Takashi Haji

Molecular characterization of S-RNase genes and S-genotypes in the Japanese apricot (Prunus mume Sieb. et Zucc.)

Abstract Three partial S-RNase genes, MSRN-1, MSRN-2, and MSRN-3, in the Japanese apricot (Prunusmume Sieb. et Zucc.) were isolated from the three cultivars Nankou, Gyokuei, and Kairyouuchidaume, respectively. The structural characteristics revealed that S-RNase genes from the Japanese apricot were in the T2/SRNase-type S-RNase family with five conserved regions (C1, C2, C3, RC4, and C5) and one variable region (RHV) as reported in the other rosaceous plants. In the phylogenetic tree of T2/S SRNase-type RNases, three S-RNase genes of the Japanese apricot did not form a species-specific subgroup but the Prunus subfamily did. At least seven S-allelic genes were present in the Japanese apricot, and S-genotypes of six representative cultivars, including Nankou, Gyokuei, Kairyouuchidaume, Baigou, Kagajizou, and Oushuku were first established in this study as S1S7, S2S6, S3S4, S3S6, S3S6 and S1S5, respectively. An extended elucidation of the S-genotype would contribute to a more efficient breeding program of the Japanese apricot.

Identification of QTLs for fruit quality traits in Japanese apples: QTLs for early ripening are tightly related to preharvest fruit drop

Many important apple (Malus × domestica Borkh.) fruit quality traits are regulated by multiple genes, and more information about quantitative trait loci (QTLs) for these traits is required for marker-assisted selection. In this study, we constructed genetic linkage maps of the Japanese apple cultivars ‘Orin’ and ‘Akane’ using F1 seedlings derived from a cross between these cultivars. The ‘Orin’ map consisted of 251 loci covering 17 linkage groups (LGs; total length 1095.3 cM), and the ‘Akane’ map consisted of 291 loci covering 18 LGs (total length 1098.2 cM). We performed QTL analysis for 16 important traits, and found that four QTLs related to harvest time explained about 70% of genetic variation, and these will be useful for marker-assisted selection. The QTL for early harvest time in LG15 was located very close to the QTL for preharvest fruit drop. The QTL for skin color depth was located around the position of MYB1 in LG9, which suggested that alleles harbored by ‘Akane’ are regulating red color depth with different degrees of effect. We also analyzed soluble solids and sugar component contents, and found that a QTL for soluble solids content in LG16 could be explained by the amount of sorbitol and fructose.

Study on Interspecific Hybridization among the Subgenera Amygdalus, Prunophora , and Cerasus

Interspecific crossing among the subgenera Amygdalus (Prunus persica, P. mira, P. dulcis, P. ferganensis, P. kansuensis, P. davidiana), Prunophora (P. salicina, P. cerasifera, P. mume, P. armeniaca), and Cerasus (P. tomentosa, P. japonica) was performed to determine their cross-compatibilities. In the combinations of species belonging to the subgenus Amygdalus, high fruit set averages were demonstrated, excluding the results when P. kansuensis was used as a seed parent. The pollination of species belonging to Prunophora and Cerasus by those of Amygdalus resulted in very few seeds. In contrast, fruit sets of Prunuphora species pollinated by Amygdalus fluctuated by cross combinations. P. cerasifera and P. salicina, when used as seed parents, bore a few seeds, but P. armeniaca and P. mume bore no seeds when pollinated by Amygdalus species. The cross using P. tomentosa as a seed or pollen parent resulted in very few fruit sets. On the other hand, several seeds were obtained from the cross between P. cerasifera and P. japonica. The pollination of P. japonica by P. cerasifera, P. dulcis, and P. mume also led to a relatively high rate of fruit sets.