Influence of rhizobacterial volatiles on the root system architecture and the production and allocation of biomass in the model grass Brachypodium distachyon (L.) P. Beauv.

Abstract

BackgroundPlant growth-promoting rhizobacteria are increasingly being seen as a way of complementing conventional inputs in agricultural systems. The effects on their host plants are diverse and include volatile-mediated growth enhancement. This study sought to assess the effects of bacterial volatiles on the biomass production and root system architecture of the model grass Brachypodium distachyon (L.) Beauv.ResultsAn in vitro experiment allowing plant-bacteria interaction throughout the gaseous phase without any physical contact was used to screen 19 bacterial strains for their growth-promotion ability over a 10-day co-cultivation period. Five groups of bacteria were defined and characterised based on their combined influence on biomass production and root system architecture. The observed effects ranged from unchanged to greatly increased biomass production coupled with increased root length and branching. Primary root length was increased only by the volatile compounds emitted by Enterobacter cloacae JM22 and Bacillus pumilus T4. Overall, the most significant results were obtained with Bacillus subtilis GB03, which induced an 81 % increase in total biomass, as well as enhancing total root length, total secondary root length and total adventitious root length by 88.5, 201.5 and 474.5 %, respectively.ConclusionsThis study is the first report on bacterial volatile-mediated growth promotion of a grass plant. Contrasting modulations of biomass production coupled with changes in root system architecture were observed. Most of the strains that increased total plant biomass also modulated adventitious root growth. Under our screening conditions, total biomass production was strongly correlated with the length and branching of the root system components, except for primary root length. An analysis of the emission kinetics of the bacterial volatile compounds is being undertaken and should lead to the identification of the compounds responsible for the observed growth-promotion effects. Within the context of the inherent characteristics of our in vitro system, this paper identifies the next critical experimental steps and discusses them from both a fundamental and an applied perspective.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0585-3) contains supplementary material, which is available to authorized users.

Small molecules below‐ground: the role of specialized metabolites in the rhizosphere

“…Besides their role in plant immunity, bacterial VOCs can have distinct effects on root architecture. