CHAPTER ONE
1.0 INTRODUCTION
Cotton (Gossypium spp) belongs to the tribe Gossypieae, the family Malvaceae and the genus Gossypium. The Gossypium genus is the largest in species number of the tribe Gossypieae with approximately 50 species (Rapp et al., 2005). The value of cotton, as well as its universally high demand, gives it an outstanding label, as the world’s most cultivated major cash crop, though it faces stiff competition from synthetic fibres (Monroy, Mulinge, & Witwer, 2012). The word “cotton” is derived from the Arabic word “alqatan”, which is used to describe fine textile (Guitchounts & Chaudhry, 2003). There are four domesticated species of cotton; two are tetraploid and the other two are diploid. The tetraploid cultivars are of American descent, Gossypium hirsutum (L) and Gossypium barbadense. The diploids, Gossypium arboreum and Gossypium herbaceum trace their lineage to Asia and Africa (Wendel & Cronn, 2003).
Gossypium hirsutum (upland cotton) is native to the Americas (Mexico, Northern South Americas) and West Indies (Brubaker & Wendel, 1994). It is cultivated in well over 50 countries worldwide on an area of about 35 million hectares making it the most cultivated cotton species in the world market, contributing 95% of all the cotton produced annually (Wilkins, Rajasekaren, & Anderson, 2000). Cotton consumption worldwide is estimated at 27 million metric tons annually and considered the major natural fibre as well as serving the purposes of food, feed and oil (Chen et al., 2007). Cotton farming is an income generator revenue for approximately 180 million people (James, 2002). Globally, its economic impact is an estimated $500 billion of which 30 billion is produced by the fibre industry through raw cotton (Chen et al., 2007).
Cultivation is usually in the tropics as well as the sub-tropic regions of over 80 countries. Countries in the Asiatic world (China, India, Turkey, Uzbekistan and Pakistan) are the major producers of cotton. It is also largely produced in the Americas (the United States of America,
Argentina and Brazil), Europe (Greece) Australia continent (Australia) and Africa (Egypt) which are responsible for about 85% of cotton produced altogether (Santhy et al., 2008). In West Africa, the largest cotton producing countries are Burkina Faso with 650,000 tons per annum, followed by Mali with 550,000 tons, Cote d’Ivoire 300,000 tons, Chad 180,000 tons, and Senegal with 31,000 tons (Sylla, 2016). In Ghana, trends in cotton production have been characteristically erratic. Seed cotton yields have fluctuated in Ghana from the year 2002 to 2017 ranging between 250-500kg/ha. In Burkina Faso however, yields ranged between 350-520kg/ha (Boafo et al., 2018).
Cotton production in Ghana based on the yields of 2017/18 was an estimated 0.03MMT (Index Mundi, 2018) while those of Asia such as India, China and Pakistan were 6.21MMT, 5.99MMT and 1.76MMT respectively. Comparative to Ghana, Burkina Faso produced 0.16MMT. Cotton production during 2017/18 in Burkina Faso more than doubled production in Ghana (FAS- USDA, 2018).
Low productivity of cotton in Ghana is attributed to several factors, paramount among them is inadequate number of improved cotton varieties. Besides that, the industry is heavily dependent on seeds imported from other countries (ICAC, 2008). The lack of appropriate strategic policy by successive governments to regulate the sector has also not helped in improving the cotton industry in Ghana (Asinyo, Frimpong, & Amankwah , 2015). Again, the lack of credit facility for cotton farmers has also discouraged farmers from actively engaging in its cultivation.
Enormous prospects exist and will positively impact the cotton sector of Ghana when fully exploited. Some of these opportunities include: availability of land especially some parts of the middle belt of the country (Brong Ahafo), parts of the Volta Region and the northern sector, good number of cotton growers, high ginning capacity, ready market for seed cotton, and a high demand for cottonseed cake by the livestock sector (ICAC, 2008). It is against this backdrop that,
the important contribution of cotton to the socio-economic development of Ghana cannot be
underestimated. However, due to lack of established breeding programs and unexploited available germplasm, there are few improved cotton varieties available to farmers as the few varieties released were developed considerably some years back.
It is necessary to develop new improved cotton varieties with desirable superior agronomic traits (such as high yielding) which when made available to the farmers could help boost cotton production in the country. Natural genetic diversity preserved within cotton germplasm collections when wholly exploited will be to the benefit of improvement programs (Abdallah et al., 2001).
Indeed, for Ghana, there is no report with regards to the nature of population structure and genetic diversity in available germplasm. Knowledge of the diversity available in a breeding programme informs selection efficiency and success. Estimation of genetic relatedness and or divergence of genotypes aid in parental combination selection for developing segregating populations so as to conserve genetic diversity and categorize germplasm into heterotic clusters for purposes of hybridization in a breeding programs (Ali, 2008).
The primary objective of the study was to access diversity of available cotton germplasm in Ghana and to select desirable genotypes as parents for breeding in the Guinea Savannah zone of Ghana.
The specific objectives were to;
- determine the genetic variation among 63 genotypes of cotton using phenotypic characters;
- characterize cotton genotypes employing simple sequence repeat (SSR) markers and
- assess relatedness of cotton genotypes based on their phenotypic and molecular traits.
