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Chieri Kubota, Natsuko Kakizaki, Toyoki Kozai, Koichi Kasahara and Jun Nemoto

Nodal explants of tomato (Lycopersicon esculentum Mill.) were cultured in vitro to evaluate the effects of sugar concentration, photosynthetic photon flux (PPF), CO2 concentration, ventilation rate of the vessel, and leaf removal on growth and photosynthesis. After 20 days of culture, the dry weights of plantlets derived from explants with leaves and cultured photoautotrophically (without sugar in the medium) under high PPF, high CO2 concentration, and high ventilation rate were more than twice as great as those of plantlets derived conventionally from explants without leaves and cultured photomixotrophically (with sugar in the medium) under low PPF, low CO2 concentration, and low ventilation rate (107 and 45 mg per plantlet, respectively). Under photomixotrophic micropropagation conditions, the dry weights of plantlets from explants with leaves increased more than did those of plantlets from explants without leaves. High PPF, high CO2 concentration, and high ventilation rate increased net photosynthetic rate and promoted growth of the plantlets under photomixotrophic micropropagation conditions. Photomixotrophic conditions produced the greatest dry weight and the longest shoots, but photoautotrophic conditions produced the highest net photosynthetic rate. The number of leaves did not differ significantly between photoautotrophically and photomixotrophically cultured plantlets. Thus, photoautotrophic micropropagation is applicable to the production of high quality tomato transplants.

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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.

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C. Kubota, N. Abe, T. Kozai, K. Kasahara and J. Nemoto

`HanaQueen' tomato plantlets were cultured under conditions with different levels of sugar, photosynthetic photon flux, CO2 concentration, and number of air exchanges of the vessel. Effects of medium substrates (Gelrite or vermiculite) and explant preparation (with or without leaves) on growth of the plantlets were also examined. After 20 days in culture, photoautotrophically cultured plantlets with leafy explants, under increased PPF, CO2, and ventilation rate of the vessel had twice as much dry weight as those cultured conventionally with non-leafy explants under low PPF, CO2, and ventilation rate of the vessel. Dry weight of the plantlets was significantly greater when cultured with leafy than non-leafy explants. Net photosynthetic rate of the plantlets increased linearly as culture period when cultured without sugar, and remained almost zero when cultured with sugar, regardless of other culture conditions. Results obtained in this experiment have shown that tomato plantlets can be grown photoautotrophically, and the net photosynthetic rate was greater under photoautotrophic than under conventional photomixotrophic conditions.

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Genhua Niu, Makio Hayashi and Toyoki Kozai

Potato (Solanum tuberosum L. cv. Benimaru) plantlets were cultured under four lighting cycles (photoperiod/dark period: 16 h/8 h, 4 h/2 h, 1 h/0.5 h, and 0.25 h/0.125 h) photoautotrophically (without sugar in the medium), and photomixotrophically (with sugar in the medium) in vitro for 28 days. Simulations of time courses of CO2 concentration in the vessel (Ci) and dry weight accumulation of the plantlets cultured photoautotrophically were conducted using a previously developed model (Niu and Kozai, 1997). While underestimation and overestimation of time courses of Ci in some treatments were observed, the simulated results of Ci and dry weight accumulation of the plantlets generally agreed with the measured ones. The difference of net photosynthetic rate response to Ci throughout the culture period was examined between the plantlets cultured photoautotrophically and photomixotrophically. Quantitative relationship between daily net photosynthetic rate (daily net production) and vessel ventilation rate per plantlet was simulated under various CO2 levels outside the vessel for given sizes of potato plantlets cultured photoautotrophically in vitro to aid appropriate CO2 enrichment and vessel design in commercial micropropagation.

