Effect of hygromycin on explant selection in genetic transformation experiments of sorghum (Sorghum bicolor (L.) Moench)

Efficient genetic transformation of sorghum plant requires an effective selection marker system that precisely differentiates transformed cells from non-transformed ones. Hence the present Hygromycin study was undertaken to optimize the selection marker antibiotic Hygromycin to screen transformed cells in sorghum transformation experiments with vectors harbouring hpt gene. Shoot meristem explants of sorghum were grown in somatic embryo induction media containing various concentrations of Hygromycin. At lower concentrations of Hygromycin (0.2 mg/L and less), the growth of shoot apices was unaffected and the survival rates were very high (87.5–100%) during the three sub-culture passages. At a Hygromycin concentration of 0.5 mg/L the percentage of survival decreased gradually with three subcultures - 62.5, 25 and 0% survival respectively, while at concentrations of 1.0 and 2.0 mg/L, these were higher mortalities of explants in the first subculture itself (only 31.3-37.5% survival). The least concentration of Hygromycin at which all susceptible explants died was 0.5 mg/L (after three subcultures). Therefore it is suggested that 0.5 mg/L of Hygromycin may be used as the optimum concentration for the selection of sorghum shoot meristem explants transformed with vectors harboring the hpt gene.