The effect of cold pre-treatment and hormonal agents on ovule callus formation in some cotton (Gossypium sp.) cultivars in vitro

The use of ovules to produce the haploid plants is one of the fundamental fields of tissue culture. Considering that the optimized tissue culture conditions varies depending on plant species, genotype within species, nutrient medium components and different environmental factors, in present study, the effects of 1, 3 and 10 days cold pre-treatments in 4ºC and different hormonal combinations of MS medium was studied on callus-formation of ovule explant in 4 cotton cultivars. Based on the results, ovules with cold induction for 10 days had the highest (83.7%) callusformation. However, less than 3 days cold pre-treatment with 28% showed significant decreasing effect on callus-formation. Explants of different cultivars had a different callus-formation rate, as Sahel cultivar produced significantly higher callus percentage than Hashemabad native cultivar. In the other hand, low concentrations of auxin (0.1 mg/l 2,4-D) had positive role in callus-formation of ovule, but by increasing BAP concentration above 3 mg/l, an inhibitory effect was observed. Therefore, different cold pre-treatment times, cultivar type, and hormonal types and concentrations affected on callus-production in ovule culture of cotton cultivars, and low concentrations of 2,4-D with increasing cold pretreatment duration had positive roles in callus-formation. In addition to callus percentage, various treatments also affected on color and size of calli, so the ovules of Sahel that had been under cold induction for 10 days, produced medium to large and bright green calli, and increasing of cold pre-treatment time until the tenth day, and also low levels of 2,4-D (0.1 mg/l) in medium increased the calli size in cotton ovule culture.