Establishment of tissue culture protocol of two Bangladeshi sunflower varieties (Helianthus annuus L.)

Abstract

Sunflower (Helianthus annuus L.) is an important commercially valuable crop with a high oil content. It is seed propagated, but poor germination, along with other abiotic and biotic factors pose problems in sunflower cultivation. Biotechnological techniques, such as, tissue culture and gene transfer systems have been used for improvement of most crops. This study aims to improve production of sunflower by optimising a tissue culture mediated regeneration protocol, to be used for micropropagation in future. Two Bangladeshi varieties: BARI Surjomukhi-2 and BRAC Hysun 33 were used here. In the present study, the effect of varying combinations of different concentrations of growth hormones on the formation of shoots, roots and flowers were demonstrated, followed by the acclimatisation of regenerated plantlets. Embryonic axes were obtained by removing the testa and excising 3-5 mm pieces from the proximal portion of the seeds. These were inoculated on MS medium supplemented with four different combinations of the hormones BAP and NAA, and were kept in a photoperiod of 18/6 hour dark/light, at a temperature of 26 ± 2°C. BRAC Hysun 33 showed best shoot formation in MS media supplemented with 1.0 mg/l BAP and 0.5 mg/l NAA (97.03%), while BARI Surjomukhi-2 gave best shoot formation in MS media supplemented with 3.0 mg/l BAP (80.00%). The regenerated shoots were transferred to rooting media that contained two different concentrations of the hormone IBA. Root formation occurred best on shoots that had been grown in MS with 1.0 mg/l BAP and 0.5 mg/l NAA for BRAC Hysun 33 and in MS with 3.0 mg/l BAP for BARI Surjomukhi-2. In relation to rooting hormone, there were no difference in percentage rooting between the two concentrations, though roots were bigger and formed faster in ½MS with 0.4 mg/l IBA. All the plantlets that formed roots were transferred to soil for hardening. Plants that formed roots in ½MS media with 0.4 mg/l IBA and underwent shooting on MS with 1.0 mg/l BAP and 0.5 mg/l NAA (for BRAC Hysun 33) or MS with 1.0 mg/l BAP and 0.1 mg/l NAA (for BARI Surjomukhi-2) survived better. BRAC Hysun 33 proved to be the best variety, giving the most surviving plantlets with tallest average height and more numbers of flowers, buds and viable seeds.