Glomerella leaf spot (GLS) is an important disease of apple plants, and the use of the algal polysaccharide ulvan represents a new technology for its control. This study aimed to verify whether the defense mechanisms involved in cultivar-specific and ulvan-induced plant resistance to GLS are associated with changes in the activities of peroxidase and β-1,3-glucanase. Seedlings were first sprayed with ulvan or water and then inoculated with Colletotrichum gloeosporioides 6 days later. The disease severity was recorded daily on both young and old leaves up to 10 days after inoculation, and the enzyme activities were monitored from 24 to 72h after inoculation (HAI). Although the young leaves were more susceptible to GLS, ulvan reduced approximately 66% of the disease severity in both of the leaf age groups. Additionally, the cultivar-specific and ulvan-induced resistance was associated with enhanced peroxidase activity at 24 and 72 HAI, respectively. Both the resistant and susceptible seedlings exhibited similar glucanase activities.
Colletotrichum gloeosporioides; Malus domestica; Ulva sp.; induction resistance; peroxidase; glucanase
