丹參細菌性軟腐病之研究

Abstract

丹參 (Salvia miltiorrhiza Bge)為唇形科 (Lamiaceae)多年生草本植物，使用部位為根部，為中國傳統之藥材，目前在臺灣多利用實生苗或組培苗繁殖，可分成秋作及春作，其中秋作品質較佳，種植後10個月可收成。目前已被研究之丹參病蟲害甚少，其中，在台灣有立枯病及疫病等病害被報導。但在2012年花蓮及宜蘭農民開始反映田間出現萎凋病害，調查後發現，其外觀為全株缺水萎凋症狀，是有青枯病特色，其葉片萎凋會垂於地面，但並不枯黃，若撥開莖葉可發現地基部脆弱腐爛，輕拉後甚至會由地基部斷裂，造成「斷頭」現象。本研究於病株分離出一可疑病原，經鑑定其序列與Pectobacterium carotovorum (Pc)相似度達99%以上，以代表性分離株YL-1接種於丹參根段及5吋盆苗皆可造成與田間相同病徵，於發病株進行再分離，其再分離率均可達95%以上。符合柯霍氏法則，證實Pectobacterium carotovorum可在丹參上造成細菌性軟腐病。此外，針對不同水分條件及肥料條件進行接種測試後，發現此菌之感染率及發病嚴重度皆與植株水分含量有所關聯，其相關係數r達0.7，而在盆栽試驗中經乾燥三天之丹參苗接種後之發病率為0%；而在肥料試驗中，每盆給予5公克台肥43號之處理組發病率100%，每盆2.5及0.5克之處理僅有50%之發病率，不給予肥料處理之組別發病率只有16.7%。以鏈四環黴、安比西林、克枯熱、撲殺熱等四種藥劑對丹參軟腐病進行藥劑防治試驗，試驗結果以鏈四環黴素100ppm處理之防治效果最佳，其餘藥劑無顯著效果。此菌代表性YL-1分離株在16℃時生長較慢，在28℃下，約在2小時後進入對數生長，而在37℃下生長極緩慢。此結果與田間好發季節略有出入，故推論丹參軟腐病之發病與水分及營養之關聯性較為強烈。另外將分離株對其他軟腐病寄主進行接種，發現此菌株在蘿蔔及高麗菜上同樣可造成軟腐症狀，但對蘿蔔之發病率為100%高於高麗菜之58%。

Danshen (Salvia miltiorrhiza Bge), a perennial herbs, is a traditional Chinese herbal drug that has been used since ancient China. It’s usually propagated by seeds or tissue culture plantlets. There is autumn crop or spring crop for this herb, while the autumn crop usually has better yield and quality. It can be harvested within 10 month of cultivation in the field. The disease found on danshen is only a few. There is a Phytophthora disease and a Rhizoctonia disease were reported recently in Taiwan. In 2012, danshen cultivators from Hualien and Yilan complained that a wilt disease attacks the herb in field. The disease symptoms are whole plant wilt in early stage, stem basal and root rot, and finally died. The diseased stem was easily broken at the basal part of stem areas. In this study, we investigated the soft rot disease of danshen in Hualien and Yilan areas. The suspect pathogen isolate, YL-1, was isolated from the diseased soft rot tissue and identified to be Pectobacterium carotovorum (Pc) with 99% sequence similarity between them. When the isolate YL-1 was inoculated to danshen root segment and 5-inch pot seedling, the same disease can develop on the root segment and the seedling, with inoculation rates of about 100%. On the inoculated plant, same symptoms as in the field were observed and same pathogen, the reisolation rates of Pc was about 95%. The Koch’ postulates were fulfilled and the pathogenicity of Pectobacterium carotovorum causing danshen soft rot disease was proven. In addition, the danshen plants were inoculated under different water and fertilizer condition. Results showed that the higher water content in the root segment or in soil could increase the disease incidence of soft rot, with a correlation coefficient (r) of 0.7. The seeding treated with 3 days of drought could prevent the development of soft rot disease with incidence of 0%. For fertilizer effects, we found that when 5 g of Taiwan Fertilize #43 was applied to each pot, the disease incidence after inoculation can be 100%, while those with 2.5 g and 0.5 g per pot showed only 50%. The seedlings without any fertilizer were not sensitive to soft rot pathogen, with disease incidence only 16.7% after inoculation. In the pesticide test, four pesticides including streptomycin +tetracycline, ampicillin, tecloftalam, and probenazole were treated. Results showed that the streptomycin + tetracycline at 100ppm was the most effective to control the disease, while the others were no or less effective. The best temperature for Pc’s growth is 28℃. It growth at 16℃ is slow and almost none at 37℃. The temperature correlation seems to be different with that found in the field. However, It may further support the hypothesis that higher water content and higher fertilize predispose this disease. When the danshen soft pathogen YH-1 was inoculated to health radish root and cabbage leaf, both of them were infected by this bacterium, indicating that isolate YL-1 can also cause soft rot on radish and cabbage, but the severity in radish is higher than that in cabbage leaves.