Propagation of edible Dioscorea species in vitro

Abstract

The three yam species Dioscorea alata (greater yam), Dioscorea rotundata (lesser yam) and Dioscorea esculenta (whiteyam) are most commonly cultivated edible yams and are propagated vegetatively. The tubers are rich in carbohydrate andare better source of protein than other tuber crops. Continuous vegetative propagation through tuber sets, prevalence ofdisease, and low viability severely hinder productivity of yams. To overcome the limitations, experiments have beencarried out to optimize the culture conditions for in vitro propagation of different yam species. Nodal explants of fastgrowing vines and tuber sprouts of released varieties viz. Sree Shilpa of D. alata, Sree Subhra of D. rotundata and SreeLatha of D. esculenta were cultured in Murashige and Skoog (MS) media containing different combinations andconcentrations of growth regulators. Response was better with tuber sprouts. Percent explant response towards axillaryshoot 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 inmedia 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 shootsper 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). Regenerationwas 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%) usingHoagland nutrient prior to transplantation in sterilized soil: sand (1:1) mixture. Yield, tuber characters like starch contentand dry matter content as well as RAPD analysis shows homology between regenerants and the source plants. Thus thestudy on axillary shoot proliferation could affect faster production of disease free quality planting materials. Moreover theresults of the study on callusing and shoot organogenesis can have a greater impact in future bio-technological developmentof yams. These techniques may facilitate faster screening of large germplasm for superior transgenic lines.