Effect of Bacillus subtilis BD233 on seedlings growth of sweet pepper (Capsicum annuum), Swiss chard ( Beta vulgaris) and lettuce (Lactuca sativa) U.V. Ogugua, K. Ntushelo, M.C. Makungu and S.A. Kanu a Department of Agriculture and Animal Health, University of South Africa, Private Bag X6, Florida, 1710, South Africa. Abstract Bacillus species are ubiquitous microorganisms that enhance growth in several crops as well as provide protection against pathogens. In this study, the effects of soil inoculation with B. subtilis BD233 on growth and development of sweet pepper (Capsicum annuum L.), Swiss chard (Beta vulgaris L.) and lettuce (Lactuca sativa L.), were investigated. Three treatments were employed: i) incubation with a lysogeny broth culture of B. subtilis BD233; ii) broth without B. subtilis BD233 (without BD233/control) and iii) tap water. Potting soil-grown seedlings of the three crops were assayed to measure growth parameters over a period of five weeks (35 days) after exposure to the treatments. Soil inoculation with B. subtilis BD233 significantly improved the growth and development of sweet pepper and lettuce seedlings relative to the other treatments but not for Swiss chard. Bacillus subtilis BD233 in lysogeny broth increased the plant height, stem elongation rate and stem diameter of sweet pepper and lettuce seedlings relative to those treated with water. Furthermore, the biomass of sweet pepper and lettuce seedlings exposed to B. subtilis BD233 was increased by 32.2 and 92.6%, relative to their respective controls. However, no statistical differences for height and biomass were found for Swiss chard in response to the treatments. The results of the study demonstrated the potential of B. subtilis BD233 to enhance the early growth of these non-indigenous vegetables in nutrient- poor African soils. Keywords: Bacillus subtilis, inoculation, lettuce, lysogeny broth, sweet pepper, Swiss chard INTRODUCTION Bacillus species are ubiquitous organisms generally known to provide direct and indirect effects on plant growth and development, and protection against pathogens (Kloepper et al., 2004). The genus Bacillus consists of a very diverse and useful species widely distributed in different ecological regions (Harwood, 1989). The optimum conditions to culture, harvest, lyophilize and store Bacillus spp. are well documented and hence, useful strains can be mass produced commercially (Korsten and Cook, 1996). The use of Bacillus spp. in agriculture is increasing steadily as it offers an alternative to expensive and environmentally unfriendly chemical fertilizers and other plant growth and yield boosters (Bhattacharyya and Jha, 2012). Certain strains of Bacillus spp. are commonly referred to as plant growth-promoting rhizobacteria (PGPR) (Mena-Violante and Olalde-Portugal, 2007) and can be used as ingredients of biofertilizer (Kennedy et al., 2004; Zhang et al., 2011). As commercial products (Borriss et al., 2006), they are reported to improve plant growth through several mechanisms but mainly either by providing promotive enzymes/metabolites (siderophores and phytohormones e.g., auxins, cytokinins, gibberellins, etc.) (Ali et al., 2009) or enhancing nutrient uptake (solubilisation of minerals) from plant rhizosphere soils (Bowen and Rovira, 1999; Vessey, 2003; Zhang et al., 2010; Schwartz et al., 2013; Meng et al., 2016). a E-mail: kanusa@unisa.ac.za Acta Hortic. 1204. ISHS 2018. DOI 10.17660/ActaHortic.2018.1204.26 Proc. VII Int. Symp. on Seed Transplant and Stand Establishment of Hort. Crops Eds.: P. Soundy et al. 201