To obtain fundamental data for using Natsuhaze and Aragenatsuhaze in the breeding and cultivation of blueberries, we examined the fruit growth characteristics and fruit components. Natsuhaze and Aragenatsuhaze had many fruits per fruit cluster compared with blueberry cultivars, and the fruit clusters were long and slender. Although the maturation period of the fruits within the same fruit cluster was different, the matured fruits did not fall for a long period. Therefore, this species may be harvested by cluster harvesting, as with grapes. The maturation periods of both Natsuhaze and Aragenatsuhaze were from September to November, one to three months later than the latest-maturing blueberry cultivars. Although the sugar-acid ratio in the fruits of Natsuhaze and Aragenatsuhaze was lower than in blueberry cultivars and the taste was inferior, the total anthocyanin content of fruits in Natsuhaze was about 6 times that of blueberries. The total polyphenol content, total proanthocyanidin content, and antioxidant activities showed high values in unripe fruits, and increased as maturity progressed in these species. Mature fruit of Aragenatsuhaze had 3 times more total polyphenols and 17 times more total proanthocyanidin than blueberry cultivars; it was suggested that total polyphenols including proanthocyanidin contribute to antioxidant activities. Natsuhaze and Aragenatsuhaze could be useful breeding materials for new cultivar production by expanding the crop season of blueberries, enabling cluster harvesting, and offering high biological functionality.

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Some cultivars of loquat [Eriobotrya japonica (Thunb.) Lindl.; Rosaceae, Pyrinae] show gametophytic self-incompatibility controlled by a single, multi-allelic S locus, as in Japanese pear and apple. The S-genotype of loquat is an important factor for crossing and breeding. In this study, we tested a method to predict the S-genotype of some loquats by sequencer analysis. Sequencing revealed ten different band sizes. The nucleotide and amino acid sequences of five of these bands were identical to S-RNase sequences of loquat previously reported. Those of the other five bands were different from previous reports, but showed high-level homology with S-RNase sequences of apple and pear, and which conserved key cysteine and histidine residues. We conclude that the different sequences are likely to be new S alleles. The predicted S-genotypes of about 145 loquat cultivars and lines could be classified into 25 types. We confirmed that the main cultivars in Japan—‘Mogi’, ‘Tanaka’, and ‘Nagasakiwase’—are self-compatible at the gene level. The results suggest that the 41 cultivars and lines were self-incompatible.

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The number of triploids in natural hybrid seeds of three lemon cultivars ranged from 0.36 to 0.70 triploids/fruit. The percentage of small seeds (weighing between one-fifth to one-third of the weight of large seeds) and extra small seeds (weighing less than one-fifth of the weight of large seeds) found to be triploid was 46.7–59.6% and 37.5–47.6%, respectively. This observation suggested that triploids could be efficiently obtained from crosses between diploids by selecting a smaller seed size in lemon. Although 88.2% of the triploids obtained from natural hybrid seeds formed pollen, the amount of pollen was low, resulting in 80% of the triploids having less than one seed/fruit. ‘Yellow Bell’, a new lemon cultivar, was bred by selecting triploids from the natural hybrid seedlings of ‘Michitani-line Villafranca’. The tree vigor of ‘Yellow Bell’ was strong, the branches were dense, branch lengths were intermediate, and the internode lengths were short. A high percentage of the branches (65.8%) had thorns. Maturation occurred in mid-December, when the relative juice content (weight of juice/total fruit weight) was high. Fruits were spherical to sub-spherical, and the average fruit weight was approximately 214 g. The thin rind (5.1 mm thick) had a relatively smooth texture, and high relative juice content. The scent was medium. The average number of seeds (2.9 seeds/fruit) was low. The acidity was approximately 5.3%, giving the fruits a mild taste. This new cultivar, with its unique characteristics of a low seed number, high relative juice content, and low acidity, will help increase the demand for lemons.

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We have been conducting F₁ hybrid breeding in ‘Sakurajima daikon’ to improve the uniformity of the variety. An F₁ purity test using PCR-RFLP has been proposed in F₁ variety Brassica vegetables; however, laborious and time-consuming restriction enzyme treatment is necessary in the test. One type of DNA marker, the microsatellite marker, has been widely used in crop genetics because of its convenience and marked reproducibility. We conducted an F₁ purity test using microsatellite markers and investigated polymorphisms of 300 microsatellite markers derived from Brassica rapa L. in parental lines and their trial F₁ crosses of ‘Sakurajima daikon’. We identified 8 markers that were highly polymorphic. Two of the markers that were detectable with agarose gel electrophoresis could be used to examine the purity of 3 elite F₁ crosses in the field performance test.

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We studied the effects of flooding on the growth of taro (Clocasia esculenta Schott cv. ‘Daikichi’) in pot culture. Under flooded conditions, the upland cultivar ‘Daikichi’ was able to grow as well as the lowland cultivar ‘Taimo’. After about 120 days of flooding, ‘Daikichi’ petioles had elongated to 1.3–1.9 times those of the control. The transpiration rate had increased to about two times that of the control. Indeed, the yields of mother and daughter tubers of ‘Daikichi’ had increased, respectively, to 1.3–4.4 and 1.6–3.7 times those of the control. These results suggest that the upland cultivar ‘Daikichi’ is highly adaptive to flooding and as well as the lowland cultivar ‘Taimo’.

