十字花科蔬菜添加於土壤中對甘藍防治幼苗立枯病之研究

Study of Brassica plant amendment to control cabbage (Brassica oleracea L. var. capitata) seedlings damping-off caused by Rhizoctonia solani Kuhn.

艾森雄(Luis Carlos Ascencion Arevalo)

指導教授 ： 梁文進 ； 顏才博

國立屏東科技大學/農學院/熱帶農業暨國際合作系所/碩士(2012年)

https://doi.org/10.6346/NPUST.2012.00150

摘要

近年來，人類在農業植物病蟲害防治上濫用農藥為環境帶來許多威脅，於是許多研究致力於尋找如何以永續的方式控制植物病害。在土壤中加入十字花科蔬菜被發現可抑制土壤病害，乃因葡萄醣苷（GSLs）中的活性物質在水解後可以改變土壤微生物群落，此種方法是目前發展替代防治之主要方法之一。本研究利用三種十字花科植物，包括小白菜、油菜和芥菜，作為土壤改良劑之材料，於實驗室和溫室中進行防治幼苗立枯病試驗與分析，評估其在三種不同的土壤中，對甘藍菜(Brassica oleracea L. var. capitata)苗立枯病(Rhizoctonia solani Kuhn.)防治之效果。在實驗室中的實驗包括使用高營養成份的培養基以及低營養成份的培養基，評估不同蔬菜組織中加入營養成分對於減少幼苗立枯病菌的影響。此外，本研究亦分析供試三種十字花科蔬菜對土壤性質以及幼苗生長和微生物群落變化的影響，進一步探討此材料當作土壤改良劑防治立枯病之機制。在高營養成份培養基的實驗中顯示，三種十字花科植物組織所釋放的物質皆會抑制幼苗立枯病菌菌絲生長。然而，結果顯示出在低營養培養基中的三種蔬菜組織對立枯病菌呈現較低之毒性。芥菜釋放的揮發性物質同時對高營養培養基和低營養培養基中幼苗立枯病菌皆具較強之毒性（98.2-100％的生長抑制）。同時，溫室實驗證實，供試材料蔬菜混合土壤後會對土壤中的微生物之種類與數量產生強烈的影響。溫室實驗中觀察到不同蔬菜混合土壤後對立枯菌之抑制會隨著不同土壤而不同，但其抑制效果並不與培養基實驗中所呈現之抑制病原真菌效果呈絕對正相關。另一方面，小白菜和油菜在三種不同的土壤中的表現佳，並且在土壤中作用時間較長。此現象可能是這兩種蔬菜有較高的水溶性真菌毒性化合物，並且在土壤中作用時間較長。然而，立枯病發病率與土壤中放線菌和真菌種群之間的比值密切相關，結果顯示，比值高於350時，疾病發病率不顯著。而如果放線菌群體超過12.2 x 105 CFU x g-1，土壤真菌低於9.1 x 103 CFU x g-1，立枯病發病率亦較低，但並不顯著。土壤微生物群落和疾病防治之間的高相關性也說明了十字花科蔬菜混合土壤主要在於改變土中微生物群落組成以達到長期性之抑病效果。土壤部分性質亦會受到混合之十字花科蔬菜而略有改變，但分析結果指出，土壤性質雖受影響，但並不影響在實驗中立枯病之發病率。同時，三種十字花科蔬菜作物混合土壤皆可使幼苗生長略為減少，這也表示，GSL水溶性物質具有輕微植物毒性，換句話說，十字花科蔬菜混合土壤可以增加具有植物毒性的細菌數量。最後，在疾病防治和微生物群落修改穩定的結果顯示小白菜和油菜使用幼苗立枯病防治上具有重大潛力。然而，在針對不同的目標作物領域，十字花科植物混合土壤的適用性及專一性必須進一步評估，以確保其在不同作物立枯病之防治效果。

