Red chlorophyll fluorescence as an ecophysiological method to assess the behaviour of wheat genotypes under drought and heat

The objective of this study was to determine the potential of the chlorophy ll (Chl) fluorescence technique to assess the behaviour of wheat varieties under drought and heal in the field. Seedlings of Flamura 85, a drought and heat resistant wheat cultivar, were exposed to 35 degrees C for 2 up to 72 h. Net photosynthesis decreased significantly after 48 and 72 h of high te mperature exposure, whereas the Chi fluorescence ratios, the Rfd-values at 690 and 735 nm, and the stress adaptation index Ap decreased much faster, a fter 4 h already, demonstrating that Chi fluorescence is a useful trait in early detection of stress in wheat cultivars. The best differentiation of c ontrols from heat-exposed plants for the Chi fluorescence indices (Rfd-valu es and Ap) was obtained at 48 h. Ten winter wheat varieties were investigat ed for the ratios of the variable Chi fluorescence, Rfd-values at 690 and 7 35 nm as vitality indices, and the stress adaptation index, Ap, in primary leaves after seedlings' exposure to 35 degrees C for 48 h. Chi fluorescence parameters significantly decreased in all genotypes, but to a higher exten t in those which are drought and heat sensitive according to field evaluati ons. The better performing varieties under stress conditions in the field a lso showed a smaller decrease of the Chi fluorescence indices. When plottin g the differences between Ap at normal and high temperature against the mea n visual score for the leaves' vitality in the field during the anthesis-gr ain filling period, a significant high correlation was found (r = 0.78**).