Abstract
Four detergents were tested as selective C sources for the plant growth-promoting rhizobacteria Pseudomonas aeruginosa 7NSK2 and Pseudomonas fluorescens ANP15. CO-720 (Igepal CO-720) or DOS (dioctyl sulfosuccinate), applied at 0.2% to the soil, increased the number of detergent-adapted, inoculated strains by almost 1.5 log units after 25 days, accounting for virtually the entire increase in total bacteria. The same dose of Tween 80 or N-laurylsarcosine, on the other hand, increased the indigenous populations by almost 2.5 log units, with only minor increases in the number of detergent-adapted inoculated strains. When CO-720 or DOS was initially supplied, the number of detergent-adapted 7NSK2 organisms was about 2 log units higher after 3 months of incubation than for the detergent-unadapted strain. This better survival resulted in a significantly higher root colonization of maize in a pot experiment with soil inoculation, with a significantly (P <= 0.05) higher shoot dry weight (18 to 33%). In a first field experiment with rhizosphere inoculation of 1-month-old maize plants, no effects on the height of two maize cultivars could be observed 1 month after inoculation. In a second field experiment, leaf and stem dry weights of yellow mustard and grass dry weight were increased in the treatments with seed and soil inoculation of the detergent-adapted 7NSK2 in combination with CO-720 application by, respectively, 7 to 8%, 19 to 23%, and 20 to 31%, although only the increases in grass dry weight were statistically significant at P <= 0.1. To some extent, 7NSK2 and DOS application also positively affected the mineral content of yellow mustard.