Establishment of in vitro callus induction and multiplication for studying salt stress in the rice cultivar Khang Dan 18

The Khang Dan 18 is one of the rice cultivars widely cultivated in Vietnam, which is threatened by saline intrusion. This study is conducted to establish an in vitro culture system for evaluate salt tolerance of the rice cultivar Khang Dan 18. First, different culture conditions, including plant growth regulator concentration, culture period, light regime, were optimized to induce and maintain callus in vitro. Culture media supplemented with 10 - 40 µM 2,4- Dichlorophenoxyacetic acid (2,4-D) are suitable for inducing callus. Different culture periods (1, 2 and 4 weeks) significantly affected the callus morphology and nature. The 10-hour light photoperiod is the most effective condition for callus induction and multiplication. Callus cultured in the medium supplemented exclusively with 2,4-D showed higher quality compared to those in media supplemented with 1-Naphthylacetic acid (NAA) and 2,4-D. Different photoperiods also affected callus differentiation in terms of root\shoot induction. The established culture system was then employed to evaluate salt tolerance of the callus. The growth of callus was significantly decreased when the concentrations of NaCl increased (3, 6 and 9‰, P = 0.05), especially at the concentration of 9‰ NaCl caused a strong decrease in callus weight and an obvious change in callus morphology. This culture system may be applied for in vitro salt stress studies on the cultivar Khang Dan 18 and similar rice cultivars.