Characterization of some cotton germplasms through molecular cytogenetics

Abstract

Eleven germplasms of Gossypium hirsutum L. (cotton) released by Bangladesh Cotton Development Board viz. CB-1 (Cotton Board-1), CB-2, CB-3, CB-4, CB-5, CB-6, CB-7, CB-8, CB-9, CB-10 and CB-11 were investigated cytogenetically and at the molecular level using RAPD- and SSR- markers for authentic characterization. The 11 cotton germplasms represented a broad spectrum of variation for several phenotypic and agronomic traits. These germplasms were found to possess a prominant nucleolus in the interphase nuclei and prophase chromosomes after orcein staining. The interphase nuclei and prophase chromosomes of these germplasms showed different types of orcein-staining pattern. Although the germplasms were found to possess 2n = 52 chromosomes, differed in respect of other karyotypic features such as total length of 2n chromosome complements, number of satellites, range of relative length, centromeric index etc. The centromeric formula of 46m + 6sm were found in CB-1 and CB-4 while it was 48m + 4sm in CB-8 and CB-10. The rest germplasms have 52 metacentric chromosomes. A wide range of CMA-positive bands (5-20) was found in the metaphase chromosomes of 11 germplasms. Different number of satellites such as 4 (CB-1), 6 (CB-2), 6 (CB-3), 2 (CB-4), 3 (CB-6), 2 (CB-7), 6 (CB-8) and 6 (CB-10) were found after CMA-staining. Entirely DAPI-fluoresced chromosomes were frequent in these germplasms. The number, location and distributions of GC- and AT-rich repeats are specific for each germplasm. Fluorescent banding revealed the occurrence of genomic alteration within these germplasms. DNA from the 11 cotton germplasms was studied with 10 oligonucleotide primers and 5 microsatellite primer pairs for RAPD and SSR assay, respectively. The ten RAPD primers generated 335 distinct bands with 100% polymorphisms indicated highly diversed nature. In addition to polymorphism, 29 unique RAPD sequences were identified in 11 cotton germplasms. The five SSR primer pairs generated 69 distinct bands of which 39 were considered as polymorphic (56.52% polymorphisms). Moreover, four unique SSR sequences were identified in CB-1, CB-5 and CB-9. The combined RAPD and SSR dendrogram made CB-11 distinct from the rest and placed alone in a separate cluster that correlated with its phenotypic, agronomic and cytogenetical features. Therefore, each germplasm could be characterized authentically by cytogenetical and molecular analysis.