請用此 Handle URI 來引用此文件: http://hdl.handle.net/11455/31429
標題: 馬鈴薯瘡痂病—病原菌於水稻田中殘存之可能性與可行之病害管理策略
Potato common scab- the possibility of pathogen survival in paddy field and the feasible strategy of disease management
作者: 莊雅蓉
Chung, Ya-Jung
關鍵字: potato common scab
馬鈴薯瘡痂病
Streptomyces scabies
thaxtomin A
Streptomyces scabies
thaxtomin A
出版社: 植物病理學系所
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摘要: 馬鈴薯瘡痂病廣泛存在於世界各馬鈴薯主要產區,已知可造成本病的病原菌有Streptomyces scabies、S. acidiscabies及S. turgidiscabies等,其可經由土壤與種薯帶菌而傳播,並於馬鈴薯表皮產生突起皺摺之壞疽性瘡痂病徵。台灣過去罕見有馬鈴薯瘡痂病危害發生,直到2006-2007年間,於台中縣潭子、雲林縣斗南地區主要馬鈴薯栽培區突見本病爆發性大面積危害。為瞭解S. scabies是否成為本土性病原而傳播病害,本研究即探討在馬鈴薯作為水稻田冬季間作作物的情況下,觀察瘡痂病菌經水稻淹水栽培過程後,於土壤中殘存之可能情況,並建立可行之病害管理策略。本研究由斗南地區於2006、2007年連續兩年馬鈴薯全面嚴重瘡痂病感染之栽培田,於2008年馬鈴薯種植前,採取大量田土於溫室以盆缽盛裝種植馬鈴薯,結果發現,種植於嚴重發病田所採集土壤之馬鈴薯,所採收之薯塊發病率為21.3%,發病度則約為5.6%,相當輕微。另外於上述相同之田地嘗試以每公頃800公升用量枯草桿菌WG6-14發酵菌液隨灌溉水施用處理,共施用兩次,另以灌溉水者作為對照處理,於馬鈴薯種植前及馬鈴薯採收後,採集處理區與對照區土壤樣品,以稀釋平板法分離檢測土壤中具病原性之瘡痂病菌含量。結果發現,WG6-14發酵液處理區所採集之土壤,於馬鈴薯種植前與採收後近似鏈黴菌分離株分別有212與167株 (5.3×105與4.2×105 CFU/g),對照區則分別有124與145株 (4.1×105 CFU與4.8×105 CFU/g)。此些分離菌株經逐一挑取更新培養,並以馬鈴薯薄片接種測試病原性,結果發現WG6-14發酵液處理區,馬鈴薯種植前與採收後所分離菌株分別有61.8%與51.5%可見薯片有褐化反應,對照區所分離菌株則分別有61.3%與44.1%有褐化反應。此些可導致褐化反應之分離菌株,隨之經燕麥培養液培養,並以LC/MS/MS檢測thaxtomin A產量則發現,相較於2006年分離自潭子病薯塊上具有強毒力的瘡痂病菌S. scabies T3,其thaxtomin A產量可達每毫升培養液2.1 μg,總計357株可導致薯片褐化之分離株皆未檢測到有thaxtomin A之產生,進一步自這些處理區及對照區分離株中挑取40株代表菌株以PCR增幅thaxtomin生合成基因txtA,增幅產物經分析亦證實此些代表菌株不具有txtA,其應不具致病性。上述結果顯示殘存於土壤中之病原菌應非導致嚴重瘡痂病發生的主因。為瞭解是否由於水稻田栽培環境造成病原菌降解,使得無法分離到具瘡痂病致病性之鏈黴菌,試驗中將瘡痂病菌T3帶菌土經淹水及水稻種植處理後,以稀釋平板法檢測其病原菌菌量。結果發現灑水保濕之對照組其T3族群量在8週處理期間維持在107 CFU/g左右,而在淹水至土上4公分之環境中相較於對照組,其T3菌量至第八週後降至1.3×106 CFU/g,減少了86.1%。另外帶菌土在淹水下每週一次施用拮抗性枯草桿菌群菌株WG6-14與TKS1-1發酵液之處理,其T3族群量之降解情形明顯加快。比較種植水稻與單純淹水之影響則發現,淹水種植水稻較之只淹水之對照處理,病原菌族群量下降確有明顯較快情形。綜合上述試驗結果,解釋了過去在台灣中南部馬鈴薯栽培田少見瘡痂病危害的可能原因,而於2006、2007年連續兩年在中南部爆發大面積為害的原因或與種薯夾帶病菌引入有關。在本病之病害管理部份,於溫室以盆缽種植方式進行試驗,發現大量施用WG6-14與TKS1-1發酵液可以有效降低T3病菌的感染,且對馬鈴薯產量有增益效果。為避免種薯夾帶病菌引入,因此建立帶菌種薯的檢測方法。試驗結果發現,利用txtA基因專一性引子對進行PCR增幅後,當種薯單位表皮 (0.79 cm2) 帶菌量為137 CFU時,可檢測到txtA片段。未來對於種薯檢疫上,期望能利用此可行之檢測方法,阻絕瘡痂病之可能感染源,保障國內馬鈴薯產業。
Common scab is a world-wide soil/seed-borne disease on potato (Solanum tuberosum L.) that plagues the crop production among most potato growing countries. The agent known to cause the disease includes Streptomyces scabies, S. acidiscabies, S. turgidiscabies and quite a few other Streptomyces species. Severe infection of the disease leads to development on tuber surface numerous erumpent or pitted necrotic lesions. The disease was never an issue of concern until 2006-2007, when a 2-consecutive years outbreak of the disease was observed in central and southern Taiwan at both Tantzu Taichung and Dounan Yunlin. In order to learn if the disease may since become indigenous and thus spread thereafter, a serial experiments were conducted to explore (1) the possibility of the pathogen survival in paddy field where that potatoes are grown as winter crop after rice cultivation, and (2) the feasible strategy of disease management. In 2008, before potato planting, mass amount of soils were collected from a field at Dounan wherein nearly 100% of tuber infections were detected during 2006 and 2007 crop seasons. The use of these soils for growing potato plants in greenhouse by plastic pots (15 cm in diameter) produced tubers with only 21.3% common scab infection and the average disease severity was very slight at only 5.6%. In the same area, field plots were chosen drenching treated with broth cultures of Bacillus subtilis WG6-14 at the rate of 800 L/ha twice during the followed potato growing season. The adjacent plots drenching treated with irrigation water were used as compared control. Additional soil samples were collected from these test plots before potato planting and after harvest, respectively. Examination on the Streptomyces population of the WG6-14 treated soils by dilution plates on chitin medium detected a total of 