SHORT COMMUNICATION Factors affecting antifungal activity of Streptomyces philanthi RM- 1-138 against Rhizoctonia solani Sawai Boukaew • Poonsuk Prasertsan Received: 5 January 2013 / Accepted: 1 July 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Sheath blight disease of rice caused by Rhizoc- tonia solani Ku ¨ hn is economically important disease in most of the world’s rice growing areas. The disease causes severe yield losses of [ 20 % of rice in Thailand. Our previous investigation reported the antifungal activity of Streptomy- ces philanthi RM-1-138 against R. solani PTRRC-9. In this study, glucose yeast-malt extract medium, initial pH of 7.5 and a temperature of 30 °C were found to be optimum for both cell growth and antifungal activity of S. philanthi RM- 1-138. The inhibition of 94 and 100 % on the growth of R. solani PTRRC-9 were achieved from the antifungal metabolites of the 6 and 9-days-old culture filtrates of S. philanthi RM-1-138, respectively. Heat treatment on the culture filtrate had slight effect on its antifungal activity. The culture broth demonstrated higher antifungal activity on growth of R. solani PTRRC-9 (90.4 %) than the culture filtrate (31.5 %) and its effective dose was at 0.1 % (v/v). The present results indicated the possibilities of using either the culture broth or culture filtrate of S. philanthi RM-1-138 to inhibit growth of R. solani PTRRC-9. Keywords Antifungal metabolite  Streptomyces philanthi  Rhizoctonia solani  Culture filtrate  Culture broth Introduction The use of antagonist species of Streptomyces as biocontrol agents has been extensively studied. There is a demand for new methods to supplement the existing disease manage- ment strategies to achieve better disease control. Many bacteria such as Bacillus spp., Trichoderma spp. and Streptomyces spp. have been used to control rice disease (Leelasuphakul et al. 2006; Sadeghi et al. 2006). Strepto- myces spp. are one of the potential biocontrol agents against plant diseases since they can produce various secondary metabolites with diverse biological activities (Prabavathy et al. 2006), such as hydrolytic enzymes (glucanase, chiti- nase), herbicides and a large number of antibiotic (Chung et al. 2005; Prabavathy et al. 2006). Several species of iso- lated Streptomyces used to control plant diseases such as sunflower head and stem rot caused by Sclerotinia sclero- tiorun (Lib.) de Bary (Baniasadi et al. 2009), sugar beet damping-off and chili pepper caused by Rhizoctonia solani and Sclerotium rolfsii (Errakhi et al. 2007; Boukaew et al. 2011) and rice blast disease caused by Pyricularia oryzae (Prabavathy et al. 2006). R. solani (Ku ¨hn) [teleomorph: Thanetophorus cucumeris; anastomosis group 1 IA (AG-1 IA)] (Syd.) causes leaf rice sheath blight and is a pathogen of a variety of economically important disease in most of the world’s rice growing areas (Ou 1985). In Thailand, rice sheath blight (caused by R. solani) is a very destructive disease and causes yield losses of [ 20 % for rice (Kanjan- amaneesathian et al. 1998). Synthetic fungicides have long been used as active agents in reducing the incidence of plant diseases; however, their use is costly, can cause environ- mental pollution, and may induce pathogen resistance. An early successful use of microbial metabolites in plant pro- tection was with streptomycin, produced by Streptomyces spp., for controlling of fire blight of apple and pear caused S. Boukaew  P. Prasertsan (&) Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Songkhla 90112, Thailand e-mail: poonsuk918@yahoo.com S. Boukaew e-mail: biotec_ph@hotmail.com 123 World J Microbiol Biotechnol DOI 10.1007/s11274-013-1424-z