關鍵字

十字花科 ； 葡萄糖苷 ； 生物薰蒸 ； 幼苗立枯病菌 ； 微生物群落 ； 土壤病害

並列摘要

The emergency of several environmental and human threats, brought from the abuse of pesticides in agriculture, has strengthened the search for sustainable strategies to control plant diseases. Suppression of soil-borne diseases observed after soil amendments with Brassica crops, attributed to bioactive compounds from glucosinolate (GSLs) hydrolysis and modifications on soil microbial communities, is currently one of the main sources for developing alternative control methods. In this study, the potential use of three Brassica species, including B. rapa, B. napus and B. juncea, as soil amendments to control Rhizoctonia solani damping-off disease was investigated in vitro and in greenhouse. In vitro, assays included the use of a nutrient-rich and a nutrient-poor medium to evaluate the effect of toxic compound and the nutritional content added with Brassica tissues on the suppression of R. solani hyphal growth (fungi-toxicity). In greenhouse, the incidence of damping-off disease was evaluated in cabbage (Brassica oleracea L. var. capitata) seedlings growing in three soil sources amended with dry Brassica tissues. The impact of Brassica amendments on soil reaction, seedling growth and microbial dynamics were also evaluated in order to elucidate possible mechanisms involved in disease reduction. Fungi-toxicity tested in the nutrient-rich medium demonstrated that tissues from all three Brassica species released fungi-toxic compound against R. solani hyphal growth. However, results in the nutrient-poor medium with water soluble extracts from Brassica tissues, indicated that nutritional content in the tissues can reduce fungi-toxicity, which may negatively influence the efficiency of bio-fumigation after field application. Moreover, greenhouse bioassays demonstrated that Brassica amendments strongly impact on microbial population, while disease suppression was not consistent with fungi-toxicity observed in vitro. Volatile compounds released by B. juncea demonstrated to be highly toxic to the growth of R. solani (98.2-100 % hyphal inhibition) in vitro; however, disease suppression by this specie observed in greenhouse varied with soils sources. On the other hand, B. rapa and B. napus revealed steady reduction of disease incidence along three different soils (< 13.3 % incidence, similar to non-diseased soil), which could partially be explained by the higher fungi-toxicity of compounds in their water soluble extractions, than those of B. juncea. Nevertheless, disease incidence on Brassica amended soils were strongly related with the ratio between actinomycetes and fungi populations, showing that at ratios higher than 350, disease incidence was not significant. Populations of actinomycetes higher than 12.2 x 105 CFU x g-1, and fungi lower than 9.1 x 103 CFU x g-1, were also related with disease suppression in some soils, but in a moderated way. The high correlation found between soil microbial community and disease control strongly supported the hypothesis that microbial modification after Brassica amendments is the main mechanism involved in disease suppression in the long term. In addition, soil reaction was similarly affected by amendments regardless Brassica specie, suggesting that released products from Brassica tissues may act as a buffer in soil determining to a specific soil reaction. However, resulting soil reaction didn’t show relationship with disease suppression or the dynamics of soil microorganisms. Similarly, seedling growth was slightly reduced followed by amendments regardless Brassica specie, which suggested that GSL hydrolysis products could possess phytotoxic activity, or that Brassica amendment could have promoted the population of phytotoxic bacteria. Stable results in disease control and microbial community modification suggest significant potential of using B. rapa (first option) and B. napus (second option) for controlling R. solani damping-off disease in field. However, the optimization of Brassica amendment in field for different target crops must be further evaluated to ensure its efficacy in different agrosystems.

並列關鍵字

Brassicaceae ； glucosinolates ； biofumigation ； Rhizoctonia solani ； microbial community ； soil-borne diseases

參考文獻

Lin, C. H. 1993. A Study on Preparation of Compost from Used Mushroom Culture Medium. Bulletin of Taichung District Agricultural Research and Extension Station 39: 17-27.

Smither-Kopperl, M. L., T. E. Hewlett, and L. P. Norris. 2001. Streptomyces for Biocological Control of Pathogenic Fungi and Nematodes. Annual International Research Conference on Methy bromide Alternatives and Emission Reduction. The U.S. Environmental Protection Agency, and the U.S. Department of Agriculture.

Barazani, O. and J. Friedman. 2001. Allelopathic bacteria and their impact on higher plants. Critical Reviews in Microbiology 27(1): 41-55.

Brazier, S. R. and K. E. Conway. 2004. Characterization of Rhizoctonia solani Isolates Associated with Patch Diseases on Turfgrass. Proceedings of the Oklahoma Academy of Science 84(1): 41-51.

Brinkman, M. A., S. A. Clay, and R. J. Kremer. 1999. Influence of deleterious rhizobacteria on leafy spurge (Euphorbia esula) roots. Weed Technology 13: 835-839.