電子鼻快速檢測柳橙及草莓儲藏病害和樹木褐根病之研究

Abstract

電子鼻開發概念是模擬人類嗅覺之原理，本研究所使用之電子鼻機型為Cyranose® 320 (Smiths Detection, Pasadena, USA)為手持式化學氣相感測裝置。此儀器主要由感測器、信號處理和模式識別三個部分組成。目前電子鼻的應用範圍極為廣泛，例如在環保監測、糧食貯存以及微生物鑑定等，其最大優點是快速檢測。本研究利用此型電子鼻測試柳橙罹染綠黴菌，在偵測6顆柳橙中如有1顆感染綠黴病時即可測出，具高準確率。另發現以32個感測器全開之方法，其準確率不如只有13個感測器開啟之模式。在桃園4號草莓感染灰黴病上，大致亦能鑑別發病與不發病的類組，但因訓練模式不甚佳因此實測的未知樣品時準確率較低。同樣也發現以32個感測器開啟者其準確度不如只有8個感測器開啟者。在樹木褐根病菌培養在Potato Dextrose Agar (PDA)之揮發性氣味偵測上，電子鼻亦能鑑別褐根病菌之氣味，約在培養3天後即可偵測到其氣味，而對其他三種病菌包括Phellium laevigatus，炭疽病菌及薰衣草疫病菌的氣味皆無法檢出顯示其高度準確能力。將此些電子鼻具有分辨能力之樣品配合頂空固相微萃取氣相層析質譜儀(Headspace Solid-phase microextraction Gas chromatography–mass spectrometry, HS-SPME-GC-MS)分析驗證，結果顯示，柳橙罹染綠黴菌時，會增加釋放揮發性氣體檸檬烯(limonene)。而健康草莓之接種灰黴病經過2天後，其草莓己酸(Hexanoic acid)含量會大幅增加。在榕樹褐根病菌於PDA上，則增加2-丁烯二晴(2-Butenedinitrile)之成分。在田間應用電子鼻偵測樹木褐根病上，如以褐根病菌在 PDA之氣味訓練電子鼻，則對田間之發病根段及菌絲面皆無法偵測出來。如以榕樹發病根段發病部位進行訓練，則發現與未發病木質部有相同之相似級數，顯示無法鑑別。再以菌絲面之氣味進行訓練，則對其他菌絲面可以檢出而對4種菇類及2種靈芝中，除鳳凰木之一種靈芝外，皆不會檢出。顯示具有不錯的鑑別力，但可能有些靈芝亦會產生類似褐根病菌絲面之氣味。綜合以上，電子鼻在植物及樹木病害之偵測應用可行，也期待可大量應用於偵測多種儲藏性病害，及偵測田間之樹木褐根病。

Electronic nose is aimed to simulate the human sense of smell. The major advantage of the electronic nose is its fast detection ability. This study uses the electronic nose Cyranose® 320 (Smiths Detection, Pasadena, USA, currently produced by IOS, Baldwin Park, USA), a handheld chemical vapor sensing device. It is composed of three parts: Sensors, signal processing and pattern recognition units. E-nose is widely applied by scientists now, mostly using in environmental monitoring, food storage inspection and microbial identification.Under this study we found that it can detect one sweet oranges infected by green mold among six sweet oranges in a PE bag, showing its high accuracy. We have tested out that when the E-nose is operated with 13 selected sensors, its accuracy is better than operated with all 32 sensors. Using this E-nose, the strawberry infected with gray mold can also be detected generally. Howeven we found the training is notsatisfactory,cansing a lower rate of accurate detection.Similarly, when the E-nose is operated with only 8 sensors,itsaccuracy is better than that operated with the 32 sensors. Phellinus noxius fungi growing on potato dextrose agar (PDA) were also dectected for their volatile gases by the E-nose. Results show that it can identify the smell of brown root rot fungi on PDA after culturing for 3 days. Wheras this E-nose showed no response to the other three fungi induding, Phellinus laevigatus, Colletotrichum gloeosporioides,and Phytophthora infestans.A headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC-MS) was applied to analyze the volatile compounds related with the above three studys. Results showed that when sweet orange infected with green mold, a volatile gas limonene increase its release. When healthy strawberry fruits is infected byBotrytis cinerea for two days, the hexanoic acid has increased greatly. The Phellinus noxius fungi on PDA can release new component as determined to be 2-Butenedinitrile. The field application of electronic nose to detect trees brown root rot disease is initiated also in this study.When the electronic nose is trained by the smell of brown root rot fungion PDA, it can not deteck the brown root rot in diseased wood section and mycelial surface in the field. When it is trained by the smell of diseased woodof banyan roottree, it can not differentiate between the diseased parts and the healthy xylem parts,showing the similler response. When the E-nose is trained by the smell of themycelium surface, it can successfully identifythe other mycelium surface. While four mushroom fungi and oneGanoderma specied showed no response to this mode of E-nose.One Ganodermaspecied found on flamboyantrree,however, showed lower positive respons to the mode of E-nose. It seems to be that some ganoderma may produce similar smell as the brownroot rot fungi mycelium surface. In conclusion, the electron nose is proven to be able to detect many plant and tree diseases. We therefore recommend that it can be used to dectect a variety of storage diseases and field trees brown root rot disease in eraly stage.