Japanese pear (Pyrus pyrifolia Nakai) has been cultivated under a flat trellis for hundreds of years in Japan. Replanting trees in a traditional orchard is difficult because it takes a long time to establish a mature orchard due to the low tree density, which requires a long labor time and skills for pruning and fixing laterals on the flat trellis. We have invented a new planting and training system called the “Tree joint training system” to solve these problems by planting young trees linearly and connecting adjacent ones by grafting. The growth of horizontally connected stems and laterals is uniform based on the structural characteristics of this system. Advantages of this methods are: early high yield, reduction of labor time and easy tree management due to a simple tree structure. We monitored the translocation of water and assimilates among jointed trees, showing the standardized promotion of growth using this system. We came up with the idea in 1993, registered a patent belonging to Kanagawa Prefecture in 2012, and its use is now expanding in Japan. This innovative system has changed the traditional practices of training and pruning techniques and should be called a new high-density planting method, using neither dwarfing rootstocks nor root-control methods. This system has now been applied to various other fruit trees. In this application research, the “Joint V-shaped trellis system” is considered the best tree shape for mechanization. Currently, we are proceeding with experiments on mechanization and automatization, such as harvesting procedures.
The development of cultivar identification technology and the protection of breeder’s rights are required for Japanese acid citrus cultivars in conjunction with the increasing domestic production and expanding overseas export of acid citrus fruits. Thirty-three acid citrus cultivars and lines were analyzed using 26 CAPS markers previously applied to the identification of table citrus cultivars. It revealed that all accessions of Yuzu (Citrus junos hort. ex Tanaka), Sudachi (C. sudachi hort. ex Shirai), Yuko (C. yuko hort. ex Tanaka), and Jabara (C. jabara hort. ex Tanaka), which had different phenotypes and local origins, had the same genotypes as their representative samples. In acid citrus cultivars, five CAPS markers detected novel alleles that were not found in table citrus cultivars. Based on the calculation of 25 CAPS markers genotypes except for Tf0001/Msp I by the MinimalMarker program, a minimal marker set comprising 6 CAPS markers can discriminate all 35 citrus cultivars. Parentage analysis of a new triploid cultivar of ‘Awasuzuka’ (C. sudachi (2n = 4x) × C. junos (2n = 2x)) bred in Tokushima Prefecture by the MARCO program indicated that ‘Awasuzuka’ was inherited from either of the parental alleles and showed no discrepancy in the parent-offspring relationship. The establishment of cultivar identification technology for major acid citrus cultivars in the Japanese market reinforces the protection of Japanese brands and breeding rights of superior citrus cultivars.
To promote polyploid breeding efficiently in Citrus, we investigated the relationship between the morphology and weight of seeds and ploidy level of seedlings obtained from a cross between diploid pummelo ‘Banpeiyu’ [C. maxima (Burm.) Merr.] and triploid grapefruit-type citrus ‘Oroblanco’ (C. Maxima × C. paradisi Macfad.). When pummelo ‘Banpeiyu’ was pollinated with pollen of the grapefruit ‘Oroblanco’, the number of seeds per fruit decreased significantly, and many undeveloped and empty seeds appeared compared with crossing with Natsudaidai (C. natsudaidai Hayata). As a result of FCM analysis of seedlings obtained from crossing with ‘Oroblanco’, most of the developed seeds were diploid, but triploids appeared frequently from developed seeds weighing less than 200 mg, and tetraploids occurred from large developed seeds weighing above 500 mg. In undeveloped seeds, many triploids and aneuploids appeared, and two haploids were also obtained. These results suggest that various polyploids can be obtained efficiently by selecting types and weights of seeds.
