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

Fruit trees have a long juvenile phase. For example, the juvenile phase of apple (Malus x domestica) generally lasts for 5-12years 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 1year, 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 Arabidopsis FLOWERING LOCUS T gene (AtFT) and silencing of apple TERMINAL FLOWER 1 gene (MdTFL1-1) using an Apple latent spherical virus (ALSV) vector (ALSV-AtFT/MdTFL1) to accelerate flowering time and life cycle in apple seedlings. When apple cotyledons were inoculated with ALSV-AtFT/MdTFL1 immediately after germination, more than 90% of infected seedlings started flowering within 1.5-3months, 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-AtFT/MdTFL1 inoculation successfully reduced the time required for completion of the apple life cycle to 1year 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.