In recent years, increasing instances of rind puffing in satsuma mandarin fruits due to global warming have made long-term post-harvest storage difficult. Although the effect of gibberellic acid (GA) on rind puffing was previously clarified, treatment with low concentrations of GA has not been visibly effective in reducing rind puffing, and significant delays in color change have been observed following treatment with high concentrations of GA. In this study, we tested the effect of various spraying times and concentrations of GA mixed with prohydrojasmon (PDJ) on the delay in color change of satsuma mandarin fruits. A mixture of GA and PDJ at the same concentrations (3.3–20 ppm) inhibited rind of puffing; on the other hand, treatment with GA of 10 ppm or more sometimes led to a significant delay in coloring. Therefore, it was concluded that using a low concentration of GA (3–5 ppm) with a high concentration of PDJ (25–50 ppm) had a stabilizing effect on rind puffing with only a slight delay in color change. In the late-maturing cultivar ‘Aoshima unshu’, the effect of spraying this mixture in early September was highest in all treated periods. However, at the production site, there was a strong demand to suppress the delay in color change associated with GA treatment as much as possible. Upon re-examination of the effects of the concentrations and period of treatment, it was determined that treatment with a mixture of GA at 1 ppm and PDJ at 25 ppm could reduce rind puffing and suppress the delay in color change. It is now possible to use this mixture in early-maturing cultivars, and widespread use in satsuma mandarin production areas has been adopted. This technology has achieved the desired reduction in rind puffing and decay for short- and long-term storage of satsuma mandarin fruits, and will be indispensable for citrus cultivation in the future.

Selection of suitable rootstock species which can improve the freezing tolerance of Japanese chestnut (Castanea crenata Sieb. et Zucc.) cultivars has been required in recent years, because the incidence of freezing injuries has been marked in newly established orchards. The three objectives of the present study were as follows: 1, selection of freezing-tolerant rootstock strain that grafts compatibly with Japanese chestnut cultivars, 2, establishment of layering propagation, 3, explanation of mechanisms of freezing-tolerant rootstocks. Among the 12 rootstock strains, graft compatibility of the ‘Ginyose’ seedling with the ‘Tsukuba’ scion was high (95%), whereas that of the Chinese chestnut seedlings was low (4–37%). However, ‘Tsukuba’ with the Chinese chestnut strain “Jiangxi” showed a high survival rate under severe environmental conditions where the mortality rate of trees grafted with other rootstock species reached 50–100%. Moreover, layering propagation could be applied to the “Jiangxi” No. 345 strain because the rooting rate reached 64.7%. The “Jiangxi” No. 345 strain showed graft compatibility with the ‘Tsukuba’ scion, and 41.2% of the nursery plants could be used for planting. The ‘Tsukuba’ with “Jiangxi” No. 345 rootstock showed a low shoot water content and high freezing tolerance of buds during winter compared with the plant plus conventional rootstocks. Consequently, the incidence of freezing injury in the field was decreased using “Jiangxi” No. 345, rootstock. These results indicate that “Jiangxi” No. 345 which can be propagated by layering, has a high potential to become a new rootstock strain for Japanese chestnut, because it can improve freezing tolerance by reducing the branch water content during winter.

‘Masui Dauphine’ (synonym of ‘San Piero’) fig trees in a study field were found to have grown progressively weaker over the last five years, and showed typical symptoms of soil sickness. Compost produced from the branches and leaves of roadside trees (about 0.4 m³・m^–2) was used to mulch the ground under these trees. Two years after mulching, the fig trees had partially recovered from the weakness as compared with un-mulched trees. This recovery lasted for six years after mulching. In addition, the decline in both fruit size (estimated from young to mature fruit size) and fruit number caused by tree weakness also recovered in the mulched trees. Compared with the un-mulched soil, the mulched soil showed a higher cation exchange capacity (CEC), as well as higher humus, NO₃-N, and K₂O contents. The results of the present study show that compost mulching is helpful to restore the health of fig trees weakened by soil sickness, and the improvement of soil physicochemical properties may have been a factor in this effect.

In Japan, gosun (six-inch) carrots are produced using the well-established relay cropping method across various production areas to ensure that they can be supplied throughout the year. On the other hand, mini carrots cannot be stably supplied throughout the year. Mini carrots are grown according to the cropping type of gosun carrots and are distributed throughout Japan, and there are no standards of shipment. To examine the possibilities of year-round cultivation of mini carrots in a region with a temperate climate, we planted mini and gosun carrot seeds in the same region a total of 20 times over 4 years. The growing period (growth rate) of mini carrots in the warm region of Japan varied with each sowing time. Except for sowing from October to February, the fresh weight of the underground parts reached the standard for shipment by 110 days after sowing. The minimum fresh weight of underground parts required for shipment is 10 g for mini carrots and 70 g for gosun carrots, and the growing period to reach this standard requirement was shorter for mini carrots compared with gosun carrots. However, in the low-temperature season, the growing period required to reach the standard was longer than that on conventional sowing in April. Therefore, the possibility of year-round cultivation of mini carrots was suggested using heat-retaining materials and adjusting the planting density to shorten the cultivation period.

As juvenile stage management suitable for the V-shaped orchard system of the columnar type apple Morioka No. 74, we investigated the effect of the number of scaffold branches on growth and the effect of gibberellin paste application. The number of scaffold branches was 2, 4, and 6. Gibberellin paste application was not applied to some of the trees with 4 scaffold branches. The application of gibberellin paste in the first and second years of planting promoted shoot elongation, and the amount of elongation in the 4 scaffold branch system was twice as much as that in the non-applied shoots. At the end of the second year of planting, more shoots reached the target length (300 cm) in the 2 scaffold branch system, however, more flower buds were formed in the 6 scaffold branch system. The number of flower buds was higher when the total growth of shoots in the first year of planting was greater, indicating that the application of gibberellin paste contributed to the increase in the number of flower buds. In the 6 scaffold branch system, completion of the tree form was delayed by one year compared with that of the 2 scaffold branch system, but the control of tree vigor is expected by producing fruits. These results suggest that the 6 scaffold branch system with gibberellin paste application is suitable for the V-shaped orchard system of Morioka No. 74/JM2.

To clarify factors determining the fresh fruit yield of sweet pepper plants, we examined and compared yield components of four kinds of sweet pepper plants (‘Artega’, ‘Nagano’, ‘Nesbitt’, and ‘Torirosso’) under a rockwool hydroponic system. Cultivation lasted for 250 days. Significant cultivar differences were found in the fresh fruit weight, fruit dry matter content, total dry matter production (TDM), dry matter fraction to fruits, intercepted amount of light by plant canopy (IL), leaf area index (LAI), and light use efficiency (LUE). In yield component analyses, the fresh fruit weight was significantly correlated with the dry fruit weight (P < 0.001). Additionally, the dry fruit weight was significantly correlated with TDM and LUE (P < 0.001), and TDM was correlated with LUE (P < 0.001). Significant cultivar differences were found in LAI, IL, and dry matter fraction to fruits, but their effects on the fresh fruit weight was low. In conclusion, LUE has a marked effect on the fresh fruit weight of sweet pepper. Choosing a high LUE cultivar and increasing LUE with CO₂ enrichment may be a promising methodology to achieve a high fresh fruit yield.

The development rate (DVR) and average temperature using cultivation data of Eustoma variety ‘Celebrity Rich White’ were calculated in Tsukuba City, Ibaraki Prefecture for the purpose of predicting the harvest date and developing technology to realize it. The relationship between the two was examined. A simple linear model was applicable to the average temperature and DVR from the start of raising seedlings to flower budding, and from flower budding to harvest. From the coefficients of the equation, the basal temperature (T_b) and thermal time (TT) were obtained as growth model parameters. The predicted date of harvest from flower budding showed high accuracy with an error of RMSE 3.1 days within 5 days with respect to the measured value. From these facts, it was considered that the harvest date can be predicted with high accuracy using the obtained parameters as the starting point of flower budding. In a greenhouse for commercial production, a cultivation test was conducted using the developmental parameters and device AMTeC, which actively controls the average temperature, with December 13 as the control starting point and March 10 as the target harvesting date. It was estimated that the average bud date of the study area was December 25, and the average harvest date was March 14. From these facts, it was demonstrated that the harvest date can be predicted using the developmental parameters starting from the flower budding date, and that planned production within ±7 days is possible by controlling the temperature.

We investigated the incidence of black stains on the skin of ‘Tone-wase’ persimmons during shipping bound for the USA. Simulation tests indicated that black stain occurrence was severe in fruit stored at 30°C for 7 days, following 1-MCP treatment during CO₂ exposure for astringency removal, but was not detected at temperatures below 15°C. Covering fruit with polyethylene (PE) bags further increased black stain incidence during storage at 30 or 25°C, compared with packing in carton boxes coated with a water-impervious material. Packaging with PE bags also decreased internal O₂ levels to around 3%, increased CO₂ to around 5%, and stimulated ethylene production. Incorporation of CO₂ absorbers decreased the CO₂ concentration in PE bags and reduced black stain development to some extent. CTSD (Constant Temperature Short Duration) de-astringency and 1-MCP treatment aggravated black stain development. These results suggest that the stress of low O₂ and high CO₂ conditions caused by CTSD de-astringency and packing into packaging bags under high temperatures above 25°C were factors influencing black stain development during export. In addition, inhibition of ethylene action by 1-MCP treatment was a contributing factor. As astringency removal and 1-MCP application are essential for long-distance transport for export of ‘Tonewase’ persimmon, temperature control during shipping is also a feasible and effective measure to avoid black stain development.