Horticulture Journal最新文献

In general, either high or low branching may contribute to the yield potential of a cultivated crop. In this study, we evaluated the varietal differences in branching characteristics in asparagus crowns and examined the relationship between branching types and harvest characteristics among six varieties tested by careful observation. ‘UC 157’ developed numerous tillers and shoot apical meristems 6 months after sowing; thus, it was considered to be a high-branching type variety. In contrast, ‘All-male Gulliver’ and ‘Ryuryoku’ developed few tillers or shoot apical meristems and, were therefore considered to be low-branching type varieties. The final order of sympodial shoots and composition of sympodial shoots by order were similar between the varieties. ‘UC 157’ had fewer scale leaves attached to the underground shoots than other varieties, which may have been advantageous for developing underground shoots more rapidly. The total spear yield of ‘UC 157’ was high, but the marketable spear yield was similar to that of other varieties owing to the large number of thin spears. Although further studies are needed to determine whether high-branching or low-branching type asparagus varieties are more high-yielding, we determined that high-branching type varieties have lower labor productivity under unimproved growing conditions such as non-sparsely planted growing conditions.

Electrostatic atomized water particles (EAWPs) treatment was applied to investigate its effect on chlorophyll (Chl) degradation and ripening delay in ‘Namwa’ bananas. Banana fruits were pretreated with EAWPs generated from a device (Panasonic F-GMK01) for 0 (control), 0.5, 1.0, 1.5, and 3.0 h in a closed 50 L container, and then kept in perforated polypropylene plastic bags and stored at ambient temperature (25 ± 2°C) under dark conditions. The results showed that 1.0 h-EAWPs treatment best retained peel greenness with a significantly higher hue angle and lower L* value than other treatments on day 6. Also, the 1.0 h-EAWPs treatment maintained the total Chl content, firmness, total soluble solids (TSS), and delayed the ripening index (RI) of fruit accompanied by a delayed climacteric rise in ethylene and respiration rate compared to the control. It was found that the 1.0 h-EAWP treatment induced accumulations of nitric oxide (NO) in peel tissues and suppressed the activities of Chl-degrading enzymes (chlorophyllase, Mg-dechelatase, Chl-degrading peroxidase, and pheophytinase) in the peel. Furthermore, Chl derivatives levels (chlorophyllide a, pheophobide a, 13²-hydroxychlorophyll a, and pheophytin a) were higher in fruits treated with EAWPs than the control fruits. The results suggest that EAWPs technology could be an alternative approach to delay Chl degradation and ripening in ‘Namwa’ bananas.

Strawberries, the most economically well-known berry crop, are known for their taste, nutritional value, and antioxidant compounds. Various spatiotemporal or seasonal factors are known to affect the strawberry pollen germination rate; however, determinating which factor most influences the variation in the pollen germination rate remains challenging. This study aimed to determine the optimal pollen germination media and pollen short-term storage methods in the Japanese strawberry cultivars ‘Shindai SUS-1’ and ‘Shindai BS8-9’. Each strawberry pollen was incubated for 3 h in the dark on a solid medium with 1.5% agar and different sucrose and boric acid concentrations. The pollen germination rate was then investigated. The optimal pollen germination medium for both cultivars was 1.5% agar, 10% sucrose, and 0.1% boric acid. The small amount of strawberry pollen used in this study was collected immediately after flowering in the morning. Therefore, we also investigated a method for collecting a large amount of pollen while maintaining pollen activity. For both cultivars, the pollen germination rate for dry pollen, incubated for 24 h with silica gel after the petals and calyx were removed, was the same as that of the fresh pollen collected immediately after flower collection. In addition, dry pollen was more efficient in terms of short-term storage than fresh pollen. For ‘Shindai BS8-9’, the germination rate for dry pollen was also higher than that of the fresh pollen when stored in vacuum at −25, 4, 15, 20, and 25°C for 3 and 7 days.

The effects of UV-C treatment on physicochemical quality, bioactive compounds and antioxidant activity of okra (Abelmoschus esculentus L.) during storage were investigated. Okra pods were exposed to UV-C irradiation dose at 1.5, 3.0 or 6.0 kJ·m⁻² before storage at 10 ± 2°C for 12 days. The results showed that UV-C treatment had a significant effect on okra bioactive compounds, such as ascorbic acid, total phenolic, flavonoid contents and antioxidant activity. The highest values of these compounds were observed in okra treated with 6.0 kJ·m⁻² UV-C irradiation. A statistical analysis of the data demonstrated that mucilage had a favorable association with antioxidant capabilities and bioactive substances in response to UV-C treatment. Moreover, UV-C treatment also effectively maintained the quality of okra during storage, as evidenced by lower weight loss and higher firmness without incidence of decay. Therefore, postharvest UV-C treatment can be a potential approach to enhance bioactive compounds and maintain the quality of okra during storage.

