The 2012 ASHS Annual Conference

Atmospheric greenhouse gases are predicted to increase global temperature, which can affect the growth and development of plants. In the present investigation, grapefruit and sweet orange were exposed to high temperature to understand the mechanism and variation in high temperature tolerances among of these two genotypes. Plants were grown in 15 x 8 cm plastic pots containing Fafard Mix 4P. Mineral nutrition was provided periodically using Peters’ professional fertilizer. Plants were kept at 700 µ·mol·m^-2 ·s^-1 PAR with a 12-h light and 12-h dark photoperiod in environmental growth chambers and acclimatized for 90 days before applying treatments. Plants were exposed to 38 °C for 10 days and then recover at 27 °C for 5 days. Among the genotypes, sweet orange appeared to be more susceptible for high temperature stress. The first visible sign of heat injury was observed at 4 days after treatment at the abaxial side of leaves in the form of numerous small circular brown necrotic areas in sweet orange. These necrotic lesions become very large by 8 days after heat treatment and accelerated the rate of leaf abscission. However no such injury was observed in grapefruit. The rate of lipid peroxidation and H₂O₂ production were higher in sweet orange than grapefruit. Higher activities of antioxidant enzymes were observed in grapefruit than sweet orange. These results showed that grapefruit is well equipped to tolerate high temperature stress. It seems Sweet orange will be most affected by rising global temperatures.