TABLE 2.
Contribution of FumA and PycB to the suppression of Pythium damping off and root rot of cucumber by P. fluorescens CHA0 in natural soil
Data represent the means from two individual repetitions of the same experimental setup, with 10 replicates (flasks containing three cucumber plants) per treatment in each experiment. ND, not detected.
| Bacterial strain addeda | Pythium addeda | Surviving plants/flask | Shoot fresh weight/flask | Root fresh weight/flask | Colonization by P. fluorescensb |
|---|---|---|---|---|---|
| % | g | g | log10 colony-forming units/g root | ||
| None | − | 100c | 1.17c | 0.26c | ND |
| CHA0 (wild type) | − | 100c | 1.31c | 0.26c | 7.10 ± 0.20 |
| CHA1322 (ΔfumA) | − | 100c | 1.23c | 0.29c | 7.27 ± 0.17 |
| CHA1201 (pycB::Tn5) | − | 100c | 1.23c | 0.27c | 7.25 ± 0.15 |
| None | + | 19d | 0.21d | 0.05d | ND |
| CHA0 (wild type) | + | 96c | 1.18c | 0.28c | 7.87 ± 0.58 |
| CHA1322 (ΔfumA) | + | 65e | 0.90e | 0.18e | 8.37 ± 0.66 |
| CHA1201 (pycB::Tn5) | + | 78e | 0.94e | 0.18e | 7.91 ± 0.59 |
aP. fluorescens strains were added at 107 colony-forming units/g of natural soil contained within 200-ml flasks (60 g of soil/flask), after planting three 92-h-old, sterile-grown cucumber seedlings per flask. P. ultimum was added as a millet seed inoculum at 2.5 g/kg of soil before planting. Plants were harvested after 7 days.
b The rhizosphere-stable plasmid pME6031 containing a tetracycline resistance determinant (44) was introduced as a selective marker into the bacterial strains to determine their root colonization capacity in natural soil.
c–eMeans within the same column followed by different letters are significantly different (p ≤ 0.05) according to Fisher's protected least squares difference test. Prior to separation of means by the least squares difference test, data of the two individual experiments could be pooled following an analysis of variance of trial-by-treatment interactions.