短波紫外線(Ultraviolet-C)誘導柑桔果實植物殺菌素scoparone之生成及對貯藏病害發生之影響

Effect of UV-C irradiation on the induction of scoparone synthesis and the incidence of postharvest decay in citrus fruit

梁穎芝(Yin-Chih Liang)

指導教授 ： 王自存

共同指導教授 ： 劉富文(Fu-Wen Liu)

國立臺灣大學/生物資源暨農學院/園藝學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01563

摘要

本試驗以不同劑量的254 nm短波紫外線(Ultraviolet-C; UV-C)照射柑桔類果實，然後觀察果皮中所生成之植物殺菌素scoparone (6,7-dimethoxycoumarin)在照射後的變化及UV-C處理對貯藏病害之影響。椪柑及柳橙經UV-C照射後之果皮萃取物以薄層色層分析(TLC)在螢光下可觀察到scoparone之生成；另以高效能液相層析(HPLC)及螢光檢測器分析，可分離並偵測到scoparone及scopoletin (6-methoxy, 7-hydroxycoumarin)二種生成物，但scopoletin之濃度很低，測得之濃度不超過1 μg/g Fwt.。柑桔果實只有受到UV-C照射的部位才會生成scoparone，而其生成之部位為外果皮(油胞層)；旦不論果皮黃綠均可生成。椪柑及柳橙果實經0.5 ~ 3.0 KJ/m2 UV-C照射後果皮中之scoparone生成量隨時間逐漸增加，至10天左右達最高量，然後又逐漸下降。照射劑量愈高，scoparone生成量也愈大，而同劑量UV-C照射誘導椪柑所生成scoparone量較柳橙為高。
椪柑及柳橙果實以人工接種綠黴菌24小時後進行UV-C照射，並未抑制病菌生長。若果實先經UV-C照射後再接種綠黴菌，則能明顯降低發病率及感染直徑。UV-C之抑菌效果以照射後24小時接種之感染率最低，隨照射後時間之增長，對所接種綠黴菌之抑菌效果逐漸下降；因此果皮中scoparone含量高低與抑菌效果間無明顯關係。
未經任何藥劑處理之椪柑以1.5及3.0 KJ/m2 UV-C照射處理，在15℃貯藏三個月後由綠黴病引起之腐爛率比對照組低；但是經UV-C處理之椪柑，其綠蒂率較低，且蒂腐病發生率增加，因而總腐爛率反而提高。椪柑以1.5 KJ/m2 UV-C照射後並在果蒂塗覆200 ppm 2,4-D，可有效維持其綠蒂率並降低貯藏期間之總腐爛率。

關鍵字

貯藏病害 ； 短波紫外線 ； 柑桔類果實 ； 植物殺菌素

並列摘要

The objects of this research were to study the formation of the phytoalexin - scoparone (6,7-dimethoxycoumarin) in the peel tissue of citrus fruit that were irradiated with short wavelength (254 nm) ultraviolet light (UV-C), the changes of the scoparone concentration after irradiation, and the efficacy of UV-C irradiation on the occurrence of postharvest decay of citrus fruit. Visible fluorescent spots of scoparone were detected by thin-layer chromatography (TLC) in the peel extracts of UV-C irradiated ‘Ponkan’ mandarin (Citrus reticulata Blanco. cv. ‘Ponkan’) and ‘Liucheng’ orange (Citrus sinensis (L.) Osbeck cv. ‘Liucheng’). By using high performance liquid chromatography (HPLC) with fluorescence detector, both scoparone and scopoletin (6-methoxy, 7-hydroxycoumarin) were detected. However, the scopoletin concentration was less than 1 μg/g Fwt and was considered as a minor product of UV-C irradiation. Scoparone was formed only in the flavedo of the citrus peel and limited to the area that was directly irradiated by the UV-C. There were no differences in the formation of scoparone with respect to peel color, either green or yellow. After irradiation with 0.5 ~ 3.0 KJ/m2 UV-C, the concentration of scoparone in the peel of ‘Ponkan’ mandarin and ‘Liucheng’ orange increased with time and reached maximum after 10 days, then started to decline. With the dosage of UV-C increased from 0.5 to 3.0 KJ/m2, the concentration of scoparone in the peel also increased. At the same dosage, higher amount of scoparone was formed in ‘Ponkan’ mandarin than in ‘Liucheng’ orange.
UV-C did not inhibit the growth of green mold in both ‘Ponkan’ mandarin and ‘Liucheng’ orange when the fruits were inoculated with fungal spores 24 hours before irradiation. However, lower infection ratio and smaller diameter of fungal growth were observed in fruits that were irradiated with UV-C 24 hours before inoculation. The highest inhibitory effect of UV-C treatment on the growth and infection of subsequently inoculated green mold was at 24 hours after irradiation. With the time after irradiation further extended, the inhibitory effect gradually declined. This result indicated that there were no direct linkage between the scoparone concentration in the peel and the inhibition of green mold infection.
‘Ponkan’ mandarin, without any fungicide or growth regulator pre-treatment, were irradiated with 1.5 and 3.0 KJ/m2 UV-C then stored at 15℃ for 3 months. At the end of the third month, the UV-C treated fruit had lower rate of green mold rot than the control. However, the UV-C treated ‘Ponkan’ mandarin had lower ratio of green button and higher incidence of stem-end rot, which rendered the total incidence of decay higher than the control. Treating the stem-end with 200 ppm 2,4-D after 1.5 KJ/m2 UV-C treatment could maintain the green button ratio and reduce the total incidence of decay ratio 3 months of storage.

並列關鍵字

postharvest decay ； UV-C ； citurs fruits ； phytoalexin scoparone

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