Effects of Vapor Heat Treatment on Symptom Development of Anthracnose in Harvested Ripe ‘Irwin’ Mango
Date Issued
2009
Date
2009
Author(s)
Chan, Wen-Li
Abstract
Mango (Mangifera indica L.) is the largest fruit cultivation in Taiwan whose cultivation area is over 20,000 ha. Among the different cultivars of mango, ‘Irwin’ , owing to its excellent fruit quality, is the cultivar that is most planted and exported one. However, ‘Irwin’ is quite susceptible to anthracnose, which is infected by the fungi Colletotrichum gloeosporioides, and forming serious fruit rots during postharvest handling processes. Commercially, hot water treatment is often used for controlling the anthracnose in mangos. Because Taiwan is the epidemic area of oriental fruit fly and fruit fly, the horticultural products from Taiwan have to be quarantine treated before exported to non-epidemic markets. The current standard quarantine procedure for ‘Irwin’ mangos exported from Taiwan is that the temperature of fruit core is raised to 46.5℃ by vapor heat, and holding for 30 minutes. Nevertheless, there is still no prevention and control measure for anthracnose. Therefore, the objective of this experiment is to develop an effective method to achieve the current quarantine standard and, at the same time, to inhibit the anthracnose in mangos by using hot water treatment. Ripen ‘Irwin’ mango were treated with simulate vapor heat machine with five vapor heat conditions: standard vapor heat treatment (SVHT), raising the chamber temperature to 56℃ and hold for 5 minutes ahead of SVHT, raising the chamber temperature to 56℃ 5 and 10 minutes after SVHT ,and raising to 58℃ 5 minutes after SVHT may have suppress anthracnose. The data shows that all these five treatments could effectively suppressed the anthracnose formation rate from 67.67% (untreated) to 5.33% while there’s no significant change on the quality of fruits. Furthermore, the ethylene productions of the mango after treatments were decreased from 0.1 μl C2H4/kg/hr to 0.35 μl C2H4/kg/hr (untreated). However, the inhibition of the anthracnose, comparing to the SVHT, had no significant differences with raising the chamber temperature to 56~58℃, neither before the SVHT nor after the SVHT. Hence, there’s no need to raise the chamber temperature in addition to the SVHT. The reasons that the anthracnose lesions on the fruit skins could not be identified might be the fruits have not been infected in the field, or the development of the anthracnose was inhibited by SVHT. In order to understand the inhibition effect of the SVHT on the development of C. gloeosporioides conidia, the conidia were inoculated on the fruit skin before the SVHT. After 20 days storage at 20℃, there was no anthracnose symptom on the inoculated fruits treated with vapor heat while the average diameter of the lesion was 24.02 mm in the inoculated fruits without the vapor heat treatment. Moreover, the development of the symptom would be more rapid and obvious on the fruits that were inoculated after the SVHT. The C. gloeosporioides conidia were further incubated on the PDA (potato dextrose agar) at 25℃, and were treated with the SVHT. The data showed that the vapor heat treatment could decrease the re-growth rate of the hypha from 94.4% to 6.8%. To sum up, the vapor heat treatment could effectively kill the C. gloeosporioides conidia and inhibit the hypha re-growth.here is significant difference in the anthracnose formation rate of “Irwin” mangos between the simulated vapor heat treatment and commercial vapor heat treatment in 2008 (5% and 36%, respectively). The commercial heat accumulation is 4311℃．min, and the fruit morbidity theoretical value is 52.5%, the investigation is 36%. The difference possibly is because waxiness rallying and bacteriostasis material production influence anthracnose develops. The simulation heat accumulation is 5700℃．min, and the theory morbidity is about 8.1%, is not remarkable with the observation value 5.3±3.2%. After the regression analysis on the heat accumulation and the re-growth rate of C. gloeosporioides hypha, the difference could be the result of the different heat accumulations treated on the fruits. The result showed that vapor heat treatment may suppress the development of the anthracnose symptom, but the current commercial heat accumulation insufficient, therefore the effect is not good. It suggested that the process period could be prolonged in commercial vapor heat time. In addition, guarantee that the vapor heat factory environment is clean, avoids the fruit encountering the infection again.
Subjects
mango
anthracnose
Colletotrichum gloeosporioides
vapor heat treatment
Type
thesis
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