A New Plant Breeding Technique Using ALSV Vectors to Shorten the Breeding Periods of Fruit Trees

Abstract

Fruit trees have a long juvenile phase. For example, the juvenile phase of apple lasts for 6-12 years and is a serious constraint for creating new varieties by breeding based on crossing and selection. In this chapter, we report a novel technology using the apple latent spherical virus (ALSV) vector to accelerate flowering time and life cycle in apple and pear seedlings. Inoculation of apple and pear cotyledons immediately after germination with ALSV-AtFT/ MdTFL1 concurrently expressing Arabidopsis FLOWERING LOCUS T (AtFT) gene and suppressing apple TERMINAL FLOWER 1-1 (MdTFL1-1) gene can shorten the period from seeding to flowering to 1.5-3 months after germination and generation times in order to obtain next-generation seeds in 1 year or less. Most next-generation seedlings obtained from ALSV vector-infected plants were free of the virus. We also developed a method for eliminating ALSV vectors from infected apple and pear plants by only high-temperature treatment. A method combining the promotion of flowering in apple and pear by ALSV vector with an ALSV elimination technique is expected to see future application as a new plant breeding technique that can significantly shorten the breeding periods of apple and pear.

Apple Russet Ring and Apple Green Crinkle Diseases: Fulfillment of Koch’s Postulates by Virome Analysis, Amplification of Full-Length cDNA of Viral Genomes, in vitro Transcription of Infectious Viral RNAs, and Reproduction of Symptoms on Fruits of Apple Trees Inoculated With Viral RNAs

“…2) ( Figure 2A , right). Though these apple seedlings were co-infected with ACLSV-RRACV2 and ALSV-AtFT/MdTFL1, ALSV-AtFT/MdTFL1 has never caused any symptoms in both leaves and fruits of infected apple seedlings ( Yamagishi and Yoshikawa, 2016 ), and it is most likely that the symptoms observed were induced by RRACV2 infection. No symptoms were observed on either leaves or fruits of apple seedlings infected with RRACV1, RRACV3, or RRACV5.…”

“…However, it generally takes at least 6–7 years for apple seedlings to bloom. For this reason, we used virus-induced flowering (VIF) system using the ALSV vector ( Yamagishi et al, 2014 , 2016 ; Yamagishi and Yoshikawa, 2016 ) for symptom reproduction on the apple fruits. VIF using the ALSV vector can reduce flowering 2 months after germination and lead to fruit formation within 1 year in apple seedlings ( Yamagishi et al, 2014 ).…”

“…In this study, we conducted the following series of experiments to determine the causal viruses (variants) of the apple russet ring and green crinkle diseases: (1) comprehensive analysis by next-generation sequencing (NGS) of all viruses in each apple tree affected by russet ring or green crinkle diseases, (2) amplification of the full-length genomic DNA of viruses using primers containing the T3 promoter and the in vitro transcription of infectious viral RNAs, (3) inoculation of virus RNA transcripts to herbaceous and apple plants, (4) analysis of sequence variants of viruses in infected plants, (5) back-inoculation of sequence variants of candidate viruses to apple seedlings combined with virus-induced flowering technology using the apple latent spherical virus (ALSV) vector ( Yamagishi et al, 2014 , 2016 ; Yamagishi and Yoshikawa, 2016 ), and (6) reproduction of symptoms on the fruits of apple trees inoculated with sequence variants and the re-isolation of each virus variant from apples showing fruit symptoms. From the results of the above studies, we were able to prove the specific sequence variants of the causal viruses of the two apple diseases.…”