Effect of metabolites from different Trichoderma strains on the growth of Rosellinia necatrix, the causal agent of avocado white root rot

Camellia japonica L. is an acidophilic ornamental shrub of high economic value that has its center of origin in Japan and has been introduced in several European environmental niches. This exotic species forms arbuscular mycorrhizas (AM), known for their ability to positively affect plant growth. However, AM fungal communities associated to C. japonica in the field have never been characterized. For the first time, the AM fungal community naturally selected by C. japonica was screened in three sites located on the shores of Lake Maggiore (Italy), where specimens of this plant were introduced in the nineteenth century. Mycorrhizal levels were assessed, and the AM fungal communities associated to roots and soil were molecularly characterized based on the small subunit (SSU) rDNA region. The frequency of mycorrhizal roots was high in all sampled root systems (>90 %). Overall, 39 Operational Taxonomic Units (OTUs; 22 Glomerales, 9 Paraglomerales, 7 Archaeosporales, and 1 Diversisporales) were found in the root and soil samples. OTU richness did not significantly differ between the root and the soil niche (5.7 ± 0.6 and 8.0 ± 1.1 average OTUs per sample, respectively) and the three sites analyzed (7.5 ± 0.7, 5.2 ± 1.0, and 7.8 ± 1.5 average OTUs per sample in the three sites, respectively). The AM fungal community composition significantly differed between root-colonizing and soil-dwelling communities and among the three sites under study. Data show a major involvement of edaphic factors, such as available N sources, P, Mg, and K content in soil and soil compaction, in the structuring of the AM fungal communities.