Increase in photosynthesis of maize hybrids (Zea mays L.) at suboptimal temperature (15 °C) by selection of parental lines on the basis of chlorophyll α fluorescence measurements

We tested the usefulness of chlorophyll a fluorescence quenching analysis for the selection of maize parental inbred lines able to produce F, hybrids with a high CO2 assimilation rate during growth at suboptimal temperature. Fifty inbred lines, grown at 15 degrees C, showed at 6 degrees C a broad genetic variability regarding the quantum yield of photosynthetic electron transport (Phi(PS2)). A decrease of Phi(PS2) in sensitive lines was caused more by reduction of the efficiency of excitation energy capture by open photosystem 2 (PS2) reaction centres (F-v'/F-m') than by a drop in photochemical quenching (q(P)). Selected inbred lines with the highest (H) and the lowest (L) values of Phi(PS2) were used for separate crossings in a diallelic arrangement. Twenty-one of HxH hybrids and 21 of the LxL hybrids were grown at 15 degrees C. The HxH hybrids showed at suboptimal temperature a significantly higher transport of photosynthetic electrons than the LxL hybrids at lower (400) as well as at higher [800 mu mol(photon) m(-2) s(-1)] irradiance. The mean net photosynthetic rate (P-N) in HxH and LxL hybrids amounted to 8.4 and 5.8 (second leaf) and 8.5 and 7.6 mu mol(CO2) m(-2) s(-1)(third leaf), respectively. Among the best 20 hybrids with regard to PN (values larger than the average) of second leaves, as many as 15 were derived from H lines (75 % of hybrids), whereas among the best 21 hybrids with regard to PN of the third leaves, 16 were derived from H lines (76 % of hybrids). The intensive PN of HxH hybrids was most often accompanied by less water lost via transpiration in relation to photosynthesis than in the hybrids of L lines. Hence an analysis of chlorophyll a fluorescence quenching enables the selection of inbred lines, which can produce hybrids with improved CO2 fixation and with efficient water management during growth at suboptimal temperature.