2022 年 91 巻 3 号 p. 286-295
This study was conducted to obtain insights into unreduced gamete formation in Citrus tamurana hort. ex Tanaka ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’, inferred from unreduced pollen and egg cell genotype information. To establish a method for fine genotyping of tissues with higher ploidy levels (up to hexaploidy), we first identified heterozygous single-nucleotide polymorphism (SNP) markers (CiC4240-04 and CiC5327-03) with close genetic distance to centromeres of ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’. Fluorescence intensity-based standard plots were generated using real-time qPCR to accurately genotype these SNP markers on a two-dimensional panel. Ten normal seeds were obtained from fertilization of unreduced gametes by self-pollination of ‘Nishiuchi Konatsu’ or ‘Hyuganatsu’ × ‘Nishiuchi Konatsu’ crosses. Inner seed coats with hexaploid endosperm tissues and tetraploid embryos were obtained from normal seeds, and their CiC4240-04 and CiC5327-03 genotypes were determined with standard plots using real-time qPCR. Genotypes of unreduced pollen and egg cells were uniquely determined from the genotype information of 6x endosperms and 4x embryos, and the unreduced gamete formation process was inferred. The results showed that unreduced pollen formation was almost entirely due to first division restitution (FDR); therefore, it was concluded that FDR was the dominant formation process for unreduced pollen in ‘Nishiuchi Konatsu’. In contrast, there was no dominant process for the formation of unreduced egg cells because both FDR and second division restitution occurred in almost the same number of individuals with unreduced egg cells.
