**3.1. Growth rate and rate of development**

The Tv-T3 (1) and Th-T4 (3) strains of *Trichoderma* spp. presented a cottony texture with abundant density and abundant mycelium, a dark green and white coloration, whereas the Tav-T7 (2) strain presented a regular density, regular mycelium and a green/yellow coloration. For the *F. oxysporum* strain in this case (Fo-A) presented a velvety texture with a regular density and mycelium of pink white color, as described by Guzman [35], in addition its mycelium is formed by septate hyphae and the conidiophores present clusters of macroconidia where chlamydospores are observed.

*T. harzianum* presented the highest growth rate with a mean of 1.25 cm/day, followed by *T. viridae* with 0.75 cm/day, with the *T. atroviridae* strain being the lowest growth rate with 0.64 cm/day. For *F. oxysporum* the growth was 0.83 mm/day, results similar to those found by Amaro-Leal [36], with a speed between 70 and 73 mm/day in PDA, results similar to those of the present investigation.


by *T. viridae* with (PIRG) 79.61% and finally *T. atroviridae* with (PIRG) 73.41%. Reports of the percentage inhibition of *Fusarium* by *Trichoderma* show values from 22.5 to 86.44% [37]. The values obtained from inhibition are higher than those obtained by Michel [38], who at evaluating the antagonistic effect of native *Trichoderma* spp., on mycelial growth and reproductive potential of *F. oxysporum* and *Fusarium subglutinans*, presented inhibition of 47.6 and 73.0%, respectively. Snyder and Hansen [39], reported a percentage inhibition of 77.8% for *F. oxysporum,* when compared with *Trichoderma viridae* isolates, results lower than those reported in

Biological Control of *Fusarium oxysporum* in Tomato Seedling Production with Mexican Strains…

http://dx.doi.org/10.5772/intechopen.72878

161

The results of the interaction of the most representative paired cultures are presented in **Figure 2**. The *F. oxysporum* Fo-A strain was given 2 days advantage because of its slow growth compared to *Trichoderma*; the days after the first contact between hyphae, the behavior was determined, which was very heterogeneous and highly significant (P = 0.0001). Most of the *Trichoderma* isolates showed a visible overgrowth zone with the hyphae of *F*. *oxysporum*; the greater the area of overgrowth, the greater the aggressiveness of the antagonistic fungus [29]. In this sense, Michel [36], reported antagonism 1, 2 and 3 of *F. subglutinans* and *F. oxysporum*,

The treatment inoculated with *F. oxysporum* showed symptoms of the disease in the root and aerial part (**Table 4**), presenting the highest values in incidence and severity, this in comparison with the other treatments evaluated in this study. These results coincide with that observed by Kim [40], who point out the damage caused by *Phytophthora* sp., at the root and crown of the stem of chile plants under greenhouse conditions, similar results in this research. In the present investigation, the lowest incidence and severity was obtained in the treatment based on *T. harzianum* with 6%, presenting slight dry circular lesions in the root and without symptomatology in the aerial part. *T. harzianum* has the ability to produce enzymes such as cellulases, β-1,3-glucanase and chitinases, which degrade the cell wall of phytopathogens [41]. Treatments based on *T. harzianum*, *T*. *atroviridae* and *T*. *viridae*. used in this research work, present antagonistic efficacy against *F. oxysporum* with a survival ranging from 62.7 to 76.4% in comparison to the control treatment (**Figure 3**), which had a survival rate of 46%; while

**Figure 2.** Antagonistic capacity, according to the scale of Bell for *Trichoderma* spp. on *F. oxysporum*. (A and B = *T. harzianum* and *T*. *atroviridae* overlapping *F. oxysporum*, has a type II interaction, covers 2/3 of the surface of the medium, stops its growth and can overgrow it, and C = *T. viridae* presents an interaction of type I, where it covers the entire surface of the

the present investigation.

similar results in the present investigation.

**3.3. Greenhouse antagonism tests**

medium and stops its growth).

**Table 3.** Macroscopic characterization of the colonies of Mexican strains *Trichoderma* spp. and *F. oxysporum* in culture PDA.

The highest development rate was 5.69 mm/day for *T. harzianum*, followed by *T*. *viridae* at 5.04 mm/day and *T*. *atroviridae* at 4.85 mm/day; with respect to strain of *F. oxysporum* Fo-A had a rate of 3.80 mm/day, where a significant difference (p = 0.023) occurs among strains of *Trichoderma* spp. (**Table 3**).

#### **3.2. Confrontation of** *Trichoderma spp.* **on** *F. oxysporum in vitro*

The results of the percentage of inhibition of *Trichoderma* spp. strains on *F. oxysporum* by the dual culture method are shown in **Figure 1**, the Mexican strains of *Trichoderma* spp. inhibited the growth of the pathogenic fungus, where they presented a percentage of inhibition of radial significant growth (PIRG) [p = 0.056] at the Fo-A strain of *F. oxysporum*, with *T. harzianum* which showed higher antagonistic activity, with an average value of 81.50% (PIRG), followed

**Figure 1.** Percentage of radial growth inhibition (PICR) in replicates of *Trichoderma* spp., on *F. oxysporum* in dual culture. \*Different letters in the columns mean statistical differences in percent inhibition with Tukey's test (p < 0.05).

by *T. viridae* with (PIRG) 79.61% and finally *T. atroviridae* with (PIRG) 73.41%. Reports of the percentage inhibition of *Fusarium* by *Trichoderma* show values from 22.5 to 86.44% [37]. The values obtained from inhibition are higher than those obtained by Michel [38], who at evaluating the antagonistic effect of native *Trichoderma* spp., on mycelial growth and reproductive potential of *F. oxysporum* and *Fusarium subglutinans*, presented inhibition of 47.6 and 73.0%, respectively. Snyder and Hansen [39], reported a percentage inhibition of 77.8% for *F. oxysporum,* when compared with *Trichoderma viridae* isolates, results lower than those reported in the present investigation.

The results of the interaction of the most representative paired cultures are presented in **Figure 2**. The *F. oxysporum* Fo-A strain was given 2 days advantage because of its slow growth compared to *Trichoderma*; the days after the first contact between hyphae, the behavior was determined, which was very heterogeneous and highly significant (P = 0.0001). Most of the *Trichoderma* isolates showed a visible overgrowth zone with the hyphae of *F*. *oxysporum*; the greater the area of overgrowth, the greater the aggressiveness of the antagonistic fungus [29].

In this sense, Michel [36], reported antagonism 1, 2 and 3 of *F. subglutinans* and *F. oxysporum*, similar results in the present investigation.
