Abstract
Biocontrol bacteria can be used for plant protection against some plant diseases. Pseudomonas chlororaphis PCL1606 (PcPCL1606) is a model bacterium isolated from the avocado rhizosphere with strong antifungal antagonism mediated by the production of 2-hexyl, 5-propil resorcinol (HPR). Additionally, PcPCL1606 has biological control against different soil-borne fungal pathogens, including the causal agent of the white root rot of many woody crops and avocado in the Mediterranean area, Rosellinia necatrix. The objective of this study was to assess whether the semicommercial application of PcPCL1606 to soil can potentially affect avocado soil and rhizosphere microbial communities and their activities in natural conditions and under R. necatrix infection. To test the putative effects of PcPCL1606 on soil eukaryotic and prokaryotic communities, a formulated PcPCL1606 was prepared and applied to the soil of avocado plants growing in mesocosm experiments, and the communities were analyzed by using 16S/ITS metagenomics. PcPCL1606 survived until the end of the experiments. The effect of PcPCL1606 application on prokaryotic communities in soil and rhizosphere samples from natural soil was not detectable, and very minor changes were observed in eukaryotic communities. In the infested soils, the presence of R. necatrix strongly impacted the soil and rhizosphere microbial communities. However, after PcPCL1606 was applied to soil infested with R. necatrix, the prokaryotic community reacted by increasing the relative abundance of few families with protective features against fungal soilborne pathogens and organic matter decomposition (Chitinophagaceae, Cytophagaceae), but no new prokaryotic families were detected. The treatment of PcPCL1606 impacted the fungal profile, which strongly reduced the presence of R. necatrix in avocado soil and rhizosphere, minimizing its effect on the rest of the microbial communities. The bacterial treatment of formulated PcPCL1606 on avocado soils infested with R. necatrix resulted in biological control of the pathogen. This suppressiveness phenotype was analyzed, and PcPCL1606 has a key role in suppressiveness induction; in addition, this phenotype was strongly dependent on the production of HPR.
Highlights
Soil is a complex and variable habitats on earth
A statistical comparison of area under the disease progress curve (AUDPC) data revealed that all of the assayed PcPCL1606 treatments resulted in a significant reduction (ANOVA, P < 0.05) in the disease index when compared to the untreated control plants
González-Sánchez et al, 2013), and recently, the potential of the strain was combined with low concentrations of fungicide, this strain as a biocontrol agent was demonstrated in which had a higher plant protection, leading to a reduction the integrated control against R. necatrix in avocado plants; in chemical residues and appearance of fungal resistance
Summary
Soil is a complex and variable habitats on earth. Soil organisms have developed different mechanisms to survive, function and replicate into a changing environment, with variable moisture, temperature, and chemical contents. Soil conditions can vary in very short distances, and there is variability over time; soil organisms must be able to adapt rapidly to different and changing conditions (Thies and Grossman, 2006). Most of the upper layer of the soils are under the influence of plant roots. Rhizosphere soil a kind of layer between roots and the surrounding soil, that takes part in the large fluxes of nutrients and non-nutrient compounds (Belnap et al, 2003). Plant rhizosphere provides a special habitat that promotes higher microbial growth, abundance, and diversity (Praeg et al, 2019)
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