316 Effects of Planting Density and Short-term Changes in Photoperiod on the Growth and Photosynthesis of Two Cultivars of Bean (Phaseolus vulgaris L.)

Abstract

The effects of planting density and short-term changes in photoperiod on the growth and photosynthesis of bean (Phaseolus vulgaris L.) was investigated. Two cultivars of bean (cv. Etna, a dry bean variety; cv. Hystyle, a snap bean variety) were grown using nutrient film technique hydroponics in a walk-in growth chamber with a 12 h/12 h (light/dark) photoperiod and a corresponding thermoperiod of 28/24 °C (light/dark) and constant 65% relative humidity. Lighting for the chamber consisted of VHO fluorescent lamps and irradiance at canopy level was 400 μmol·m-2·s-1 PPF. For each cultivar, plants were grown at densities of 16 or 32 plants/m2. Short-term photoperiod changes were imposed during vegetative growth (21-29 DAP) and pod-fill (42-57 DAP). From the base 12 h/12h (light/dark) photoperiod, lighting in the chamber was cycled to provide 18 h/06 h (light/dark) or 24 h/0 h(continuous light) for 48 h. Diurnal single leaf net photosynthetic rates (Pn) and net assimilation vs. internal CO2 (Aci) measurements were taken during the short-term photoperiod adjustments. Results showed that there was no difference between cultivars or planting density with regard to total biomass or single leaf photosynthetic rates, but cv. Etna produced 35% more edible biomass than cv. Hystyle. Additionally, there was no effect of short-term photoperiod adjustment on single leaf Pn or Aci.