African Journal of Biotechnology Vol. 8 (22), pp. 6220-6227, 16 November, 2009 Available online at http://www.academicjournals.org/AJB DOI: 10.5897/AJB09.1211 ISSN 1684–5315 © 2009 Academic Journals Full Length Research Paper Effects of zeatin and activated charcoal in proliferation of shoots and direct regeneration in cotton (Gossypium hirsutum L.) Farzaneh Tafvizi 1* , Farah Farahanei 2 , Masoud Sheidai 3 and Taher Nejadsattari 1 1 Biology Department, School of Basic sciences, Science and Research Branch, Islamic Azad University (SRBIAU), Poonak, Tehran, Iran. 2 Department of Biology, Islamic Azad University, Qhom Branch, Qhom, Iran. 3 Faculty of Biological Sciences, Shahid Beheshti University, Tehran, Iran. Accepted 29 September, 2009 A multiple shoot induction protocol was optimized for cotton (Gossypium hirsutum L.). Three cultivars of cotton (Sahel, Siokra, Hybrid, that is, Sahel × Siokra) were used to study the effects of zeatin and activated charcoal on proliferation of shoots and direct regeneration from shoot tip explant excised from 10 – 15 day-old seedlings cultured in vitro. Growth response of different varieties varied. Root and shoot formation was observed in all varieties. The best treatment for multiple shoot induction in cultivars was the treatment containing Murashig and Skoog (MS) basal medium supplemented with zeatin (0.1 mg/l) and activated charcoal (0.5 mg/l), while treatment containing zeatin (0.1 mg/l) and activated charcoal (2 mg/l) was not good medium for regeneration. Culture of every cultivar continued for 7 subcultures and morphological characteristic was evaluated during every subculture. Maximum length of shoots (4.65 cm), the highest percentage of root development (55%) and maximum number of nodes (6.7) was observed in Siokra variety in the second subculture, Hybrid genotype and siokra in the last subculture, respectively. Also the shape of leaves changed in Siokra variety during subcultures. Key words: Gossypium hirsutum L., regeneration, shoot tip culture, zeatin. INTRODUCTION Cotton is an excellent natural source of textile fiber and is cultivated in many countries. Both diploid (Gossypium herbaceum) and tetraploid (G. hirsutum) cultivars are cultivated in different regions of Iran and are considered as important crop plants of the country because of its high economic importance. Considerable attention has been paid to improving cotton plants by conventional plant breeding methods (Agrawal et al ., 1997). Although great progress has been made in the field of improve- ment of cotton with conventional breeding methodology, it is time-consuming and commercialization of new cotton varieties often takes 6 to 10 years (Sheidai et al., 2008). Cotton is considered recalcitrant to in vitro proliferation (McCabe and Martinell, 1993). Though somatic embryo- *Corresponding author. E-mail: farzaneh.tafvizi@yahoo.com. Tel: +98-912-103 7400. Fax: +98-21-33954660. genesis in cotton has been reported (Davidonis and Hamilton, 1993; Trolinder and Goodin, 1987; Finer, 1988), the response is restricted to only a few cultivars (Trolinder and Xhixian, 1989; Firoozabady and DeBoer, 1993). In vitro culture of shoot apical tips has been reported to give single or sporadically, a few shoots (Bajaj and Gill 1989; Gould et al., 1991). Different regeneration protocols for induction of multiple shoots have been developed for cotton using various explants and through manipulation of media composition but still there is scope for improvement (Saeed et al., 1997; Gupta et al., 1997; Ouma et al., 2004; Rauf et al., 2004). The composition of the culture medium is an important factor in regeneration of shoots in vitro. Some problems such as browning, mortality of the cultured explants and rooting deficiencies are major problems for many tissue cultures because of phenolic components that produce in culture medium (DeProft et al., 1985). Cytokinins stimulate shoot proliferation in tissue culture. Zeatin is an