Biocontrol Potential of Streptomyces griseus H7602 Against Root Rot Disease (Phytophthora capsici) in Pepper

Corporation of Nature and People, Gunsan 573-952, Korea(Received on March 29, 2012; Revised on May 7, 2012; Accepted on May 24, 2012)The root rot of pepper ( Capsicum annuum L.) caused byPhytophthora capsici is one of the most important di-seases affecting this crop worldwide. This work presentsthe evaluation of the capacity of Streptomyces griseusH7602 to protect pepper plants against Phytophthoracapsici and establishes its role as a biocontrol agent. Inthis study, we isolated an actinomycete strain H7602from rhizosphere soil, identified it as Streptomyces griseusby 16S rRNA analysis and demonstrated its antifungalactivity against various plant pathogens including P.capsici. H7602 produced lytic emzymes such as chitinase,β-1,3-glucanase, lipase and protease. In addition, crudeextract from H7602 also exhibited destructive activitytoward P. capsici hyphae. In the pot trial, results showedthe protective effect of H7602 against pepper from P.capsici. Application of H7602 culture suspension reduced47.35% of root mortality and enhanced growth ofpepper plants for 56.37% in fresh root and 17.56% g infresh shoot as compared to control, resulting in greaterprotection to pepper plants against P. capsici infestation.Additionally, the enzymatic activities, chitinase and β-1,3-glucanase, were higher in rhizosphere soil and rootsof pepper plants treated with H7602 than other treatedplants. Therefore, our results indicated a clear potentialof S. griseus H7602 to be used for biocontrol of root rotdisease caused by P. capsici in pepper. Keywords : antifungal activity, biocontrol, Phytophthoracapsici, Streptomyces griseusBased on increasing public concern about residues offungicides in food products, as well as about their soil-degrading effects, availability of a sustainable and environ-mentally friendly method for disease control in pepper ishighly desirable. Technical, economical and environmentalfactors are forcing to adopt new sustainable methods, suchas use of microbial antagonists for the control of soilbornepathogens. Recently, the interest in biological control bybeneficial microorganisms has increased consistently as analternative disease control to substitute for various chemicalcontrols against airborne or soilborne plant pathogens (Anet al., 2010; Mukherjee and Sen, 2006; Sang et al., 2011),and antagonistic microorganisms have been shown toinhibit the growth and proliferation of various phytopatho-gens with little or no side effects (Arthurs et al., 2009). Phytophthora root rot (PRR), caused by Phytophthoracapsici, is one of the most devastating soilborne diseases inthe world. Due to a lack of resistant cultivars, control ofsoilborne pathogens of pepper is mainly aimed at P. capsiciand involves numerous applications of fungicides bothbefore and after transplanting in the field (Hwan and Kim,1995). To combat wilt caused by P. capsici in pepper,cultural practices based on the biology and ecology of thepathogen have been suggested (Ristaino and Johnston,1999). One of the strategies is use of biocontrol agents inorder to reduce the number of applications of fungicidesand the pathogen population resistant to the fungicides(Sang et al., 2008). There have been considerable efforts to find biologicalcontrol agents against PRR of pepper and several potentialcandidates have been reported including: Penicilliumstriatisporum (Ma et al., 2008), Pseudomonas fluorescens(Paul and Sarma, 2006), and Streptomyces rochei (Ezziyyaniet al., 2007). The mechanisms of disease suppression byantagonistic bacteria have been extensively studied andthey involved the production of antibiotics, extracellularenzymes, biosurfactant or cyanide production and/or the