title: Genetic diversity analysis of Bt cotton genotypes in  Pakistan using simple sequence repeat markers.
abstract: The popularity of genetically modified insect  resistant (Bt) cotton has promoted large scale monocultures, which is thought  to worsen the problem of crop genetic homogeneity. Information on genetic  diversity among Bt cotton varieties is lacking. We evaluated genetic divergence  among 19 Bt cotton genotypes using simple sequence repeat (SSR) markers. Thirty-seven  of 104 surveyed primers were found informative. Fifty-two primers selected on  the basis of reported intra-hirsutum polymorphism in a cotton marker database  showed a high degree of polymorphism, 56% compared to 13% for randomly selected  primers. A total of 177 loci were amplified, with an average of 1.57 loci per  primer, generating 38 markers. The amplicons ranged in size from 98 to 256 bp.  The genetic similarities among the 19 genotypes ranged from 0.902 to 0.982,  with an average of 0.947, revealing a lack of diversity. Similarities among  genotypes from public sector organizations were higher than genotypes developed  by private companies. Hybrids were found to be more distant compared to  commercial cultivars and advanced breeding lines. Cluster analysis grouped the  19 Bt cotton genotypes into three major clusters and two independent entries.  Cultivars IR-3701, Ali Akbar-802 and advanced breeding line VH-259 grouped in  subcluster B2, with very narrow genetic distances despite dissimilar parentage.  We found a very high level of similarity among Pakistani-bred Bt cotton  varieties, which means that genetically diverse recurrent parents should be  included to enhance genetic diversity. The intra-hirsutum polymorphic SSRs were  found to be highly informative for molecular genetic diversity studies in these  cotton varieties.
authors.affiliation: Agricultural Biotechnology Research Institute, Faisalabad, Pakistan. ihsan.ullah_tlw@yahoo.com
authors.forename: I
authors.initials: I
authors.lastname: Ullah
authors.forename: A
authors.initials: A
authors.lastname: Iram
authors.forename: M Z
authors.initials: MZ
authors.lastname: Iqbal
authors.forename: M
authors.initials: M
authors.lastname: Nawaz
authors.forename: S M
authors.initials: SM
authors.lastname: Hasni
authors.forename: S
authors.initials: S
authors.lastname: Jamil
mesh_terms: D016000:Cluster Analysis; D005838:Genotype; D003368:Gossypium / Q000145:classification / Q000235:genetics*; D018895:Microsatellite Repeats; D010154:Pakistan; D010802:Phylogeny; D011110:Polymorphism, Genetic