The practical use of marker-assisted selection (MAS) is limited in conifers because of the difficulty with developing markers due to a rapid decrease in linkage disequilibrium, the limited genomic information available, and the diverse genetic backgrounds among the breeding material collections. First, in this study, two families were produced by artificial crossing between two male-sterile trees, ‘Shindai11’ and ‘Shindai12’, and a plus tree, ‘Suzu-2’ (Ms1/ms1) (S11-S and S12-S families, respectively). The segregation ratio between the male-sterile and male-fertile trees did not deviate significantly from the expected 1:1 ratio in either family. These results clearly suggested that the male-sterile gene of ‘Shindai11’ and ‘Shindai12’ is MALE STERILITY 1 (MS1). Since it is difficult to understand the relative positions of each marker, due to the lack of a linkage map which all the closely linked markers previously reported are mapped on, we constructed a partial linkage map of the region encompassing MS1 using the S11-S and S12-S families. For the S11-S and S12-S families, 19 and 18 markers were mapped onto the partial linkage maps of the MS1 region, respectively. There was collinearity (conserved gene order) between the two partial linkage maps. Two markers (CJt020762_ms1-1 and reCj19250_2335) were mapped to the same position as the MS1 locus on both maps. Of these markers, we used CJt020762 for the MAS in this study. According to the MAS results for 650 trees from six prefectures of Japan (603 trees from breeding materials and 47 trees from the Ishinomaki natural population), five trees in Niigata Prefecture and one tree in Yamagata Prefecture had heterozygous ms1-1, and three trees in Miyagi Prefecture had heterozygous ms1-2. The results obtained in this study suggested that ms1-1 and ms1-2 have different geographical distributions. Since MAS can be used effectively to reduce the labor and time required for selection of trees with a male-sterile gene, the research should help ensure that the quantity of breeding materials will increase to assist future tree-breeding efforts.

Practical use of marker-assisted selection (MAS) is limited in conifers because of the difficulty with developing markers due to a rapid decrease in linkage disequilibrium, the limited genomic information available, and the diverse genetic backgrounds among breeding material collections. First, in this study, two families were produced by artificial crossing between two male-sterile trees, Shindai11 and Shindai12, and a plus tree, Suzu-2 (Ms1/ms1) (S11-S and S12-S families, respectively). The segregation ratio between male-sterile and male-fertile trees did not deviate significantly from the expected 1:1 ratio in either family. These results clearly suggested that the male-sterile gene of Shindai11 and Shindai12 is MALE STERALITY 1(MS1). Because some markers reported previously have not been linkage mapped, we constructed a partial linkage map of the region encompassing MS1 using the S11-S and S12-S families. For the S11-S and S12-S families, 19 and 18 markers were mapped onto the partial linkage maps of MS1 region, respectively. There was collinearity (conserved gene order) between the two partial linkage maps. Two markers (CJt020762_ms1-1 and reCj19250_2335) were mapped to the same position as the MS1 locus on both maps. Of these markers, we used CJt020762 for MAS in this study. According to the MAS results for 650 trees from six prefectures of Japan (603 trees from breeding materials and 47 trees from the Ishinomaki natural population), five trees in Niigata Prefecture and one tree in Yamagata Prefecture had heterozygous ms1-1, and three trees in Miyagi Prefecture had heterozygous ms1-2. The results obtained in this study suggested that there may be geographical hotspots for the ms1-1 and ms1-2 alleles. Because MAS can be used effectively to reduce the labor and time required for selection of trees with a male-sterile gene, the number of breeding materials should increase in the future.

No abstract

Sugi (Cryptomeria japonica D. Don) is an important forestry species in Japan. C. japonica ‘Spiralis’ is a mutant with twisted needles. The mutant is called Yore-sugi in Japan and is known as ‘Rasen’ in other countries. The twisted trait is regulated by a dominant gene called TWISTED NEEDLES, and it can be identified by observing the needles within 1 to 2 months after germination. The TWISTED NEEDLES gene may be useful for improving the efficiency of genome editing technology in C. japonica. In this study, we attempted to identify the linkage group of the TWISTED NEEDLES locus and investigate markers that sandwich this locus using the mapping family. First, we identified the linkage group containing the TWISTED NEEDLES locus based on the distortion from the expected segregation ratio using 32 mutant individuals of the mapping family. The segregation distortion showed that the TWISTED NEEDLES locus was located on the 11th linkage group (LG11). Next, a linkage map of LG11 was constructed based on genotype data from the single-nucleotide polymorphism (SNP) markers and double digested restriction site-associated DNA sequencing (ddRAD-seq) using 123 individuals of the MMY-1 family. On this map, six markers were located at the same position as the TWISTED NEEDLES locus. To investigate markers sandwiching the TWISTED NEEDLES locus, a partial linkage map around the TWISTED NEEDLES locus was constructed using 643 individuals of the MMY-1 family. The TWISTED NEEDLES locus was located in the 0.6 cM region between gSNP01822 and the other five markers (Contig_4705-179, Contig_4518-93, Contig_4398-118, gSNP04056, and Contig_4970-113).