Induced resistance to Cladosporium cucumerinum in cucumber by pectinases extracted from Penicillium oxalicum

Pectinases extract (PE) from the fermentation product of Penicillium oxalicum BZH-2002 was tested for its ability to induce protection against scab caused by Cladosporium cucumerinum on cucumber (Cucumis sativus L.) plants. Seedlings with one true leaf were sprayed with various concentrations of PE (10-200 units ml(-1)) 3 days before inoculation with C cucumerinum. Results showed that the induced local protection against the pathogen was dose-dependent when the concentrations of PE were between 20 and 120 units ml(-1); systemically induced resistance against the pathogen was not observed. Boiled PE had a slight effect on disease reduction. Commercial pectinases prepared from Aspergillus niger showed lower protection against scab compared with PE when they were used at the same concentration of enzyme activity. No inhibitory activity was observed on conidial germination or germ-tube growth of C. cucumerinum. PE was further evaluated for its enhancement of defense-related enzymes. Peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) increased in cucumber seedlings after treatment with PE. PO and PPO remained at a higher level in PE-pretreated seedlings throughout the experiment period whether pathogen-inoculated or non-inoculated, whereas PAL activity began to decrease 2 days after PE treatment.