Annual produntion of bulb onion (Allium cepa L.) is the third largest among vegetables in Japan. In Japan, bulb onion cultivars are mainly divided into two groups: spring-sowing (late-maturing) and autumn-sowing (early-maturing) cultivars. The cultivars belonging to these groups have been difficult to compare regarding their morphological traits under the same cultivation conditions, but now we can evaluate their traits under newly developed spring-sowing cultivation in the Tohoku region. We extracted a total of 50 traits using 95 domestic and foreign cultivars/genetic resources through two trials each of spring-sown and autumn-sown cultivation. Because most of the trait data obtained from the spring-sown trial were correlated with those from the autumn-sown trial, the spring-sown cultivation is considered effective for reproducible evaluation of cultivar traits, especially in cases of severe conditions during winter due to climate instabilities such as heavy snow (freezing) and a warm winter. Principal component analysis of 30 traits revealed a 51.3% cumulative contribution of the primary and secondary components, with the former determining earliness and latter determining bulb traits. A scatter diagram of the primary and secondary components indicated some specific clusters according to conventional cultivar classification. The principal component and cluster analyses obtained from our data representing each cultivar group may be useful as references for objective evaluation of the characteristics of bulb onion cultivars.
In order to clarify the nitrogen absorption characteristics of Japanese yam ‘Inabu-2 gou’, we investigated the dry matter weight and nitrogen absorption of each part at different times when the nitrogen application rate was changed. The total amount of nitrogen uptake in stems and leaves increased significantly from July to August and reached the maximum in August. On the other hand, the dry weight and amount of nitrogen uptake of new rhizosphere increased after August. Total nitrogen absorption peaked in September. Therefore, it was considered that the nitrogen supply until September was significant for the growth of Japanese yam. Especially, the nitrogen supply from July to August when the growth of foliage increased was considered to be important. The weight, Brix value, and viscosity of the new rhizosphere cultivated without nitrogen fertilization were not different from those with nitrogen fertilization (30 g-N・m–2). The estimated value of nitrogen mineralization from the soil of the experimental field was higher than the total value of nitrogen absorption at each time. This suggests that the soil may supply the necessary nitrogen with mineralized nitrogen even under the condition that polyethylene mulch is applied but nitrogen is not.
To investigate the possibility of simultaneously reducing nitrate and oxalate by amino acid application just before harvesting in spinach, plants were cultivated hydroponically until 7 days before harvesting, and then were treated by adding glutamine (1, 2, 3, 4 and 5 mM), glycine, glycolate, and glyoxylate (1, 3 and 5 mM) to nutrient solution. The treated plants were harvested after 7 days of treatment, and analyzed regarding their nitrate and oxalate concentrations of leaf blades, and nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate-glyoxylate aminotransferase (GGAT) activities of leaf blades. The nutrient solution on treatment of glutamine, glycolate and glyoxylate became cloudy, especially at high concentrations. These phenomena led to decreases in the fresh weight of leaf blades and petioles. However, the fresh weights on treatment with glycine were comparable to those of the control. The application of glycine at 5 mM simultaneously decreased nitrate and oxalate concentrations of leaf blades. The NR activity of glycine treatment at 5 mM was markedly decreased, possibly caused by the depletion of nitrate as the substrate for NR. These results indicate that the simultaneous reduction of nitrate and oxalate by glycine application occurred by the deactivation of NR with a decrease in nitrate, diminishing the role of oxalate as a neutralizer for the reduction reaction of nitrate.
