GENETIC-TRANSFORMATION AND REGENERATION OF MATURE TISSUES OF WOODY FRUIT PLANTS BYPASSING THE JUVENILE STAGE

Regeneration and transformation systems from mature plant material of woody fruit species have to be achieved as a necessary requirement for the introduction of useful genes into specific cultivars and the rapi d evaluation of resulting horticultural traits. We report here, for th e first time, a procedure for genetic transformation and regeneration of mature tissues of woody plants that overcomes the long juvenile per iods and high heterozygosity that are characteristic of most of these species. An improved regeneration frequency from mature explants was o btained by invigoration of the plant material through grafting of matu re buds on juvenile seedlings. Co-cultivation of the explants in feede rplates after inoculation with Agrobacterium tumefaciens resulted in e nhanced transformation frequencies. Furthermore, in vitro shoot-tip gr afting of the regenerated mature shoots on seedling rootstocks provide d a rapid and efficient system for plant production. Citrus is the mos t extensively grown fruit crop worldwide and sweet orange (Citrus sine nsis L. Osbeck) accounts for approximately 70% of the Citrus total pro duction. Mature transgenic sweet orange plants have been obtained, whi ch flowered and bore fruit in 14 months.