Regeneration of three sweet potato (Ipomea batatas (L.)) accessions via meristem, Nodal and callus induction

In vitro regeneration of three sweet potato accessions UE007, UK-BNARI and SA-BNARI using meristem, nodal cuttings or callus induction was studied. Meristematic explants cultured on Murashige and Skoog (1962) basal medium supplemented with low concentration of benzylaminopurine (BAP) or kinetin resulted in callus with or without shoot development which delayed shoot emergence. The degree of callus development increased as the concentration of the cytokinin in the culture medium increased. Although, callus development was comparatively lower on kinetin amended medium than BAP amended medium, Murashige and Skoog medium supplemented with 0.25mg/1BAP had the highest shoot induction (80%). For further differentiation of callus or shoots into distinct stem and leaves, the culture were transferred into fresh MS medium supplemented with 0.25mg/1 BAP, 0.1 mg/1 NAA and 0.1 mg/1 Gibberellic acid (GA3. To overcome the delay in shoot initiation using meristem culture, nodal cuttings of sweet potato were used as explants and cultured on MS medium amended with 0.3 - 0.9mg/1 BAP. All explants cultured on 0.3 or 0.6mg/1 BAP developed shoots. Furthermore, liquid MS medium amended with 0.25mg/1 BAP, 0.1mg/I NAA, and 0.1mg/1 GA3 also enhanced early shoot development from nodal cutting explants compared to solid culture. Post flask acclimatisation of meristem or nodal cutting-derived plantlets showed that meristem derived plantlets were better acclimatised than nodal cutting plants due to vigorous root development leading to higher percentage survival in pots and subsequent tuber production. Callusogenesis was achieved when leaf lobe explants were cultured on CLC/ Ipomoea medium supplemented with 1.0 - 4.0mg/1 2,4-D with 4.0mg/1 2,4-D being the optimal concentration. However, the calli were non-embryogenic and therefore could not produce embryos when transferred to 0.1mg/1 BAP amended medium but rather produced either single or multiple shoots. The highest percentage shoot (83.3%) was obtained from 4.0mg/1 2,4-D-derived callus. The successful regeneration of sweet potato plantlets in vitro using meristem and nodal cutting explants as well as via indirect shoot development via a callus phase could be used to complement conventional propagation methods and integration into plant breeding programmes for sweet potato. (au)