A cytogenetic study of differentiation between G. hirsutum and G. barbadense chromosomes using heterozygous translocations involving certain chromosomes of the A and D genomes

Abstract

The primary object of this study was to determine some of the difference at the chromosome level between the two tetraploid species, G. hirsutum and G. barbadense, which cross readily and the F₁ hybrid is fertile but the succeeding generations are characterized by sterility and hybrid breakdown. The technique employed for this assessment was the study of chiasma frequency in seven translocations, five radiation-induced and two of hybrid origin. These involve seven chromosomes of the A genome and two of the D genome. The homozygous translocations were crossed to inbred lines of G. hirsutum and G. barbadense. The chiasma frequency per translocation, with a potential of four for each configuration at metaphase I, ranged from 3.58 to 3.92 in the seven translocations when heterozygous in G. hirsutum. By applying the Duncan multiple test to the chiasma frequency, the translocations fell into two groups, translocation IV₂ (T4-5) in a group itself and the other six in another group. ...