Red Chlorophyll Fluorescence as an Ecophysiological Method to Assess the Behaviour of Wheat Genotypes Under Drought and Heat

Abstract

The objective of this study was to determine the potential of the chlorophyll (Chl) fluorescence technique to assess the behaviour of wheat varieties under drought and heat in the field. Seedlings of Flamura 85, a drought and heat resistant wheat cultivar, were exposed to 35°C for 2 up to 72 h. Net photosynthesis decreased significantly after 48 and 72 h of high temperature exposure, whereas the Chl fluorescence ratios, the Rfd-values at 690 and 735 nm, and the stress adaptation index Ap decreased much faster, after 4 h already, demonstrating that Chl fluorescence is a useful trait in early detection of stress in wheat cultivars. The best differentiation of controls from heat-exposed plants for the Chl fluorescence indices (Rfd-values and Ap) was obtained at 48 h. Ten winter wheat varieties were investigated for the ratios of the variable Chl fluorescence, Rfd-values at 690 and 735 nm as vitality indices, and the stress adaptation index, Ap, in primary leaves after seedlings’ exposure to 35°C for 48 h. Chl fluorescence parameters significantly decreased in all genotypes, but to a higher extent in those which are drought and heat sensitive according to field evaluations. The better performing varieties under stress conditions in the field also showed a smaller decrease of the Chl fluorescence indices. When plotting the differences between Ap at normal and high temperature against the mean visual score for the leaves’ vitality in the field during the anthesis-grain filling period, a significant high correlation was found (r = 0.78**).