PHOSPHATE-DISSOLVING MICROORGANISMS ON SEED AND IN THE ROOT ZONE OF PLANTS
A high proportion (40–70%) of the bacteria on most of the seed tested solubilized phosphate precipitated in agar; flax and red clover were two striking exceptions with 11% and 24% respectively. The percentage incidence of these bacteria was considerably lower on the roots and in the rhizosphere of four out of the five crop plants studied than on their seed, being in the order of 10%. There was no strong evidence of a selective effect of plant roots on these organisms although barley appeared to favor them and oats to repress them somewhat.Phosphate-dissolving fungi were readily isolated from seed and plant roots. Cereal seed carried surprisingly few such fungi whereas grasses and clover had greater numbers. The phosphate-dissolving fungi isolated most frequently were species of Penicillium, Aspergillus, and Rhizopus; in addition, Candida, Oidiodendron, and Pseudogymnoascus species were isolated from roots and root-free soil.