Table 2.
Competition of NGR234 and rRNA-deletion mutants for nodulation of V. unguiculata and L. leucocephala.
| Inoculated cell ratios |
Growing nodule isolates |
|||||
|---|---|---|---|---|---|---|
| Competing strains | Aimed | Real | Host plant | Total | KmR | % KmR |
| NGR234 vs. NGRΔrRNA1 | 1:1 | 42:58 | 187 | 133 | 71.1 | |
| 4:1 | 70:30 | V. unguiculata | 241 | 54 | 22.4 | |
| 1:4 | 14:86 | 235 | 208 | 88.5 | ||
| NGR234 vs. NGRΔrRNA1,3 | 1:1 | 43:57 | V. unguiculata | 147 | 5 | 3.4 |
| 1:1 | 45:55 | L. leucocephala | 140 | 69 | 49.3 | |
To compare NGR234, NGRΔrRNA1, and NGRΔrRNA1,3 nodulation competitiveness, plants were challenged with mixed inoculants. On V. unguiculata, NGR234 and NGRΔrRNA1 were inoculated at ratios of 1:1, 1:4, and 4:1 for a total of 106 cells per plant. Given its slower growth and poor competitiveness in initial tests on cowpea, the NGRΔrRNA1,3 mutant was inoculated at equal numbers with NGR234. For each inoculum, strain ratio was verified by plating serial dilutions of the inoculum onto TYA plates containing rifampicin or kanamycin, with kanamycin resistant (KmR) colonies or nodule isolates scored as being or containing mutant strains. For these analyses, nodules were collected on a minimum of 10 plants per treatment and at 24 and 28 dpi for V. unguiculata and L. leucocephala, respectively.