Antioxidant enzyme activities in apple varieties and resistance to superficial scald development

The activities and isozyme profiles of superoxide dismutase (SOD), guaiacol peroxidase (POX) and ascorbate peroxidase (APX) were monitored in skin tissues of scald-resistant and scald-susceptible apple cultivars (Malus domestica Borkh.). SOD activity was high in Gala, with moderately high levels in Idared, McIntosh and Delicious, and low levels in Cortland and Empire. Guaiacol peroxidase activities were high in Empire, McIntosh and Delicious, with moderate to low levels in Cortland, Gala and Idared. Ascorbate peroxidase activity was nearly similar in all the cultivars. Native PAGE and activity staining showed great differences in the guaiacol peroxidase isozyme profiles. Ascorbate peroxidase isozyme profiles showed a fast moving isozyme present in all cultivars. Tissue printing for peroxidase in varieties such as Empire and Crispin showed intense activity, especially in the epidermal region. α-Farnesene levels were variable in all the cultivars. The results suggest that other biochemical characteristics in addition to the antioxidant enzyme activities and α-farnesene levels may be involved in determining the susceptibility/resistance to superficial scald development.