In recent years, extremely late-harvesting peach ‘Fuyumomogatari®’, which is commercially harvested in November, has been grown in Okayama, Japan. The fruit developmental pattern of ‘Fuyumomogatari®’ was investigated at an orchard across two seasons and compared with ‘Akizora’, which is harvested in late-August. In ‘Fuyumomogatari®’, Stage 1 of fruit growth was completed at almost the same time in ‘Akizora’, while Stage 2 of fruit growth continued for more than two months, one month longer than ‘Akizora’. In this period, the relative fruit growth rate in ‘Fuyumomogatari®’ was clearly lower than that in the other stages. On the other hand, no significant difference was observed in developmental speeds of the endosperm and embryo between ‘Fuyumomogatari®’ and ‘Akizora’. Fruit growth during Stage 3 in ‘Fuyumomogatari®’ continued until the end of October at a slower growth rate than that observed in ‘Akizora’. Thereafter, several weeks of possible mature stage were observed before commercial harvest in ‘Fuyumomogatari®’. Significant levels of ethylene were already present in ‘Fuyumomogatari®’ fruit at harvest in both experimental seasons. Harvested fruits were ripened at 20°C for 15 days and the ripening characteristics were investigated. The decrease in flesh firmness was relatively slow in both seasons, and all fruit showed optimum edible quality from Days 6 to 12 during ripening at 20°C. Similar developmental and ripening characteristics were observed in ‘Fuyumomogatari®’ grafted onto its seedling and grown on the experimental farm of Okayama University, suggesting that these unique traits shown in ‘Fuyumomogatari®’ are stable traits that can be transferred by grafting.
In order to develop a non-destructive method to measure the chlorophyll concentration of fruit skin in apple (Malus × domestica Borkh.), reflectance of diffused light through the skin of fruit was measured using a portable spectrometer. Reflectance was acquired in the 650–740 nm wavelength range to establish a model to predict chlorophyll a and b concentrations using partial least squares regression. The chlorophyll concentration was precisely predicted by each model (r2 = 0.918–0.982) in ‘Akane’, ‘Sansa’, ‘Kitaro’, ‘Jonagold’, and ‘Fuji’ in 2018. Chlorophyll concentrations of ‘Akane’, ‘Sansa’, ‘Toki’, ‘Kitaro’, ‘Jonagold’, and ‘Fuji’ in 2019 were also estimated with small errors using the prediction model of ‘kitarou’ in 2018. The chlorophyll concentration showed a relatively high correlation with the ground color index (r2 = 0.783–0.903) and starch index (r2 = 0.694–0.947) in all cultivars. The prediction model was not significantly affected by the temperature of fruit. From these results, the chlorophyll concentration could be non-destructively, precisely, and rapidly estimated using a portable spectrometer, and there is possibility that this can be used to confirm the best time to harvest apple.
NAC (1-naphthyl N-methylcarbamate) has been used as a fruit thinner in apple orchards of Japan. It has long confused apple growers that the thinning efficacy of NAC varies widely from year to year. So, we searched for factors that could influence the thinning efficacy in weather data and data that describe conditions of trees, and tried to estimate the annual variation of the efficacy by developing a regression model using the factors. Whenever trees were treated with NAC, the time at which fruitlets of the trees stopped growing was the same as the time as when the untreated fruitlets destined to drop physiologically stopped growing. The thinning efficacy could be largely estimated by four factors: the number of fruitlets within a cluster when treated with NAC, the number of leaves on a cluster, the maximum temperature for three days after treatment, and the solar radiation for one week after three weeks of treatment. The regression model using the four factors as independent variables indicated that fruitlets on a cluster with many fruitlets and few leaves easily fall, especially under the conditions of a high maximum temperature and low solar radiation. The difference in the thinner efficacy by years was mainly due to the annual fluctuation of solar radiation for one week after three weeks of treatment.
Mango ‘Aiko’ is a large-fruited and medium-late cultivar that has a stronger biennial-bearing nature than ‘Irwin’. In this study, we applied the intentional alternate bearing method, which has been practiced in citrus cultivation, to mango ‘Aiko’ and examined its applicability. Two treatments, alternate branch unit bearing and whole-tree annual bearing, were set up and compared with the control of the conventional method. Although there was no significant difference in the proportion of reproductive shoots between the control and two treatments, the proportion of reproductive shoots on ON-trees or ON-branches was consistently high. No significant difference was observed in yield between the control and treatments, while the mean fruit weight was significantly lower in both treatments compared with control fruits. The percentage of small fruits was higher in both treatments. With respect to work efficiency, it was shown that both alternate bearing methods could reduce the time required to prune a tree. On the other hand, the expression level of the MiFT gene was shown to be related to the biennial-bearing nature of ‘Aiko’, suggesting that it could be used to predict the number of flowers in the following season. Our results show that the intentional alternate bearing method for mango ‘Aiko’ is an effective method to control the fluctuation of yield and reduce labor while maintaining the same level of fruit quality and yield as the conventional method.
