Selection of the Root Endophyte Pseudomonas brassicacearum CDVBN10 as Plant Growth Promoter for Brassica napus L. Crops

Abstract

Rapeseed (Brassica napus L.) is an important crop worldwide, due to its multiple uses, such as a human food, animal feed and a bioenergetic crop. Traditionally, its cultivation is based on the use of chemical fertilizers, known to lead to several negative effects on human health and the environment. Plant growth-promoting bacteria may be used to reduce the need for chemical fertilizers, but efficient bacteria in controlled conditions frequently fail when applied to the fields. Bacterial endophytes, protected from the rhizospheric competitors and extreme environmental conditions, could overcome those problems and successfully promote the crops under field conditions. Here, we present a screening process among rapeseed bacterial endophytes to search for an efficient bacterial strain, which could be developed as an inoculant to biofertilize rapeseed crops. Based on in vitro, in planta, and in silico tests, we selected the strain Pseudomonas brassicacearum CDVBN10 as a promising candidate; this strain produces siderophores, solubilizes P, synthesizes cellulose and promotes plant height in 5 and 15 days-post-inoculation seedlings. The inoculation of strain CDVBN10 in a field trial with no addition of fertilizers showed significant improvements in pod numbers, pod dry weight and shoot dry weight. In addition, metagenome analysis of root endophytic bacterial communities of plants from this field trial indicated no alteration of the plant root bacterial microbiome; considering that the root microbiome plays an important role in plant fitness and development, we suggest this maintenance of the plant and its bacterial microbiome homeostasis as a positive result. Thus, Pseudomonas brassicacearum CDVBN10 seems to be a good biofertilizer to improve canola crops with no addition of chemical fertilizers; this the first study in which a plant growth-promoting (PGP) inoculant specifically designed for rapeseed crops significantly improves this crop’s yields in field conditions.

A New Perspective of Pseudomonas—Host Interactions: Distribution and Potential Ecological Functions of the Genus Pseudomonas within the Bark Beetle Holobiont

“…These sequences do not allow a robust classification of the sequences at species level [ 67 ]. To obtain the most accurate identification at species level, there are nowadays massive parallel sequencing platforms with the potential to obtain nearly complete 16S rRNA gene sequences (~1500 bp), which allow a better identification of the microbiome at species level [ 35 , 37 , 68 ]. Moreover, amplicons of Pseudomonas housekeeping genes such as rpoB , rpoD , and gyrB [ 49 ] can be obtained for a more accurate identification at species level of those bacterial strains belonging to Pseudomonas .…”

Connecting the Lab and the Field: Genome Analysis of Phyllobacterium and Rhizobium Strains and Field Performance on Two Vegetable Crops

“…These findings confirmed that in silico genome analyses are a good tool for detecting potential plant growth-promoting bacteria since the strains whose genome contains several genes involved in plant colonization and growth promotion mechanisms also display these mechanisms in vitro, and moreover, they showed good behavior in plant experiments carried out in microcosm conditions [26,32,33]. However, the incorporation of these strains in commercial inoculants requires conducting field experiments that have rarely been performed to date after the genome analysis of endophytic PGPB strains [27][28][29].…”

“…However, the presence of these genes in the genome of a strain is not enough to ensure its effective performance on plants, and thus in silico genome mining should be accompanied by the analysis of plant effects, with field trials being the only way to verify the real potential of strains as crop biostimulants. Although this was the approach in some recent research on inoculating endophytic bacteria on non-legumes [27,28] and rhizobia on common bean [29], there are no studies relating in silico analysis and field performance for endophytic bacteria inhabiting legume nodules.…”

Phylogenomic Analyses of the Genus Pseudomonas Lead to the Rearrangement of Several Species and the Definition of New Genera

“…Members of the genus Pseudomonas have been identified in human and animal related sources, plants, soil, water environments, psychrophilic environments, and other environmental niches and hosts [ 3 , 4 , 5 ]. Also, some species of this genus are known to play relevant roles in their hosts, such as P. aeruginosa , which causes human lung infections [ 6 ], species belonging to the P. fluorescens lineage, which are able to promote plants growth [ 7 , 8 ], or even some diverse species suggested to interfere with insects’ biology [ 9 , 10 ], amongst many other cases. The multiplicity of environments where Pseudomonas grow and diversify has led to the broad evolution of its members, making it one of the most diverse bacterial genera.…”