Co-culture of Rhizobium meliloti and a phosphorus-solubilizing fungus (Penicillium bilaii) in sterile peat

A biofertilizer containing Penicillium bilaii, which increases phosphate uptake of several field crops by solubilizing phosphorus, has been developed. Laboratory investigations were carried out to determine if Rhizobium meliloti and Penicillium bilaii can be co-cultured in a common sterile peat carrier. A combination inoculant was prepared by mixing equal proportions of yeast-extract mannitol broth (YEMB) cultures of both organisms with sterile (γ-irradiated) peat. The cured inoculant contained 6.1 × 109Rhizobium cfu g−1 and 1.1 × 107Penicillium cfu g−1. New inoculant of equal quality was obtained by suspending mature inoculant in YEMB, and adding the suspension to sterile peat at a rate of 10 mg g−1. Addition of 26 mg ml−1 sucrose to YEMB resulted in populations of 6.2 × 109Rhizobium cfu g−1 and 2.3 × 108Penicillium cfu g−1. The results showed that a common production and delivery system for R. meliloti and Penicillium bilaii is possible by co-culturing the organisms in sterile peat.