Aims
Pseudomonas spp. have been widely studied for their plant growth–promoting effects. However, their capacity to promote lipid accumulation in oilseed crops is not well characterized. In this study, we evaluated the effect of Pseudomonas fluorescens LBUM677 on lipid accumulation in three oilseed crops: soybean (Glycine max), canola (Brassica napus) and corn gromwell (Buglossoides arvensis), a plant of high nutraceutical interest for its accumulation of the omega‐3 stearidonic acid.
Methods and Results
Pot experiments were conducted under controlled conditions where seeds were inoculated or not with LBUM677 and plants were harvested at 4, 8 and 12 weeks. A qPCR assay specifically targeting LBUM677 was used in parallel to correlate LBUM677 soil rhizosphere competency to growth promotion and seed lipid accumulation. Total oil seed content and fatty acid composition were analysed at seed maturity. Results showed that LBUM677 was able to establish itself in the rhizosphere of the three plant species at similar levels, but it differentially increased plant biomass, total oil content and lipid composition in a plant‐specific manner.
Conclusions
Despite some species‐specific differences observed in P. fluorescens LBUM677's effect on different crops, the strain appears to be a generalist plant growth–promoting rhizobacteria of oilseed crops.
Significance and Impact of the Study
LBUM677 shows great potential to be used as an inoculum to promote oil yield and fatty acid accumulation in oilseed crops.
The bacterial communities inhabiting the rhizosphere play an important role in plant development and health. Here we studied the effect of inoculation with
Pseudomonas fluorescens
LBUM677, a plant growth promoting rhizobacterium that promotes seed oil accumulation, on the rhizosphere microbiome of three oilseed crops (
Brassica napus
,
Buglossoides arvensis
, and
Glycine max
) over time. Next-Generation high-throughput sequencing targeting the V4 region of 16S rDNA was used to characterize the microbial communities associated with the three different crops, inoculated or not with LBUM677, over a time period of up to 90 days post-inoculation. A total of 1,627,231 amplicon sequence variants were obtained and were taxonomically grouped into 39 different phyla. LBUM677 inoculation and sampling date were found to significantly influence the rhizosphere microbiome of the three oil-producing crops under study. Specifically, inoculation with LBUM677 and sampling date, but not the plant species, were found to significantly alter the alpha- and the beta-diversity of the rhizosphere microbial communities. Differential abundance analyses found that 29 taxonomical bacterial groups were significantly more abundant in the LBUM677 treatments while 30 were significantly more abundant in the control treatments. Predicted functions of the microorganisms were also enriched, including 47 enzymatic pathways in LBUM677 treatments. These non-targeted effects on rhizosphere bacterial communities are discussed in the context of oilseed crops.
Somatic embryogenesis can be induced in the leaves of cork oak (Quercus suber L.) trees. The use of this propagation system in multivarietal forestry requires the mass production of cloned plants at low cost. Investigations were made into the influence of three types of Erlenmeyer flask and three orbiting speeds (60, 110, and 160 rpm) on oxygen transfer rate (K L a), the shear force index (SFI), biomass production, and the proliferation of embryogenic clumps (EMCs) in cultures during the proliferation phase. K L a varied between 0.11 and 1.47 h −1 without biomass production being limited by oxygen availability. The EMCs grew even in hypoxic conditions, although the suppression of gaseous exchange strongly reduced biomass production. Cultures with different levels of hydrodynamic stress and SFI values (1.4·10 −3 -8.8·10 −3 cm min −1 ) were obtained. Proliferation rates of EMCs increased with agitation rate and the SFI. The largest number of EMCs was obtained in baffled flasks agitated at 160 rpm (K L a of 1.47 h −1 , and SFI of 8.8·10 −3 cm min −1 ) with mild hydrodynamic stress enhancing growth. Biomass production increased with agitation and hydrodynamic stress, but only when the SFI value was below 5·10 −3 cm min −1 . The greatest biomass production was obtained in smooth 100 ml flasks agitated at 160 rpm. The differentiation of embryos was favoured by the lowest K L a (0.11 h −1 ) and SFI (1.40·10 3 cm min −1 ) values, achieved using these flasks when agitated at 60 rpm.
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