Endophytic <i>Trichoderma</i> Species Isolated from <i>Persea americana</i> and <i>Cinnamomum verum</i> Roots Reduce Symptoms Caused by <i>Phytophthora cinnamomi</i> in Avocado

Avocado root rot caused by the oomycete <i>Phytophthora cinnamomi</i> is a severe disease that affects avocado production in Mexico and worldwide. The use of biological control agents such as <i>Trichoderma</i> species isolated from places where the disease is always present, represents an efficient alternative to reduce losses. Thus, the objective of this research was to evaluate the biocontrol ability of 10 endophytic <i>Trichoderma</i> spp. strains against <i>P. cinnamomi</i> tested both in vitro and in the greenhouse. The endophytic <i>Trichoderma</i> spp. were recovered from <i>Persea americana</i> and <i>Cinnamomum verum</i> roots, isolated and purified on potato–dextrose–agar medium. Ten strains were identified by phylogenetic reconstruction of the internal transcribed spacer region of rDNA sequences as <i>T. </i><i>asperellum</i> (T-AS1, T-AS2, T-AS6, and T-AS7), <i>T. harzianum</i> (T-H3, T-H4, and T-H5), <i>T. hamatum</i> (T-A12), <i>T. koningiopsis</i> (T-K8 and T-K11), and <i>P. cinnamomi</i> (CPO-PCU). In vitro dual-culture assay, the percentage of inhibition of radial growth (PIRG) between <i>Trichoderma</i> spp. and <i>P. cinnamomi</i> strains was measured according to the Bell’s scale. PIRG results indicated that T-AS2 reached the highest value of 78.32%, and T-H5 reached the lowest value of 38.66%. In the greenhouse, the infection was evaluated according to the percentage of disease incidence. Plants with the lowest incidence of dead by avocado root rot were those whose seedlings were inoculated with T-AS2 and T-AS7, resulting in only 5% death by root rot caused by <i>P. cinnamomi</i>. The disease incidence of seedlings with wilt symptoms and death decreased more than 50% in the presence of <i>Trichoderma</i> spp. Relying on the results, we conclude that <i>T. asperellum</i> and <i>T. harzianum</i> contribute to the biocontrol of soil-borne pathogenic oomycete <i>P. cinnamomi</i>.