Yuya Mochizuki

In Japan, strawberries are produced in the off-season (June to November) in cool regions; however, the high temperatures and strong sunlight limit fruit production. Dark septate endophytic fungi (DSEs) support growth and flower bud formation of plants grown in environments unsuitable for plant growth. In this study, we investigated the effects of DSE on dry matter production and flower bud formation in strawberry plants grown in the summer and autumn. The seeds were sown in soil mixed with DSE on 5 February 2024. The DSEs used were Cladophialophora chaetospira SK51 (S) and Cc. MNB12 (M), and Veronaeopsis simplex Y34 (Y). Plants were planted in a plastic house on April 18. The total dry weight was significantly increased by DSEs. This is because S and Y-cultured plants did not show a significant decrease in leaf emergence under high temperatures, unlike those grown with M; however, its leaf area was larger than that of the control. This resulted in a larger leaf area for receiving light and higher cumulative light reception and light-use efficiency. Although the DSEs increased cumulative fruit yield, the harvest period was limited to July because of the extreme summer heat. In addition, there was no difference in the budding date or flowering date between the treatments. These results suggest that DSEs improve light use efficiency, thereby increasing total dry matter weight and contributing to increased fruit yield in summer-autumn cultivation.

Blueberries are in high demand worldwide because of their taste and functional components. However, the shelf life of blueberries is short owing to their perishability and rapid quality deterioration. Therefore, a sterilization technology must be developed that can extend the shelf life of blueberries while maintaining their appearance and taste. As such, we verified the effectiveness of three pre-storage sterilization treatments (UV-C, ozone gas, and ozone water) using mercury-free excimer UV lamps that did not adversely affect the environment. We then created a device that continuously treated blueberries with approximately 2.57 ppm of ozone gas to ensure sterilization during the storage period, and we verified the effectiveness of the device. We found that the pre-storage ozone treatment reduced the number of fungi on the blueberry surface without adversely affecting fruit quality. The continuous ozone treatment suppressed the decrease in anthocyanin content, further reduced the number of fungi on the fruit surface and maintained fruit appearance for a longer period compared with the control. This suggests that continuous low-concentration ozone treatment suppresses the decay and extends the storage period of blueberries intended for raw consumption.

Strawberries have high respiration rates, and their quality deteriorates quickly during storage. Therefore, we investigated quinone, ascorbic acid, and anthocyanin content changes during storage of fruits. Additionally, we further investigated whether these substances could be measured nondestructively in strawberry fruit before storage (day 0) and on days 3 and 5 of storage using hyperspectral imaging. Partial least squares (PLS) regression analysis was performed using the obtained image data, and a calibration curve was created and evaluated using complete cross-validation. The anthocyanin and quinone contents increased during the storage with weight loss. The accuracy of the quinone content calibration curve using hyperspectral imaging was high (R2 = 0.78), suggesting it may be used to measure quinone content during storage nondestructively.

Excimer fluorescent ultraviolet (UV) lamps (UV–228) function as mercury–free sources that use excimer emissions as excitation light sources. First, we evaluated the effects of UV–228–based irradiation (λ_max = 228 nm) on the viability of fungi, using Penicillium digitatum, and compared these effects with those of other light sources, such as OEL–222 (λ_max = 222 nm) and GL–6 (λ_max = 254 nm), to evaluate the effectiveness of the excimer fluorescent lamp. Next, we investigated the effects of UV–228–based irradiation on strawberry storage. Although UV–228 affected weight loss, Brix, ascorbic acid, polyphenol, and DPPH, the effects of UV irradiation for 5 min on strawberry fruit quality were minimal; i.e., only weight loss and ascorbic acid content were higher than those in the non–irradiated treatment. We found that 5 min of UV–C irradiation using UV–228 prevented mold emergence for up to 11 days of storage in strawberries These results indicate that UV–228 contributes to long–term strawberry storage.

Strawberries can be categorized into June-bearing and ever-bearing depending on the environmental conditions that determine flower bud initiation. In Japan, the harvest yield and distribution of strawberry fruits during summer and autumn are low because of high temperatures and heavy fruit load. Therefore, cultivation of ever-bearing strawberries is limited to areas with cool summers such as Hokkaido and Tohoku. In this study, we investigated whether air treatment before liquefied carbon dioxide (CO₂) application within the strawberry plant canopy could improve CO₂ absorption efficiency and increase dry matter production. Four treatments were investigated: application of air within the plant canopy, application of CO₂, application of CO₂ after air application, and a control. We investigated the CO₂ concentration, dry matter production, yield characteristics, individual leaf photosynthesis characteristics, projected leaf area, cumulative light interception, light use efficiency, and fruit quality. The results showed that the local application of only CO₂ or Air and, application of CO₂ after air application (Air/CO₂) treatment within the plant canopy considerably increased the dry matter production. Total fruit yield of Air/CO₂ was the highest among all treatments. This is probably because the application of CO₂ and air expanded the leaf area, increased cumulative light interception, and improved light use efficiency. In addition, the photosynthetic rate of Air, CO₂ and Air/CO₂ treatments was higher than that of the control because of higher stomatal conductance. This suggests that local application of liquefied CO₂ after air application can effectively increase fruit yield, and that air treatment will improve plant vigor, further increasing strawberry production in summer and autumn.

June-bearing strawberry cultivars have been widely grown in Japan. Since they are harvested in winter and spring, little produce is available in summer and autumn. To achieve stable year-round supply, we need to expand the production area of ever-bearing cultivars. Here, we examined whether it is possible to increase dry matter (DM) production and fruit yield by increasing the CO₂ concentration within the plant canopy through local application to promote photosynthesis in summer and autumn protected culture. We investigated the CO₂ concentration in the plant canopy, DM production characteristics, yield characteristics, fruit quality, projected leaf area, cumulative light interception, and light use efficiency. We confirmed that the CO₂ concentration within the plant canopy could be increased in summer and autumn (Control; 398 ppm, CO₂; 1280 ppm), significantly increasing DM production and total yield (Control; 349 g, CO₂; 447.5 g). We consider that local application of CO₂ increased the projected leaf area and thus cumulative light interception. This method may help to increase fruit yield in summer and autumn protected culture.