The growing-degree-days (GDD) model for pineapple was developed to predict flowering and harvest dates; however, it has not been adapted to the climate in Japan’s growing regions, where air temperatures fluctuate over a wide range, and the prediction accuracy is low. The present study aimed to develop models for predicting flowering and harvest dates with high accuracy by analyzing a large phenological dataset from Japan’s main (Nago) and warmer (Ishigaki) production areas. The number of days between budding and flowering decreased at air temperatures of up to approximately 25°C and remained constant above 25°C. The number of days between flowering and harvest decreased until approximately 23°C. The effect of day length on both days to flowering and harvest was small. The relationship between air temperature and the developmental rate after budding to flowering and after flowering to harvest was modeled using the GDD and exponential function models, both with upper limits. The GDD model with an upper limit temperature was more accurate at predicting flowering and harvest dates compared to the conventional GDD model. In particular, the prediction accuracy of the harvest date was dramatically improved. Because the relationship between the developmental rate until flowering and the air temperature was exponential rather than linear, the exponential function model provided a more accurate prediction of the flowering date. The root-mean-square errors of the most accurate models were 3.7–6.1 days for predicting the flowering date and 6.1–10.2 days for the harvest date. We believe that these models will be useful for planning shipments of pineapple in regions with wide temperature ranges, such as Japan, and for cultivation management in response to climate change.

Three rose varieties, ‘Meivildo’, ‘Meikatana’, and ‘Korcut0122’ were grown using an “arching” method for three years. The relationship between temperature and light intensity, and the yield and quality of cut flowers, were analyzed. Flowering flushes were observed 18 times in ‘Meivildo’ and ‘Meikatana’ and 16 times in ‘Korcut0122’ during the experimental period. In three varieties, significant negative linear regressions between the interval of flowering flush (growth period, GP) and the mean temperature per GP were observed. Significant positive correlations and linear regression were observed between the number of cut flowers per plant and the mean temperature in ‘Meivildo’ and ‘Meikatana’, and the total light integral per GP (TLI) in ‘Korcut0122’. In three varieties, significant positive correlations and linear regressions were observed between the total cut flower weight per plant, and the mean daily light integral per GP (DLI) and TLI. Highly significant positive correlations and linear regressions were observed between the daily gain in flower weight (DGW) of cut flowers per plant (the total cut flower weight divided by the number of days of GP) and the mean DLI in all three varieties. In ‘Meivildo’ and ‘Meikatana’, cut flower weight per stem had significant negative correlations and linear regression with mean temperature and positive ones with TLI, while ‘Korcut0122’ showed no significant correlation with the three environmental factors. Significant positive correlations and linear regressions existed between the specific cut flower weight (the cut flower weight per stem length) and TLI in all three varieties, and negative ones existed between the specific cut flower weight and mean temperature in ‘Meivildo’ and ‘Meikatana’. The relationship between the results in this experiment and previous reports on the relation between the environment and cut flower yield quality are discussed. Finally, we present the significance of the method used in this experiment for 1) prediction of flowering and shipping of cut flowers, 2) evaluation of differences in characteristics among the rose varieties, and 3) contribution to the development of a growth model.

