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J.G. Carew, K. Mahmood, J. Darby, P. Hadley and N.H. Battey

The effects of temperature, photosynthetic photon flux density (PPFD) and photoperiod on vegetative growth and flowering of the raspberry (Rubus idaeus L.) `Autumn Bliss' were investigated. Increased temperature resulted in an increased rate of vegetative growth and a greater rate of progress to flowering. Optimum temperatures lay in the low to mid 20°C range. Above this the rate of plant development declined. Increased PPFD also advanced flowering. While photoperiod did not significantly affect the rate of vegetative growth, flowering occurred earliest at intermediate photoperiods and was delayed by extreme photoperiods. These responses suggest that there is potential for adjusting cropping times of raspberry grown under protection by manipulating the environment, especially temperature.

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Kazuhiro Fujiwara, Toshinari Sawada, Yoshikatsu Kimura and Kenji Kurata

A light-emitting diode (LED)-low light irradiation (LLI) storage system was developed for suppressing the change in dry weight and maintaining the quality of green plants during long-term storage. In this system, the carbon dioxide (CO2) exchange rate was maintained at zero by automatically adjusting the photosynthetic photon flux density (PPFD) with a proportional-integralderivative (PID) controller. The voltage supplied to the LEDs was controlled by the difference between the inflow (400 μmol·mol-1) and outflow CO2 concentrations in the storage case. Grafted tomato (Lycopersicon esculentum; scion = `House Momotaro'; rootstock = `Anchor T') plug seedlings were stored at 10 °C for 35 days under four different LLI conditions as a system operating test: fixed red light irradiation at 2 μmol·m-2·s-1, PID-controlled red light irradiation with no blue light, and PID-controlled red light irradiation with blue light at 0.2 or 1.0 μmol·m-2·s-1. The results showed that the automatic PPFD control during LED-LLI helped suppress changes in dry weight during storage as expected. Furthermore, it was found that addition of a low percentage of blue light improved the morphological appearance of the seedlings and reduced the PPFD required to suppress the change in dry weight.

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Richard P. Marini, Donald Sowers and Michele Choma Marini

Abbreviations: DAFB, days after full bloom; DBH, days before harvest; IPPFD, incident photosynthetic photon flux density; PPFD, photosynthetic photon flux density. 1 Associate Professor. 2 Laboratory Technician. 3 Research Technician. The cost of

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Mengmeng Gu, James A. Robbins, Curt R. Rom and Hyun-Sug Choi

photoautotrophic plants depend ( Lambers et al., 1998 ). Photosynthesis is highly correlated with photosynthetic photon flux density (PPFD), and thus net carbon gain and biomass production, if other factors are optimal such as water and nutrient supply. Low PPFD

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Thitipat Weeplian, Tsair-Bor Yen and Yunn-Shy Ho

/white without far red (RW−Fr) in the early growth stage and later removing the covers red/white with far red (RW+Fr). Light spectra were measured at 15 cm under the LED lamps. Table 1. Photosynthetic photon flux density ( PPFD ) of each light spectrum treatment

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Marc W. van Iersel, Geoffrey Weaver, Michael T. Martin, Rhuanito S. Ferrarezi, Erico Mattos and Mark Haidekker

(top) and a simplified diagram of the duty cycle control board (bottom). A fluorometer is used to measure the quantum yield of photosystem II and the datalogger calculates the electron transport rate from this and the photosynthetic photon flux density

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David J. Ballantyne

The influence of photosynthetic photon flux density (PPFD) and gibberellic acid (GA3) sprays on shoot elongation was determined for `Coral Bells' (Kurume or R. obstusum hybrid), `Fashion' (Glen Dale or R. indicum × Kurume hybrid), `Hexe' (R. obtusum × R. simsii hybrid), `Hinocrimson' (Kurume or R. obtusum hybrid), `Hinodegiri' (Kurume or R. obtusum hybrid), and `Red Wing' (Brooks hybrid) azalea. GA3 at 1 mm was more effective in stimulating shoot elongation of `Coral Bells', `Fashion', `Hinodegiri', and `Red Wing' than of `Hexe' or `Hinocrimson'. GA3 sprays were more effective in stimulating elongation when applied to plants growing at irradiance levels of 350 μmol·s-1·m-2 than to plants growing at either 200 or 100 μmol·s-1·-2. Gross photosynthesis of leaf segments was higher for a slow-growing cultivar (Hinocrimson) than for a faster-growing cultivar (Fashion). `Hinocrimson' produced stouter shoots (greater dry weight/cm) than did `Fashion'.

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Stephen C. Myers

Abbreviations: DAH, days after harvest; DBH, days before harvest; PPFD, photosynthetic photon flux density; WSR. watersprout removal. 1 Associate Professor of Horticulture. A contribution of the Univ. of Georgia Agricultural Experiment Station

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Richard J. Campbell and Richard P. Marini

Percent instantaneous incident photosynthetic photon flux density (%INPPFD) was measured within an apple (Malus domestica Borkh.) canopy for various sky conditions and used to predict the percent cumulative incident photosynthetic photon density (PPD) for the last 10 weeks of the growing season (%CPPDLS) and the total growing season (%CPPDTS). Instantaneous measurements from overcast conditions were superior to measurements from clear or hazy conditions for the prediction of %CPPDLS in 1989 and 1990. A one-to-one relationship between %INPPFD and %CPPDLS was found for overcast conditions in both years, even though there was an 11% difference in total cumulative PPD between the years. The models had good predictive accuracy, with prediction coefficients of determination (R 2 Pred) >0.83 in both years (n = 30). %lNPPFD from overcast conditions also yielded accurate predictive models for %CPPDTS (R > 0.84, n = 30), which differed from the models for %CPPDLS. Predictive models (for both %CPPDLS and %CPPDTS) from %lNPPFD made before the canopy was fully developed differed from the models developed after canopy development was complete. The models still had good predictive accuracy, with R 2 Pred >0.76 (n = 30). Predictive models developed for cloudless conditions had inferior predictive accuracy (R 2 Pred = 0.49 to 0.80, n = 30) compared to models for overcast conditions. R 2 Pred were higher for hazy than for clear conditions. Time of day (1000 to 1400 hr) had no consistent effect on the development of predictive models for any weather condition. The most reliable models resulted from the average of several measurements within a day, particularly for cloudless conditions.

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Richard J. Campbell and Richard P. Marini

Photosynthetic photon flux density (PPFD), measured at various canopy positions throughout the growing season in 1989 and 1990, was used to explain variation in fruit characteristics of `Delicious' apples (Malus domestica Borkh.) harvested from these positions at 135, 145, 155, and 165 days after full bloom (DAFB). Hours above an average PPFD threshold of 250 μmol·m-2·s-1 (HR250) explained an average of only 2% more variation in fruit characteristics than other PPFD threshold levels or total cumulative photosynthetic photon density (PPD) in each year. Percent of red surface had a positive linear relationship with HR250 on all harvest dates in both years; intercepts increased on each successive harvest. The slopes and R 2 were highest at 135 DAFB and decreased on each successive harvest. Intensity of red pigmentation and soluble solids concentration also increased linearly with HR250, with equivalent slopes and increasing intercepts on each successive harvest. Fruit weight, flesh firmness, length: diameter ratio, and starch index were not consistently affected by any measure of canopy light levels. Except for intensity of redness, relationships developed between fruit characteristics and cumulative late-season PPD during the final 10 weeks before harvest (CPPDLS) had trends similar to the models for HR250 for all harvests in both years. Models developed with instantaneous light measurements were similar to those developed with the more detailed cumulative light measurements.