Identification of the best ovule maturity stage for interspecific hybridization in cotton

In order to identify the best maturity time for excision of fertilized ovules in interspecific hybridization, intercrosses were made between two diploid (Gossypium herbaceum and G. arboreum, 2n=26) and two tetraploid species
(G. barbadense and G. hirsutum, 2n=52). Flower morphology, growth rate of ovules and ovaries, as well as fiber growth pattern in various time scales post anthesis were recorded in parents and hybrid plants and the data were analyzed based on factorial design. The results showed that the effect of genotype (G), day after pollination (DAP) and their interaction term (G×DAP) on ovule and ovary specifications were significant (P≤0.01). Various pre or post-fertilization factors affects on ovule growth and viability duration of in-ovulo embryos. Our data showed pollination is crucial for flower retention on plants, induction of ovary growth leading to embryo development. The studied cotton species showed differences in duration of non-fertilized flowers retention. Furthermore, we found that after emasculation the flowers retention period in G. arboreum was the shortest while in G. barbadense it was the longest. Our data reveal that the best time for excision of fertilized ovules to be transplanted in vitro in diploid × diploid and diploid × tetraploid hybridization was two or three days after pollination, respectively. Based on its cross ability, flower maintenance, ovule size and embryo growth in vitro cultures, G. barbadense was found to be superior to other parental lines; thus, might be suggested as a suitable donor parent in interspecific cotton hybridizations.