The effects of ultrasound, temperature, light, chitosan and plant growth regulators on callus induction in saffron (Crocus sativus L.)

Saffron is one of the most important pharmaceutical plants in the world due to its valuable secondary metabolites. The aim of this study is to investigate the different factors on callus induction and growth in saffron corm explants. In the first experiment, saffron corms surface were sterilized and were excised to equal segments, then they were treated with ultrasound and then they were cultured on MS medium supplemented with 2 mg.L-1 auxin (NAA and 2,4-D) and 0.5 mg.L-1 Kinetin. In the second experiment, the effect of temperature, light and chitosan were evaluated. The results of analysis of variance showed that there were significant differences (P≤0.05) among temperature, light, chitosan as well as ultrasound treatments in terms of callus induction percentage and fresh weight of callus. Callus induction and growth on MS medium containing 2 mg.L-1 NAA + 0.5 mg.L-1 Kin was higher than those containing 2 mg.L-1 2,4 -D +0.5 mg.L-1 Kin. In MS medium containing 2,4-D which had low callus induction and callus growth rate, utilization of ultrasound stimulated callus induction and especially it stimulated callus growth from saffron corm explants. In addition, in MS medium containing 2,4-D, utilization of 0.25 g.L-1 chitosan stimulated callus induction and increased callus induction of saffron corm explants. However, increasing chitosan concentration from 0.25 mg.L-1 to 0.75 g.L-1 decreased callus induction and callus growth, while, in MS medium containing NAA, which had efficient callus induction and growth, utilization of these treatments reduced callus induction and callus growth from saffron corm explants. In other words, the effect of ultrasound and chitosan on response of saffron explants in vitro cultures was used, depending on the type of auxin used in composition of the culture medium. Generally, the highest percentage of callus induction occurred on MS medium supplemented with 2 mg.L-1 NAA + 0.5 mg.L-1 Kin and incubated at 25 ºC in the dark, which could be suitable for in vitro culture and gene transfer studies in saffron.