蒸熱處理對採後軟熟愛文芒果炭疽病發生之影響

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論文名稱: 蒸熱處理對採後軟熟愛文芒果炭疽病發生之影響
研究生姓名: 詹文莉
指導教授姓名: 吳俊達
出版年: 2009
學校名稱: 國立臺灣大學
系所名稱: 園藝學研究所
關鍵字: 愛文芒果;炭疽病;蒸熱處理;mango;anthracnose;Colletotrichum gloeosporioides;vapor heat treatment
摘要: 台灣芒果(Mangifera indica L.)種植面積超過兩萬公頃,是本省單一種類栽培面積最大宗的果樹, ‘愛文’為主要種植與外銷品種,雖然‘愛文’芒果果實品質良好,但對炭疽病菌(Colletotrichum gloeosporioides)相當敏感,一般商業上常以溫湯處理作為抑制芒果炭疽病的採後防治方法。由於台灣為東方果實蠅(Bactrocera dorsalis Hendel)及瓜實蠅(Bactrocera cucurbitae Coquillett)疫區,園產品必須經過檢疫處理才能出口到非疫區市場,而目前台灣輸出之‘愛文’芒果需以蒸熱處理使果心溫度提高到46.5℃後,維持30分鐘作為標準檢疫的條件,但並未就炭疽病問題進行採後處理防治措施。因此,本試驗目的在探討利用有效溫湯處理抑制芒果炭疽病的溫度及時間,在標準檢疫蒸熱處理流程額外增加一高溫階段,使蒸熱室溫度提高至有效溫湯處理之溫度及時間,期能開發兼具檢疫滅蟲處理與抑制芒果炭疽病雙重功能之蒸熱處理條件。 軟熟‘愛文’芒果利用模擬蒸熱機進行不同條件的蒸熱處理結果顯示,以標準檢疫處理、標準檢疫處理前提高蒸熱室溫度到56℃ 5分鐘,以及標準蒸熱檢疫處理後提高蒸熱室溫度到56℃ 5、10分鐘、58℃ 5分鐘之五種高溫蒸熱步驟結合標準蒸熱檢疫處理(果心溫度達46.5℃,維持30分鐘)在芒果炭疽病徵發展上皆有抑制效果。相較於未蒸熱對照組炭疽病徵發生率66.67%,上述五種蒸熱處理皆可以有效抑制炭疽病發生率至5.33%以下,且對果實品質無顯著影響,經蒸熱處理後果實乙烯釋放量維持在0.1μl/C2H4/kg/hr以下,顯著低於對照組乙烯產生率0.35 μl/C2H4/kg/hr。但四組額外提高蒸熱室溫度處理組與標準檢疫蒸熱處理組相較下,並沒有更好的抑制炭疽病徵之效果,且標準蒸熱處理亦具有減輕蒂腐病發生,但額外高溫處理則無此效果,因此,在蒸熱處理流程並無增加額外提高56~58℃高溫步驟的需要性。 由於蒸熱處理後樣品表面不發生炭疽病斑無法判別是因為蒸熱處理抑制炭疽病徵發展或是因為該果實在田間並未遭受炭疽病感染,為確認蒸熱處理對C. gloeosporioides發展的抑制作用,以人工接種C. gloeosporioides分生孢子之軟熟‘愛文’芒果果實進行蒸熱處理探討模擬標準蒸熱處理對於炭疽病徵發展的影響。經20℃貯放二十天後,接種後蒸熱處理組果實表面並未發現炭疽病徵,而經接種未蒸熱處理之對照組平均炭疽病斑直徑24.20 mm呈現顯著差異;蒸熱後接種處理其病斑發展較接種處理更為快速且明顯,經20℃貯放二十天後,炭疽病斑直徑已擴展達29.0 mm,表示蒸熱後若再感染,病徵發展會更迅速。為了排除因果實樣品個體差異影響蒸熱處理效果及能量化評估蒸熱處理的抑菌比例,本試驗進一步將C. gloeosporioides分生孢子進行體外同步培養至附著器形成階段後,乾燥使其進入休眠狀態,再進行標準蒸熱處理,經移至PDA(potato dextrose agar)25℃培養後,未經蒸熱處理對照組菌絲再生長率高達94.4%;反之,標準檢疫蒸熱處理的確可以抑制休眠炭疽病菌附著器再生長率至6.8%,綜合上述結果,蒸熱處理確實具有殺滅潛伏感染C. gloeosporioides,抑制其菌絲再萌發之效果。 調查2008年商用蒸熱廠處理之軟熟‘愛文’芒果炭疽發生率為36%,與本試驗用模擬蒸熱機標準蒸熱處理後之樣品炭疽病罹病率5%左右有明顯落差。為探究其原因,以蒸熱模擬機不同炭疽病致死熱積溫(45℃以上溫度×處理時間)條件對體外培養C. gloeosporioides處理之菌絲再生長率進行迴歸分析,再比對本試驗實際芒果蒸熱處理後炭疽病罹患率試驗結果。商業蒸熱處理熱積溫4311℃.min,果實罹病率理論值為52.5%,實際調查結果為36%,但商用蒸熱處理只有單筆數據,因此無法與理論值做比較;而兩者的差異推測可能是果實經熱處理後,因表皮受熱導致蠟質重新覆蓋及抑菌物質生成抑制炭疽病發展,造成實際調查炭疽病感染率低於理論值。而模擬蒸熱處理熱積溫5700℃.min,理論罹病率為8.1%左右,與觀察值5.3 ± 3.2%差異不顯著。因此推測本試驗模擬蒸熱處理與商業用蒸熱廠處理後芒果炭疽病發生率差異可能主要源於兩者處理期間果實接受的熱積溫不同所致。 本試驗結果顯示蒸熱處理確實可以抑制芒果炭疽病徵的發展,但目前商業蒸熱廠之標準滅蟲檢疫蒸熱處理之熱積溫累積量不足,所以對芒果炭疽病的抑制效果不彰,仍有三分之一的發病率。因此,建議在商業蒸熱處理流程,在不造成果實熱傷害的前提下,可考慮延長蒸熱處理時間。此外,確保蒸熱廠環境、包裝用材料及包裝人員的清潔、蒸熱室內水質等炭疽病感染源密度都需嚴格控管,避免在蒸熱處理後抵抗力較弱的芒果果實遭到感染,反而加劇芒果炭疽病的發生。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. There 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.
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