2.6. Antagonistic In Vitro Assessment of Trichoderma spp.

The variables considered for this analysis were the percentage of inhibition of radial growth (PIRG) and colonization with Bell’s scale [39]. For the in vitro test, T. asperellum (T-AS1, T-AS2, T-AS6, and T-AS7), T. harzianum (T-H3, T-H4, and T-H5), T. hamatum (T-A12), and T. koningiopsis (T-K8 and T-K11) were considered for dual confrontations versus P. cinnamomi in a completely randomized experimental design with 10 treatments and four repetitions. PDA discs (5 mm in diameter) with mycelia of Trichoderma spp. and P. cinnamomi were placed at the extremes of Petri plates containing PDA and incubated at 28 °C for 72 h. Then, mycelial growth was scored every 12 h until the first contact between the mycelia of each antagonist T. harzianum, T. asperellum, T. koningiopsis, and T. hamatum with the oomycete P. cinnamomi occurred [15,40,41].

Antagonism and percentage of inhibition were evaluated considering the mycelial growth radius of Trichoderma spp. and P. cinnamomi (with its respective control). Invasion of the antagonist or colonization on the surface of the P. cinnamomi mycelium was taken as the index of antagonism with the scale proposed by Bell [39] (Table 2).

Trichoderma strain antagonism evaluated in vitro using Bell’s scale [39], considering the invasion of the surface.

The PIRG was calculated based on the formula proposed by Ezziyyani [41] (Equation (1)).

where PIRG = Percent inhibition of radial growth; R1 = Radial growth (mm) of P. cinnamomi without Trichoderma spp; R2 = Radial growth (mm) of P. cinnamomi with Trichoderma spp.