[Pseudomonas fluorescens survival in soils with different contents of organic matter]

Pseudomonas fluorescens are plant growth promoting rhizobacteria (PGPR). The survival of this inoculated heterotrophic bacterium may be affected by soil organic matter content (SOM). To confirm this hypothesis, three strains of P. fluorescens: UP61, C7R12 y P190 (native of Balcarce, Buenos Aires) were inoculated, in laboratory conditions, into three argentine rhizospheric soils: two Argiudolls (Balcarce, and Zavalla, Santa Fe) and a Torrifluvens (Cipolletti, Río Negro) with different SOM: 7.2; 4.3; and 2.6%, respectibily. The results indicated that the all three isolates survival in general was not different. The slopes of the regression curves in Zavalla soil were very similars, while in the Balcarce soil the strains behaviour were very different. CO2 production was superior in the Balcarce than the Zavalla soil. These results suggest that the situations that affected the survival in the Balcarce soil may be associated with the presence of a larger number of functional microflora compared with Zavalla soil. The survival in the Cipolietti soil was the lowest; independently of the protective effect of the SOM in relation with the capability of survival of the inoculated bacteria, the scarcity of survival in this soil, specially after the great fall observed, is not attributable to the low SOM content, it might be related with its high electric conductivity. The UP61 had the best survival rate in all soils.