Effects of plant growth-promoting rhizobacteria on organic lettuce production

This study was conducted in order to determine the effects of plant growth promoting rhizobacteria (PGPR) on seedling and head production of organically grown iceberg lettuce ('Papiro'). Seeds treated with Bacillus subtilis (strain 66/3), Pseudomonas putida (strain 18/1K), P. fluorescens (strain 112), P. punonensis (strain 56), B. subtilis + P. fluorescens were sown into vermicompost:local peat (1:1.5, v/v) on January 14, 2015. After germination in growth chamber (18/18 degrees C day/night, 80% relative humidity for 3 days), seedlings were drenched with PGPR suspensions, then plants were moved to a PE greenhouse which is specialized for seedling growing. Seedlings were fertilized by liquid composted farmyard manure (30 L ha(-1)) once a day. Germination rate and period of seeds, fresh and dry weight of seedlings and their nutrient composition were determined when they are ready for planting in 35 days. Then seedlings were transferred into a PE greenhouse and grown according to the rules laid down in organic regulations. Heads were harvested in two months and yield and head quality parameters were determined. It was concluded that observable differences were obtained in the seedling stage. Bacillus subtilis treatment increased the seed germination rate and B. subtilis + P. fluorescens was found promising due to the higher seedling biomass. However, the effects of PGPRs on yield, head size and plant biomass was found insignificant.