Forty yeast strains isolated from soils taken from different
locations in Egypt were tested for their P-solubilizing
activities on the basis of analyzing the clear zone around
colonies growing on a tricalcium phosphate medium after
incubation for 5 days at 25oC, denoted as the solubilization
index (SI). Nine isolates that exhibited P-solubilization
potential with an SI ranging from 1.19 to 2.76 were
genetically characterized as five yeasts belonging to the
genus Saccharomyces cerevisiae and four non-Saccharomyces,
based on a PCR analysis of the ITS1-26S region amplied
by SC1/SC2 species-specific primers. The highest Psolubilization
efficiency was demonstrated by isolate PSY-
4, which was identified as Saccharomyces cerevisiae by a
sequence analysis of the variable D1/D2 domain of the 26S
rDNA. The effects of single and mixed inoculations with
yeast PSY-4 and Bacillus polymyxa on the P-uptake and
growth of corn were tested in a greenhouse experiment
using different levels of a phosphorus chemical fertilizer
(50, 100, and 200 kg/ha super phosphate 15.5% P2O5).
The results showed that inoculating the corn with yeast
PSY-4 or B. polymyxa caused significant increases in the
shoot and root dry weights and P-uptake in the shoots and
roots. The P-fertilization level also had a significant
influence on the shoot and root dry weights and P-uptake
in the shoots and roots when increasing the P-level from
50 up to 200 kg/ha. Dual inoculation with yeast strain
PSY-4 and B. polymyxa at a P-fertilization level of 200 kg/ha
gave higher values for the shoot and root dry weights and
P-uptake in the shoots and roots, yet these increases were
nonsignificant when compared with dual inoculation with
yeast strain PSY-4 and B. polymyxa at a P-fertilization
leveldual inoculation with yeast strain PSY-4 and B. polymyxa
at a P-fertilization level of 100 kg/ha, which induced the
following percentage increases in the shoot and root dry
weights, and P-uptake in the shoots and roots; 16.22%,
46.92%, 10.09%, and 31.07%, respectively, when compared
with the uninoculated control (fertilized with 100 kg/ha). of 100 kg/ha. The best increases were obtained from