Ex vitro rooting: A low cost micropropagation technique for Tea (Camellia sinensis (L.) O. Kuntz) hybrids

Tea (Camellia sinensis (L.) O. Kuntz) hybrid seeds were obtained by crossing high yielding drought and stem canker tolerant cultivar TRI 3013 (female parent) with the cultivar DT 95 (male parent) which is moderately yielding and resistant to nematodes. Embryos of hybrid seeds were isolated and regenerated on MS medium supplemented with 3mgL−1 BAP (Benzylaminopurine), 0.5mgL−1 IBA (Indole-3-butyric acid), 8gL−1 agar and 30gL−1 sucrose (multiplication medium). Regenerated shoots were multiplied on the same medium by sub-culturing at 8 weeks intervals. Eight weeks old micro-shoots from 4th subculture were treated with 50mgL−1 IBA for 3h and effect of six different rooting mixes on ex vitro rooting was investigated. All the micro-shoots transferred to the rooting mix consisting of coir dust, soil and sand at 1:1:1 ratio (v/v) (ex vitro rooting mix) survived and produced a well developed root system.Effect of in vitro medium and in vitro culture duration on ex vitro rooting was investigated. Micro-shoots were transferred to multiplication medium or half MS medium devoid of growth regulators and cultured for 6, 8 or 10 weeks before transferring into ex vitro rooting mix with or without 50mgL−1 IBA treatment. All micro-shoots treated with IBA produced higher numbers of roots in ex vitro rooting mix irrespective of the in vitro medium composition. Shoots grown on multiplication medium produced higher number of roots compared to half MS medium without growth regulators. Root initiation increased significantly when the culture duration increased from 6 to 8 weeks. Ex vitro rooted micropropagated shoots had better growth under nursery conditions compared to conventionally propagated tea plants of the same age and could be transferred to the field at 18 months after the production of hybrid seeds, saving almost 5 years from a cultivar evaluation program. Ex vitro rooting of tea micro-shoots with simultaneous acclimatization reduced the cost of production of micropropagated plant by 71% compared to that of micropropagation with an in vitro rooting step.