Influence of sucrose and cytokinin stress on shoot regeneration in cotyledon culture of oilseed crop black sesame (Sesamum indicum L.)

This study involves the evaluation of in vitro shoot regeneration during cotyledon culture in black sesame ( Sesamum indicum L. cv. TMV3) under various concentrations of sucrose and cytokinin (BAP) in Murashige and Skoog (MS) nutrient medium. Cotyledon explants were cultured on MS basal medium supplemented with various concentrations of sucrose (2%, 4%, 6%, and 8%) and combinations of BAP (1.0mg/L, 2.5mg/L, 3.5mg/L, 4.5mg/L, 5.5mg/L, 6.5mg/L, and 7.5mg/L) and IAA (1.0mg/L). The multiple-shoot regeneration was achieved after 5-weeks of culture initiation. Significantly, the maximum mean percentage of shoot regeneration (75±4.3%) and number of shoots/explants (1.3±0.8) was recorded with explants that were treated with MS medium supplemented with sucrose (4%) including BAP (3.5mg/L) and IAA (1.0mg/L) while the high concentration (8%) of sucrose was proved to be completely ineffective to induce shoot regeneration on same nutrient medium (BAP+IAA). Furthermore, results indicate that sucrose (8%) could be observed slightly effective for shoot regeneration with higher concentrations of BAP (6.5mg/L and 7.5mg/L) in presence of IAA (1.0mg/L). Significantly, cotyledon explants that were growing with low concentration of sucrose (2%) were failed to show regeneration if BAP concentration exceeds to (5.5mg/L). Moreover, optimal frequency of shoot regeneration (64.4±1.4%) could be recorded with 2% of sucrose in presence of lower concentration of BAP (2.5mg/L) and IAA (1.0mg/L). The regenerated shoots were further transferred to half strength of MS medium supplemented with various concentrations of IBA (0.5, 1.0, and 1.5mg/L) for induction of roots and complete plantlets formation. Significantly, optimal mean percentage of shoots showing root formation (90±2.8%) was obtained in shoots regenerated with 4% of sucrose in presence of IBA (1.0mg/L) and shoot-root length ratio was recorded to be the maximum (4.2±0.11cm/2.81±0.12cm). However, in contrast, shoots that were regenerated on medium containing high sucrose (8%) with high BAP (7.5mg/L) + IAA (1.0mg/L) were found to exhibit lack of root formation irrespective of IBA concentrations. Present study reports that sucrose and BAP contents of the medium influences the sesame cotyledon explants regeneration. In comparison to control (2%) of sucrose, increase in sucrose concentration (4%) with BAP (3.5mg/L) and IAA (1.0mg/L) proved to be the optimal combination for shoot regeneration and moreover, regenerated shoots could induce the maximum root length in MS1/2 medium supplemented with IBA (1.0mg/L). In contrast, the IBA medium containing very high concentration of sucrose (8%) was turned out to be completely inhibitory for root regeneration. Study indicates that concentration of sucrose and BAP cytokinin in nutrient medium influences considerably the regeneration potential of explants tissues in black sesame oil crop. Moreover, the regenerated plantlets were further gradually acclimatized and transferred to plastic cup soil under the greenhouse conditions.