GROWTH-STIMULATION FOR CORN AND COS LETTU CE USING PHOSPHORUS-SOLUBILIZING MICROORGANISMS

Phosphorus solubilizing microorganisms constituted 26 to 46% of the mi crobial population of the four Quebec soils studied. Among the microor ganisms isolated 10 bacteria and 3 fungi were selected for their abili ty to form a large clarification zone on solid media containing differ ent insoluble P salts. In a glasshouse assay, the inoculation of maize seeds with the 13 organisms selected did not significantly influence maize growth or P content, after 3 weeks of growth. In field trials, t he Enterobacter sp. isolates 22a and 22c and the Pseudomonas sp. isola te 24 significantly increased (7-9%) plant height after 60 days of gro wth. After 108 days of growth, only isolate 22c caused a significant i ncrease (23%) of shoots fresh mass. Field trials with Paris Island Cos lettuce seeds inoculated with the bacterial isolates 22a and 24 resul ted in 14 and 18% increase in shoots fresh mass yields, respectively. Isolate 68 of Rhizopus sp. also increased lettuce yield by 11% over th e control. The growth improvement observed in maize and lettuce probab ly did not result only from P solubilization activity but also, in par t, from the ability of the four organisms inoculated to produce sidero phores and auxins.