Abstract: Culture of unfertilized ovules in sunflower (Helianthus annuus L.) could be induced to form parthenogenetic embryoids, endothelial embryoids and integumentary calli. Various factors exerted regulatory influences on the production of these structures. The key factors were exogenous hormone, sucrose concentration and cold-pretreatment. In hormone-free condition, parthenogenesis was promoted without any occurence of somatic embryoids or calli. Addition of exogenous hormone MCPA induced proliferation of sporophytic tissue and meanwhile, reduced the induction frequency of parthenogenesis. Relatively high sucrose level favored the Froduction of parthenogenetic embryoids. Reducing sucrose concentration favored the integumentary calli. The optimal sucrose concentration for endothelial embryoids was intermediate between them. Cold-pretreatment also played an effective role in promoting parthenogenesis and inhibiting integumentary calli. By combining these three factors, we were able to. work out a culture technique which significantly enhanced the inductionfrequency and growth. of parthenogenetic embryoids and completely eliminated somatic embryoids and calli.

Key words: Sunflower, Ovule culture, In vitro parthenogenesis, Embryoid