A genomic selection (GS) trial was conducted to simultaneously improve the soluble solid content and total marketable fruit weight, which are important traits in tomato breeding but they ordinarily display a trade-off relationship with each other. Recombinant inbred lines (GM RILs), derived from a cross between the high-yielding Dutch F₁ hybrid cultivar ‘Geronimo’ and high-quality Japanese F₁ hybrid cultivar ‘Momotaro 8’ were used as a training population to construct a model predicting breeding values from genome-wide markers (genomic breeding values, GBVs). Based on genome sequencing data from the two F₁ cultivars, single nucleotide polymorphism (SNP) markers were detected, and two marker sets including a genome-wide marker set of 4,323 markers (GMRIL_4K) and a smaller set of 384 selected markers (GMRIL_384) were developed. A prediction model for GBVs was constructed using the phenotypes of GM RILs and genotypes of GMRIL_384. To validate the practical utility of GS for tomato breeding, we conducted a breeding scheme utilizing GBVs for a population initially consisting of lines selected from GM RILs based on GBVs calculated with the prediction model. The subsequent populations were obtained through repeated cycles of GS, where seven plants with higher GBVs of the targeted traits, predicted by the model using the GMRIL_384 genotypes, were selected and crossed to generate the next generation in a round-robin fashion. After three rounds of such selection based on GBVs, the resultant lines were evaluated. An increase in phenotypic values was observed, and finally developed line showed a soluble solid content similar to ‘Momotaro 8’ and total marketable fruit weight exceeding it. These results demonstrate that selection by this GS model is effective for simultaneous improvement of two traits that otherwise exhibit a trade-off relationship.

‘Shielding-mulch cultivation’ (‘S. mulch’), a method of mulching planting rows and the surrounding root area of each plant with its own plastic sheet (‘S. sheet’), has been utilized in the production of satsuma mandarin (Citrus unshiu Marcow.) in Japan. ‘S. mulch’ can induce drought stress, leading to the production of high-quality fruit. However, the effects of ‘S. mulch’ in stone-walled terraced fields remain unclear. Here, we investigated the effectiveness of ‘S. mulch’ in stone-walled terraced fields of satsuma mandarin trees. We also developed a technique to improve poor drainage in the unique case of flat terraced fields. Consequently, the ridged soil preparation that conformed to the basic design of ‘S. mulch’ was sufficiently effective in achieving drought stress at –1.0 MPa (maximum water potential in leaves [ψmax]), which is appropriate for high-quality fruit production. The application of ‘S. mulch’ produced fruit with sugar content >12°. In contrast, the non-ridged soil preparation that we used with ‘S. mulch’ resulted in ψmax values of –0.6 to –1.0 MPa, and we considered that it might not generate sufficient drought stress in rainy years. We thus tested an easy-drainage technique for use with ‘S. mulch’ that would eliminate much of the effort that is necessary to make ridges, and we observed that this method was able to generate sufficient drought stress and produce fruit with sugar content >13°, being similar to the ridged soil preparation. These results indicate the following: (i) the importance of using appropriate drainage measures when applying ‘S. mulch’ in stone-walled terraced fields, and (ii) the ease with which the easy-drainage method of ‘S. mulch’ can produce high-quality fruit compared with ridge-making.

High efficiency and labor-saving chestnut harvesting is crucial for maintaining and expanding production in Japan, where the number of growers is declining and workforce is aging rapidly. Mechanized harvesting offers promising solutions for managing large-scale fields. Despite their widespread adoption in Europe, one of the world’s main production areas, these methods are not prevalent in Japan owing to the poor suitability of available machines, which are generally too large for Japanese field conditions. We evaluated the efficiency and fruit quality when using two types of small harvesters: self-propelled and tractor-mounted (vacuum), potentially suitable for smaller fields. Self-propelled harvesters manufactured in Japan and Turkey achieved chestnut picking success rates of 80–90% (depending on vehicle speed) and 75%, respectively. Harvest efficiency was correlated positively with the density of matured, fallen fruits, irrespective of the machine type. When combined with a bur-removing machine, mechanized harvesting increased efficiency by 2.2 to 4.0 times compared with hand-picking. The Japanese self-propelled machine exhibited the best performance, maintaining fruit quality without any significant deterioration during two-month storage at nearly 0°C. Overall, this study demonstrated that mechanized harvesting can contribute to reduction of the working hours necessary for chestnut cultivation in Japan without compromising fruit quality under field conditions.

