The effects of CO₂ enrichment (700-900 ppm in the day time) and planting density on yield, fruit quality and water and mineral uptake by plants were investigated with strawberry (Fragaria × ananassa Duch. cv. Nyoho) grown in peat bag culture (width : 30 cm, length : 80 cm, media : 18 L) . Under CO₂ enriched condition, total amount of uptake in each mineral increased with vigorous plant growth and increase in yield. Therefore, concentration of minerals and EC in drainage were quite low and only 3-10, 10 and 7-12% of supplied N, P and K were wasted with drainage, respectively. Total yield per plant increased by 50 to 70% with CO₂ enrichment. Yield per peat bag (equal to area basis) increased with increasing planting density under CO₂ enriched condition, however, that in control (200-400 ppm in the day time) increased little with increase in planting density. Average fruit weight and fruit total soluble solid content decreased with increasing planting density. Supplemental CO₂ enrichment may serve to increase the yield of strawberry grown in peat bag culture where little CO₂ supply from the soil could be expected, and eight plants in a 80 cm long peat bag may be a reasonable planting density to obtain both high yield and fruit quality.

View full abstract

Low synchronization of somatic embryogenesis prevents the application of a large-scale production bioreactor to a transplant production system. We attempted to improve synchronization of carrot somatic embryogenesis for large-scale production by controlling the dissolved oxygen concentration. A suitably low dissolved oxygen concentration repressed excessive development of cotyledonary-stage embryos but did not affect the development of globular, heart, and torpedo-stage embryos. As a result the development of somatic embryos stopped at the torpedo stage under this condition. Moreover, the number of torpedo-stage embryos increased, and it was larger than the maximum number of torpedo-stage embryos in culture with ambient oxygen aeration. These torpedo-stage embryos regenerated normal plantlets after mild dehydration treatment. This method does not require changing the medium nor filtration of the somatic embryos during the culture period for synchronization of the culture. If this simple method is used for large-scale production of somatic embryos with a bioreactor, effective synchronization can be achieved by only controlling the dissolved oxygen concentration.

View full abstract

Grafted tomato (Lycopersicon esculentum Mill., scion: cv. Momotaro; rootstock: cv. Herupa M) plug seedlings were stored at 10°C for 28 d under different gas compositions (0.05% CO₂+20% O₂, L; 0.5% CO₂+ 10% O₂, M; 1% CO₂+5% O₂, H) at a photosynthetic photon flux density of 0 (dark, D) or 2 (low light irradiation, LLI, using an array of red light emitting diodes, R) μmol m^-2 s^-1. The percentages of the seedlings with subjective visual quality scores 5 and 4 (seedlings with scores 5 and 4 are considered stored successfully and acceptable) in MR and HR were both about 70% on the last day of storage (day 28), while the percentage in LD (control: usual low temperature storage) was 0%. The total percentage of the seedlings with scores 5 and 4 in LD, MD and MR did not fall below 90% until day 9, day 15 and day 24, respectively, indicating that acceptable storage duration of the seedlings stored under controlled atmosphere (CA) and CA combined with LLI was prolonged nearly 1.7 times and 2.7 times longer, respectively, than that under usual low temperature storage. There was no significant difference in dry weight of the seedlings in R between day 0 and day 28, while the seedling in D lost their dry weight during storage. Regardless of the gas composition, survival percentages of the seedlings after storage in R were 100%, in contrast to 20% in LD, 60% in MD and 80% in HD. These results indicate that CA combined with LLI was more effective than both CA without LLI and LLI without CA, respectively, for low temperature storage of grafted tomato plug seedlings with high visual quality and growth potential after storage.

View full abstract

Exposing seedlings of Eustoma and Delphinium to high temperature induces rosetting. Therefore, in the cultivation for earlier flowering of these species, the utilization of a cooling system during raising of seedlings in the summer seems to be necessary in order to prevent rosetting. Eustoma and Delphinium seeds were sown in a greenhouse on 17 May. The seedlings were planted in 7.5 cm pots on 17 July. These were transferred under the spot-cooling condition or outdoors on 19 July. The daily mean temperature under the spot-cooling condition was kept less than 20°C, 10°C lower than that of outdoors where the control plants were placed. The potted plants were transplanted on the soil beds in a plastic house on 18 September in Eustoma, on 14 October in Delphinium. They were exposed to a photoperiod of a 16-h day and maintained above 10°C from the end of October. As a result, Eustoma seedlings raised under the spot-cooling condition did not show any rosetting and produced floweres of high quality in late March, 2 months earlier than those grown outdoors. As for Delphinium, 48% of control plants raised outdoors showed flower stalk development of 10-20 cm in length during the summer season. Almost all of them subsequently died. The rest of the live plants showed rosetting after transplanting and flowered in late April, while none of the plants under the spot-cooling condition showed either flowering during the summer season or rosetting after transplanting. These plants flowered with an infloresence of high quality and long flower stems in mid January.

