Cotton is one of the world’s most important natural fiber and cash crops. The research carried out studies of plants F₁-F₄ considering the importance of cytogenetic analysis of interspecific hybrids for identifying structural differences between homologous chromosomes of crossed forms and substitution of individual chromosomes or chromosome segments because of introgression of interspecific hybrids in cotton breeding. The article comprised a cytogenetic analysis of introgressive lines obtained through the participation of intergenomic crosses and F₁-F₄ cotton hybrids. The results revealed that in crossed variants of F₁-F₄ hybrid plants, the presence of open bivalents and univalents in PMC (pollen mother cell) showed the absence of complete conjugation in the chromosomes. It could be due to the structural differences between the homologous chromosomes in the crossed forms caused by exchanging chromosomes with alien ones. According to the tetrad analysis, the average value ranged from 95.65% F₁L-158/16 × Sultan to 99.61% F₁L-4747-48/16 × Sultan in F₁ hybrids. Based on the tetrad analysis in 16 combinations, the meiotic index ranged from 96.76 ± 0.34 to 99.54 ± 0.19 in F₂ hybrids and 96.51 ± 0.56 to 99.34 ± 0.30 in F₃ hybrids, and in 17 combinations, the range was from 97.14 ± 0.29 to 98.92 ± 0.12 in F₄ hybrids. It also confirmed that meiosis is preceding naturally in the remaining hybrid variants, with a decrease observed in the meiotic index. The results also increased the number of other types of gametes (Monod, dyad, triad, pentad, hexad, and polyad), negatively affecting normal gametes formation.

Keywords: Upland cotton, G. barbadense L., G. hirsutum L., hybrids, introgressive lines, meiosis, tetrad, sporadic, bivalent, degree of fecundity

Key findings: The cytological analyses of introgressive cotton lines and hybrids confirmed their donor ability to enrich the cotton genome. Results established the stabilization of the meiotic division that raised the meiotic index and pollen fertility. The structural differences between homeologous chromosomes confirm the introgressed fragments of wild forms and valuable traits in the cultivated cotton genomes.