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Akihiko Sato, Masahiko Yamada and Hiroshi Iwanami

Berry texture of grapes (Vitis labruscana Bailey, V. vinifera L., and their hybrids) can be characterized by two factors: 1) difficulty of breakdown in mastication and 2) firmness, which can be mechanically measured as deformation at first major peak (DFP) and maximum force (MF) of the force-deformation curve in flesh puncture tests. Crisp texture (easily breakable and firm flesh texture), one of the most important factors for the quality of table grapes, corresponds to a combination of small DFP (≤2.5 mm) and large MF (≥0.9 N). Obtaining offspring with crispy flesh is a primary objective in grape interspecific hybrid breeding at the National Institute of Fruit Tree Science, Japan. In this study, the expected proportion (EP) of offspring with crispy flesh as a genotypic value was estimated using a population consisting of 23 full-sib families each with eight offspring. An analysis of variance in the offspring, which estimated between-family and within-family variances, and the regression analysis of the family mean (Fm) of eight offspring in each full-sib family on mid-parental value (MP) were conducted for DFP and MF. The results revealed that the total genetic variation in offspring was mostly explained by the variance due to the regression and the within-family variance for both DFP and MF. No significant heterogeneity of within-family variance was detected by Bartlett's test for either DFP or MF. Therefore, a simple model was used to calculate EP: Fm is solely determined by the regression of Fm on MP, and all families have an equal within-family genetic variance due to segregation. Since merely a weak correlation relationship existed between DFP and MF, its influence was omitted in calculating EP. The EP of offspring having crisp texture was estimated to be 11% for an MP value of DFP of 2.5 mm (DFP for `Italia'), 6% for a DFP of 3.5 mm (DFP for `Athens'), and 3% for a DFP of 4.5 mm (DFP for `Bath'); the MP value of MF was assumed to be 0.7 N (MF for `Steuben' and `Italia') in this calculation.

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Nobuhiro Kotoda, Hiroshi Iwanami, Sae Takahashi and Kazuyuki Abe

Because fruit trees such as apple (Malus ×domestica Borkh.) flower and set fruit only after an extended juvenile phase lasting several years, efficient breeding of fruit trees is limited. We previously suggested that MdTFL1 (Malus ×domestica TFL1) functions analogously to TERMINAL FLOWER 1 (TFL1) and that MdTFL1 is involved in the maintenance of the juvenile/vegetative phase in apple. To clarify the function of MdTFL1 in apple, we produced transgenic `Orin' apple trees expressing MdTFL1 antisense RNA. One of them flowered only 8 months after the transfer to the greenhouse, whereas the nontransformed control plants have not flowered in nearly 6 years. As expected, the expression of endogenous MdTFL1 was suppressed in the transgenic lines that showed precocious flowering. In addition, the expression level of the transgene was correlated with the reduction of the juvenile phase. These findings confirm that MdTFL1 functions like TFL1 and that MdTFL1 maintains the juvenile and vegetative phase in apple. Flower organs of the transgenic apple trees were normal in appearance, and a precocious flowering transgenic line set fruit and seeds. Interestingly, some flowers of the transgenic apple trees developed without undergoing dormancy. The expression of MdTFL1 in apple may affect flower development as well as flower induction.

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Hiroshi Iwanami, Shigeki Moriya, Nobuhiro Kotoda, Sae Takahashi and Kazuyuki Abe

Progenies from 38 unbalanced crosses using 20 apple (Malus ×domestica Borkh.) cultivars/selections as parents were evaluated for changes in flesh firmness after harvest in two seasons to determine the mechanism of inheritance of fruit softening. The change in firmness was fitted by linear regression, and the softening rate (N·d−1) expressed as the regression coefficient was used as the phenotypic value of softening after harvest. Fruit were stored under 20 °C and 85% relative humidity after harvest for up to 40 days. The softening rates in the progeny populations were distributed continuously around the softening rates of parents, despite a distinct segregation in the degree of mealiness at 30 days of storage. The narrow-sense heritability of the softening rate was estimated by parent-offspring regression, and the estimate was high (h2 = 0.93). Because the softening rate can be influenced by mealiness, an undesirable trait in the apple industry, the progenies were divided into individuals with and without mealiness, and the breeding values of the parents were estimated based on the softening rate of the nonmealy progeny. The softening rate of the nonmealy progeny was analyzed using a mixed linear model and the restricted maximum likelihood method, with general combining ability (GCA) as parental effects and specific combining ability (SCA) as parental interaction effects. The variance of GCA was significant, but the variance of SCA was small and nonsignificant. The narrow-sense heritability of the softening rate in the nonmealy progeny was estimated by sib analysis, and the estimate was moderately high (h2 = 0.55). A significant correlation was observed between the phenotypic value and the breeding value (twice the GCA effects) in nonmealy parents, but the phenotypic value did not significantly correlate with the breeding value in mealy parents. Therefore, contribution of a mealy parent to the softening rate of nonmealy progenies cannot be predicted by its phenotypic value.

