted in Oromiya Regional State, Arsi Zone, Arsi Negale Research sub-center in the summer of 2014 G.C main cropping season, Which was located in western Oromiya region, with an altitude of¬ 1960 meter above sea level and 7o20’N latitude and 38o09’E longitude. 117 Sorghum accessions and two standard checks (Geremew and Baji) which were obtained from Melkasa Agricultural Research Center (MARC) were used for yield and drought resistance traits comparison for the research respectively. The research design used was augmented design with no replication among the sorghum accessions except for the two standard checks replicated in every block due to insufficient seed availability. The sorghum genotypes were planted in two rows with a spacing of 75cmx30cm between and within rows respectively, with a row length of 5m. DAP, Urea, and other management practices were applied as per recommended for the site.
The morphological data was recorded using the International Plant Genetic Resources Institute (IPGRI) now a day’s known as “Bioversity International” based in Italy, characterization descriptor list for the crop( E and F1993) by selecting 20 individual plants from each accession as Basal tiller (BT), Nodal tiller (NT), Leaf number at Maturity (LN), Plant height (PH) in cm, Panicle length (PL) in cm, Panicle width(PW) in cm, thousand grain weight (GY) in gm, Days to 50% flowering (DF), and Days to 50% maturity (DM). The collected data were calculated by statistical analysis of variance using MINITAB (version 13.0) and SAS (9.2). Variances and coefficient variation were calculated as per formula as it was suggested [23].