Morphological, cytological, and molecular characterization of interspecific cotton hybrids derived from Gossypium hirsutum and G. arboreum crosses

Diploid cotton Gossypium arboreum (2n = 2x = 26, A^dA^d) is a valuable genetic resource to improve widely cultivated American cotton G. hirsutum (2n = 4x = 52, A^tA^tD^tD^t). In this study, successful generation of four unique interspecific hybrids (G. hirsutum / G. arboreum) was confirmed through morphological, cytological, and molecular characterization. The morphological evaluation included different stem and leaf characters, trichome density, floral characters, and cotton leaf curl disease reaction. Interspecific hybrids were recorded with either complete dominance of some characters or an intermediate expression. However, variation among the F₁s was observed for some traits, especially for pollen size and fertility. Two of the four F₁s were found to possess relatively bigger pollen sizes with partial fertility which enabled their utilization as male parents in backcrosses. Mitotic analysis of F₁s was made possible through the induction of fresh roots by air layering. Of the four hybrid plants, two were triploid (2n = 39) and the other two were tetraploids (2n = 52). Meiotic irregularities in interspecific hybrids were also observed. Successful amplification of polymorphic parental bands in all four F₁s using simple sequence repeat markers added another line of evidence supporting their hybridity. Results of this experiment provided useful insight and base material to introgress stress tolerance from G. arboreum to G. hirsutum.