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Department of Plant Medicine, Sunchon National University, Suncheon 540-742, Korea (Received on August 3, 2010; Accepted on October 10, 2010)Two similar microbial fungicides (termed as MA andMB) developed in a Korean biopesticide company wereanalyzed and compared each other in their biocontrolactivities against the phytophthora blight of chili peppercaused by Phytophthora capsici. MA and MB containedthe microbe Paenibacillus polymyxa and Bacillus sub-tilis, respectively, with concentrations over those postedon the microbial products. In comparison of the isolatedmicrobes (termed as MAP from MA and MBB fromMB) in the antagonistic activities against P. capsici waseffective, prominently against zoospore germination,while MBB only significantly inhibited the myceliagrowth of the pathogen. Some effectiveness of MAP andMBB was noted in the inhibition of zoosporangiumformation and zoospore release from zoosporangia;however, no such large difference between MAP andMBB was noted. In a pot experiment, MA reduced theseverity of the phytophthora blight more than MB,suggesting that the disease control efficacy would bemore attributable to the inhibition of zoospore germi-nation than mycelia growth of P. capsici. These resultsalso suggest that the similar microbes MA and MBtargeting different points in the life cycle of the patho-gen differ in the disease control efficacies. Therefore,to develop microbial fungicides it is required to ex-amine the targeting points in the pathogen’s life cycleas well as the action mode of antagonistic micro-organisms.Keywords : biocontrol, chili pepper, microbial fungicides,Phytophthora capsiciPhytophthora blight of chili pepper caused by Phytophthoracapsici is a serious disease in the crop cultivation, of whichthe main control measures include fungicide spray andcultural practices such as crop rotation (Hwang, 2002;Hwang and Kim, 1995; Ristano and Johnston, 1999). Severalfungicides including metalaxyl, oxadixyl, propamocarb,copper oxychloride, chlorothalonil, dithianone, etc. areavailable, but it is very difficult for them to exert theirefficacy in controlling the disease because of the soilbornenature and exceedingly rapid spread of the disease (Hwang,2002; Kim, 2004). Crop rotation also is not capable ofexerting sufficiently effective controlling of the diseasebecause the pathogen survives as oospores (primary inoculum)in soil without host plants for several years (Hwang andKim, 1995). It is necessary to develop alternative strategiesfor the control of the phytophthora blight of chili pepper.Use of antagonistic microbes as biological control agents(BCAs) is suggested as a good way to cope with this kindof disease problem (Hwang, 2002). Over a hundred microbial products are currently register-ed or marketed as BCAs worldwide (Whipps and McQuiken,2009), and presently a total of 14 microbial fungicides arecommercially registered in Korea. However, inconsistencyin the efficacy of BCAs in large-scale glasshouse or fieldconditions is one of major constraints in biological diseasecontrol (Whipps and McQuiken, 2009). This kind of pro-blem may also hold true to the above microbial fungicidesmarketed in Korea, especially those for targeting soil-bornepathogens, for which crop growers are not convinced oftheir practical usage in large-scale crop plantations. There-fore, every possible way should be sought to increase effi-cacy and consistency of BCAs even after their commerciali-zation in the market. Selection of good antagonists and their characterizationsuch as mode of actions are important processes and criteriafor the successful development of BCAs (Whipps andDavies, 2000). Especially the understanding on the actionmode (mechanism) of BCAs in the biological control mayprovide crucial information that can be used for practicalapplications of BCAs, promoting their consistent controlefficacy. In this study, two similar microbial fungicides re-gistered and marketed in Korea (both targeting Phytophthoraspp.) were compared in antagonistic mechanisms and bio-logical control efficacies against the phytophthora blight ofchili pepper caused by P. capsici to examine their relationsin the biological control.

plant pathology journal/the plant pathology journal

Comparison of Microbial Fungicides in Antagonistic Activities Related to the Biological Control of Phytophthora Blight in Chili Pepper Caused by Phytophthora capsici