Investigation of the tissue-specific ploidy levels of mature complete seeds produced by the cross-breeding of citrus varieties demonstrated that the ploidy level of the inner seed coat is consistent with that of the endosperm. We carried out another investigation using seeds obtained by natural crossing of a diploid ‘Otachibana’ to examine changes in the tissue-specific ploidy levels and structures over time, and found that the endosperm exhibited triploidy and retained a jelly-like structure until mid-August, which then transformed into a membrane structure lining the inner surface of the inner seed coat (except where the chalaza is present) by late August. By late October, the membrane-like endosperm had been assimilated into the inner seed coat. As the seeds matured, the inner seed coat that had initially exhibited diploidy eventually displayed no polyploidy at all. The endosperm, on the other hand, exhibited polyploidy even after late October. Although it was previously thought that the endosperm degenerates and disappears over time, our study demonstrated that it actually transforms into a membrane structure and attaches itself to the inner surface of the inner seed coat. In fact, the tissue that was believed to constitute the inner seed coat actually turned out to be the transformed endosperm that has been assimilated into the inner seed coat. Our study also showed that, by measuring the ploidy level of this tissue, we can estimate the ploidy levels of the embryos and its gametes without damaging the embryos.
To develop a new onion cropping type using onion sets for early winter harvesting, we investigated the effects of mulching films (white-on-black, black, and green mulching films) and planting dates (August 2, 12, 22, and September 1) of sets in the northern Tohoku area of Japan. The daily mean soil temperature was lower under the white-on-black mulching film than under the green or black mulching films, especially in August. The duration from planting to sprouting was shorter whereas the plant growth, marketable bulb weight, and yield were higher under the white-on-black film than under the other films, possibly because of the lower temperature leading to less plant growth inhibition. Among the planting dates, the plant growth, marketable bulb weight, and yield were the highest in the case of August 12, resulting from a longer duration from planting to bulb initiation and moderate daylength and temperature during bulb growth. Therefore, it was considered that planting onion sets around August 12 and the use of the white-on-black mulching film were optimal adaptations to the cropping type for early winter harvesting. However, the number of decayed bulbs, likely caused by freezing injury just before the end of harvesting, was high under the white-on-black mulching film.
The effects of long-day treatment (day-extension and night break treatment with an incandescent lamp) were investigated to obtain hypertrophied seed bulbs of Allium × wakegi Araki for early summer-harvesting cultivation. A day length longer than 15 hours accelerated bulb hypertrophy (bulb hypertrophy index about 2.5 compared with conventional production) and early plant growth in ‘Shimonoseki’. Similar effects were observed by 3–4 hour night break treatment, which reduced the cost of electricity. Long and early long-day (16 hr) treatment increased the bulb hypertrophy index, but this index and the bulb weight at planting were lower after experimental periods of 40 and 60 days. A period of supplemental lighting treatment longer than 80 days and starting on January 1st would promote bulb enlargement, as in conventional production.
In strawberry propagation, a 35-hole tray (6.5 × 6.5 cm apart and cell volume of 130 mL) is easy to handle and convenient for the establishment of runner cuttings in a nursery. It is also efficient for artificial flower-inducing treatment, such as intermittent low-temperature storage (ILTS). However, flower bud differentiation and consequent flowering are generally later and the effects of ILTS have been inferior compared with 9-cm polyethylene pot- or 24-hole tray-grown plants. In this experiment, we examined the effect of plant spacing of tray grown runner cuttings of ‘Nyoho’, at densities of 17, 25, and 35 plants per tray (50, 70, and 100% PPT, respectively) before flower induction with ILTS treatment on flowering. In 100% PPT, the petiole was significantly longer and the root sugar content per plant was low, compared with 50 and 70% PPT. Each plant grown under 50 or 70% PPT was then planted at 100% PPT, and 9-day ILTS (3 days under ambient conditions inserted between two 3 days at 15°C in the dark) was conducted from 25, 28, and 31 August. In 50% PPT, flowering was early and uniform, but in 100% PPT it was markedly delayed compared with 50 and 70% PPT, when ILTS was conducted earlier. From these results, it is considered that the effectiveness of early ILTS can be improved by plant spacing in the middle stage of tray plant propagation, after the establishment of runner cuttings and before flower-inducing treatment.
Effects of temperature conditions on fruit development were examined in tomato (Solanum lycopersicum L.) with different planting seasons and in each fruit truss. Nine cultivars were planted in July and September in 2014 and 2015. The period during anthesis and fruit set (fruit-set stage) was longer, and the period during fruit set and break (fruit-development stage) was significantly shorter with July planting than September planting for all cultivars at both years tested. The fruit weight, diameter, and number of seeds were reduced significantly in most cultivars with July planting compared with September planting. Additionally, with July planting in both years, more than half of the cultivars showed a significant increase in the production ratio of small fruit (less than 50 g). The cultivars showing a markedly decreased fruit weight with July planting also showed a markedly reduced number of seeds, and the number of days in the fruit-set stage was much higher and that in the fruit-development stage was much lower. In the cultivars, the fruit weight was markedly reduced in the first truss with July planting in both years tested, and the temperature of the fruit-set stage was higher in the first truss. The fluctuations in the fruit weight and seed number of each fruit truss were correlated with the temperatures of the fruit-set stage of each fruit truss with July planting. In this experiment, it was considered that the decrease in fruit development with July planting was correlated with the seed number and days of the fruit-development stage, and strongly affected by the temperature of the fruit-set stage.
