Abstract
Plant Growth-Promoting Rhizobacteria (PGPR) enhance plant health and growth using a variety of traits. Effective PGPR strains typically exhibit multiple plant-beneficial properties, but whether they are better adapted to the rhizosphere than PGPR strains with fewer plant-beneficial properties is unknown. Here, we tested the hypothesis that strains with higher numbers of plant-beneficial properties would be preferentially selected by plant roots. To this end, the co-occurrence of 18 properties involved in enhanced plant nutrition, plant hormone modulation, or pathogen inhibition was analyzed by molecular and biochemical methods in a collection of maize rhizosphere and bulk soil isolates of fluorescent Pseudomonas. Twelve plant-beneficial properties were found among the 698 isolates. Contrarily to expectation, maize preferentially selected pseudomonads with low numbers of plant-beneficial properties (up to five). This selection was not due to the predominance of strains with specific assortments of these properties, or with specific taxonomic status. Therefore, the occurrence of only few plant-beneficial properties appeared favorable for root colonization by pseudomonads.
Highlights
Plant roots interact with huge amounts of soil microorganisms, constituting their rhizomicrobiota, which participate to optimal plant development in response to environmental conditions
In Ysa5 soil, pseudomonads were more abundant in PR37Y15 than in DK315 maize rhizosphere, whereas no significant differences were observed between cultivars in the three other soils
Contrarily to expectations, we found that Pseudomonas rhizobacteria with high numbers (>5) of plantbeneficial properties were not prevalent in the maize rhizosphere in our experimental conditions, as they were outcompeted by counterparts with lower numbers (1–5) of these properties
Summary
Plant roots interact with huge amounts of soil microorganisms, constituting their rhizomicrobiota, which participate to optimal plant development in response to environmental conditions. It is not unusual that a given PGPR strain displays several different plant-beneficial properties (Loper et al, 2012; Bruto et al, 2014), which is thought to provide higher positive effects on the plant (Bashan and de-Bashan, 2010). Since strains with multiple plantbeneficial properties can provide higher benefits to the host, they might be more prevalent in the rhizosphere than related PGPR strains displaying a smaller number of plant-beneficial properties. This situation is reminiscent of the accumulation of virulence factors in pathogens, which allows a better fitness and host infection (Friesen et al, 2006). The objective of the present study was to assess whether the rhizosphere preferentially selects bacteria with high numbers of plant-beneficial properties
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