Rhizogenesis of regenerated shoot in Bangladeshi Sunflower (Helianthus annuus L.) varieties

Abstract

Sunflower (Helianthus annuus L.) is a highly nutritious oil-producing crop of Bangladesh. But the yield of this crop is disrupted by several biotic and abiotic factors. Application of biotechnological techniques is necessary for the improvement of this plant. The purpose of this study was to establish a tissue culture mediated plant regeneration protocol for two Bangladeshi varieties, namely, BARI Surjomukhi 2 and BRAC Hysun 33. Embryonic axis and hypocotyl were the two explants used from these selected varieties. Suitability and regeneration capacity of these explants, optimization of the hormone supplementation for shoot and root formation and following acclimatization stage of the regenerated plantlets were accomplished in this study. Hypocotyl explants were excised from (3-9) days old seedling and for embryonic axis, proximal portion of the seed was excised before culturing on MS medium supplemented with ten different combinations of BAP and NAA. For embryonic axis explants, BAP singly gave direct regeneration and BAP combined with NAA showed indirect regeneration in both the sunflower varieties. The highest shoot regeneration (66.67%) was found in MS media supplemented with 2.0 mg/l BAP in BRAC Hysun 33 variety. In case of BARI Surjomukhi 2 variety the regeneration rate was 46.67%. To obtain proper shoot length, a shoot elongation medium, full strength MS with 2.0 mg/l BAP and 0.1mg/l GA3 was used. At the rooting stage, three concentrations of IBA were examined, among them 1.0 mg/l IBA showed better root formation capacity. All the rooted plantlets were transferred to soil for hardening and BRAC Hysun 33 variety gave highest survival rate at this stage. So, it can be determined that in vitro regeneration potential of BRAC Hysun 33 variety is better compared to BARI Surjomukhi 2 variety. Shoot regeneration efficiencies of another explant, hypocotyls on the same hormonal treatments were found lower in comparison with the embryonic axis explants. Hypocotyl explants of both the varieties produced shoots only on 1.0 mg/l BAP containing MS media and BARI Surjomukhi 2 variety showed better regeneration response than BRAC Hysun variety. Further studies are required to modify the acclimatization stage of the regenerated plantlets of sunflower.