Abstract
Associations of endophytic bacterial community composition of oilseed rape (Brassica napus L.) with quantitative resistance against the soil-borne fungal pathogen Verticillium longisporum was assessed by 16S rRNA gene amplicon sequencing in roots and hypocotyls of four plant lines with contrasting genetic composition in regard to quantitative resistance reactions. The plant compartment was found to be the dominating driving factor for the specificity of bacterial communities in healthy plants. Furthermore, V. longisporum infection triggered a stabilization of phylogenetic group abundance in replicated samples suggesting a host genotype-specific selection. Genotype-specific associations with bacterial phylogenetic group abundance were identified by comparison of plant genotype groups (resistant versus susceptible) and treatment groups (healthy versus V. longisporum-infected) allowing dissection into constitutive and induced directional association patterns. Relative abundance of Flavobacteria, Pseudomonas, Rhizobium and Cellvibrio was associated with resistance/susceptibility. Relative abundance of Flavobacteria and Cellvibrio was increased in resistant genotypes according to their known ecological functions. In contrast, a higher relative abundance of Pseudomonas and Rhizobium, which are known to harbor many species with antagonistic properties to fungal pathogens, was found to be associated with susceptibility, indicating that these groups do not play a major role in genetically controlled resistance of oilseed rape against V. longisporum.
Highlights
Plant-associated microbiota including bacterial and fungal organisms are key determinants for plant growth, health and yield (Muller et al 2016)
Associations of endophytic bacterial community composition of oilseed rape (Brassica napus L.) with quantitative resistance against the soil-borne fungal pathogen Verticillium longisporum was assessed by 16S rRNA gene amplicon sequencing in roots and hypocotyls of four plant lines with contrasting genetic composition in regard to quantitative resistance reactions
The following questions were addressed: (i) Do genotype-specific endophytic bacterial communities occur in roots and hypocotyls? (ii) If differences occur, are these mainly linked to differences in the diversity or the phylogenetic composition of the bacteria communities? (iii) Does the presence of V. longisporum affect the endophytic root and/or hypocotyl bacterial communities? (iv) Can specific bacterial community patterns be correlated to susceptibility or resistance of the plant genotypes? In addition, we aimed to identify potential key bacterial phylogenetic groups which could be linked to the root and hypocotyl plant compartments of the resistant genotypes
Summary
Plant-associated microbiota including bacterial and fungal organisms are key determinants for plant growth, health and yield (Muller et al 2016). Their genomes, sometimes referred to as the ‘second genome of plants’, can be considered a fundamental part of the plant holobiome (Berg et al 2014; Vandenkoornhuyse et al 2015). Rhizosphere ectophytic bacteria as well as internal root endophytic bacteria have been shown to indirectly trigger systemic plant defense responses, to confer broad-spectrum resistance and to directly antagonize soil-borne pathogen development (van Wees et al 2008; Berendsen, Pieterse and Bakker 2012; Santoyo et al 2016; Duran et al 2018). The mode of action and underlying mechanisms of health promotion seems to be complex and is poorly understood (Wei et al 2015)
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