Karyotype and Chromosome Pairing Analysis in Some Iranian Upland Cotton (Gossypium hirsutum) Cultivars

Abstract

Karyotypic studies of 9 tetraploid cotton cultivars showed that all the cultivars possessed 2n=4x=52 chromosome number. The chromosomes were mostly metacentric (M or m) and sub-metacentric (sm) but sub-telocentric chromosomes (st) occurred in the cultivars Sahel, Zeta2, Tashkand and Siokra. The size of chromosomes varied from 0.82 to 4.30 μm in the cultivars studied. The highest size difference among the chromosomes was observed in the cultivar Siokra while the highest value of mean haploid total chromatin length and size of the longest chromosome occurred in Tashkand cultivar. The cotton cultivars differed significantly in the size of chromosomes and the size of chromosomes arms indicating the occurrence of quantitative change in the chromatin material (DNA) during the cultivars diversification. They differed in karyotypic formulae and symmetry of karyotype indicating the occurrence of chromosomes structural changes. Meiotic analysis showed mainly bivalent formation in most of the cultivars, however quadrivalents were formed in three cultivars and hexavalent was formed only in the cultivar Bakhtegan. The genotypes studied also differed significantly in chiasma frequency and chromosome pairing due to genetic differences.