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Toshihiro Saito, Norio Takada, Hidenori Kato, Shingo Terakami and Sogo Nishio

Genotypic variations in and environmental variance components of the total sugar content (TSC) and sugar composition, including sucrose (SUC), fructose (FRU), glucose (GLU), and sorbitol (SOR), in the fruit juice of 13 Japanese pear cultivars were analyzed. The TSC of ‘Kanta’ and TSC of ‘Hoshiakari’ were high (both >14.5 g/100 mL). The contents of SUC and FRU were higher than those of the other sugars. The SUC contents were ranked as follows: ‘Gold Nijisseiki’, 7.3 g/100 mL; ‘Shuurei’, 6.2 g/100 mL; and ‘Akizuki’, 6.1 g/100 mL. The FRU content in ‘Kanta’ was the highest among all monomeric sugars evaluated (6.8 g/100 mL). These results suggest that ‘Kanta’ is superior in terms of both TSC and sugar composition, which determine sweetness. The yearly environmental variance components were negligible for all traits. The genotype × year ranged from 4.4% to 13.7% of the total variance. Within-tree variance was 17.1% for TSC, whereas that for the sugar composition ranged from 1.4% to 6.1%. The tree × year ranged from 2.7% to 7.4%. Variance among fruits within trees was the largest environmental variance component—except for FRU—and ranged from 8.8% to 35.6%. Broad-sense heritability (h B 2) values based on single tree, single year, and single fruit measurements were 0.33, 0.64, 0.69, 0.71, and 0.76 for TSC, SUC, FRU, GLU, and SOR, respectively. These results suggest that it would be easier to estimate genetic differences in sugar components with a higher level of precision than those in TSC. Increasing the fruit number up to five, in combination with yearly repetition increased to two (without tree repetition), significantly increased the h B 2 of all traits undergoing study. The information obtained during this study will be useful for improving the accuracy of phenotypic selection and future genomic-based breeding studies performed to improve the sweetness of Japanese pear fruits.

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Sogo Nishio, Masahiko Yamada, Norio Takada, Hidenori Kato, Noriyuki Onoue, Yutaka Sawamura and Toshihiro Saito

We evaluated the nut harvesting date (NHD), nut weight (NW), pericarp splitting (PS), and infestation by insects (II) in eight cultivars/selections of Japanese chestnut, including a Japanese–Chinese hybrid, over 6 years. Data were analyzed by analysis of variance (without transformation for NHD, after log-transformation for NW and PS, and after square root transformation for II). The among-tree variance accounted for only 1.1% to 8.5% of the total variance. The variance component resulting from residual factors for the tree × year interaction and sampling errors was the largest component for NW, PS, and II, accounting for 46% to 54% of the total environmental variance. Because tree replication is costly and time-consuming in chestnut breeding, increasing the number of yearly repetitions is more efficient than increasing the number of tree replicates. Broad-sense heritability was 0.84 for NHD, 0.27 for NW, 0.48 for PS, and 0.17 for II in evaluations with one tree without yearly repetition. It increased to 0.91 for NHD, 0.40 for NW, 0.62 for PS, and 0.29 for II in evaluations with one tree in 2 years. For NHD, the heritabilities are sufficiently high to distinguish genetic differences among cultivars/selection. In contrast, the low heritability of II suggests that this trait should not be evaluated with an emphasis on the initial selection stage but rather with an emphasis on the secondary selection stage based on testing at several locations with a large number of yearly and tree replications.