2.6.2. Effect of Treatments against *Rhizoctonia solani in Planta*

For treatments conducted with seedlings grown in non-sterilized soil, significant differences between treatments were observed for their effect on both DSstem (*p* = 0.0015) and DSroot (*p* ≤ 0.0001). In all cases, DSstem was lower than DSroot, ranging from 18.7 ± 2.21 to 4.4 ± 0.77% for seedlings treated with *Streptomyces* sp. CBQ-EA-2 and Celest® Top 312 FS, respectively. But no important differences were observed for their effect on DSstem compared to the positive control (DSstem = 10.6 ± 3.78%). However, all the treatments showed significantly higher effectiveness on DSroot compared to the positive control (DSroot = 86.8 ± 4.38%). Treatments with *Streptomyces* sp. CBQ-EA-2 (DSroot = 36.9 ± 1.53%) or CBQ-B-8 (DSroot = 40.6 ± 2.21%) were the least effective, while the treatment that combined the two strains was highly effective (DSroot = 21.2 ± 1.53%) showing results similar to those observed for *T. harzianum* A-34 (DSroot = 27.5 ± 2.07%) (Figure 5).

Regarding the treatments conducted with seedlings grown on sterilized soil, significant differences were also observed between treatments for their effect on both DSstem (*p* ≤ 0.0001) and DSroot (*p* ≤ 0.0001). In this case, all the treatments were highly effective compared to the positive control (DSstem = 100%), but no significant differences in effectiveness between treatments were observed. DSstem ranged from 18.1 ± 2.50 to 15.6 ± 1.71% for treatments with *Streptomyces* sp. CBQ-EA-2+ CBQ-B-8, and with *Streptomyces* sp. CBQ-EA-2, respectively. On the other hand, all the treatments also showed significantly lower DSroot values compared to the positive control (DSroot = 100%), but significant differences were also observed between treatments for their effect against the disease. The most effective treatment was *Streptomyces* sp. CBQ-EA-2+ CBQ-B-8 (DSroot = 40.6 ± 2.21%), and the

least effective were *Streptomyces* sp. CBQ-EA-2 (DSroot = 72.5 ± 1.82%), *Streptomyces* sp. CBQ-B-8 (DSroot = 71.3 ± 1.17%) and *T. harzianum* A-34 (DSroot = 68.7 ± 2.62%) (Figure 5).

**Figure 5.** Disease severity (%) in stem (**A**; DSstem) and roots (**B**; DSroot) of *Phaseolus vulgaris* of cv. Quivicán seedlings treated with biological or chemical compounds and inoculated with *Rhizoctonia solani* isolate CCIBP-Rh1 at 28 days growing on non-sterilized or sterilized soil. Each column represents the mean of 40 seedlings per soil and treatment combination. Columns with a common uppercase or lowercase letter do not differ significantly according to Fisher's protected LSD test (*p* = 0.05) for treatments on non-sterilized or sterilized soil, respectively. Vertical bars are the standard errors of the means.

A pattern similar to that observed for seedlings inoculated with *M. phaseolina* was found for the effect of the treatments on the DI of seedlings inoculated with *R. solani*, with significant differences in DI being between all treatments and the positive control (*p* ≤ 0.0001 in all cases). In all cases, the treatment with *Streptomyces* sp. CBQ-EA-2 + CBQ-B-8 showed significantly less DI than the treatments with *Streptomyces* sp. CBQ-EA-2 or *Streptomyces* sp. CBQ-B-8, and also showed DI values similar to those observed for *T. harzianum* A-34 and Celest® Top 312 FS (Figure 6).

**Figure 6.** Disease incidence (DI, %) in *Phaseolus vulgaris* cv. Quivicán seedlings treated with biological or chemical compounds and inoculated with *Rhizoctonia solani* isolate CCIBP-Rh1 at 28 days growing on non-sterilized or sterilized soil. Each column represents the mean of 40 seedlings per soil and treatment combination; and columns with a common uppercase or lowercase letter do not differ significantly according to Zar's multiple comparisons for proportions test (*p* = 0.05) for treatments on non-sterilized or sterilized soil, respectively.

Finally, for both lots of plants growing in non-sterilized and sterilized soil, the linear correlation analysis showed that there was not significant linear correlation between DSstem and DSroot (non-sterilized soil: *r* = 0.2869; *p* = 0.5815; sterilized soil: *r* = 0.7739; *p* = 0.0709), and DSstem and DI (non-sterilized soil: *r* = 0.3826; *p* = 0.4541; sterilized soil: *r* = 0.7409; *p* = 0.0920). Nevertheless, a significant positive linear correlation was observed between DSroot and DI in both non-sterilized soil (*r* = 0.9944; *p* = 0.0001) and sterilized soil (*r* = 0.9710; *p* = 0.0013).
