Wheat High Temperature Tolerance during Reproductive Growth. I. Evaluation by Chlorophyll Fluorescence

Photosynthesis is highly sensitive to high temperature stress, an important problem in many regions during reproductive growth of wheat ( Triticum aestivum L.). Our objective was to evaluate chlorophyll fluorescence, which indirectly measures photosynthetic efficiency, as a screening criterion for high temperature tolerance in wheat. Six genotypes differing in adaptation to the southern Great Plains were tested in two controlled environments and in the field. Plants in controlled environments were subjected to 37/25 °C and 25/20 °C day/night regimes during grain filling and at different developmental stages from late boot to 10 d after anthesis. The field experiment was planted during late winter to increase the probability of high temperature stress after anthesis. Initial (Fo), variable (Fv), and maximum fluorescence (Fm) were measured using a portable fluorometer on flag leaves of intact plants. Fluorescence parameters differed significantly among genotypes in controlled environments and field conditions. Relative stability of Fv was positively related to yield when high temperature treatment was applied to all genotypes after anthesis. The Fv and grain yield were negatively correlated in controlled environments but positively and not significantly correlated in the field. Genotypes in the high Fv group were also in the high yield group. Chlorophyll fluorescence, especially Fv, may be a useful tool for screening wheat of similar maturity for high temperature tolerance during reproductive growth, but the technique should be used with other criteria that might indicate resistance to stress.

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