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  • Author or Editor: Kazuyuki Abe x
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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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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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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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As the parents of the some of the apple cultivars were unknown and others were uncertain, we investigated the parent-offspring relationships of eight apple cultivars by S-RNase analysis and SSR markers. The paternal parent of `Hida' was identified as `Golden Delicious', not the previously mentioned `Orin'. It was indicated that `Ryoka No Kisetsu' and `Korin' showing identical SSR genotype are likely sports of `Fuji'. `Fuji', rather than `Toko', seemed to be a maternal parent of `Kotoku', but was not a paternal parent of `Orei', `Starking Delicious', `Nero 26', `Empire', or `Aori 3'. Previously mentioned `Mutsu', `Indo', and `Shin Indo' were excluded as paternal parents of `Hokuto'. `Tsugaru' and `Jonathan' and were identified as the respective paternal parents of three cultivars described as having unknown paternal parents, i.e., `Aika No Kaori', `Yoko', and `Tsugaru'.

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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.

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