Micropropagation of mulberry (Morus indica L.) using explants from mature tree: Effects of plant growth regulators on shoot multiplication and rooting

A reliable procedure for in vitro propagation was standardized with shoot tip and nodal explants collected from a 4-year old tree of Morus indica cv. Kalimpong Local-1, a clonal selection from West Bengal, India. Eighty-three percent contamination-free cultures were obtained with the treatment of 0.1% mercuric chloride for 10 min. An average multiplication rate of 2–4 folds was achieved on Murashige and Skoog's (MS) medium supplemented with 1 or 2 mg/l 6-benzylaminopurine (BAP). Thidiazuron (TDZ) (0.5 and 1 mg/l) enhanced the multiplication rate to up to 4-5-fold, but with high callus induction. Incorporation of 0.1 mg/l gibberellic acid (GA3) along with 1 mg/l BAP and 0.1 mg/l Indole-3-butyric acid (IBA) further enhanced the multiplication rate up to 6-fold per subculture, producing maximum shoot number (4.7) of maximum shoot length (4.2). In vitro shoots rooted on 1 mg/l Indole-3-acetic acid (IAA), IBA and α-naphthalene-acetic acid (NAA) resulting 42, 83 and 33% rooted shoots, respectively. Rooting was improved to 71, 100 and 50% when 4-week old shoots from IAA, IBA and NAA medium were transferred on MS medium with no growth regulator. This rooting protocol standardized in the present study ensured rooting of up to 100% shoots with very high no. of roots per shoot (5.4) and good root length (3.7) which was not reported earlier on Morus spp. Rooted plantlets were hardened and established in pots, then to the soil with a survival rate of 80%.