Preliminary Study on In vitro Conservation of Dioscorea bulbifera L. Virus-free Plantlet Germplasm and its Genetic Stability and Virus Change Rapid propagation ofMomordica grosvenori virus-free plantlets Establishment of Regeneration System of Leaves and Stems of Dioscorea bulbifera L. Virus-free Plantlets Rapid propagation technology of Dioscorea bulbifera virus-free plantlets