Aspects of Applied Biology 120, 2013 Positive Plant Microbial Interactions: Their role in maintaining sustainable and natural ecosystems 23 Screening of large collections of plant associated bacteria for effective plant growth promotion and colonisation By NICHOLAS OTIENO, JOHN CULHANE , KIERAN J GERMAINE, DINA BRAZIL, DAVID RYAN and DAVID N DOWLING EnviroCORE Research Centre, Department of Science and Health, Institute of Technology, Carlow, Ireland Corresponding Author Email: David.Dowling@itcarlow.ie Summary The use of potent and effective live microbial biofertilisers in agricultural has signiicant potential to reduce the costs of crop production and in mitigating greenhouse gas emissions and water pollution associated with excessive fertiliser use. Many plant associated bacteria possess plant growth promotion traits. However, when used as plant inoculants these bacteria often do not result in statistically signiicant plant growth promotion. This paper describes the screening process used to identify a number of endophytic strains with multiple plant growth promotion traits and effective plant colonisation ability in Brassica napus crops. Key words: Plant growth promoting bacteria, Endophytes, inoculation, Brassica napus Introduction Intensive use of chemicals in conventional agriculture is one of the factors leading to increased food prices, a reduction in biodiversity, greenhouse gas emissions and soil and water contamination. These negative effects could potentially be reduced by decreasing the quantities of agri-chemicals applied to crops through the use of microbial biofertilisers. The development of crop systems with high yields and low chemical inputs should improve both the economics and environmental impacts of food and biofuel production, and could be a major component of developing sustainable agriculture in the future. In the EU-27 states, the use of microbial biofertilisers has the potential to save €1−2bn per annum in the cereal sector (wheat, oats, barley, oilseed rape) alone (calculated from data supplied by Adesemoye et al. (2009), Rhibac (2011) and Germaine et al. (2010). The potential savings obtained through the adoption of microbial fertiliser technology would not only signiicantly enhance the proit margin of the grower but could also increase the competitiveness of crops on the international market. However, there has been only limited commercial use of plant growth-promoting bacteria in agriculture. The main reason behind this is the reported variability and inconsistency of results between laboratory, greenhouse, and ield trials. Long et al. (2008) concluded that natural plant associated bacteria with PGP traits do not have consistent and predictable effects on the growth and itness of all host plants. These inconsistent and irreproducible results may relect variations in inoculant-crop compatibility, soil composition and moisture content, and, perhaps