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The effects on fruit set of adding forchlorfenuron (CPPU) to media in which pollen grains were suspended and used for spray pollination was investigated in ‘Hosui’ japanese pear (Pyrus pyrifolia). The percentages of fruit set after spray pollination were lower than those after hand pollination; however, media with 2 or 10 mg·L⁻¹ CPPU used for spray pollination resulted in greater percentages of fruit set than media without CPPU. The media with CPPU also resulted in higher levels of pollen germination compared with the medium without CPPU; however, the number of seeds per fruit with CPPU treatment tended to be almost the same or less than for fruit without CPPU treatment. From these results, the higher levels of fruit set by CPPU might not be due to the high germination rate of the pollen grains but due to the induction of partial parthenocarpic properties. The medium with 10 mg·L⁻¹ CPPU gave the highest levels of fruit set, but the fruit had abnormally thickened and enlarged calyxes, and the fruit shape tended to be deformed at ≈21 days after flowering. In addition, all of the harvested fruit were calyx-perpetual fruit in which the calyx remains until harvest time. Fruit treated with 2 mg·L⁻¹ CPPU also yielded calyx-perpetual fruit with high frequency, but the fruit had normal calyxes and the fruit shape tended to be more normal. Thus, we conducted experiments focusing on the medium containing 2 mg·L⁻¹ CPPU. Although the results were variable from year to year, more than 70% of hand-pollinated flowers set fruit during the 3-year study; this level of fruit production is sufficient for practical use. Thus, spray pollination using a medium with 2 mg·L⁻¹ CPPU is an acceptable method for pollinating ‘Hosui’ japanese pear.

The effect of 9-hydroxy-10-oxo-12(Z), 15(Z)-octadecadienoic acid (KODA) on endodormancy breaking was studied in flower buds of japanese pear (Pyrus pyrifolia Nakai). The optimal concentration of KODA (100 μM) for endodormancy breaking was established over a 2-year period during the endodormancy stage of 2006 and 2007 in japanese pear cultivars Kosui, Natsushizuku, and Hosui. The effect of KODA on endodormancy breaking in flower buds was similar between ‘Natsushizuku’ and ‘Kosui’ but somewhat lower in ‘Hosui’. These results indicate that KODA can be an effective agent for promoting endodormancy breaking of flower buds in ‘Natsushizuku’ and ‘Kosui’. Although not as effective as hydrogen cyanamide, KODA may be preferable at late endodormancy stages because it has no apparent phytotoxicity.

To understand the role of the MIKC-type dormancy-associated MADS-box (DAM) genes in the regulation of endodormancy in japanese pear (Pyrus pyrifolia), we isolated two DAM genes from ‘Kosui’ and characterized their expression throughout the seasonal endodormancy phases in ‘Kosui’, as well as in TP-85–119 taiwanese pear (P. pyrifolia), which is a less dormant type. Several copies of the corresponding DAM genes are present in the P. pyrifolia genome. Rapid amplification of cDNA ends enabled the isolation of two full-length cDNAs, designated as PpMADS13–1 and PpMADS13–2, with complete open reading frames encoding 227 and 234 amino acids, respectively. Multialignment of the two ‘Kosui’ and the database DAM genes (based on the deduced amino acid sequences) showed that PpMADS13–1 and PpMADS13–2 were highly identical to the Rosaceae DAM genes and encoded the conserved domains characteristic of other MIKC-type MADS-box genes. The phylogenetic relationships showed that PpMADS13–1 and PpMADS13–2 were more closely related to the Prunus DAM, though they formed a unique subclade. The specific expression analysis of PpMADS13–1 and PpMADS13–2 by real-time polymerase chain reaction showed that both DAM genes are gradually down-regulated concomitant with endodormancy breaking. PpMADS13–1 and PpMADS13–2 showed similar fluctuations in expression patterns, although PpMADS13–2 was more highly expressed relative to PpMADS13–1. The expression of PpMADS13–1 and PpMADS13–2 in the less dormant taiwanese pear, TP-85–119, was quite low (nearly zero level), which is consistent with a down-regulated pattern of expression of the DAM genes in japanese pear, peach (Prunus persica), and japanese apricot (Prunus mume). Differential genomic DNA methylation patterns detected in PpMADS13–1 and PpMADS13–2 were not concomitant with seasonal endodormancy transition phases, suggesting that DNA methylation in these loci under investigation may not be linked to endodormancy progression in ‘Kosui’.