IN VITRO culture establishment from hypocotyl and cotyledon explants of two Bangladeshi sunflower (Helianthus annuus L. ) varieties

Abstract

Sunflower (Helianthus annuus.L) is the world’s second most important oilseed crop. Plant tissue culture and gene transformation are the important tools for improvement of this crop. The purposes of this study are to optimize seed sterilization procedure, determine the most suitable and efficient explants along with their suitable age and size, and to optimize the hormonal concentration for shoot regeneration. Seeds being treated with 70% ethanol for 3 minutes and 14% Clorox for 20 minutes, with their testa being removed before being inoculated into the germination medium, were found to be optimum for the tissue culture technique. In this study, two varieties, BARI surjomukhi 2 and BRAC Hysun 33 were used as plant materials. Hypocotyls and cotyledons were excised from 5, 7 and 9 days and cultured on MS medium supplemented with eight different combinations of BAP and NAA hormones. The experiments were kept in 18/6 hour light/dark photoperiod at 26±2ºC. It was determined that MS medium supplemented with 1 mg/l BAP and 0.1 mg/l NAA is the best combination for 7 day old hypocotyl explants of both BARI surjomukhi-2 and BRAC Hysun 33 varieties. From 7 day old hypocotyl explants, the best shoot regeneration response of BARI surjomukhi-2 and BRAC Hysun 33 variety was 60% and 53.3%, with the best grown shoot that grew up to 2.08 cm and a of length 1.61 cm within 30 days of regeneration respectively. This clearly showed that MS medium supplemented with 1 mg/l BAP and 0.1 mg/l NAA is the best hormonal media combination for hypocotyl explants. Shoot regeneration efficiencies of the cotyledon explants on the same medium were lower in comparison with the hypocotyl explants. Cotyledon explants only grew large in size with time, but did not show any positive response like shoot regeneration. So, hypocotyls were proved to be better explants than cotyledons. In future, rooting at the base of the regenerated shoots will be tried to generate whole plantlet.