The storage characteristics of the newly developed squash fruit with a mealy texture were investigated. The firmness of steamed mesocarp of some of the squash fruit during the storage decreased slowly, revealing the tendency to retain the mealy texture for a long period. The total sugar content was significantly lower before storage but increased sharply after storage. The a* value of the flesh color immediately before storage tended to increase rapidly after storage, but the L* value tended to be higher from immediately before storage. Whereas ‘Ebisu’, which is a control variety, had a high total sugar content even before storage, and a high a* value for the fruit color, the fruit firmness decreased sharply due to the storage and the mealy texture was lost. The fruit were classified into two types based on changes in quality during the storage. ‘Ebisu’ is a variety that needs to be shipped immediately after harvesting or within 1 month of storage. However, some varieties of squash fruit with a markedly mealy texture, such as ‘Jeje-J’, TC 58 and TC 59, can be shipped after storage for 1 month or longer.
An experiment involving the open field culture of asparagus was conducted. Asparagus was planted using the planting implement, and spears of first-year stocks that had sprouted in the spring following planting were all harvested until the stocks completed spear emergence, and this cultivation method was termed: “Whole harvest cultivation method for one-year-old plants”. The new cultivation method, in which plug seedlings of asparagus are planted deeply using a new hole-maker, overcame obstacles faced by the permanent conventional method in early spring, including damage caused by frost and low temperatures. To examine the appropriate planting time for the Whole harvest cultivation method for one-year-old plants, two varieties of asparagus: a purple asparagus, ‘Manmi-murasaki’, and a green asparagus, ‘Taiho-wase’, were planted at different times, and their growth and yields were compared. The early planting of both varieties using the new hole-maker produced large stocks. The earlier the time of planting, the greater the yield of thick spears (L or larger size), total yield, and marketable yield. Furthermore, the yield in April—the best season for asparagus and a lean season for other vegetables, was larger, and the yield in the first year was equal to or larger than the mean annual yield per unit of land in open field culture. The Whole harvest cultivation method for one-year-old plants is a new labor-saving, low-cost, and profitable cultivation method that can produce a large yield of high-quality asparagus.
The distribution of domestic onions decreases due to the off-crop season of large production areas such as Hokkaido, Saga, and Hyogo from late June until early September, while imported products compensate to meet the market needs during this period. In Aomori, a conventional autumn-sowing cultivation technique is normally used for growing onions; however, production in this area is not so common because of low yield (due to the bad-weather conditions) and/or competition with garlic cultivation in the same area and the same season. Our preliminary study showed that a number of cultivars could be successfully harvested from mid-July if the seeds were sown in February and the seedlings were planted in April in the Tsugaru region—namely the ‘Spring-sowing technique’. In this study, a 3-year trial was conducted with the aim of choosing suitable varieties for the February-sowing technique. ‘Queru-tama’ and ‘Marusou’ could be harvested in mid-July and showed a sufficient yield and low rate of rotten bulbs. ‘Kita-momiji 2000’ and ‘Okhotsk 222’ were harvested from late July to early August and showed high yields. These two varieties were characterized as suitable varieties for storage and long-term shipping. ‘Quergold’ contained markedly high levels of quercetin glycosides; thus, this variety may be characterized as ‘a high-functional variety’. We showed an effective method for the multifaceted visual evaluation of cultivars using radar chart graphs in order to adjust to the various needs of growers and consumers.
With the aim of regional revitalization using a newly developed local cultivar, the new local pungent radish “Izumo Orochi Daikon”; ‘Susa-no-o’, with a distinctive root appearance and strong pungency, was bred from the genetic resources of wild radish (Raphanus sativus L. f. raphanistroides Makino) in the Izumo region of Shimane Prefecture. The improvement of the late bolting trait and resistance to mosaic disease were suggested in this cultivar as a result of repeating mass selections to achieve the breeding objectives. The seeds of ‘Susa-no-o’ after harvesting show a transition of germination rate similar to that of general radish. This cultivar can be evaluated as a high-functional radish with especially high free amino acid levels, isothiocyanate levels and 1,1-diphenyl-2-picrylhydrazyl (DPPH) antioxidative properties compared with other cultivars. This local pungent radish, registered as a Shimane University brand, has gradually spread and been popularized in the region. Recently, it was recognized as one of the local varieties of Shimane Prefecture, and it has begun to contribute to regional agriculture and revitalization.