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Hiroshi Iwanami, Shigeki Moriya, Nobuhiro Kotoda, Sae Takahashi and Kazuyuki Abe

Changes in flesh firmness and mealiness during storage were investigated in 24 apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars and selections (genotypes) up to 40 days after harvest under 20 ± 2 °C and 85% ± 5% relative humidity storage conditions. Flesh firmness was measured using a penetrometer, while mealiness was quantified by measuring the degree of cell separation in tissue induced by shaking discs of tissue in a sucrose solution. According to the relationship between the change in firmness and mealiness, the genotypes can be divided into four groups: those that did not soften and remained hard and nonmealy during storage; those that softened without mealiness; those that softened with slight mealiness; and those that softened with mealiness. Firmness decreased below 30 N in fruit that softened with mealiness, and the minimum firmness during storage was correlated with the degree of mealiness at 30 days of storage. The rate of softening was the highest in fruit that softened with mealiness. Therefore, it was concluded that, by measuring the firmness and changes in firmness that take place during storage, the genotypes resulting in softening with mealiness and those that result in softening without mealiness could be identified.

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Hiroshi Iwanami, Shigeki Moriya, Nobuhiro Kotoda and Kazuyuki Abe

Changes in turgor and flesh firmness during storage at 20 °C were investigated using 27 apple (Malus ×domestica Borkh.) cultivars for 2 years. Flesh firmness was measured using a penetrometer, and turgor was determined using a thermocouple psychrometer. Firmness and turgor of fruit decreased during storage. The cultivars with little softening during storage had low rates of reduction in turgor. The softening rates in mealy cultivars were high, but there were cultivars with low rates of turgor reduction. When the rates of reduction in turgor after harvest were low, the mealy cultivars of the fruit tended to develop severe mealiness during storage. Therefore, a low rate of reduction in turgor could contribute to cultivars with both good shelf life and severe mealiness. The reduction rates of turgor in progeny cultivars were nearly identical to the mean reduction rates of turgor of their parents. This suggests that a cultivar with a low reduction rate of turgor, although it can be mealy, has the potential to produce a progeny with a low reduction rate of turgor.

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Hiroshi Iwanami, Nobuyuki Hirakawa, Hiroyasu Yamane and Akihiko Sato

Crosses between seedless cultivars had been conducted to produce seedless table grape efficiently by combining with ovule and embryo culture in Vitis vinifera L. But very few plants grew normally in this method. Four plant growth regulators (Cycocel, B-Nine, Uniconazole-P, Ethrel) were applied to shoots 4 weeks before anthesis to develop the seeds of two seedless cultivars `Flame seedless' and `A1706'. Correlation was significant in each cultivar between the shoot length at anthesis and the number of seed traces per berry in all combined treatments. Analysis of covariance revealed that the number of seed traces per berry was significantly higher when the shoots were applied with Uniconazole-P (240 ppm) than B-nine (2000 ppm), Cycocel (500 ppm) and Ethrel (400 ppm) in `Flame seedless' and Uniconazole-P and B-nine than Ethrel in `A1706'. Ovules of these two seedless cultivars crossed with seedless cultivar `Perlette' after the application of four plant growth regulators were cultured on half-strength MS medium with 10 μm IAA and the percentage of developed embryos in ovules was higher when the shoots were applied with Uniconazole-P and B-nine than Cycocel, Ethrel in `Flame seedless' and B-nine than others in `A1706'. These results indicate that the use of certain plant growth regulators promotes the embryo development.

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Hiroshi Iwanami, Makoto Ishiguro, Nobuhiro Kotoda, Sae Takahashi and Junichi Soejima

The firmness of the flesh in 27 apple (Malus ×domestica Borkh.) cultivars and selections (genotypes) was measured as an indicator of storage potential at 20 days after harvest under 20 ± 2 °C, 80% ± 5%relative humidity storage conditions. Softening ranged from 9% to 58% of initial values among genotypes after 20 days of storage. In some genotypes, softening was not continuous, a minimum firmness being reached before day 20. After a period of rapid softening, firmness declined to at least 20% of that at harvest. For each genotype, linear regression analysis of firmness changes from harvest until when firmness decreased by 20% was carried out. In genotypes in which firmness did not drop >20% within 20 days of storage, the entire dates to 20 days were used for analysis. The homogeneity of the regression residual variances and their normal distribution was not rejected at P = 0.05, and the linear regression analysis was assumed to be applicable to the change in firmness for each genotype. Results of the regression analysis showed that the regression was significant for all genotypes except one. Therefore, storage potential could be evaluated by comparing the regression coefficient of each genotype.

