Figure 7. Rhodococcus has a dose-dependent effect on the root elongation of N. benthamiana seedlings.

(A) Quantification of the seedling root lengths of plants grown in exogenously applied cytokinin (6-benyzlaminopurine; BA). Three-day-old N. benthamiana seedlings were transferred to media supplemented with BA (0.01, 0.1, 1.0, and 10 µM) or dimethyl sulfoxide (DMSO). (B) Quantification of the root lengths of seedlings inoculated with increasing doses of Rhodococcus. Three-day-old N. benthamiana seedlings were inoculated with isolates D188, PBTS2, or PBTS2 + pFiD188Δatt, with doses ranging from 2.5 × 10² to 1.0 × 10¹² colony-forming units (cfu). The sample shaded in gray highlights the inoculum of OD₆₀₀ = 0.5 (1x = 2.5 × 10¹⁰ cfu) used in all other assays. Inocula below this decrease in 100-fold intervals. Inocula above increase at 2x, 4x, 10x, and 20x. All treatments are significantly different from mock unless otherwise noted with ‘ns’. (C) Representative image of morphological changes in seedlings. Seedlings inoculated with Rhodococcus D188 or PBTS2 (5 × 10¹¹ cfu; 10x typical amount) or water (mock) were photographed. Red arrows indicate true leaves. White arrows indicate lateral roots and the proliferation of root hairs.

Figure 7—figure supplement 1. Rhodococcus isolates PBTS1 and PBTS2 do not cause disease symptoms in tested plant species.

(A) Representative images of disease symptoms or beneficial effects on seedlings of N. benthamiana. Three-day-old seedlings were inoculated with Rhodococcus or water (mock) and grown vertically for seven days under constant light. (B) Quantification of seedling root length of N. benthamiana. All were significant relative to mock. There were no significant (ns) differences between treatments with PBTS1, PBTS2, or their mixture. (C, D) Quantification of stem number (C) and stem length (D) of peas inoculated with Rhodococcus or mock-inoculated. * indicates a significant difference when comparing to the mock treatment. (E, F) Quantification of height (E) and internode length (F) of pistachio UCB1 rootstock inoculated with Rhodococcus or mock-inoculated. No treatment effect was significantly different from the time-matched mock treatment. One representative experiment of three is shown.