Development and Characterization of Synthetic Allotetraploids Between Diploid Species Gossypium herbaceum and Gossypium nelsonii for Cotton Genetic Improvement

Expanding genetic variability of cultivated cotton (<i>Gossypium hirsutum</i>) is essential for improving fiber quality and pest resistance. This study synthesized allotetraploids through interspecific hybridization between <i>G. herbaceum</i> (A₁) and <i>G. nelsonii</i> (G₃). Upon chromosome doubling using 0.2% colchicine, fertile F₁C allotetraploids (A₁A₁G₃G₃) were developed. Cytogenetic analysis confirmed chromosome stability of synthetic allotetraploids, and 74 polymorphic SSR markers verified hybridity and parental contributions. The F₁C hybrids exhibited enhanced resistance to cotton aphids (<i>Aphis gossypii</i>) and whiteflies (Aleyrodidae), with respective infestation rates of 5.2-5.6% and 5.4-5.8%, lower than those of <i>G. hirsutum</i> cv. Ravnak-1 (22.1% and 23.9%). Superior fiber length (25.0-26.0 mm) was observed in complex hybrids and backcross progeny, confirming the potential for trait introgression into elite cultivars. Phylogenetic analysis based on SSR data clearly differentiated <i>G. herbaceum</i> from Australian wild species, demonstrating successful bridging of divergent genomes. The F₁C hybrids consistently expressed dominant <i>G. nelsonii</i>-derived traits regardless of the hybridization direction and clustered phylogenetically closer to the wild parent. These synthetic allotetraploids could broaden the genetic base of <i>G. hirsutum</i>, addressing cultivation constraints through improved biotic stress resilience and fiber quality traits. The study establishes a robust framework for utilizing wild <i>Gossypium</i> species to overcome genetic bottlenecks in conventional cotton breeding programs.