Physiological analysis of C3 rice [Oryza sativa (L.)] and C4 millet [Setaria italica (L.)] to identify photosynthetically efficient plants

The study was undertaken with the aim of developing a reliable and rapid screening protocol to identify crop plants with higher photosynthetic efficiencies. The vascular architecture and physiological functions of the leaves of C3 and C4 photosynthetic genetic model systems were compared. Vein densities, leaf chlorophyll index, Chlorophyll a fluorescence and gas exchange parameters were correlated with photosynthetic efficiency to develop an efficient protocol. The photosynthetic rates of Setaria italica were almost double when compared with the C3 plants. The higher photosynthetic efficiency of Setaria italica was supported by high photosynthetic rates coupled with moderate to high stomatal conductance and low transpiration rates. Setaria italica showed a significant increase in PSII efficiency as the growth progressed, while no significant changes in Fv/Fm values were observed in Oryza sativa genotypes. The distribution of SPAD index values among the rice genotypes during the entire growth period did not exceed 34.35. Setaria italica genotypes exhibited a denser arrangement of SLV’s, almost three times higher than Oryza sativa, with an interveinal distance of 0.317–0.329 mm. Denser networks of small longitudinal veins, higher SPAD indices and PSII efficiency were key traits to look for photosynthetic efficiency in crop plants. © 2018, Indian Society for Plant Physiology.