Effect of photon flux densities on photosynthetic behaviour of rice, ragi, barnyard millet and soybean genotypes in relation to photosynthetic pigments

In the present study the influence of different levels of photon flux densities (PFD) on photosynthetic rate of four khari crops, namely rice, ragi, barnyard millet and soybean was worked out using three genotypes of each crop. In all genotypes of different crops, an increase in photosynthesis rate was recorded with the increase in photon flux densities and photosynthetic pattern exhibited more or less sigmoidal shape of curve in all the crops. Sybean genotypes which possessed high photosynthetic rate under normal light, maintained relatively a higher photosynthesis under low light conditions. However, the genotypes of rice, ragi and barnyard millet, which showed higher photosynthesis rate under low light, could not maintain the higher photosynthesis under nor:mallight conditions. Photosynthetic rate recorded at low photon flux densities (400 μ mol/m²/s) had the significant positive association with Chl b, total carotenoids and significant negative association with chl a/b and Chl a/total carotenoids ratio, while photosynthesis recorded at normal light (1500 μ mol/m²/s) showed the significant positive correlation with chl a/total carotenoids ratio. Besides this, the photosynthetic pigment content of the genotypes which had higher photosynthesis rate under low light conditions, exhibited better absorption of light at lower wave lenghts. This study suggests that for selection of rice, ragi and barnyard genotypes suitable for low light/cloudy conditions, high contents of chl b, total carotenoids and high photosynthetic efficiency under low light conditions may comprise tlie important criteria instead of high photosynthetic efficiency under normal light conditions for the hills.