Epiphytic and endophytic bacteria on olive tree phyllosphere: exploring tissue and cultivar effect

Variation on bacterial communities living in the phyllosphere as epiphytes and endophytes has been attributed to plant host effects. However, there is contradictory or inconclusive evidence regarding the effect of plant genetics (below the species’ level) and of plant tissue type on phyllosphere bacterial community assembly, in particular when epiphytes and endophytes are considered simultaneously. Here, both surface and internal bacterial communities of two olive (Olea europaea) cultivars were evaluated in twigs and leaves by molecular identification of cultivable isolates, with an attempt to answer these questions. Overall, Proteobacteria, Actinobacteria and Firmicutes were the dominant phyla, being epiphytes more diverse and abundant than endophytes. Host genotype (at cultivar level) had a structuring effect on the composition of bacterial communities and, in a similar way, for both epiphytes and endophytes. Plant organ (leaf vs. twig) control of the bacterial communities was less evident when compared with plant genotype and with a greater influence on epiphytic than on endophytic community structure. Each olive genotype/plant organ was apparently selective towards specific bacterial operational taxonomic units (OTUs), which may lead to specific feedbacks on fitness of plant genotypes. Bacterial recruitment was observed to happen mainly within epiphytes than in endophytes and in leaves as comparedwith twigs. Such host specificity suggested that the benefits derived fromthe plant– bacteria interaction should be considered at genetic levels below the species.The authors are grateful to the FEDER and Foundation for Science and Technology (FCT, Portugal) under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2019) and BioISI (UID/MULTI/04046/2013), as well as the Horizon 2020, the European Union’s Framework Programme for Research and Innovation, for financial support the project PRIMA/0002/2018 INTOMED—Innovative tools to combat crop pests in the Mediterranean. D. Mina thanks FCT, POPH-QREN and FSE forMSFRH-BD-105341/2014 grant.