Abstract
In nature, pathogens live and interact with other microorganisms on plant tissues. Yet, the research area exploring interactions between bacteria-fungi and microbiota-plants, within the context of a pathobiome, is still scarce. In this study, the impact of olive knot (OK) disease caused by the bacteria Pseudomonas savastanoi pv. savastanoi (Psv) on the epiphytic and endophytic fungal communities of olive tree twigs from three different cultivars, was investigated in field conditions. The ITS-DNA sequencing of cultivable fungi, showed that OK disease disturbs the resident fungal communities, which may reflect changes in the habitat caused by Psv. In particular, a reduction on epiphyte abundance and diversity, and changes on their composition were observed. Compared to epiphytes, endophytes were less sensitive to OK, but their abundance, in particular of potential pathogens, was increased in plants with OK disease. Host genotype, at cultivar level, contributed to plant fungal assembly particularly upon disease establishment. Therefore, besides fungi - Psv interactions, the combination of cultivar - Psv also appeared to be critical for the composition of fungal communities in olive knots. Specific fungal OTUs were associated to the presence and absence of disease, and their role in the promotion or suppression of OK disease should be studied in the future.
Highlights
The above-ground plant parts are naturally inhabited by a great diversity of microbes[1]
We used the olive knot disease caused by the bacterial pathogen Pseudomonas savastanoi pv. savastanoi (Psv) as a model system for understanding interactions between pathogenic bacteria and epi- or endophytic fungal communities, taking place on host plants in the field
179 fungal operational taxonomic unit (OTU) belonging to two phyla, 47 families, and 89 genera were identified as inhabitants of olive tree twigs
Summary
The above-ground plant parts (phyllosphere) are naturally inhabited by a great diversity of microbes[1]. Savastanoi (Psv) as a model system for understanding interactions between pathogenic bacteria and epi- or endophytic fungal communities, taking place on host plants (olive trees) in the field. The fungal community composition in olive knots remains unknown, as well as the way the bacterial pathogen interacts and impacts this fungal community Using this model system, the simultaneous study of interactions occurring within members of epiphytic or endophytic microbial communities is possible, due to the recognized ability of Psv to live as an epiphyte or endophyte in the olive phyllosphere[12]. Fungal communities were assessed through PCR identification of culturable isolates These isolates will be very useful to study the mechanisms of interactions among the most prominent fungi, the pathogen Psv and host plant, and their implication in the control of OK disease. This work is the first step for ascertaining the role of such fungi on OK disease establishment/development in olive tree
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