Development of pollination and in vitro germination techniques to improve the hybridization in Hydrangea spp.

Abstract

Hydrangea is a genus of ornamental plants which is gaining new markets mainly as a fresh or dried cut flower, but it is also important as a pot plant and for landscaping. To expand its market, new hybrids should be developed. To increase the hybridization efficiency, some techniques were developed and tested: i) evaluation of two pollination systems; ii) comparison among fruit-cut systems before in vitro cultivation to develop embryos and to allow the growth of new genotypes; iii) evaluation of seed disinfection systems for in vitro germination; iv) sowing systems using seeds and fruits from stocks cultivated in two environments. To increase inter- and intra-specific hybridization, pollination by dispersion of previously collected pollen on the top of a corymb by a brush was more effective than pollination using the corymb itself as a brush. A longitudinal cut system can be considered the best treatment to be applied on fruits before in vitro cultivation to allow growth of seedlings. Sterilization of seeds can be done by immersion in a solution of commercial bleach for 5 minutes on MS culture medium with PPM®. When stocks are cultivated in greenhouses, in vitro contamination is lower and seeds have a better rate of germination. The results of these experiments were applied in a breeding program on Hydrangea using sexual crosses.