Genetic Characterization and Relationships Among Egyptian Cotton Varieties as Revealed by Biochemical and Mecular Markers

Abstract

Cotton is an economic plant of world importance. It is the world's leading textile fiber crop and it is also a source of secondary products such as oil, live-stock feed (cotton seed cake) and cellulose (Anderson, 1999 and Frelichowski et al., 2006).
Assessment of genetic markers and diversity form an integral part of any successful breeding program. Morphological features are indications of the genotype but are represented by only a few loci because there are not a large enough number of characters available. Moreover, they can also be affected by environmental factors and growth practices. To overcome the limitations associated with morphological markers, various biochemical and molecular marker techniques have come up in recent years. Biochemical markers such as isozymes have been used to study the genetic distances and estimate the level of genetic variability of cotton varieties and accessions (Wendel et al., 1989; Percy and Wendel, 1990; Abdel-Tawab et al., 1990 & 1993; Melchinger et al., 1991; Wendel et al., 1992; Sukumar and Allan, 1998; Farooq et al., 1999). However, isozyme analysis has certain limitations due to the availability of a limited number of marker loci, a general lack of polymorphism for these loci in elite breeding materials, and the chance of variability in banding patterns being due to plant development (Tanksley et al., 1989). Protein markers have also been used to identify different cotton species, varieties and lines (Khan, 1991; Goyal, 1993; Renata et al., 2004; Murtaza et al., 2005; Yunuskhanov et al., 2007; Kurbanbaev et al., 2008) DNA based molecular markers such as RFLP, AFLP, SSR, ESTs, SNP and RAPD have been widely used in genetic analyses, breeding studies and investigations of genetic diversity and the relationship between cultivated species and their wild parents. They have several advantages, including high polymorphism and independence from effects related to environmental conditions and the physiological stage of the plant. Among these marker techniques, the randomly amplified polymorphic DNA (RAPD) markers generated by polymerase chain reaction (PCR) is technically the simplest, less expensive, fast and does not require prior knowledge of the target sequences for the design of primers (Williams et al., 1990; Welsh and McClelland, 1990). The RAPD markers have already been used in cotton for the assessment of genetic variability, diversity and fingerprinting cotton genotypes (Pillay and Myers, 1999; Jing et al., 2000; Hussein et al,. 2002, 2006, and 2007; Muhammad et al., 2009; Zahid et al., 2009) as well as for the detection of variation between closely related cultivars (Multani and Lyon 1995; Rahman et al., 2002; El-Defrawy et al., 2004; Masoud et al., 2007).
The objectives of this investigation were to: (1) determine the genetic differences between nine Egyptian cotton varieties using six isozyme systems, protein patterns and 10 RAPD markers, (2) identify variety specific RAPD markers in the tested genotypes, and (3) assess the genetic distance and relationships among these varieties.