In vitro culture has become a useful tool for studies concerning the assessment of physiological and biochemical factors controlling floral morphogenesis. For sunflower, in vitro techniques starting from different explants yield good results on culture initiation and plant regeneration. Although inflorescence generation on cultured shoots is sometimes achieved there are no reports about in vitro florets developed from cultured young capitula. This work describes a protocol for the in vitro culture of sunflower reproductive meristems where floral organogenesis can be expressed. Experiments were carried out using undifferentiated sunflower capitula excised from plants grown under greenhouse conditions. White (W) and Linsmaier and Skoog (LS) culture media were compared. LS medium induced a comparatively large capitula receptacle area expansion, reduced the explant hyperhydration and calli formation and was chosen for further experiments. The presence of casein hydrolysate (CH) in LS culture media was tested resulting in reduced surgical stress and recovery of explants. The addition of Kinetin to LS medium plus CH proved to induce differentiation of new primordia at the capitulum generative front. Explants cultured with 0.1 mg l-1 Kinetin only differentiated mother bract primordia. Explants cultured with 1 mg l-1 Kinetin showed larger expansion of the receptacle area and new floret primordia did not differentiate their mother bract. Intermediate levels of kinetin (0.5 and 0.8 mg l-1) were tested in addition to two levels of IAA (1.3 and 2.5 mg l-1). The combination 0.8 mg l-1 Kinetin and 2.5 mg l-1 IAA was capable of differentiating floret primordia that closely resembled those formed in the capitula developed in vivo.

capitulum; casein hydrolysate; floral morphogenesis; Helianthus; in vitro; kinetin; sunflower