Effect of inoculum preparation and formulation on survival and biocontrol efficacy of Pseudomonas fluorescens F113

Abstract

Sugarbeet seeds used by farmers are often pelleted using an EBTM‐based mix. During the pelleting process, the seeds are dried immediately after application of the mix. In this work, the effects of inoculum preparation and formulation on survival and biocontrol efficacy of Pseudomonas fluorescens F113Rif were investigated using a 1:1 EBTM/vermiculite mix and sugarbeet seeds pelleted with this material. Growing F113Rif for 3 d (28 °C) within the EBTM/vermiculite mix amended with nutrients (sucrose asparagine broth), instead of adding the cells to the unamended mix immediately before drying the mix or the pelleted sugarbeet seeds, resulted in improved survival of the strain in the mix or on the seeds, respectively, during subsequent storage. A slower drying (20 h instead of 3 h) of the F113Rif‐inoculated EBTM/vermiculite mix to 11% w/w water content enhanced strain survival in the mix during storage, but the drying conditions studied had no effect on inoculant survival on the seed during storage when pelleted seeds were dried to 10% w/w water content. Biological control of damping‐off disease of sugarbeet (caused by Pythium spp.) in soil microcosms was achieved when F113Rif was inoculated in the unamended mix 3 d before pelleting the seeds, but not when nutrient‐amended mix was used. Inoculum preparation and drying of the formulation are key factors to consider when optimizing the use of a commercial EBTM/vermiculite seed formulation for delivery of a biocontrol Pseudomonas inoculant.