3.3.2. Biological Assays in Tomato Seedlings

The efficacy of the selected antagonist for the control of *R. solanacearum* was evaluated on tomato seedlings (Figure 4 and Figure S9, Table 3). The disease assessment was carried out using the method described in Kumar [23]. For the plants in the TR 1 group, the 109 cfu mL−<sup>1</sup> suspension of NEAU-HV9 was effective against *R. solanacearum* when compared with the control (CK 2); all seedlings were as healthy as the CK 1 group. The 10<sup>8</sup> cfu mL−<sup>1</sup> suspension of NEAU-HV9 showed very weak bioactivity against *R. solanacearum* compared with the control (CK 2); only one seedling was healthy and others were wilted. The 107 cfu mL−<sup>1</sup> suspension of NEAU-HV9 exhibited no bioactivity against *R. solanacearum*; all seedlings were wilted, the same as the seedlings that were dried.

**Figure 4.** Control efficiency of strain NEAU-HV9 against *R. solanacearum*. A, tomato seedlings were inoculated with sterile water (CK 1); B, tomato seedlings only were inoculated with *R. solanacearum* (CK 2); C, tomato seedlings were pre-inoculated with suspension (107 cfu mL<sup>−</sup>1) of NEAU-HV9 and then inoculated with *R. solanacearum* (TR 1); D, tomato seedlings were pre-inoculated with suspension (108 cfu mL<sup>−</sup>1) of NEAU-HV9 and then inoculated with *R. solanacearum* (TR 1); E, tomato seedlings were pre-inoculated with suspension (10<sup>9</sup> cfu mL<sup>−</sup>1) of NEAU-HV9 and then inoculated with *R. solanacearum* (TR 1); F, actinomycin D at the concentration 1 × MIC (TR 2); G, actinomycin D at the concentration 2 × MIC (TR 2).



Data shown are the mean of three replications. Means within the same column followed by the same letter are not significantly different (*p* = 0.05) according to Fisher's least significant difference test.

Actinomycin D was highly effective against *R. solanacearum* in tomato seedlings (Figure 4 and Figure S9, Table 3). It was notable that all seedlings of the control (CK 2) were wilted, however after treatment with actinomycin D at the concentration 1 × MIC and 2 × MIC, none of the seedlings exhibited disease symptoms; the control efficacy of the formulation was 100%.
