Improvement of the formulation and antagonistic activity of Pseudomonas fluorescens B5 through selective additives in the pelleting process

Two types of wood flour, diatomaceous earth, bentonite, cotton flour and peat were investigated for their suitability in the pelleting process of sugar beet seeds as carrier materials for Pseudomonas fluorescens B5 (Pf B5). After 1 year of storage at 5 °C no significant decline in the survival rate of Pf B5 was observed after pelleting in materials with an initial water content of 60%. In contrast, pelleting the antagonists in dry materials with 10% initial water content resulted only with peat and bentonite to a moderately high survival rate of Pf B5, with a reduction of only 1 log cfu/g material and no negative effects on the antagonistic activity of Pf B5 were observed. Five different nitrogen compounds and seven trace elements were tested as formulation additives. None of the tested nitrogen compounds enhanced the antagonistic activity of Pf B5 in vitro and ad planta. The production of antifungal metabolites of Pf B5 in vitro was enhanced by the addition of manganese sulphate, zinc sulphate and boric acid at the rate of 0.05 mM. The use of manganese sulphate and zinc sulphate as formulation additives at the rate of 0.05 mM significantly increased the biocontrol activity of Pf B5 ad planta without any negative effect on sugar beet seedlings. In contrast, the use of manganese (Mn2+) caused an increase in plant height and manganese and zinc (Mn2+ and Zn2+) increased the fresh weight of the treated seedlings.