Detection of Core Rot Symptom of Japanese Pear (Pyrus pyrifolia cv. Kosui) by a Nondestructive Resonant Method

One of the main factors for the lower rating of Japanese pear (Pyrus pyrifolia, cv.Kosui) is contamination of core-rotten fruit in the market. An acoustic resonance method originally developed to measure firmness of fruit with the second resonant frequency was applied to the detection of core rot fruit. Second and third resonant frequencies of 'Kosui' Japanese pear with different degrees of core rot were nondestructively measured by a resonant method. Resonant frequency of fruit was determined by sandwiching fruit between the vibrator and detector of a resonant device. Obtained vibration voltage signals were analyzed by fast Fourier transformation. An infected pear with core rot was artificially prepared with injections of conidia suspension of Phomopsis sp. or Colletotricum sp. into the fruit on the tree. Degree of core rot was estimated by the area of the equatorial plane of cut surface. Fruit with less than 500 Hz second resonant frequency had core rot of more than 5% of fruit volume. Discrimination rate was 96.9%. Second resonant frequency more effectively discriminates infected pears with more than 5% core rot from that with less than 5% than the third resonant frequency.