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Damien de Halleux and Laurent Gauthier

Transpiration and water uptake play an important role in the growth of horticultural crops, such as tomatoes. Water uptake ensures the transport of nutrients. However, the transpiration rate is affected by the humidity level in the greenhouse. High levels of humidity restrict transpiration and lead to fungal diseases resulting in yield losses. Under northern latitudes, using more airtight structures combined with high levels of artificial lighting increase the humidity level inside the greenhouses. To decrease humidity, growers have to dehumidify by ventilating and heating at the same time, leading to increased energy consumption. However, to our knowledge, the literature does not report on the energy consumption needed to dehumidify. To evaluate this energy consumption, we used a greenhouse simulation model of heat and mass exchanges integrated into a general greenhouse control and management software system (GX). Evapotranspiration, condensation on the cladding, and infiltration and ventilation rates were taken into account for the water balance. Based on 1 year of climatic data, three sets of simulation were realized: 1) no dehumidification; 2) standard dehumidification by ventilation and heating; 3) dehumidification with heat exchangers. Results indicate that for an acceptable level of humidity within a greenhouse tomato crop (vapor pressure deficit >5 kPa), the energy consumptions with standard dehumidification and with heat exchangers are 25% and 15% higher, respectively, than without dehumidification. These results are being used to establish recommendations for the management of humidity under northern latitudes.

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Sandra B. Wilson, Jeongwook Heo, Chieri Kubota and Toyoki Kozai

Sweetpotato [Ipomoea batatas (L.) Lam., `Beniazuma'] plantlets were grown photoautotrophically (without sugar) for 12 days in an improved forced ventilation system designed with air distribution pipes for uniform spatial distributions of carbon dioxide (CO2) concentration. Enriched CO2 conditions and photosynthetic photon flux (PPF) were provided at 1500 μmol·mol-1 and 150 μmol·m-2·s-1, respectively. The forced (F) ventilation treatments were designated high (FH), medium (FM), and low (FL), corresponding 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. Total soluble sugar (TSS) and starch content were determined on day 12. Total soluble sugars (sucrose, glucose, fructose) of FH plantlets were lowest in leaf tissue and highest in stem tissue as compared to other ventilation treatments. Starch concentration was higher in leaf tissue of FH or FM plantlets as compared to that of FL or NE plantlets. Plantlets subjected to FH or FM treatments exhibited significantly higher net photosynthetic rates (NPR) than those of the other treatments; and on day 12, NPR was almost five times higher in the FH or FM treatment than the FL or NE treatments. Carbohydrate concentration of plantlets was also influenced by the position of the plantlets in the vessel. Within the forced ventilation vessels, leaf TSS of FH and FM plantlets was similar regardless of whether plantlets were located near the inlet or outlet of CO2 enriched air. However, under FH or FM conditions, leaf starch concentration was higher in plantlets located closest to the CO2 inlet as compared to the outlet.

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Julie M. Tarara, Bernardo Chaves and Bernadine C. Strik

tube and 20.5 °C for the opaque tube. The T mulch in the translucent tube was up to 11 °C higher than that in the opaque tube. At the low ventilation rates characteristic of these grow tubes, the daytime average difference between T a and T mulch (T

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and outside of the culture vessel. Heo et al. ( p. 90 ) developed a forced ventilation micropropagation system for growing plants without sucrose on a large scale. Increasing the forced ventilation rate during the culture period with air distribution

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How-Chiun Wu, Mei-Ling Kuo and Chia-Min Chen

plantlets to exogenous carbohydrates, which promotes the gradual development of photoautotrophic characteristics ( Kozai and Kubota, 2005 ). According to Xiao et al. (2011) , the most challenging task of ventilation is to regulate the ventilation rate of

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Meijun Zhang, Duanduan Zhao, Zengqiang Ma, Xuedong Li and Yulan Xiao

; Kubota and Kozai, 2001 ). A high CO 2 level in the vessel can be achieved by increasing CO 2 concentration in the culture room and the number of air exchanges in the vessel. The latter, defined as the hourly vessel ventilation rate divided by the air