Search Results

You are looking at 1 - 10 of 33 items for

  • Author or Editor: Toyoki Kozai x
  • All content x
Clear All Modify Search
Free access

Chieri Kubota and Toyoki Kozai

A storage method of transplants in vitro was developed using light compensation points in conjunction with low temperatures. Broccoli (cv. Ryokurei) plantlets, aseptically germinated and cultured for three weeks in vitro, were used as model transplants. Culture conditions were: 23C air temperature, 160 μmol m-2s-1 PPF, and 3.6 air exchanges per hour of the vessel. Prior to storage, light compensation points were determined at 3, 5, 10, and 15C for the plantlets cultured with or without 20 g liter-1 sugar in the medium. Plantlets were stored for six weeks at 5, 10, and 15C under either 0 or 2 μmol m-2s-1 continuous PPF. The light compensation points varied with air temperature and with medium sugar level. Plantlet dry weight during storage was best maintained by keeping CO2 exchange rate of the plantlets close to zero throughout the storage period. High transplant qualities were successfully preserved at light compensation points: 2 μmol m-2s-1 PPF at 5-10C without sugar, and at 5C with sugar in the medium. This method may be applicable for storage of other crop transplants, plug seedlings and cuttings as well.

Free access

Chieri Kubota and Toyoki Kozai

Growth and net photosynthetic rate of potato (Solanum tuberosum L.) `Benimaru' plantlet in vitro were studied under a conventional photomixotrophic condition [with 20 g sucrose/liter in the medium and under 70 μmol·m-2·s-1 photosynthetic photon flux (PPF)] with minimal ventilation (MV) and under photoautotrophic conditions (without sugar in the medium and under 190 μmol·m-2·s-l PPF) with enhanced natural ventilation using an air diffusive filter (DV) or with forced ventilation (FV). Fresh weight of the plantlets cultured in the FV and DV treatments was 2.4 times that of the plantlets cultured in the MV treatment. Net photosynthetic rate and dry weight per plantlet were the highest in FV followed by DV. For photoautotrophic micropropagation, FV was superior to DV.

Free access

Toyoki Kozai and Tadashi Ito

Commercial transplant production in Japan has been increasing rapidly since 1985. Transplant production began with plug seedlings for bedding plants, followed by carnation and Chrysanthemum plug transplants vegetatively-propagated using cuttings. Next, production more recently includes plug seedlings of lettuce and cabbage, and micropropagated tubers of potato plants and grafted transplants of tomato, eggplant, cucumber, and watermelon plants. The reasons for the rapid increase in commercial production of transplants will be reviewed. The current “cutting edge” practices include hardening before shipping or planting. The pros and cons of current transplant production systems in Japan will be discussed. Recent research advances in production of micropropagated, grafted and seedling transplants are reviewed with special reference to environmental control for hardening or acclimatization. Research on robotic or automated systems for micropropagation, grafting, and transplanting currently developed in Japan are described.

Free access

Chieri Kubota and Toyoki Kozai

Broccoli (Brassica oleracea L. Botrytis Group `Ryokurei') plantlets, cultured photoautotrophically (without sugar in the medium) in vitro for 3 weeks at 23C and 160 μmol·m–2·s–1 photosynthetic photon flux (PPF), were stored for 6 weeks at 5, 10, or 15C under 0 (darkness) or 2 μmol·m–2·s–1 PPF (continuous lighting) supplied by fluorescent lamps (white light). Dry weight of the plantlets stored for 6 weeks at 5 or 10C in light was not significantly different from that of the plantlets before storage. Dry weight of the plantlets decreased as temperature increased and was maintained at higher levels in light than in darkness. Chlorophyll concentrations of the plantlets were higher at the lower temperatures. Chlorophyll fluorescence kinetics indicated higher activities of chlorophyll of the plantlets stored in light than in darkness. Lighting at as low as 2 μmol·m–2·s–1 PPF was important to preserve photosynthetic and regrowth abilities and dry weight of the plantlets during low-temperature storage.

