Propagation of edible Dioscorea species in vitro

The three yam species Dioscorea alata (greater yam), Dioscorea rotundata (lesser yam) and Dioscorea esculenta (white yam) are most commonly cultivated edible yams and are propagated vegetatively. The tubers are rich in carbohydrate and are better source of protein than other tuber crops. Continuous vegetative propagation through tuber sets, prevalence of disease, and low viability severely hinder productivity of yams. To overcome the limitations, experiments have been carried out to optimize the culture conditions for in vitro propagation of different yam species. Nodal explants of fast growing vines and tuber sprouts of released varieties viz. Sree Shilpa of D. alata, Sree Subhra of D. rotundata and Sree Latha of D. esculenta were cultured in Murashige and Skoog (MS) media containing different combinations and concentrations of growth regulators. Response was better with tuber sprouts. Percent explant response towards axillary shoot proliferation was observed to be highest in D. esculenta (84%), followed by D. alata (68%) and D. rotundata (60%). Mean shoots per explant was recorded as high as 6.8 to 7.8 in D. rotundata and D. esculenta, respectively in media supplemented with relatively high concentration of Gibberellic acid (GA₃₎ (2 mg/L) and 1-Naphthaleneacetic acid (NAA) (0.5 mg/L) and low concentration of 6-Benzyl Adenine (BA)(1 mg/L) while D. alata showed highest mean shoots per explant (7.4 ± 0.78) in media with BA (2.5 mg/L), GA₃ (1 mg/L), NAA (0.25 mg/L) and 2,4-D (0.5 mg/L). Regeneration was also achieved through callusing and organogenesis. Shoot organogenesis could be enhanced (20–24%/50 mg callus) by optimizing concentrations of BA (2–2.5 mg/L). Field establishment was achieved in high frequency (85–90%) using Hoagland nutrient prior to transplantation in sterilized soil: sand (1:1) mixture. Yield, tuber characters like starch content and dry matter content as well as RAPD analysis shows homology between regenerants and the source plants. Thus the study on axillary shoot proliferation could affect faster production of disease free quality planting materials. Moreover the results of the study on callusing and shoot organogenesis can have a greater impact in future bio-technological development of yams. These techniques may facilitate faster screening of large germplasm for superior transgenic lines.