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Development of a Powder Formulation of Rhizobacteria for Inoculation of Potato Seed Pieces. J. W. Kloepper, Department of Plant Pathology, University of California, Berkeley 94720; M. N. Schroth, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 71:590-592. Accepted for publication 4 November 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-590.

A dried formulation of plant growth-promoting rhizobacteria (PGPR) that could be applied to potato seed pieces was developed. Genetically marked bacterial suspensions were mixed with various concentrations of commercially available plant gums, xanthan gum (XG), or methylcellulose and then mixed with talc. Populations of PGPR per gram of dried talc mixtures were 1 × 10³ with 10% gum guar, 1 × 10³ with gum locust bean, 1.4 × 10³ with 1% methylcellulose, 6.9 × 10⁵ with 50% gum arabic, and 8.2 × 10⁷ with 20% XG. PGPR did not survive in mixtures containing gum karaya or gum tragacanth. Population of PGPR did not decline in the talc mixture with 20% XG after storage for 2 mo at 4 C, while populations decreased in mixtures containing 5 and 10% XG and 50% gum arabic. In field experiments PGPR placed on potato seed pieces in a powdered XG preparation developed root populations greater than on roots of plants inoculated with aqueous preparations. The powdered inoculum resulted in significant increases in early plant development in field tests as did the aqueous inoculum. These results suggest that the powdered formulation of PGPR in XG could be used commercially to promote plant growth.