Plant growth-promoting endophytic fungi from forest trees: potential applications for sustainable agro-forestry systems

The rising global population has intensified the demand for food production, resulting in extensive exploitation of natural resources and creating an urgent need for sustainable agricultural practices that minimize pollution and reduce the use of hazardous chemicals. One viable approach is the application of beneficial microorganisms to enhance plant growth and protect crops from pathogens. This thesis explores such an approach through the collection of samples across 13 experimental sites, ranging from Mediterranean coastal areas to the high-altitude alpine environment, in the Veneto and Sardinia regions. Among the sampled species, the endophytic biodiversity of Pinus mugo was studied across clusters of plants at various disease stages, highlighting endophyte-pathogen interactions in a natural setting and their implications at biodiversity levels. For the isolates obtained from each host plant, in vitro dual-culture assays of endophytic microorganisms and plant pathogens facilitated an initial screening of potential biocontrol agents. Further in vivo trials allowed the identification of organisms from this pool that demonstrated effective activity on plants. Among these, the strain Trichoderma guizhouense TG14, isolated from Pinus pinea in Arborea, showed high trophic competitiveness and effective parasitism abilities of key pathogens, including Athelia rolfsii, Rhizoctonia solani, Diplodia sapinea, Phytophthora palmivora, and Armillaria mellea. TG14 successfully colonized Phaseolus vulgaris var. Borlotto, establishing itself from seed inoculation through the stem to apical shoots and leaves, where it was re-isolated and molecularly identified. As a biocontrol agent, TG14 significantly mitigated root biomass loss under Rhizoctonia solani soil infestation and reduced lesion severity from foliar inoculation with the same pathogen. Although TG14 did not induce statistically significant growth stimulation in common beans, the average biomass produced in its presence was nonetheless greater than in control treatments.