To investigate the practicality of using own-rooted trees in pot culture, the growth, yield, and fruit quality of pot-planted ‘Irwin’ mango trees, propagated by air layering versus grafting, over an 11-year period after planting were measured. The trunk diameter of the own-rooted trees propagated by air layering was significantly smaller than that of the grafted trees propagated by conventional methods until six years of age, after which there was no significant difference between the two tree types. The trunk diameter of the own-rooted trees was significantly greater than that of the scion diameter of the grafted trees after seven years of age. The total length of green branches was significantly longer in the own-rooted trees than in the grafted trees after nine years, and the number of leaves was significantly greater on the own-rooted trees than the grafted trees after six years. The height of the own-rooted trees was 35 cm shorter than that of the grafted trees. The fresh and dry weights of the leaves, green branches, thick branches, scaffold branches, and fine roots of the own-rooted trees were significantly greater than those of the grafted trees. However, the fresh and dry weights of the trunks and thick roots of the own-rooted trees were significantly smaller than those of the grafted trees. The weights (fresh and dry) of the aboveground parts of whole own-rooted trees were significantly greater than those of the grafted trees, but the weights of the underground parts did not differ significantly between the two tree types. The T-R ratio (the weight of the aboveground part of the tree excluding the leaves/the weight of the underground part of the tree) of the own-rooted trees was significantly greater than that of the grafted trees. The yield per tree of the own-rooted trees was significantly lower than that of the grafted trees for two years after fruiting; however, this difference resolved after 10 years. The average yield per unit land area over nine years was 2.46 kg·m⁻² for own-rooted trees and 2.32 kg·m⁻² for grafted trees. The numbers of fruits per tree did not differ significantly between tree types, except during years 4 and 5. The average fruit weight did not differ significantly between the tree types up to nine years, with one exception in year 5. However, the average fruit weight of the own-rooted trees was significantly greater than that of the grafted trees after 10 years. Fruit quality did not differ significantly between the two tree types. Since the height of the own-rooted trees was shorter, and their growth and yield were equal or greater than those of the grafted trees, pot culture using own-rooted trees of ‘Irwin’ mango appears to be highly beneficial.

The pineapple (Ananas comosus (L.) Merr.) is an economically important tropical fruit crop. In this study, we performed quantitative trait locus (QTL) analysis using 168 individuals of the F₁ population of ‘Yugafu’ × ‘Yonekura’ for 15 traits: leaf color (L*, a*, b*), harvest day, crown number, slip number, stem shoot number, sucker number, fruit weight, fruit height, fruit diameter, fruit shell color, soluble solid content, acidity, and ascorbic acid content. The constructed single-nucleotide polymorphism (SNP)-based genetic linkage map consisted of a total genetic distance of 2,595 cM with 3,123 loci, including 22,330 SNPs across 25 chromosomes. QTL analysis detected 13 QTLs for 9 traits: leaf color a*, harvest day, fruit weight, fruit height, fruit diameter, fruit shell color, soluble solid content, acidity, and ascorbic acid content. The causative gene for each QTL was predicted with two genes identified as candidate genes. The AcCCD4 gene on Aco3.3C08 was the predicted causative gene for the shell color QTL, which negatively controls shell color by carotenoid degradation. The Myb domain protein-encoding gene on Aco3.3C02 was the predicted causative gene for shell color and leaf color a* QTL, which positively regulates anthocyanin accumulation. The QTL and gene information provided here contributes to future marker-assisted selection for fruit quality.

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.

Chili pepper is cultivated in the absence of fruit-promoting treatments or insect pollinators. The fertilization ability of both males and females, as well as natural self-pollination ability under high temperatures, are necessary for autonomous set fruit under high temperatures. The reproductive traits related to autonomous self-pollination ability and fertilization ability of both males and females after pollination under control (CK) and high temperature (HT) treatments were investigated in this study. ‘Takanotsume’ (TK) showed a significantly higher percentage of autonomous fruit set than ‘Peruvian Purple’ (PP) in both CK and HT treatments, suggesting that TK has a strong autonomous fruit set regardless of temperature. On the other hand, the percentage of autonomous fruit set of PP was 0% in the HT treatment, while autonomous fruit set was observed in the CK treatment. Therefore, TK had autonomous fruit set ability even at high temperatures when PP did not have any. TK had more pollen on the stigma than PP, suggesting that TK has a higher ability for autonomous self-pollination. Flower morphology was not considered a factor in the autonomous self-pollination of TK. In contrast, TK tended to release more pollen than PP. One factor that can support autonomous self-pollination is pollen dispersion. A significant difference was observed in the fruit set rate during artificial pollination between the treatments (CK and HT) of the pollen parent and the cultivars (TK and PP) of the seed parent. In fact, female fertility in TK was higher than that in PP, regardless of the temperature condition. Almost no fruit set of PP was observed via autonomous self-pollination in the HT treatment, but fruits were set by artificial pollination using both the pollen and pistil of PP in the HT treatment. This result is consistent with the finding that PP exhibits decreased autonomous self-pollination at high temperatures. The higher autonomous fruit-set ability of TK than PP under high temperatures may be attributed not only to superior female fertility, but also to its autonomous self-pollination ability under high temperatures. Therefore, pollen dispersal ability under high temperatures was considered a key factor for autonomous fruit-set.