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  • Author or Editor: Kazuyuki Abe x
  • Journal of the American Society for Horticultural Science x
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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.

Free access

Soluble sugar content and activities of the sucrose-metabolizing enzymes sucrose synthase (SS) (EC 2.4.1.13), sucrose-phosphate synthase (SPS) (EC 2.4.1.14), and acid invertase (EC 2.4.1.26) were analyzed in the pericarp of fruit from pear cultivars that differed in their potential to accumulate sucrose to identify key enzymes involved in sucrose accumulation in Asian pears. The Japanese pear `Chojuro' [Pyrus pyrifolia (Burro. f.) Nakai] was characterized as a high-sucrose-accumulating type based on the analysis of mature fruit, while the Chinese pear `Yali' (P. bretschneideri Rehd.) was a low-sucrose-accumulating type throughout all developmental stages. The activity of SS and SPS in `Chojuro' increased during maturation concomitant with sucrose accumulation, whereas the activity of these enzymes in `Yali' did not increase during maturation. The activity of SS and SPS in the former were seven and four times, respectively, higher than those in the latter at the mature stage. Further, among 23 pear cultivars, SS activity was closely correlated with sucrose content, while SPS activity was weakly correlated. Soluble acid invertase activity in `Chojuro' and `Yali' decreased with fruit maturation, but the relationships between soluble invertase activity and sucrose content were not significant. The results indicate that SS and SPS are important determinants of sucrose accumulation in Asian pear fruit and that a decrease of soluble acid invertase activity is not absolutely required for sucrose accumulation.

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The development of new high-quality apple (Malus ×domestica) cultivars that are resistant to flesh browning is needed to expand the use of apples in the food service and catering industry. However, conventional methods for evaluating apple flesh browning can be both time-consuming and costly, thereby rendering such methods unsuitable for breeding programs that must characterize a large number of product samples. Therefore, it is necessary to develop new, simple, and inexpensive methods. The aim was to develop a method for simultaneously measuring the color values of 42 apple samples using a digital camera. The processing time per sample was reduced to less than one-tenth of that of the conventional method. The measurement dispersion [sd of the color difference between two colors ( Δ E ab * ) ] of this system was less than 0.08, equivalent to the nominal value of a general colorimeter. Time-series analysis of six apple cultivars using this method showed that the calculated browning index values correlated well with the degree of browning judged by human perception. Further, the measurement data showed that the CIE L* a* b* value trends associated with browning in reddish- and watercored-flesh samples, was different from the corresponding trends in yellowish-flesh samples. This work reports the development of a high-throughput analytical system of apple browning and provides cautionary notes for evaluating reddish- and watercored-flesh browning, which should be measured on a different basis from that used for normal-flesh browning.

Open Access

We examined the genetic diversity and relatedness among apple (Malus ×domestica Borkh.) cultivars in Japan. The 42 apple cultivars, including major cultivars in Japan, were divided into five groups based on SSR genotypes. Most economically important cultivars belong in three groups: Fuji-Delicious, Golden Delicious, and Jonathan groups, and their genetic backgrounds seemed to be narrow. We also investigated the parent-offspring relationships of nine apple cultivars. `Jonathan', `Fuji', and `Rero 11' were identified as the respective paternal parents of three cultivars described as having unknown paternal parents (i.e., `Akagi', `Ambitious', and `Hokuto'). `Starking Delicious', `Senshu', and `Golden Delicious', rather than `Ralls Janet', `Hatsuaki', and `Indo', seemed to be the paternal parents of `Kinsei', `Kiou', and `Mellow', respectively. `Carolina Red June' was excluded as a paternal parent of `Ranzan'. Both attributed parents of `Scarlet' (`Akane' and `Starking Delicious') were excluded, and it was suggested that `Fuji' was used as either a maternal or a paternal parent of `Scarlet'. `Jonathan' rather than `McIntosh' seems to be a maternal parent of `Yukari'.

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Two apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] homologous fragments of FLO/LFY and SQUA/AP1 (AFL and MdAP1, respectively) were analyzed to determine the relationship between floral bud formation and floral gene expression in `Jonathan' apple. The AFL gene was expressed in reproductive and vegetative organs. By contrast, the MdAP1 gene, identified as MdMADS5, which is classified into the AP1 group, was expressed specifically in sepals concurrent with sepal formation. Based on these results, AFL may be involved in floral induction to a greater degree than MdAP1 since AFL transcription increased ≈2 months earlier than MdAP1. Characterization of AFL and MdAP1 should advance the understanding of the processes of floral initiation and flower development in woody plants, especially in fruit trees like apple.

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