Virus-Induced Flowering by Apple Latent Spherical Virus Vector: Effective Use to Accelerate Breeding of Grapevine

Apple latent spherical virus (ALSV) was successfully used in promoting flowering (virus-induced flowering, VIF) in apple and pear seedlings. In this paper, we report the use of ALSV vectors for VIF in seedlings and in vitro cultures of grapevine. After adjusting experimental conditions for biolistic inoculation of virus RNA, ALSV efficiently infected not only progeny seedlings of Vitis spp. 'Koshu,' but also in vitro cultures of V. vinifera 'Neo Muscat' without inducing viral symptoms. The grapevine seedlings and in vitro cultures inoculated with an ALSV vector expressing the 'florigen' gene (Arabidopsis Flowering locus T, AtFT) started to set floral buds 20-30 days after inoculation. This VIF technology was successfully used to promote flowering and produce grapes with viable seeds in in vitro cultures of F-1 hybrids from crosses between V. ficifolia and V. vinifera and made it possible to analyze the quality of fruits within a year after germination. High-temperature (37 degrees C) treatment of ALSV-infected grapevine disabled virus movement to newly growing tissue to obtain ALSV-free shoots. Thus, the VIF using ALSV vectors can be used to shorten the generation time of grapevine seedlings and accelerate breeding of grapevines with desired traits.