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Hiroshi Iwanami, Shigeki Moriya, Nobuhiro Kotoda, Sae Takahashi and Kazuyuki Abe

To compare changes in fruit quality during cold storage with those during shelf life conditions, flesh firmness and titratable acidity (TA) were measured during storage in 20 apple (Malus ×domestica Borkh.) cultivars. Fruit of each cultivar were divided into two groups and stored in chambers controlled at 20 ± 2 °C and 85 ± 5% relative humidity (RH) (shelf life conditions) or 0.5 ± 0.3 °C and 95 ± 5% RH (cold storage). Five of the stored fruit were removed for measurements at 5- or 10-d intervals for 40 d and at 1-month intervals until 10 months after harvest at 20 °C and 0.5 °C, respectively. Data for firmness and TA were subjected to a linear regression and a nonlinear regression, respectively. Moreover, to determine the advantages of 0.5 °C storage over 20 °C storage for retaining firmness and TA, the effect of storage type on extending the storage period was introduced as a parameter. The estimate of the effect of storage type showed that firmness and TA could be retained 8.9 and 3.7 times, respectively, longer at 0.5 °C than 20 °C, independently of the cultivar. Therefore, firmness and TA after cold storage could be predicted by the change in firmness and TA during shelf life conditions. Moreover, cultivar differences regarding quality change under cold storage could be determined in a short period after harvest because the cultivar differences under shelf life conditions were detected within 1 month after harvest.

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Chikako Honda, Hideo Bessho, Mari Murai, Hiroshi Iwanami, Shigeki Moriya, Kazuyuki Abe, Masato Wada, Yuki Moriya-Tanaka, Hiroko Hayama and Miho Tatsuki

The objective of this study was to investigate the effects of temperature treatments on anthocyanin accumulation and ethylene production in the fruit of early- and medium-maturing cultivars that were harvested early during fruit ripening. We first investigated the effects of various temperature treatments on anthocyanin accumulation in detached apples of ‘Tsugaru’, ‘Tsugaru Hime’, ‘Akane’ and ‘Akibae’ using an incubator. Three years of experiments demonstrated that at harvest, the lower-temperature treatments induced anthocyanin accumulation in ‘Tsugaru’, ‘Tsugaru Hime’, and ‘Akibae’ fruits, whereas the increases in anthocyanin accumulation under the 25 °C treatment were similar to those under the 15 and 20 °C treatments in ‘Akane’ fruit. The rate of ethylene production did not increase substantially during the temperature treatments in any of the four cultivars, except after the treatments of ‘Tsugaru’ fruit at harvest. The inhibition of ethylene action by the application of 1-methylcyclopropene (1-MCP) to detached fruits at harvest suppressed anthocyanin development under 15 and 20 °C temperature treatments in ‘Tsugaru’, ‘Tsugaru Hime’, and ‘Akibae’, but not in ‘Akane’. In the second experiment, we investigated changes in the anthocyanin concentration in attached fruit of ‘Misuzu Tsugaru’ under different temperature conditions in a greenhouse. At harvest, the anthocyanin concentration in fruit under the hotter climatic condition (29 °C 12 hours/19 °C 12 hours) was lower than that under the control condition (25 °C 12 hours/15 °C 12 hours). During the last week before harvest, anthocyanin development proceeded rapidly in fruit skin not only under the control condition, but also under the hotter climatic condition. The rapid accumulation of anthocyanin in the fruit skin of ‘Misuzu Tsugaru’ at harvest under a relatively high temperature (25 °C) condition was confirmed by the experiment using an incubator. At harvest, the maximum level of ethylene production in fruits sampled from trees grown under the hotter climatic condition was 9-fold higher than that in fruits from trees grown under the control condition. These results indicate that the comparison of pigmentation potential after the 15 or 25 °C treatments using detached fruit was effective for estimating anthocyanin accumulation in fruit skins under hotter climatic conditions in early- and medium-maturing cultivars that were harvested early and that a hotter climatic condition during ripening increased ethylene production in apple fruit after harvest.