CALLUS INDUCTION AND ORGANOGENESIS IN DIOSCOREA SPECIES

Hitherto, there is little information on species or line and organ specificity concerning callus and organ formation, plant regeneration from calli and proliferation from explants in yam species. To address, we examined variation in species/organ specificity for callus induction and organogenesis using three yam species, i.e. Dioscorea esculenta BURK., D. rotundata POIR. and D. alata L. Axillary buds or shoot tips and single-node segments with one or two axillary buds were inoculated onto the culture media containing various combinations of plant hormones. Using axillary buds, D. esculenta acc. LE 030 produced calli on MS medium containing 2.0 mg/l NAA in combination with 0.0, 0.2 and 0.5 mg/l BA followed by green spot (45 to 75%), shoot (20 fo 30%) and root (20 to 90%) formation from calli. Similarly, D. alata L. cv. Farm Lisbon produced calli only on MS medium containing 1.0 mg/l BA and 2.O mg/l NAA followed by high green spot (75%), shoot (50%) and root (10%) formation from the calli. On the other hand, two accessions of D. rotundata i.e. HR 018 and 020 produced calli followed by green spot (13 to 100%) and root (15 to 85%), but no shoot formation from the calli. Using single-node segments, two accessions of D. esculenta produced shoots at an average of 2.8 directly from nodal explant without callus formation on MS medium containing 0.l mg/l NAA and 0.2 mg/l BA. Similarly, two accessions of D. rotundata produced shoots at an average of 3.2 to 4.8 on MS medium containing 1.0 to 2.0 mg/l and 0.2 to 2.0 mg/l BA. However, two cultivars of D. alata and two accessions of D. rotundata produced at an average of 4.0 and 6.0 shoots, respectively through the proliferation of bud on MS medium containing 15.O mg/l adenine sulfate. This proliferation was not affected by the addition of NAA at 0.1, 0.5 and 1.0 mg/l NAA. The present experiment showed species or line and organ specificity for callus and organ formation and plant regeneration from calli and direct proliferation from axillary buds. Particularly, it is important that D. alata with poor seed formation regenerated plants from calli and also directly from single-node segment through the proliferation of axillary buds.