The astringency types of fruit-bearing offspring were identified by a sensory test and observations of flesh color. The astringency type/non-astringency types of offspring were distinguished by determining whether the fruit’s flesh could or could not bekept in the mouth. For pollination-variant cultivars, fruits with many seeds were determined to be non-astringent, and fruits with only a few seeds were astringent and had many brown specks around the seeds. PCNA flesh was determined to be astringent irrespective of the number of seeds, with or without brown specks.
Total DNA was extracted from ca. 1 cm2of young leaves sampled from each 1-year-old seedling or grafted scion from offspring plants using the Nucleon Phytopure plant DNA extraction kit (GEHealthcare Biosciences, USA).Two PCR primer combinations (i.e., E4/A2r and 7H9F/AST-R; Table 1) were used to distinguish between PCNA and non-PCNA offspring derived from progeny A. Primer A2r was designed based on the right-end sequences of the A2region (Kanzaki et al., 2009;GenBank accession number AB428738; see Fig. 2), and the E4/A2rcombination detects A2specifically (Fig. 3). The 7H9F/AST-R combination detects both A2and A3(Kanzaki et al., 2010, seeFigs. 2 and 3). PCR was performed on a total volume of 10 L containing 0.2 mM of each dNTP, 0.25 U of Ex Taq (Takara Bio), 0.5 M of each primer, 1× reaction buffer, and 50 ng of the total DNA sample. The PCR conditions were as follows: initial denaturation at 94◦C for 30 s; 35 cycles for E4/A2r or 40 cycles for 7H9F/AST-Rat 94◦C for 20 s; 56◦C for 20 s; and 72◦C for 30 s for 7H9F/AST-Rand 2 min for E4/A2r; and a final additional extension at 72◦C for 5 min. The amplified PCR products were separated on a 2% agarose gel and visualized by staining with ethidium bromide.