View full abstract

In solution culture of sweetpotato (Ipomoea batatas Lam.), tuberous root can grow in the air. Then the tuberous root growth was analyzed to examine the effect of air humidity around the tuberous root. Sweetpotato (cv. Koganesengan) was planted in the hydroponic system, and the tuberous root was kept in the air space separated from the shoot and the fibrous root environments. The tuberous root was grown under 50, 70 or 90%RH, and the volume change was measured on-line. Quantitative analysis of water balance in the growing tuberous root was also carried out for each humidity. Volume increments of the tuberous root during four days were about 0.6 cm³ at 50%RH, 1.5 cm³ at 70%RH and 0.2 cm³ at 90%RH, indicating that the tuberous root growth was enhanced most at 70%RH and depressed most at 90%RH. Diurnal pattern of the growth rate revealed that the humidity effect was brought during the nighttime. At 50%RH, water influx into the tuberous root through vascular bundle was almost similar to that at 70%RH, whereas the largest evaporative water loss depressed the water accumulation for growth. On the other hand, the smallest water influx into the tuberous root was found at 90% RH, which resulted in the smallest water accumulation in spite of the least evaporative water loss. Responses of the tuberous root to step changes in the ambient humidity suggested that 90%RH induced quick and strong inhibition on the growth.

View full abstract

Whole chervil (Anthriscus cerefolium L.) harvested in a commercial operation was placed in a plastic container at 5°C under different CO₂ concentrations (0.05, 0.5 or 1.0%) and PPFDs (photosynthetic photon flux density ; 0, 0.5, 1.0 or 2.0μmol m^-2 s^-1) to determine CO₂ exchange rate at an atmospheric O₂ conc. of 20%. The CO₂ exchange rate was calculated from the difference between CO₂ conc. of outflow and inflow air (flow rate : 4.8L h^-1) through the plastic container. The CO₂ exchange rate decreased with increasing CO₂ conc. or increasing PPFD. Relationship of CO₂ conc. and PPFD where the CO₂ exchange rate becomes 0 was obtained by drawing a 3-dimensional (CO₂ conc., PPFD and CO₂ exchange rate) graph. Three combinations of CO₂ conc. and PPFD (0.05%+ 1.6μmol m^-2 s^-1: C0.05P1.6 ; 0.5%+0.5μmol m^-2 s^-1: C0.5P0.5 ; 1.0%+0.2μmol m^-2 s^-1: C 1.0P0.2) were then selected among the relationship for the following storage experiment. Whole chervil was stored at 5°C and at O₂ conc. of 20% for 27 d under the conditions of the 3 combinations or under the usual low temperature storage conditions (0.04%+0 pmol m^-2 s^-1: Cont) as control. The color difference (ΔEab) values of the leaves of chervil in Cont, C0.05P1.6, C0.5P0.5 and C1.OPO.2 on the last day of storage (day 27) were 36, 22, 10 and 17 respectively, and there were significant differences among those values each other. The ΔEab values in Cont, C0.05P1.6, C0.5P0.5 and C1.0P0.2 were kept less than 9 until day 6, day 12, day 24 and day 15 respectively. A five-rank subjective visual quality score of chervil on day 27 in C0.5P0.5 was significantly higher than those in Cont and C0.05P1.6, and that in C 1.0P0.2 was significantly higher than Cont. These results indicate that the optimum conditions, at 5°C and at O₂ conc. of 20%, of low light irradiation-CA storage for preservation of the visual quality of postharvest whole chervil exist around the combination of 0.5%CO₂ and 0.5μmol m^-2 s^-1 PPFD.

View full abstract

To investigate the effects of flooding and anoxic stresses on respiratory metabolism in maize (Zea mays L.), the seedlings of two cultivars (cv. Jelly Bantam and Popcorn) were subjected to the stresses, and the activities of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) were determined. The relative importance of lactic and ethanolic fermentation was also characterized under such conditions. Flooding and anoxic stresses increased ADH activity in shoots and roots of two cultivars but the stresses did not increase LDH activity. The increases were greater in the roots than in the shoots of both cultivars under the flooding and the anoxic stresses, and greater in cv. Jelly Bantam than in cv. Popcorn under the flooding stress. Using polyacrylamide gel electrophoresis, only one ADH band was identified in extracts of the shoots and the roots of both cultivars under non-stress and three ADH isozemes were identified in the extracts under the stresses, which indicates that ADH subunit translation is increased by the stresses. These results suggest that the flooding and the anoxic stresses increase ADH activitiy in shoots and roots of two cultivars of maize but stresses do not increase LDH activitiy, and increased ADH activity may be due to increased synthesis of the enzyme.

View full abstract

Short-term effects of super-elevated CO₂ on stomatal aperture of potato (Solanum tuberosum L.) were investigated by serial observation of individual stomata of an attached leaf. Potato plantlets cultured in vitro from nodal cuttings were acclimatized and used for observation of stomata. Changes in stomatal aperture of attached leaves exposed to 25 000 pmol mol^-1 CO₂ were observed using a video microscope under an artificial light. The stomatal aperture on adaxial surface enlarged to 1.7 times the size in ambient air at 15-min exposure to super-elevated CO₂ and did not visibly change from 15 to 30 min. The result shows that short-term exposure to super-elevated CO₂ causes stomatal opening of potato under the light condition.

View full abstract

Stem tips of Zantedeschia hybrida ‘Black Magic’ were inoculated onto solid MS medium containing ABM1 (SIGMA ; antibiotics mixture) in vitro. A great majority of the explants became contaminated by endogenous bacteria. For comparison, sections of the tuber bearing a bud were soaked in ABM 1 solution for 5 d, and then stem tips were excised and planted onto MS medium. This treatment also showed no effect in suppressing contamination. In a third set of treatments, tubers bearing 2-3 foliage leaves were soaked in silver nitrate solutions (0.02-2.0 g L^-1) and then stem tips were excised and planted on MS medium. A 24-h treatment in 0.2 g L^-1 silver nitrate solution reduced the outbreak of endogenous contamination by 14%.

View full abstract