Free access

Yulan Xiao and Toyoki Kozai

A photoautotrophic or sugar-free medium micropropagation system (PAM) using five large culture vessels (volume = 120 L each) with a forced ventilation unit for supplying CO2-enriched air was developed and applied to commercial production of calla lily (Zantedeschia elliottiana) and china fir (Cunninghamia lanceolata) plantlets. The culture period of calla lily plantlets in the PAM was reduced by 50%, compared with that in a conventional, photomixotrophic micropropagation system (PMM) using small vessels each containing a sugar-containing medium. Percent survival ex vitro of calla lily plantlets from the PAM was 95%, while that from the PMM was 60%. The production cost of calla lily in the PAM was reduced by about 40%, compared with that in the PMM, and the initial investment per plantlet for the PAM was ≈10% lower than that for the PMM. The sales price of ex vitro acclimatized calla lily plantlet was increased by 25% due to its higher quality, compared with plantlets produced in the PMM.

Full access

Kee Yoeup Paek and Toyoki Kozai

We report the results of serial studies aimed at clarifying several factors affecting organogenesis in rhizome culture of temperate Cymbidium species and their hybrids. The growth patterns and regeneration ability of rhizomes derived from asymbiotic seed or shoot tip culture vary according to media composition, kinds and concentrations of plant growth regulators, culture conditions, and species and varieties. N6-benzyladenine was the best cytokinin for inducing shoot formation, for switching rhizome tissues into protocorm-like bodies, and for directly forming multiple shoots from branched rhizomes. Activated charcoal appeared to be necessary for producing healthy plantlets and for stimulating shoot growth at levels of 0.1% to 0.3% but concomitantly decreased rhizome growth. Sucrose at 5% was the most effective concentration for shoot induction from rhizomes. The above results support the conclusion that organogenic pathways between tropical, subtropical, and temperate Cymbidium species may be controlled by the genetic backgrounds of the species or cultivars.

Full access

Jeongwook Heo, Sandra B. Wilson, and Toyoki Kozai

An improved forced ventilation micropropagation system was designed with air distribution pipes for uniform spatial distributions of carbon dioxide (CO2) concentration and other environmental factors to enhance photoautotrophic growth and uniformity of plug plantlets. Single-node stem cuttings of sweetpotato [Ipomoea batatas (L.) Lam. `Beniazuma'] were photoautotrophically (no sugar in the culture medium) cultured on a mixture of vermiculite and cellulose fibers with half-strength Murashige and Skoog basal salts in a scaled-up culture vessel with an inside volume of 11 L (2.9 gal). CO2 concentration of the supplied air and photosynthetic photon flux on the culture shelf were maintained at 1500 μmol·mol-1 and 150 μmol·m-2·s-1, respectively. Plantlets grown in forced ventilation systems were compared to plantlets grown in standard (natural ventilation rate) tissue culture vessels. The forced (F) ventilation treatments were designated high (FH), medium (FM), and low (FL), and corresponded to ventilation rates of 23 mL·s-1 (1.40 inch3/s), 17 mL·s-1 (1.04 inch3/s), and 10 mL·s-1 (0.61 inch3/s), respectively, on day 12. The natural (N) ventilation treatment was extremely low (NE) at 0.4 mL·s-1 (0.02 inch3/s), relative to the forced ventilation treatments. On day 12, the photoautotrophic growth of plantlets was nearly two times greater with the forced ventilation system than with the natural ventilation system. Plantlet growth did not significantly differ among the forced ventilation rates tested. The uniformity of the plantlet growth in the scaled-up culture vessel was enhanced by use of air distribution pipes that decreased the difference in CO2 concentration between the air inlets and the air outlet.

Free access

Chieri Kubota, Chalermpol Kirdmanee, and Toyoki Kozai

Cymbidium (cv. Lisa rose) PLB (protocorm-like bodies) were cultured in liquid 1/2 MS medium with/without 20 mg g-1 sucrose under continuous lighting conditions. The vessels were shaken at 100 rpm under PPF (photosynthetic photon flux) of 20 and 140 μmol m-2 s-1 and CO2 concentrations outside the vessel (Cout) of 450 and 2000 μmol mol-1 conditions. Photoautotrophic growth was obtained at high PPF and high Cout. The chlorophyll content of the PLB in the medium without sucrose at high PPF and high Cout was almost 3 times that with sucrose at low PPF and low Cout. The number of newly developed PLB with sucrose at low PPF and low Cout was 1.6 times that without sucrose at high PPF and high Cout; the dry weight per unit PLB with sucrose at low PPF and low Cout was almost 3 times that without sucrose at high PPF and high Cout. Photoautotrophic growth of the PLB might be further promoted at higher CO2 concentration (> 1%).