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To study the effect of the growth temperature on the nitrate concentration and nitrate reductase (NR) activity in komatsuna (Brassica rapa L. var. perviridis), cv. ’Harumi-komatsuna’ and ’Rakuten’ plants were hydroponically grown under growth temperatures of 10/5, 15/10, 20/15, 25/20, 30/25, and 35/30°C, and a 12-hr photoperiod at a PPFD of 300µmol・m⁻²・s⁻¹. Generally, the nitrate concentration in ’Rakuten’ plants was higher than that in ’Harumi-komatsuna’. As the growth temperature increased, the nitrate concentration increased and NR activity decreased in both cultivars. A negative correlation between NR activity and the nitrate concentration was observed. Under high temperature conditions, the NR activity decreased, and, therefore, the nitrate concentration in komatsuna plants increased.

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We designed a method of limb girdling with renewal pruning included in cane pruning to improve the pigmentation of berry skin, and avoid a decrease in tree vigor due to the girdling treatment in ‘Queen Nina’ grape. The pigmentation of berry skin with a 12-mm girdling treatment on primary scaffold limbs at 35 days after full bloom was superior to a 4-mm girdling or control non-girdling treatment (girdling was performed for the renewal pruning trees). The cluster number per shoot was significantly increased in trees undergoing renewal pruning, compared with cordon-spur pruning. The berry weight from trees with renewal pruning was significantly lower than in those with cordon-spur pruning. Berry skin pigmentation was superior in the girdling-treatment trees, but there was no significance in the pruning methods. The carbohydrate concentration was significantly higher in the 2–5-mm-diameter roots on the girdling of renewal pruning trees than that of cordon-spur pruning trees. Renewal pruning may be effective to relieve the root stress of poor nutrient accumulation by girdling treatment of the primary scaffold limbs.

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‘Soshu’ and ‘Tonewase’ are major early maturing varieties of Japanese persimmon (Diospyros kaki Thunb.). The skin of ‘Soshu’ is red, whereas the color of ‘Tonewase’ is orange at harvest. In the present study, we investigated carotenoid accumulation in fruits of these two persimmon varieties. In the fruit skin, the levels of expression of carotenoid biosynthetic genes except for lycopene-ε-cyclase increased with carotenoid accumulation during fruit maturation. In ‘Soshu’, a large accumulation of carotenoids was observed at harvest. The total carotenoid content in ‘Soshu’ was nearly twice as high as that in ‘Tonewase’. Both varieties predominantly accumulated β-carotene, zeaxanthin, and β-cryptoxanthin, accounting for nearly 90% of the total carotenoids. The composition of carotenoids in ‘Soshu’ was similar to that in ‘Tonewase’. In the flesh, the level of expression of carotenoid biosynthetic genes except for lycopene-ε-cyclase and zeaxanthin epoxidase increased with carotenoid accumulation during fruit maturation. The total carotenoid content in ‘Soshu’ was nearly four times as high as that in ‘Tonewase’. The composition of carotenoids in ‘Soshu’ was similar to that in ‘Tonewase’.

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Ambient temperatures affect many important traits of tree crops, including persimmon (Diospyros kaki Thunb.). Recent effects of global warming have adversely influenced persimmon fruit in terms of softening and inferior coloration. This study presents insights into air temperature effects on the coloration and harvest time of ‘Fuyu’ persimmon fruit over the last 20 years (1993–2012). The monthly mean air temperature in September and October had a significantly negative correlation with fruit coloration on November 25. The fruit apex coloration on November 25 (7.8), measured with Yamazaki and Suzuki’s color chart (CC), was significantly higher by around CC1.5 in cool years when September and October had a monthly mean air temperature of less than 21°C, than in years with 21°C or more. The date when the daily mean air temperature first decreased to a given temperature after mid-August, was negatively correlated with the fruit skin color on both October 25 and November 25. The date when the daily mean air temperature first decreased to 23°C or less showed the most significant correlation coefficient: r = −0.59** and −0.60** for October 25 and November 25 fruit skin color, respectively. These results indicate that fruit skin coloration is markedly influenced by the air temperature during September and October, and by encountering a given low temperature before the start of coloration.

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We have bred a new radish cultivar called ‘Akinoushi-39’, which is an F₁ hybrid of two lineages derived from the cultivar ‘Yamagata’. With its hard flesh, ‘Akinoushi-39’ is suitable for making Iburi-takuan-zuke (smoked daikon pickles), which is a traditional dish of Akita Prefecture. ‘Akinoushi-39’ has a number of characteristics that make it suitable for large-scale cultivation. It has high scores for uniformity, it rarely develops pithiness and cavitation, and its average production-to-sales rate is 95%. In 2012, the total cultivation area of the cultivar was approximately 20 ha.

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