*2.1. In Vitro Effect of Actinobacterial Strains against Macrophomina phaseolina and Rhizoctonia solani: Dual Culture Assays*

For both fungal pathogens *M. phaseolina* and *R. solani*, significant differences between actinobacterial strains were observed on their effectiveness in the Mycelial Growth Inhibition (MGI; %) (*p* < 0.001 in both cases). Regarding their effect against *M. phaseolina* isolate CCIBP-Mp1, 40 out of the 60 strains tested showed antagonistic activity against the pathogen. For this group of 40 strains, the MGI ranged from 70.4 ± 1.23 to 3.24 ± 1.01% for CBQ-EA-2 and CBQ-ESFe-11, respectively. The most effective strains against *M. phaseolina* were CBQ-EA-2, -Plat-2 and -CD-24 with mean MGI values of 70.4 ± 1.23, 66.6 ± 0.78 and 64.6 ± 1.48%, respectively. On the other hand, 25 out of the 60 actinobacterial strains tested showed antagonistic effect against *R. solani* isolate CCIBP-Rh1. For this group of 25 strains, the MGI ranged from 78.3 ± 0.37 to 5.6 ± 0.47% for CBQ-EA-12 and CBQ-C-5, respectively. The most effective strains against *R. solani* were CBQ-EA-12, -EA-2 and -CD-24 with mean MGI values of 78.3 ± 0.37, 77.4 ± 1.20 and 75.4 ± 1.22%, respectively. In addition, 19 out of the 60 actinobacteria strains evaluated showed a MGI efficacy higher than 50% for both phytopathogenic fungi, with the strains CBQ-EA-2 (MGI = 70.4 ± 1.23 and 77.4 ± 1.20% for *M. phaseolina* and *R. solani*, respectively) and CBQ-CD-24 (MGI = 64.6 ± 1.48 and 75.4 ± 1.22% for *M. phaseolina* and *R. solani*, respectively) showing the highest common effectiveness for the two pathogens. At the same time, 5% of the total actinobacteria tested did not show any effect on MGI for any of the two pathogens evaluated (Table 1; Figure 1).


**Table 1.** Antagonistic effect of the 60 actinobacterial strains on mycelial growth of *Macrophomina phaseolina* and *Rhizoctonia solani* in dual cultures.


**Table 1.** *Cont.*

<sup>a</sup> Mycelial Growth Inhibition (MGI; %) for *Macrophomina phaseolina* isolate CCIBP-Mp1 and *Rhizoctonia solani* isolate CCIBP-Rh1 were obtained by dual culture assays on PDA at 30 ◦C for 7 days in darkness. Data represent the average of twelve Petri dishes for each BCA or control ± the standard error of the means. <sup>b</sup> For each pathogen, significant differences between treatment means of MGI are given by a critical value for means comparison [HSD0.05 = 6.7 and 8.5% for *M. phaseolina* and *R. solani*, respectively] according to Tukey's honestly significant difference (HSD) tests at *p* = 0.05.

**Figure 1.** Antagonistic effect of *Streptomyces* strains against *Macrophomina phaseolina* isolate CCIBP-Mp1 (top row photos) and *Rhizoctonia solani* isolate CCIBP-Rh1 (bottom row photos) growing in dual culture on PDA at 7 days after inoculation and incubated at 28 ◦C in the dark. *Streptomyces* strains evaluated were: (**A**) CBQ-B-8, (**B**) CBQ-EA-2, (**C**) CBQ-CB-14, (**D**) CBQ-EBa-5, and (**E**) CBQ-CD-24 (top row photos); and (**A**) CBQ-B-8, (**B**) CBQ-CB-14, (**C**) CBQ-EA-12, (**D**) CBQ-EBa-21, and (**E**) CBQ-EA-2 (bottom row photos).
