Gossypium genus includeds 50 species, classified cytologically in two diploid and tetraploid groups. Diploids and tetraploids are incompatible and therefore embryo rescue has to be employed for hybridization. In order to optimize this technique for making crosses among different species as well ashe response of embryo to various media, some crosses among two tetraploid (G.hirsutum,G.barbadense(2n=4x=52)) ando diploid species (G.herbaceum and G.arboreum (2n=2x=26)) were made in Karaj Agriculture Faculty Research Center. The best time for choosing and transfer of embryos to in vitro was found out. The resulting in ovulo embryos of hybrids and parents were cultured on four different media. The analysis of data on the basis of a factorial experiment in randomized complete block design indicated that genotype, media and the interaction among them affect callus size, callus percentage as well as germination percentage. G.herbaceum,G.arboreum and G.hirsutum exhibited more callogenesis while G.barbadense along with its hybrids demonstrated higher germination and regeneration, suggesting that G.barbadense is a useful donor parent and MS3 a suitable medium.
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