Reduced generation time of apple seedlings to within a year by means of a plant virus vector: a new plant‐breeding technique with no transmission of genetic modification to the next generation

Summary Fruit trees have a long juvenile phase. For example, the juvenile phase of apple ( M alus × domestica ) generally lasts for 5–12 years and is a serious constraint for genetic analysis and for creating new apple cultivars through cross‐breeding. If modification of the genes involved in the transition from the juvenile phase to the adult phase can enable apple to complete its life cycle within 1 year, as seen in herbaceous plants, a significant enhancement in apple breeding will be realized. Here, we report a novel technology that simultaneously promotes expression of A rabidopsis FLOWERING LOCUS T gene ( At FT ) and silencing of apple TERMINAL FLOWER 1 gene ( Md TFL 1‐1 ) using an A pple latent spherical virus ( ALSV ) vector ( ALSV ‐At FT /Md TFL 1) to accelerate flowering time and life cycle in apple seedlings. When apple cotyledons were inoculated with ALSV ‐At FT /Md TFL 1 immediately after germination, more than 90% of infected seedlings started flowering within 1.5–3 months, and almost all early‐flowering seedlings continuously produced flower buds on the lateral and axillary shoots. Cross‐pollination between early‐flowering apple plants produced fruits with seeds, indicating that ALSV ‐At FT /Md TFL 1 inoculation successfully reduced the time required for completion of the apple life cycle to 1 year or less. Apple latent spherical virus was not transmitted via seeds to successive progenies in most cases, and thus, this method will serve as a new breeding technique that does not pass genetic modification to the next generation.