Development of Triploid Seedless Nagpur Mandarin (Citrus reticulata Blanco) through Endosperm Rescue

Nagpur mandarin is a popular table fruit across India and is exported to various countries. Only 1% of the total production is processed into various products. The development of seedless cultivars will boost agricultural incomes by enhancing the potential for export and processing. At present, only a couple of commercially seedless varieties are available, but these have yet to become popular. A research study was undertaken to quickly develop a high-quality seedless variety of Nagpur mandarin by combining the available technologies, viz., endosperm rescue, somatic embryogenesis, and mini-grafting, at CCRI, Nagpur. Complete plantlets of C. reticulata Blanco cv. Nagpur mandarin was successfully regenerated from hybrid endosperm tissue via somatic embryogenesis after attempting various permutations and combinations of media at various stages of regeneration, right from the primary callus to complete plantlet production. Maximum response (93.33%) and survival (91.67%) for primary callus induction were obtained in Murashige and Tucker (MT) + Malt Extract (ME) + Casein Hydrolysate (CH) (500 mg/L) +2,4-dichlorophenoxyacetic acid (2,4-D) (2 mg/L) medium. Maximum stimulation for embryogenesis and morphogenesis occurred in 2MT + CH (500 mg/L) + adenine sulfate (ad.s) (2 mg/L) + Benzyl Adenine (BA) (0.25 mg/L). The highest response (95.84%) for shoot differentiation occurred in MT + adenine sulphate (2 mg/L) + Gibberellic Acid (GA3) (1 mg/L) + BA (1 mg/L) (94.85%). The surviving plantlets were tested for ploidy status through flow Cytometry, chromosomal counting/cytogenetic technique, leaf morphology, stomatal characteristics, and the appearance of prominent thorns. In initial evaluation trials, the fruits of the triploid field-planted trees were found to be commercially seedless. These results demonstrated the recovery of stable triploids from the hybrid endosperm via somatic embryogenesis, which is the first of its kind in the field of Citrus triploid breeding in India.