Soil Science
Department,Agricultural college, Tehran University,Tehran, Iran
__________________
About 450 isolates of
different cross- inoculation groups of Rhizobia , obtained from Iranian soils were screened for their ability
to dissolve inorganic and organic phosphate.
From a total of 453 Rhizobial
isolates assessed for phosphate solubilization in the qualitative plate method , 198 (43.7%) and 321(72%) of
the isolates , solubilized inorganic and organic phosphate respectively. The
best phosphate solubilizing isolates were among the Rhizobium leguminosarom bv
viciae , Sinorhizobium meliloti and Mesorhizobium ciceri , for both inorganic
and organic phosphate. All 51 isolates of bradyrhizobium japonica showed
negative response to both organic and inorganic phosphate media and no clearing
zone of solubilization were observed in the case of this bacteria. In
quantitative method on liquid media containing Ca3(PO4)2
as P source , up to 473.6 mgl-1 of P was released by an isolate of
Mesorhizobium ciceri during 360 hours of incubation with the corresponding
decrease of pH from 7 to 3.9.The average of solubilized P and decrease of pH
were 197.9 mgl-1 and 4.5 respectively. Significant correlations were
obtained between pH and solubilized P and the range of the coefficients of
correlation were 65 to 89 for different Rhizobial groups. The decrease of pH
and release of P in non – inoculated medium (control) were insignificant.
Abd-Alla,M.H.(1994)Biol Fertil Soils,18,216-218