Abstract: Objective: The study aimed to define the acid-alkali property of Trichothecium roseum when inoculated to apple fruit and to determinate the effect of inoculation with its spore suspensions at three different pH values (3, 5 and 7) on lesion diameter and extracellular enzymes activities in apple fruit. Method: ‘Fuji’ apple fruit was artificially wounded and inoculated with T. roseum, and the pH change in lesion tissue was detected during incubation. Meanwhile, the lesion diameter and the activities of pectinase and cellulase in the inoculated fruit were determined. Results: The pH of lesion tissue increased by 36.7% from 3.54 on day 0 to 4.84 on day 12 after inoculation. The fruit inoculated with the spore suspension at pH 7 showed the largest lesion diameter, which was respectively 35.2% and 68.0% higher than that of the spore suspensions at pH 5 and pH 3 on day 9 after inoculation. The fruit inoculated with the spore suspension at pH 7 also had the highest activities of pectinase and cellulose in lesion tissue. The activities of pectin methylesterase, pectin methyl polygalacturonase and polygalacturonase were 2.95, 1.61 and 1.68 folds higher than those in the fruit inoculated with the spore suspension at pH 3, and were 2, 1.25 and 1.39 folds higher than those in the fruit inoculated with the spore suspension at pH 5, respectively. Moreover, the activities of cellulase and β-glucosidase in the fruit inoculated with the spore suspension at pH 7 were 1.97 and 1.64 folds higher than those in the fruit inoculated with the spore suspension at pH 3, and 1.33 and 1.3 folds higher than those in the fruit inoculated with the spore suspension at pH 5, respectively. Conclusion: T. roseum can produce alkaline substances. A neutral or alkaline environment increases the activities of extracellular enzymes in lesions, and enhances the pathogenicity of the pathogen.

Key words: Trichothecium roseum, apple fruit, pH, pathogenicity, extracellular enzymes