Study of Callus Formation and Salinity Tolerance in Different Explants of Cotton (Gossypium sp.) Cultivars in Vitro

Achievement to low-priced and short-term methods for obtaining of tolerant lines to abiotic stresses in plant breeding programs is one of the main applications of tissue culture. In present study, the callus formation potential of immature embryo, hypocotyl and root explants of Sahel, Sepid, No. 200, Barbadense and Khordad cotton cultivars were investigated on MS basal medium containing various hormonal combinations of 2, 4-Dichlorophenoxy acetic acid (2, 4-D) and 6-Benzylamino purine (BAP). According to analysis of variance, callus formation percent was significant at 1% level for cultivar, explant type, hormonal combinations of medium and explant × hormonal combinations of medium interaction. On the basis of the mean comparisons by Least Significant Difference (LSD) Test, the highest callus formation was related to immature embryo explant of No. 200 cultivar on the MS medium containing 0.5 mg/l 2, 4-D, whereas, the root explant of Sepid cultivar showed the lowest callus formation percent. By transferring the produced calli on MS medium containing different concentrations of sodium chloride (NaCl) and then studying the relative growth rate of calli, it was revealed that the tolerance of explants to different concentrations of NaCl was significant at 1% level affected to cultivar, explant type, NaCl density and all their interactions. The highest relative growth rate of calli on the salinity medium was related to immature embryo explant and Khordad and Sepid cultivars with 77.3% and 76.2%, respectively, while the root explant of No. 200 cultivar with 17.9% showed the lowest tolerance to NaCl. The relative growth rate of calli showed significant reduction in all explants and cultivars with increasing of NaCl densities, as, the control treatment (without NaCl) has been the highest relative growth rate with 51.6%, and the lowest relative growth rate with 20.6% was observed on MS medium containing 3 mg/l NaCl. By transferring of the selected tolerant explants to the media with higher concentrations of 3.5 and 4 mg/l NaCl, it was determined that none of the calli and explants could not tolerate the higher NaCl densities in the medium.