Optimizing In Vitro Organogenesis in Sunflower (Helianthus annuus L.) Using Cotyledon and Root Node Explants

Sunflower (Helianthus annuus L.) is widely recognized as a recalcitrant species in tissue culture, which severely restricts its micropropagation and genetic transformation efficiency. To address this limitation, this study establishes a novel, highly efficient, and reproducible in vitro organogenesis protocol tailored for the commercial hybrid 'Sun 2239 CL. Cotyledon node and root node explants were cultured in MS medium supplemented with various concentrations of BAP (0.00, 0.25, 0.50, 0.75, and 1.00 mg/L) in combination with NAA (0.10 mg/L). The results indicated that cotyledon node explants exhibited the highest shoot regeneration potential, with the highest shoot regeneration (3.0 shoots per explant) observed at BAP 0.25 mg/L + NAA 0.10 mg/L. Shoot length varied between 3.33 cm and 11.00 cm, with the longest shoots observed in the control group. Root node explants did not produce adventitious shoots but showed callus formation, with the highest callus weight (1.60 g) at BAP 1.00 mg/L + NAA 0.10 mg/L. These findings confirm that cotyledon node explants are more suitable for in vitro sunflower regeneration, providing a promising approach for the genetic improvement and micropropagation of sunflower.