212 isolates (approximately 5.3105 CFU/g soil) before planting and 167 isolates (approximately 4.2105 CFU/g soil) after harvest, whereas that of control soils was 124 isolates (approximately 4.1105 CFU/g soil) before planting and 145 isolates (approximately 4.8105 CFU/g soil) after harvest. A followed bioassay by potato slices indicated that from WG6-14 treated soils, 61.8% of the pre-planting isolates and 51.4% of the after-harvest isolates may cause slight necrosis responses. While from the control soils, 61.3% of the pre-planting isolates and 44.1% of the after-harvest isolates showed similar responses. A total of 357 of these necrogenic isolates were then examined for their competence of thaxtomin A production in oatmeal broth. Detection by LC/MS/MS indicated that comparing to Streptomyces scabies T3-a virulent strain isolated from Tantzu in 2006 which produced 2.1 ppm thaxtomin A in the culture, none of these tested strains produced the toxin. The lack of thaxtomin A producing ability indicated clearly none of these test isolates are common scab causing agents. The view was further strengthened by the evidence that 40 representative strains were chosen from each of these pre-planting and after-harvest isolates groups, and a followed PCR amplification by use of txtA specific primer pairs indicated that all 40 chosen isolates lacked the targeted gene. The accumulated evidences seem to downplay the role of pathogen survival in soil as primary factor for severe common scab outbreak in the succeeding potato crop season. A plausible reason for the detection of only non-pathogenic Streptomyces strains appears to be the cultivation of paddy rice in the test field. In a greenhouse model system, square plastic pots were used to evaluate the effect of flooding treatment and paddy rice cultivation on survival of S. scabies T3. For the artificially inoculated soil which contains 2.45107 CFU/g of T3 strain, a continuous 1 inch depth flooding treatment led to quick decline of the pathogen population to 1.3106 CFU/g level (about 86.1% reduction of the initial population) in 8 weeks. Whereas for the compared control treatment which was treated by daily drenching in stead of flooding, the population density of T3 remained at nearly the same level during the 8 weeks experimental period. The population decline observed in flooding treatment appeared to be further accelerated when the microbial formulation WG6-14/TKS1-1 was applied as an adjunct treatment. The cultivation of paddy rice also showed certain additive effect in regard to the decline of pathogen population comparing to that only by flooding treatment. The data presented seemed to explain why the occurrence of potato common scab was rare in Taiwan, and implied further that the sporadic disease outbreak of 2006/2007 was likely due to the introduction of pathogen from an exotic source. For the disease management, mass introduction of the antagonistic bacilli WG6-14 and TKS1-1 was shown to be effective in reducing the infection by the virulent T3 strain in a greenhouse trial. The use of these antagonistic bacilli was further encouraged by their additional promotive effect on growth and yield of potato. To prevent the accidental introduction of the pathogen from the exotic source, method for detection of the pathogen from seed tuber was established. By PCR amplification of txtA using specific primer pairs, the established method showed a detection limit down to 137 CFU/tuber disc (0.79 cm2). The method provided should be useful for routine quarantine inspection to ensure seed potato quality thus to safeguard the potato industry in Taiwan from reintroduction of common scab disease.
URI: http://hdl.handle.net/11455/31429
其他識別: U0005-2308201009503200
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-2308201009503200
顯示於類別:植物病理學系

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