ORIGINAL ARTICLE Plant growth-promoting rhizobacteria, Paenibacillus polymyxa and Paenibacillus lentimorbus suppress disease complex caused by root-knot nematode and fusarium wilt fungus S.H. Son, Z. Khan, S.G. Kim and Y.H. Kim Department of Agricultural Biotechnology, Seoul National University, Seoul, Korea Introduction The association of plant parasitic nematodes with the fungus is reported to produce greater loss than caused by either alone (Francl and Wheeler 1993). Root-knot nema- todes are sedentary endoparasites of roots, attacking a wide range of crops worldwide. The infection starts with root penetration of second stage juveniles (J2) hatched in soil from eggs encapsulated in egg masses laid by females on the infected roots. Wilt fungus (Fusarium spp.) causes wilting of the infected plants that lead to death. Infection of roots by root-knot nematodes predisposes plants to infection by soil-borne root-infecting fungi resulting in the development of root-rot and wilt diseases (Armstrong et al. 1976). Disease complexes in soil caused by root- knot nematodes, Meloidogyne spp. and soil-borne fungal pathogens such as Fusarium spp. often damage plants more severely and render the disease control more diffi- cult than single pathogens alone. During the last few decades, plant disease control has been based largely on the use of chemicals. However, most of the synthetic pesticides are banned due to their adverse effect on human health and phytotoxicity, alarm- ing side effects causing environmental and ground water pollution by leaving toxic residual problem and deleteri- ous effect on the beneficial micro-organisms in soil (Stirling 1991). Because of concern about the quality of the environment and food in recent years, there have Keywords biological control, disease complex, Fusarium oxysporum f. sp. lycopersici, Meloidogyne incognita, Paenibacillus, rhizobacteria. Correspondence Young Ho Kim, Department of Agricultural Biotechnology, Seoul National University, Seoul 151–921, Korea. E-mail: yhokim@snu.ac.kr 2008 ⁄ 1355: received 4 August 2008, revised 20 October 2008 and accepted 24 December 2008 doi:10.1111/j.1365-2672.2009.04238.x Abstract Aim: To screen and evaluate the biocontrol potential of Paenibacillus strains against disease complex caused by Meloidogyne incognita and Fusarium oxyspo- rum f. sp. lycopersici interactions. Methods and Results: Paenibacillus strains were collected from rotten ginseng roots. The strains were tested under in vitro and pots for their inhibitory activi- ties, and biocontrol potential against disease complex caused by M. incognita and F. oxysporum f. sp. lycopersici on tomato. In in vitro experiments, among 40 tested strains of Paenibacillus spp., 11 strains showed antifungal and nemati- cidal activities against F. oxysporum f. sp. lycopersici and M. incognita, respec- tively. Paenibacillus polymyxa GBR-462; GBR-508 and P. lentimorbus GBR-158 showed the strongest antifungal and nematicidal activities. These three strains used in pot experiment reduced the symptom development of the disease complex (wilting and plant death), and increased plant growth. The control effects were estimated to be 90–98%, and also reduced root gall formation by 64–88% compared to the untreated control. Conclusion: The protective properties of selected Paenibacillus strains make them as potential tool to reduce deleterious impact of disease complex plants. Significance and Impact of the Study: The study highlights biocontrol potential of Paenibacillus strains in management of disease complex caused by nematode-fungus interaction. Journal of Applied Microbiology ISSN 1364-5072 524 Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 107 (2009) 524–532 ª 2009 The Authors