INFLUENCE OF LIGHT INTENSITY ON GROWTH AND CO₂ ASSIMILATION RATES OF THREE GENOTYPES OF CUCUMBER SEEDLINGS GROWN IN CHAMBERS

We compared the growth and CO2 assimilation rates among seedlings of ‘Khassib RZ’ (Beit Alpha type), ‘Proloog RZ’ (greenhouse type), and ‘Eterno’ (oriental type) cucumbers. Seedlings at the 5-leaf stage were grown for 7 days in assimilation chambers (length x depth x height: 500x500x800 mm) under 1 of 4 light levels (139, 204, 320, and 489 μmol m^-2 s^-1) supplied by 3-wavelength fluorescent lamps. Temperature and humidity were controlled at the same levels, and the CO₂ concentration was controlled from 400 to 1,200 ppm. The CO₂ assimilation rate increased significantly with light intensity. It was significantly higher in the oriental type than in the other types, which did not differ. However, the leaf area was significantly lower in the oriental type than in the other types. The dry weight of each organ also increased with light intensity, especially in the roots. The relative growth rate (RGR) and net assimilation rate (NAR) were significantly positively correlated with light intensity, and significantly negatively correlated with the leaf area ratio (LAR). There was no significant difference in RGR among the cultivars. The oriental type had a significantly higher NAR but a significantly lower LAR than the other cultivars. These results show that the cultivars differed in their growth and assimilation rates. Although the photosynthetic rate per unit leaf area was significantly higher in the oriental type than in the other types, the total dry matter production was similar among the three types. This is because the oriental type produced dry matter by a low leaf area at a high photosynthetic rate, but the other types produced it by a high leaf area at a low photosynthetic rate.