The effect of day and night temperature on translocation and distribution of 13C-photosynthetic assimilates was investigated for clarifying fruit growth and ripening. The translocation rate in the daytime was significantly higher than twice that in the nighttime, and the effect of day temperature on translocation and fruit growth was greater than that of the night temperature. 13C-photosynthetic assimilates was most distributed to new leaves in the flowering stage, whereas the distribution rate to fruit was more than 90% at the high day-temperature and 70% at the low day-temperature in the white ripening stage (32 days after flowering). The dry weight of fruit in the white ripening stage was significantly heavier at the high day-temperature than at the low day-temperature, suggesting that the high temperature in the daytime promoted fruit development. The ripening days of top fruit at the secondary inflorescence were longer at the low day-temperature than at the high day-temperature, but the days were not affected by the night temperature. Furthermore, the effect of day temperature on the ripening days was greater than that of the daily average temperature. From the above results, it was clarified that increasing the day temperature in the greenhouse during a severe cold season promotes the translocation and ripening of strawberry fruit. It could be used as one of the means to control the growth of strawberry.
Gerbera flowers are harvested by hand picking without scissors in Japan. Harvested gerbera flowers are cut and wet-transported, but some are not cut and dry-transported. We investigated the effects of stem cutting on electrolytes and sugars released from cut stems, the turbidity of vase water, and vase life in gerbera. The average stem length of ‘Minou’ gerbera at harvest was 57 cm. In this cultivar, electrical conductivity, sugar concentrations, and turbidity of vase water were affected by positions of stem cutting and the method of cutting. These values were relatively low in uncut stems and stems cut at the site proximal to the base of stems, whereas they were relatively high in stems cut at a distance of 40 cm from the flower head. Electrical conductivity, turbidity, and sugar concentrations in the vase water were significantly correlated. Variations in vase life, turbidity of vase water at 7 days after cutting, and water uptake were investigated using seven cultivars. The vase life was negatively correlated with electrical conductivity and sugar concentrations in the vase water at 2 days after cutting. Next, we investigated the effect of cutting on turbidity and sugars in ‘Pinta’ and ‘Picture Perfect’, whose vase life was the longest and shortest among the seven cultivars, respectively. In cut ‘Pinta’, turbidity and sugar concentrations in vase water were only slightly increased and the vase life was significantly extended by cutting stems. In contrast, these values were markedly increased and vase life was not extended in ‘Picture Perfect’. These results suggest that sugars and electrolyte were released into vase water by cutting stems, and difference in the amounts of these compounds may be associated with cultivar variations in vase life in cut gerbera flowers.
The deep red strawberry cultivar ‘Shinku-no-misuzu’ was newly bred from a crossing between ‘Fusanoka’ and ‘Reiko’, and was characterized regarding aspects of the flowering time, yield, and fruit quality under forcing culture in Kanagawa Prefecture. ‘Shinku-no-misuzu’ exhibited slightly slower floral bud differentiation than the conventional cultivar ‘Tochiotome’, but showed high fruit hardness and a >20 brix/acid ratio. Relatively large amounts of glucose and fructose accumulated in ‘Shinku-no-misuzu’ fruit. The total anthocyanin content of the fruit was 185 μg・g-1 FW, which reached around three-fold the content of ‘Tochiotome’. The higher amount of anthocyanins, which are also known as antioxidants, in ‘Shinku-no-misuzu’ did not boost the total antioxidant activity of juice. Because >80% of anthocyanins were composed of pelargonidin glycosides in all cultivars investigated, the deep red color of ‘Shinku-no-misuzu’ fruit may not have been due to the anthocyanin composition but simply to the higher anthocyanin content.