EMBRYO RESCUE THROUGH IN OVULO CULTURE IN HELIANTHUS

In vitro rescuing of interspecific embryos between sunflower (Helianthus annuus L.) and other Helianthus species has been limited by the inability to culture embryos less developed than the vascular stage. The objective of this research was to develop a technique for rescuing X Helianthus embryos at an earlier growth stage. This objective was achieved by culturing the embryos for 1 wk in ovulo on artificial agar media. During that culture period, 51 to 84% of the embryos from five sunflower genotypes developed to the vascular stage like in vivo sib-embryos of the same age left as checks on greenhouse plants. Survival and development of sunflower embryos grown in ovulo were not affected by the salt composition of the four media tested (B5, B5S, MS and NN), or benefited by high sucrose levels (90 or 120g L-1). The technique of in ovulo culture resulted in rescuing 52% of H. annuus X H. maximiliani Schrad. hybrid embryos. This indicates that sunflower ovules cultured on standard media fulfilled the requirements of Helianthus hybrid embryos at an early stage of development. After excision from the ovule and subsequent culturing for 2 wk on fresh media with the same composition, 40 to 60% of H. annuus embryos and 25% of H. annuus X H. maximiliani hybrid embryos germinated into plantlets. Six H. annuus X H. maximiliani plantlets survived transfer to the greenhouse and grew into flowering plants that exhibited traits from both parents. These are the first reported hybrid plants between H. annuus and H. maximiliani using sunflower as the female parent.