Epiphytic and endophytic bacterial strains isolated from healthy lettuce plants were evaluated for growth promotion of seedlings and plants respectively under greenhouse and field conditions of organic production of lettuce, in Brazil. The cultivar Verônica was utilized in the greenhouse experiments and cvs. Verônica and Verdinha were evaluated in the field. The strains were applied by simultaneous bacterization of seed and substrate. In the field the most efficient strains C25 (Bacillus thuringiensis subvar. kenyae) and C116 (Bacillus pumilus) were utilized separated and in mixture after the compatibility assay. In greenhouse root fresh weight (MFR), shoot fresh weight (MFPA) and total fresh weight (MFT) were evaluated 21 days after bacterization. In field the total fresh weight of commercial plants was determined 21 and 28 days after transplant, respectively for cvs. Verdinha and Verônica. The mechanisms of BPCP studied were production of indolacetic acid, cyanidric acid, phosphate solubilization and alterations of N, P, K, Ca and Mg foliar levels. In the greenhouse, seedlings treated with C116 showed significant increase in relation to controls for MFR, MFPA and MFT as well as those treated with C25 for MFR and MFT. In the field cvs. Verdinha and Verônica treated with C25, C116 or mixture did not significantly differ from control. None of the analyzed mechanisms were positive but strain C25 significantly increased the level of foliar N.
Lactuca sativa; Bacillus pumilus; Bacillus thuringiensis subvar; plant growth-promoting bacteria; mechanisms; organic system
