Control of Shoot Tip Necrosis and Plant Death during in Vitro Multiplication of Pistachio Rootstock UCB1 (Pistacia integrima × P. atlantica)

Pistachio is one of the most important nuts and its mass production using tissue culture techniques is of great importance. Micro-propagation has many complications. Contamination is one of the critical limitations in the establishment stage. This study focused on different NaClO and HgCl2 concentrations and exposure times. Shoot tip necrosis (STN) is one of the most common problems during large-scale in vitro propagation of UCB1 rootstock. This physiological disorder is associated with the deficiency of calcium and boron content in the medium. Thus, in order to prevent STN, in this study, explants were cultured in varying concentrations of calcium using multiples of concentrations of calcium chloride (1x, 1.5 x and 2x), and boric acid (1x, 2x and 3x) in Murashige and Skoog (MS) medium with Gamborg's vitamins containing 30 gl-1 sucrose, 2 mgl-1 BA and 6.2 gl-1 agar. To evaluate the effects of various concentrations of calcium and boron on STN, the experiment was conducted as a factorial on completely randomized design. Results showed that soaking explants in 15% NaClO for five minutes followed by soaking in 0.01% HgClO for seven minutes efficiently removed contamination. It was also revealed that increasing calcium concentration enhanced proliferation rate and decreased STN. Moreover, doubling boric acid decreased the rate of necrosis while, tripling its concentrations increased the rate of necrosis. Increasing the concentration of boric acid also decreased proliferation. Finally, the lowest necrosis rate (17%) was obtained in the treatment containing 3x calcium chloride concentrations in combination with 2x boric acid concentration. In contrast, maximum rate of necrosis was obtained in the treatment containing 1x calcium chloride concentration in combination with 1x boric acid. Finally, in order to improved proliferation of shoot deferent, concentrations of NH4NO3 and KNO3 were used. The maximum proliferation rate of shoot was obtained for 2280 mgL-1 KNO3 as well as 1320 mgL-1 NH4NO3 .