評估 Bacillus licheniformis (31-1) 對於甜椒疫病之生物防治潛力

Abstract

甜椒為臺灣重要經濟作物，主要種植於南投、嘉義、雲林及屏東等地，年產量約26,000公噸，年產值約新臺幣10億元。甜椒屬於茄科作物，易受病害感染，重要病害包括疫病、青枯病、細菌性斑點病及炭疽病等。甜椒疫病由Phytophthora capsici (Leonian) 引起，其寄主範圍廣泛，包括茄科、瓜類及部分豆科作物，且其為半殺生性病原菌，感染植物後迅速造成組織細胞壞死萎凋，常造成農民損失慘重。疫病的主要感染源為孢囊、游走子及菌絲，於雨季高濕時造成嚴重病害，且其有性繁殖構造-卵孢子可於土壤中殘存很久，易造成連作障礙。目前防治甜椒疫病的方法主要為輪作、清園、耕作防治、藥劑防治、抗病育種等，然而，傳統的防治方法對於土媒性疫病菌效果有限，因此本研究的目的為開發甜椒疫病菌的生物防治技術。本研究於宜蘭、臺中、南投及雲林等地之有機田區收集44個土壤樣本，經由評估對孢囊發芽抑制效果來篩選可能含有拮抗微生物之抑病土，並自其中獲得一株拮抗菌，以16S rDNA及gyrase B基因序列鑑定後，定名為Bacillus licheniformis (31-1)。此菌於固態培養基可釋放抗生物質以及揮發性有機物抑制P. capsici菌絲生長，另以對峙培養實驗發現其可抑制引起番茄疫病、番茄萎凋病、香蕉黃葉病、草莓炭疽病、褐根病、水稻徒長病及稻熱病等病原菌之生長，其中又以對甜椒疫病菌及草莓炭疽病菌之抑制效果最好。測試以不同碳素源對B. licheniformis (31-1) 生長之影響發現此菌於黃豆粉-玉米澱粉培養基生長最佳。植物生長箱試驗中，澆灌B. licheniformis (31-1) 於栽培介質可降低甜椒疫病及青枯病的發病嚴重度。此外，持續澆灌此菌亦可促進甜椒根系發展及增加其乾重，顯示其具有促進植物生長的效用。這些研究結果顯示B. licheniformis (31-1) 於植物生長箱試驗中，具有防治甜椒疫病及促進甜椒生長之潛力。

Bell pepper (Capsicum annuum L.), a member of Solanaceae, is an important economic crop in Taiwan, with the main crop regions encompassing Nantou, Chiayi, Yunlin, and Pingtung. The average annual yield of pepper is 26,000 tons and the output value is about one billion New Taiwan Dollars. Bell pepper is susceptible to various diseases including Phytophthora root rot caused by Phytophthora capsici (Leonian), bacterial wilt caused by Ralstonia solanacearum, and anthracnose caused by Colletotrichum gloeosporioides, to mention only the most important ones. P. capsici is a very aggressive pathogen known to cause severe diseases in a wide variety of plant species such as beans, cucumber, and crops of the solanaceae family. A variety of strategies have been developed for the control of Phytophthora root rot including crop rotation, exclusion, cultural control, fungicides, and genetic resistance. However, these methods have limitation for controlling this soil-borne disease. The purpose of this study is to develop a biocontrol method for Phytophthora root rot of bell pepper. Soil samples collected from 44 organic farms in Yilan, Taichung, Nantou, and Yunlin were screened for their ability to suppress sporangia germination of P. capsici. Subsequent analyses based on gene sequences of both 16S rDNA and gyrase B led to the identification of one potential biocontrol agent, Bacillus licheniformis (31-1). When grown in the V8 agar plates, B. licheniformis (31-1) was able to produce antibiotics and volatile organic compounds which inhibited the growth of P. capsici. Moreover, dual culture analysis indicated that B. licheniformis (31-1) could inhibit the growth of other pathogens including Phytophthora parasitica, C. gloeosporioides, Phellinus noxius, Magnaporthe grisea, Fusarium moniliforme, Fusarium oxysporum f. sp. lycopersici, and F. oxysporum f. sp. cubense. When cultured in different carbon sources, B. licheniformis (31-1) grew best in a medium consisting of soybean and corn starch. Applications of B. licheniformis (31-1) by soil drench reduced the disease severity of Phytophthora root rot and bacterial wilt of bell pepper. Furthermore, B. licheniformis (31-1) was able to enhance root growth and increase the dry weight of bell pepper, indicative of its potential to promote plant growth. These results show that B. licheniformis (31-1) may serve as an effective biocontrol agent for Phytophthora root rot of bell pepper.