Somatic embryogenesis mediated micropropagation of polyembryonic cultivars of mango Vellaikolumban and Olour using nucellus tissue

Somatic embryogenesis mediated micropropagation from nucellus tissue was attempted in polyembryonic mango at the ICAR-Indian Institute of Horticultural Research, Bengaluru during 2016–2019. Studies were conducted to optimize the different stages of somatic embryogenesis namely induction, proliferation, conversion, maturation, germination of somatic embryos and ex vitro establishment of plantlets using nucellus tissue. For culture initiation, various developmental stages of fruits ranging from less than 20 days post-pollination to more than 60 days-post pollination of cultivars Vellaikolumban and Olour were utilized. Fruits of 30–40 days post-pollination in Vellaikolumban and 40–50 days post-pollination in Olour gave better percentage callusing with fewer days for callus initiation and callus formation. Embryonic calli developed on induction medium containing Rugini olive (RO) constituents, 6% sucrose, and 5 ppm each of 2, 4-Dichlorophenoxyacetic acid (2, 4-D) and Giberellic acid (GA3). Upon shifting to proliferation medium (RO with 6% sucrose, 5 ppm each of 2, 4-D and GA3, 400 mgL-1of glutamine and 20% v/v coconut water) pro-globular and globular embryos were formed within 4–5 weeks. Further development of somatic embryos through early heart, late heart and cotyledonary stages occurred in conversion medium (half strength B5 salts, full RO organics, 5 ppm of Indole-3-Acetic Acid (IAA), 20% coconut water and 200 mgL-1 of casein hydrolysate). Maturation of embryos was obtained by using 0.01 mg L-1of Abscisic acid (ABA) and 100 mg L-1of Polyethylene glycol (PEG). Germination of embryos with shoot and root initiation was observed in the presence of 5 ppm of zeatin. Our results show that somatic embryogenesis can be used as an alternative method to conventional propagation methods for rapid multiplication of uniform planting material in polyembryonic mango cultivars.