*3.4. Evaluation of Antagonism in Field*

Field results showed that the treatments with antifungal activity were effective in reducing the incidence of charcoal rot in the root, stem, and pods of "Virginia Champs" variety peanut plants under induced infection (Table 3).

The peanut plants that were inoculated with *M. phaseolina* at the time of transplantation presented root rots at 110 days; necrosis and elongated reddish-brown lesions were observed that covered 40% of the total surface of the main root (Figure 4a). In addition, a considerable loss of secondary roots, with abundant dark mycelium that formed black and rounded microsclerotia (Figure 4a) as well as necrosis in peanut pods, affecting their development, was observed (Figure 4b).

Inoculation with *M. phaseolina* caused a reduction in the height of the plant, presenting significant differences (*p* = 0.0056). It was possible to corroborate that *T*. *koningiopsis* (T-K11) was more effective in promoting the total growth of the plant, which reached a weight of 1417.60 g as well as reduced the incidence of charcoal rot by 76% (Table 3), compared to *T. harzianum* (T-H3), *T. asperellum* (T-AS1), *T. hamatum* (T-A12), and the strain native of *T. harzianum* (T-Ah).

**Figure 3.** Antagonism of *T. asperellum* (**a**), *T. harzianum* native (**b**), *T. hamatum* (**c**), *T. koningiopsis* (**d**), and *T. harzianum* (**e**) with *M. phaseolina* on the scale by Bell et al. [34] after 132 h in dishes with PDA medium, incubated at 28 ◦C for 10 days. (**d**,**e**) Class I antagonism; (**a**–**c**) class II antagonism; (**f**) control group of *M. phaseolina*.

**Table 3.** Antagonistic activity on the incidence of disease, the weight per plant, weight of 100 grains the peanuts, weight, and number of pods.


\* Media followed by the same letter do not present significant statutory differences (*p* < 0.05) according to Tukey's test. (*n* = 100 plants per treatment), M = mean, SE = Standard Error. Means followed by the same letter (a, b, c, d, e and f) are not significantly different for *p* ≤ 0.05 according to Tukey test.

> Chemical treatment (Cercobin®) presented a 51% reduction of the incidence of charcoal rot without presenting significant differences with *T. harzianum* (T-H3), *T. asperellum* (T-AS1), *T. hamatum* (T-A12), and the strain native of *T. harzianum* (T-Ah) in comparison with plants inoculated only with *M. phaseolina* (Table 3). This can be explained in the following way: the *M. phaseolina* strain is native to the study region and may have acquired resistance towards Cercobin®, which is why the chemical treatment is no longer as effective to control charcoal rot.

**Figure 4.** Charcoal rot in peanut plants that were inoculated with *M. phaseolina*. (**a**) reddish brown necrosis \* present on the surface of the main root with abundant dark mycelium that formed black and rounded microsclerotia on the lateral roots \*\*; (**b**) necrosis in peanut pods.

The potential yield per hectare showed highly significant differences between the treatments (*<sup>p</sup>* = 0.001), where *T. koningiopsis*(T-K11) showed higher production (1.60 ± 0.01 t/ha<sup>−</sup>1), presenting 64.04 pods per m2. The chemical treatment (Cercobin®) was characterized by generating the second highest production, obtaining 60.88 pods per m2. The lowest production occurred in plants inoculated only with *M. phaseolina* (0.67 ± 0.01 t/ha<sup>−</sup>1), presenting 44 pods per m2. The average performance of the yields for the remaining strains of *Trichoderma* spp. oscillate between 1.28 ± 0.01 and 1.38 ± 0.01 ton ha−<sup>1</sup> (Figure 5). If we consider the average yield per hectare in the region (1.30 t/ha−1), the results reported in the present investigation are superior to the treatments inoculated with biological agents, being able to generate a strategy in the future to control charcoal rot in the rural communities of Buenavista de Benito Juárez, which belongs to the municipality of Chietla in Puebla, Mexico.

**Figure 5.** Potential yield (t/ha−1) of peanuts for each treatment in Buenavista de Benito Juárez, which belongs to the municipality of Chietla in Puebla, Mexico. Media followed by the same letter do not present significant statutory differences (*p* ≤ 0.05) according to Tukey's test.