Rejuvenation pinching is one of the training techniques for lowering cultivation of cucumber (Cucumis sativus L.), in which the harvesting shoot is regularly updated with a new axillary shoot stimulated by pinching. It is considered utilizable for managements of labor and fruit development; however, the ecophysiological effects of its repetition on cucumber growth and yield remain elusive. To address this, we analyzed the winter-spring greenhouse cultivations of ‘S-27Z’ conducted in 2021 and 2020 with and without rejuvenation, respectively, based on yield components. The cucumber plants undergoing rejuvenation exhibited a reduced fresh yield (23.3 kg・m^–2) compared with those without rejuvenation (51.5 kg・m^–2). Fruit abortions were not frequent with either cultivation. Total aboveground dry-matter production was also decreased in the rejuvenating cultivation, and the corresponding light-use efficiency was suppressed. It was suggested that the yield decrease was caused mainly by a reduction in the number of nodes and consequent decrease in fruit sets, which suppressed the dry-matter distribution to the fruits. Consistent with this, axillary shoot outgrowth after pinching was temporarily and continuously suppressed in winter and spring, respectively, with accompanying changes in the aboveground dry-matter partitioning. We propose that rejuvenation pinching is preferable on taking its negative effects on the yield and incidence of fruit abortions into account.

Yield fluctuation, a significant challenge in sweet pepper production, is likely related to suppression of flower development and the fruit set ratio due to competition from dominant fruits with strong fruit sink strength. First, we examined the effect of pollinated or unpollinated (stigma removed before anthesis) treatments on fruit development and dry matter partitioning in the medium-fruit sweet pepper ‘Papriko’, with two levels of fruit load in an unheated greenhouse setting. With the unpollinated treatment, the fruit set ratio was lower than that in the pollinated treatment, and the fruit weight was 60–70% of that of the pollinated fruit, regardless of the fruit load. In the pollinated treatment, the dry matter weights of leaf blades, petioles, and stems decreased, whereas in the unpollinated treatment, stem and leaf weights did not decrease. The incidence of blossom-end rot in fruits was higher in pollinated plants. Second, we sprayed the stigma-removed flowers with parachlorophenoxyacetic acid (PCPA) and forchlorfenuron (FCF) as plant growth regulators to achieve more stable parthenocarpic fruit growth. The fruit set ratio and fruit fresh weight post 30 ppm PCPA treatment were lower than those after the pollination treatment. Spray treatment (30 ppm PCPA and 100 ppm FCF) induced parthenocarpic fruit with 70% of the weight of pollinated fruit, and an intermediate fruit set ratio between that in the non-pollinated and pollinated plants. FCF tended to increase mesocarp cell numbers and thicken the pulp. Parthenocarpic fruits contain high levels of ascorbic acid. Finally, spray treatment with 30 ppm PCPA and 100 ppm FCF at anthesis without stigma removal suppressed seed formation and induced parthenocarpic fruit formation. These results suggest that parthenocarpy effectively reduces harvest fluctuations by decreasing dry matter competition and controlling fruit sink strength.

We investigated the impact of shading, truss removal, and pinching on adventitious shoot formation from the main vein tissue connecting with the leaflet in tomato (Solanum lycopersicum L.) leaves. Under 50% shading, ‘Momotaro’ tomato plants exhibited significantly higher total sugar and starch contents in the main vein tissue, and a greater rate of adventitious shoot formation than unshaded plants. Plants were cultivated with or without inflorescence removal and pinching (yes or no). Following inflorescence removal, the total sugar and starch contents in the main vein tissue significantly increased, along with the incidence of adventitious buds. Pinching treatment led to a significant increase in the number of adventitious shoots elongating to 5 cm compared with plants not subjected to pinching. These findings suggest that regulating the light intensity and sink-source balance can enhance assimilate content in the main vein tissue, thereby improving adventitious shoot formation, while pinching promotes the elongation of adventitious shoots.

Rind blemish causing the fruit of ‘Kara Mandarin’ (Citrus unshiu Marcow × C. nobilis Lour.) to turn brown has been observed, jeopardizing yields and resulting in economic losses in Ehime Prefecture. While the reduction of rind blemish, such as fruit cracking and citrus water spot, by gibberellic acid (GA₃) has been verified in other citrus species, this issue in ‘Kara Mandarin’ has not been examined. Therefore, this study investigated the suppressive effect of GA₃ application on rind blemish in ‘Kara Mandarin,’ focusing on the timing and concentration of treatment. Both 0.5 and 1 ppm GA₃ applications, administered from the 80% coloration stage to full coloration, demonstrated significant effects without delaying coloration or causing green spots. Regarding the application timing, results indicated that treating from the 80% coloration stage to full coloration, as well as at the 50% coloration stage, yielded the greatest reduction in rind blemish severity. However, symptoms of phytotoxicity, such as green spots, appeared when GA₃ was applied at the 50% coloration stage, suggesting that the optimal application period is from the 80% coloration stage to full coloration. Additionally, no differences in fruit quality were observed across any of the tested concentrations or timings.