Somatic embryogenesis and plant regeneration from zygotic embryo explants of onion

The study was undertaken to examine the effect of two synthetic auxins on somatic embryogenesis and plant regeneration from mature embryo explants of 16 onion cultivars. Cotyledons were removed from the embryos and remaining portions were cultured on MS medium supplemented with 1.0 mg/L 2,4-D and 5.0 mg/L picloram alone or in combination (1.0 mg/L 2,4-D + 2.5 mg/L picloram) to produce embryogenic callus. MS medium supplemented with 5.0 mg/L picloram was found to be the best one for both embryogenic callus induction (85%) and callus diameter (3.8 mm). Of the 16 cultivars studied, Yeoeuijuhwang exhibited the lowest frequency of embryogenic callus induction (50.5%), whereas all the other 15 cultivars showed more than 60% embryogenic callus induction. Scanning electron micrograph (SEM) analysis of embryogenic callus showed all stages of somatic embryos such as globular, scuetellar and coleoptilar. Plant regeneration was significantly affected by the composition of embryogenic callus induction medium. The greatest frequency of somatic embryo conversion was obtained from embryogenic callus developed in MS medium with 2,4-D (70.1%) followed by picloram (38.9%) and 2,4-D + picloram (34.5%). The germinated plantlets were further developed on the half-strength MS medium containing 3% sucrose and were acclimatized in the culture room with 98% survival rate.