Significance of time lapse between harvest and postharvest hot water treatment on a local avocado variety.
Karunaratne, A. M.; Adikaram, N. K. B.;
ACIAR Proceedings Series Year: 1998 Issue: No. 80 Pages: 146-154 Ref: 20 ref.
1998
บทคัดย่อ
Anthracnose (Colletotrichum gloeosporioides [Glomerella cingulata]) contributes to about 80% of total disease in avocado. Mature avocado fruit were treated with hot water at 3 different temperature-time regimes: 55 deg C for 5 minutes, 50 deg for 10 minutes, or 45 deg for 15 minutes. Five separate batches of fruits were treated at different times after harvest: i.e., soon after harvest, and 12, 24, 36 or 48 hours after harvest. It was found that a treatment at 55 deg for 5 minutes caused browning of the skin and enhanced disease development. The other 2 temperature-time regimes did not cause any discoloration of the skin. Treatment at 50 deg for 10 minutes did not appreciably reduce anthracnose development. When fruit were treated at 45 deg for 15 minutes on the day of harvest, or 1-5 days after harvest, a considerable reduction of anthracnose development was seen in fruit treated 1 day after harvest. It was found that the fruit have to be fully mature for this treatment to be effective. The eff
ect of the above treatments on G. cingulata, and on the fruit, were determined by the following methods, but neither gave a satisfactory explanation for the above observations. Conidial germination assays were carried out with an isolate obtained from the surface of avocado fruit by exposing them separately to the 3 temperature-time regimes given above. It was observed that although the 3 temperature-time regimes were capable of reducing the % germination progressively, this did not explain the reduced anthracnose development in fruit treated at 45 deg . The preformed antifungal compounds in the peel of avocado fruit were assayed daily for 4 consecutive days in fruit treated at 45 deg for 15 minutes on the day of harvest, or 1 or 2 days after harvest. A TLC-bioassay showed that the daily fluctuations of the total antifungal activity present in the peels of fruit were similar for all treatments. Therefore, no convincing explanation could be found for the reduction in anthracnose development when fruit were tr
eated a day after harvest at 45 deg for 15 minutes. The formation of heat shock proteins may offer an explanation for this.