TABLE 2.
Comparative characteristics of S. plymuthica IC1270 and its grrA, grrS, and rpoS mutants
| Property | Strain or mutanta
|
|||
|---|---|---|---|---|
| IC1270 | IC1270#20 (grrA) | IC1270#93 (grrS) | IC1270#823 (rpoS) | |
| Suppression of R. solani (halo size, mm)b | 14 ± 2.0 | 10 ± 1.4 | − | − |
| Suppression of P. aphanidermatum (halo size, mm)b | 13 ± 1.5 | 9 ± 1.5 | − | − |
| Pyrrolnitrin production (μg/ml)c | 108 ± 14 | 13.2 ± 3.1 | 2.8 ± 0.2 | 3.6 ± 0.4 |
| Exoprotease productionb | + | − | − | − |
| Siderophore production (mm)b | 19 ± 4 | 14.3 ± 3.2 | 12.6 ± 2.3 | 21 ± 4.1 |
| Biocontrol of R. solani in beans (IDR, %)d | 48.5a | 8.8b | 11.1b | 7.9b |
| Biocontrol of P. aphanidermatum in cucumber (seedling emergence)e | 95.3a | 74.6b | 60.8b | 76.4b |
| Biocontrol of P. aphanidermatum in cucumber (seedling survival)f | 84.8a | 58.5b | 56.0b | 53.6b |
| Biocontrol of P. aphanidermatum in cucumber (IDR, %)g | 68.5a | 37.5b | 24.4b | 29.7b |
+, detected; −, not detected.
Mean ± SD for four independent plates.
Data from HPLC analysis. Values are means ± SD from three replicate preparations.
Index of disease reduction (IDR) in treatments was calculated according to the formula 1 − [(percent of root rot-affected seedlings out of the total number of apparently healthy seedlings)/66.8] × 100, where percent disease in disease control, 66.8% ± 4.9%, was estimated as the number of root rot-affected seedlings divided by the total number of apparently healthy seedlings and multiplied by 100. The data from four independent experiments with five replicates for each treatment variant are summarized.
Percent seedling emergence was estimated as the percentage of germinated seedlings divided by the percentage of seedlings that emerged in a germination control (89.2 ± 3) multiplied by 100. In the disease control (treatment with water), percent seedling emergence was 33.6. Here and below, values not followed by the same letter were significantly different, as determined by the all-pairs Tukey-Kramer test at P = 0.05 with the JMP 5.0.1a (SAS Institute Inc., Cary, N.C.) program.
Percent postemergence seedling survival was calculated by dividing the number of seedlings that were alive 12 days after planting by the number of emerged seedlings and multiplying by 100. For the disease control, it was 29.0.
Calculated by the formula 1 − [(percentage of total disease in treatment)/(percent of total disease in disease control)] × 100, where the percentage of total (pre- and postgermination) disease in the disease control was calculated as [(number of nongerminated seedlings plus number of germinated seedlings affected by damping-off)/(average number of seedlings germinated in the germination control)] × 100. Data from three independent experiments with five replicates in each treatment are summarized.