Comparison of physiological and biochemical responses of Thomson oranges and Lisbon lemons to cold stress

Citrus sinensis cv Thomson Navel and Citrus limon cv Lisbon are known as relatively resistant and cold-sensitive garden products. Thus, in the present study attempts are made to investigate the vulnerability of Thomson oranges and Lisbon lemons to cold stress under controlled environmental conditions compared to treatment temperatures (4, -4 and -8 °C). This factorial experiment was conducted according to a completely randomized design. The ANOVA results showed that the temperature/cultivar interaction can significantly affect some traits such as lipid peroxidation, superoxide dismutase, ascorbate peroxidase, total flavonoids, ion leakage, chlorophyll a, carotenoids, total chlorophyll and LT50 (P> 0.001). However, the catalase/chlorophyll b interaction was found to be significant at p= 5%. The highest levels of ion leakage (59.65%), lipid peroxidation reaction (0.77 µg g−1 FW MDA) in lemon and catalase and superoxide dismutase (33.43 µmol•g−1 FW and 160.3.3 μmol g −1FW min respectively) in orange was recorded at -8 °C. In contrast, the highest levels of ascorbate peroxidase (39.7 µg g−1 FW) was recorded in lemon and total flavonoids (32.48 mg g−1 FW of catechin) was recorded in oranges at 4 °C. in the present study, different reactions were also observed at different temperatures. Oranges showed higher resistance to cold compared to lemons. As for the measured traits, however, oranges were mostly ranked higher than lemons. Exposure of genotypes to cold stress led to an increase in malondialdehyde.