Long-term survival of the plant-growth-promoting bacteria Azospirillum brasilense and Pseudomonas fluorescens in dry alginate inoculant

Two plant-growth-promoting bacteria, Azospirilliun brasilense Cd and Pseudo monas fluroescens 313, immobilized in 1983 in two types of alginate-bead in ocuiant (with and without skim-milk supplement) and later dried and stood a t ambient temperature for 14 years, were recovered in 1996. The population in each type of bead had decreased, yet significant numbers survived (10(5) -10(6)cfu/g beads). Population numbers depended on the bead type and the th ree independent bacterial counting methods: the conventional plate-count me thod, indirect enzyme-linked immunosorbent assay and the limited-enrichment technique. Both bacterial species retained several of their original physi ological features. When inoculated onto wheat plants, both species colonize d and produced plant-growth effects equal to those of the contemporary stra in from a culture collection or to their own 1983 records. This study showe d that bacteria can survive in alginate inoculant over long periods.