Picloram-Induced Embryogenic Callus Formation and Proliferation from Nucellar Embryo of Mandarin ‘Berastagi’ (Citrus reticulata Blanco)

Mandarin ‘Berastagi’ (Citrus reticulata Blanco) is a key horticultural commodity in North Sumatra, Indonesia, with increasing demand for high quality, genetically uniform planting material. Biotechnological approaches, somatic embryogenesis, hold particularly significant potential enhancing propagation efficiency and crop quality. This study aimed to determine the optimal culture medium and picloram concentration for the induction and proliferation of embryogenic callus from nucellar explants of Mandarin ‘Berastagi’ in vitro. Two experiments were conducted: (1) induction of embryogenic callus from nucellar embryos isolated from young fruits (60–70 days after anthesis) cultured on different basal media supplemented with varying picloram concentrations, and (2) proliferation of embryogenic callus on media containing different carbohydrate concentrations. The Murashige and Wetmore (MW) medium supplemented with 1.5 mg/L picloram resulted in the highest callus induction rate (37.8%) and largest mean callus diameter (17.8 mm). For proliferation, MW medium containing 4% sucrose produced the best response, with an average callus diameter of 14 mm and 96% of explants developing globular stage somatic embryos. These results establish an efficient somatic embryogenesis protocol that can support large-scale propagation and future crop improvement programs in Mandarin ‘Berastagi’.