Chromosome Pairing Behaviour in Intra- and Inter-specific Hybrids of Tetraploid Cotton (Gossypium spp.)

Cotton (Gossypium spp.) is one of the most important fiber crops worldwide. However, its productivity and stability are increasingly constrained by climate-related factors such as drought, salinity, high temperatures, and the rising impact of pests. Although conventional breeding methods are effective for improving yield and fiber quality, their precision and efficiency remain limited when addressing polygenic traits and complex stress tolerance. This study presents the results of cytogenetic investigations conducted on intraspecific and interspecific F1 hybrids of tetraploid cotton species (Gossypium hirsutum L. and Gossypium barbadense L.). The analysis focused on the chromosome pairing in pollen mother cells at the metaphase I stage of meiosis. The results showed that in some intraspecific hybrids, normal chromosome pairing with 26 bivalents was observed, indicating cytogenetic uniformity. In contrast, some intraspecific hybrids exhibited considerable frequencies of univalents and quadrivalents. The highest mean number of univalents was recorded in ssp. punctatum var. gambia × ssp. punctatum (10.70±0.51) and ssp. punctatum var. gambia × ssp. mexicanum var. microcarpum palmerii (9.36±0.43). Quadrivalents were observed at low frequencies in ssp. punctatum var. florida × ssp. punctatum var. hopi (0.21±0.11) and ssp. glabrum var. mari galante × ssp. punctatum (0.14±0.10). These cytogenetic abnormalities suggest the presence of structural chromosomal differences and partial de-synapsis. In interspecific hybrids, univalents (0.12-0.28) and quadrivalents (0.11 ± 0.07) were detected at low frequencies, indicating the presence of karyotypic heterogeneity. However, the formation of 26 bivalents in the majority of hybrids confirmed their high level of phylogenetic relatedness. The obtained results are important for understanding the evolutionary and systematic relationships between G. hirsutum and G. barbadense, and provide a scientific basis for the targeted use of genetic resources in cotton breeding programs.

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