Biological control capabilities of plant growth promoting bacteria against plant parasitic nematodes and their potential for oilseed rape bioremediation, assessed by nematode bioindicators
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The global population is increasing and the availability of land suitable for food production is in decline. Growing bioenergy crops on contaminated land is an innovative approach to alleviate this land shortage, which in turn has the potential to help meet global food demands. Bioenergy plants like oilseed rape (Brassica napus) can be grown on these contaminated brownﬁeld sites with an aim to phytoremediate the soil. Beneﬁcial bacteria such as Pseudomonas ﬂuorescens, colonising the rhizosphere and bioenergy plants, have the capacity to increase plant growth and aid bioremediation. On the other hand, there is considerable crop loss globally due to pests and diseases, such as those caused by phytoparasitic nematode infections each year. With the current use of chemical pesticides and nematicides heavily regulated,there is huge potential for the development of a low-cost,natural and sustainable biobased solutions. Three different capabilities of P. ﬂuorescens were explored in the present study: biocontrol, plant growth promotion and bioremediation. Susceptibility of free-living bacterial feeding and plant parasitic nematodes to these bacterial strains was investigated. The plant-parasitic nematode biocontrol properties of the P. ﬂuorescens strains was further explored in in planta with Meloidogyne javanica. The plant growth promotion capacity of P. ﬂuorescens strains was determined in both tomato (Solanum lycopersicum) and oilseed rape plants. The nickel bioremediation capacity of the bacterial strains in oilseed rape was also evaluated. Nematode assemblages were utilised as bioindicators of the bioremediation process. It was found that the bacterial strains investigated in the current study, were producing compounds associated with plant growth promotion and biocontrol of root pathogens, including nematicidal and antimicrobial properties, as assessed by gas chromatography-mass spectrometry analysis. Oilseed rape nickel bioremediation determined by atomic absorption spectroscopy and nematode assemblage bioindicator analysis was not successful, although the bacterial strain L321 was found to have the potential for nickel biosorption. Tomato and oilseed rape plant biomass treated with the bacterial strains L124 and L321, respectively, was increased. Treatment with the bacterial strain L321 resulted in high plant-parasitic nematode mortality and delayed M. javanica infection in tomato plants. In addition, Fourier transform - infrared spectroscopy was assessed as a successful novel method for nematode characterisation, in particularfor M. javanica. The results in relation to these two key bacterial strains contribute to the toolkit of sustainable agricultural practices that can be utilised as effective alternatives to chemical applications for phytoparasitic nematode management and plant growth promotion reducing the use of mineral fertilisers. Nickel biosorption is also an additional beneﬁcial property they acquire that enhances soil remediation.
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