Chlorophyll fluorescence as a selection tool for cold tolerance of photosynthesis in maize (Zea mays L.)

The possibility of using quenching analysis of chlorophyll a fluorescence as a selection tool for improving the cold tolerance of maize was investigated in six genotypes differing greatly in the ability to develop a competent photosynthetic apparatus at low temperature. Upon gradual cooling, measurements of the quantum yield of electron transport (Phi(PSII)) indicated that leaves of tolerant genotypes, that developed at suboptimal temperature (15 degrees C), maintained higher rates of electron transport than leaves of sensitive genotypes. This difference was largely due to the ability of the tolerant plants to keep higher efficiency of excitation energy capture by open photosystem II reaction centres (F'F-V'(m)). The absence of genotypic differences in leaves that developed at optimal temperature indicates that the trait is not expressed constitutively, but relies on adaptation mechanisms, Furthermore, the genotypic difference was not expressed under increasing illumination at 15 degrees C and 25 degrees C suggesting that the trait is also low-temperature-specific and is not expressed solely in response to increasing excess light energy. Applying the method to flint and dent breeding population led to a substantial increase (up to 31%) in the photosynthetic capacity of hybrids between selected F-3 inbreeding families grown at suboptimal temperature, demonstrating that the method is an efficient selection tool for improving the cold tolerance of maize through breeding.