Apple (Malus × domestica Borkh.) is the second most produced fruit tree species in Japan. Many public research institutes and private breeders throughout the country breed apple cultivars. DNA markers can accelerate breeding by facilitating the selection of parents and progenies based on their genotypes. As research on the apple genome advances, many DNA markers associated with agronomic traits have been developed. The Institute of Fruit Tree and Tea Science, National Agriculture and Food Research Organization (NARO), has utilized DNA markers in its apple breeding program since the mid-2000s. This article reviews the techniques and background knowledge of the markers employed in NARO’s apple breeding program. The breeding program utilizes DNA markers associated with resistance to scab (Rvi6) and Alternaria blotch (Alt), fruit quality characteristics such as texture and storability (MdACS1, MdACO1, and MdPG1), skin color (MdMYB1), and columnar tree shape (Co). In addition, marker genotypes were evaluated for self-incompatibility (S haplotype) and lethality (l = MdPHYLLO). A comprehensive list of the genotypes of these markers collected from principal Japanese apple cultivars was created. We developed a computer program called the ERAB-genotype database to store, manage, and utilize this information. In addition, the consequences of indirect selection due to the linkages among important traits are discussed.

The effects of various types of potassium fertilization on potassium absorption, yield, and quality of new rhizospheres grown from virus-free seedlings in the Japanese yam ‘Inabu-2 gou’ using black-and-white polyethylene mulch (mulch), which has been used in recent conventional cultivation, were studied to establish growth characteristics and potassium fertilization guidelines for ‘Inabu-2 gou’ at different growth stages. Furthermore, desirable application amounts of potassium fertilizer were estimated from the amount of potassium absorption in the study. Potassium uptake in stems and leaves increased from July to August, reaching a maximum in August. The potassium uptake of new rhizospheres and aerial tubers gradually increased after August. The potassium uptake of the whole plant was almost maximal in September. It is suggested that potassium supply until September is effective for the growth of ‘Inabu-2 gou’. The fresh weight and viscosity of new rhizospheres grown without potassium were similar to those grown with 25 g-K・m^–2 potassium, and the effect of potassium application on ‘Inabu-2 gou’ was not clear. There was a significant positive correlation between the potassium balance and change in exchangeable potassium content in the soil before and after cultivation. It is indicated that potassium absorbed by ‘Inabu-2 gou’ was supplied from the soil, and that potassium not absorbed by ‘Inabu-2 gou’ remained in the soil after cultivation. However in conventional cultivation with mulch, it was considered that the application of 21 g・m^–2 of potassium, equivalent to the absorption of ‘Inabu-2 gou’, as a base fertilizer would provide sufficient potassium without the need for additional fertilization.

The high ambient temperature of summer causes the occurrence of many lusterless eggplant fruits, which have no commercial value. Measures to reduce the occurrence of lusterless fruits, such as cooling, are thus required. In this study, we investigated the effects of temperature on a lusterless appearance in the cultivation of the Osaka eggplant cultivar ‘Mizunasu’. In an experiment using phytotrons, cultivations were conducted under two temperature conditions: a high day temperature/low night temperature (38.6°C–14.7°C, average: 24.4°C), and a low day temperature/high night temperature (26.7°C–22.8°C, average: 24.4°C). The rate of occurrence of lusterless fruits when cultivated under the high day/low night temperature condition was higher than that under the low day/high night temperature condition. Furthermore, the effect of the mist cooling system (which automatically maintains air humidity of a greenhouse under 4.0 g・m^–3) on the occurrence of a lusterless appearance in ‘Mizunasu’ eggplants cultivated in the greenhouse during the summer was studied. The day temperature of the greenhouse in August while the mist cooling system was in operation was more than 2°C lower than that when there was no mist cooling system installed. The yield of marketable fruits without a heavy lusterless appearance increased during cultivation in the greenhouse with the mist cooling system. These results suggest that lowering of the day temperature via the use of the mist cooling system could improve the quality of ‘Mizunasu’ eggplants in summer.

To clarify the suitable conditions of nutrient solution in deep-water hydroponic kiwifruit culture grafted on wet-tolerant rootstock, the effects of concentration, pH adjustment, and cooling of nutrient solution on vegetative growth of young trees were investigated. In experiment 1, nutrient concentration effects in culture solution on tree growth were surveyed. Water supply, shoot growth, and photosynthetic rates were higher in OAT’s standard solutions of 1/2 and 1/4 strength compared with that of 1. In experiment 2, the effect of pH adjustment on tree growth was investigated. No marked differences were observed in water supply, shoot growth, or leaf photosynthesis between pH-adjusted and non-adjusted samples. In experiment 3, the effects of solution cooling on shoot growth and leaf photosynthesis in summer were surveyed. Cooling increased water supply and shoot growth only when the summer temperature was high. These results suggest that in deep-water hydroponic kiwifruit culture with wet-tolerant rootstock, suitable concentrations of the solution are 1/4 and 1/2 of the standard, pH adjustment dose not affect tree growth, and solution cooling during hot summers can accelerate plant growth.

To reduce the occurrence of sunburn injury in eggplant ‘Senryo’ during forcing culture, the difference in mitigating effect of several agents sprayed on the fruits was investigated. As a result, the occurrence was clearly reduced by spraying agents containing sorbitan fatty acid ester (SFE), a non-ionic surfactant. For investigation of the mitigation mechanism, the decreased weights of fruits which were sprayed with SFE or deionized water two days before harvest were examined for three days under 25°C in darkness. The rate of reduction of the fresh weight was significantly smaller in fruits with SFE than in those with deionized water both one and two days after harvest. Therefore, it is considered that the occurrence of sunburn injury is mitigated by spraying of SFE through the suppression of transpiration from fruit skin. Both 0.07% and 0.023% SFE were applied to the fruits, and the incidence of sunburn injury was significantly lower than that of the control (deionized water). As a practical method, 0.023% SFE, which is considered to have few adverse effects on the natural enemies used for integrated pest management, was sprayed at intervals of 10–14 days from late February to late May. As a result, the occurrence rate of brown sunburn injury was 2.4% being significantly lower than that of the control agent (7.0%). Spraying of SFE significantly increased the yield of fruits with high quality to 7.26 kg・m^–2 from 6.14 kg・m^–2 with the control agent, and was considered to be a practical method.

Production of the traditional Japanese spicy vegetable wasabi faces a concerning decline, with market data revealing a reduction from its 1989 peak of 460 tons to 220 tons in 2021, an approximately 50% decrease. Shizuoka Prefecture, known for strong branding, dominated domestic production in 2021, contributing 89% of the total and 90% of the production value. Shimane Prefecture, once second in production (1962), witnessed a marked decline due to distribution issues, disasters, and falling unit prices, among other factors. Regarding annual changes in wasabi production, the declining trend was notably pronounced in western Japan. Additionally, many of the “native species” that were once cultivated in approximately 80% of prefectures may have disappeared. This production decline also extended to traditional Japanese seasonings, and a comparison with newly introduced vegetables suggested a link with the Westernization of food. Japan’s unique food culture and ingredients, as well as its forested landscape, offer a valuable income source and potential for regional development in mountain villages. Protecting producers is essential for preserving resources and culture; thus, urgent measures are required to safeguard this heritage.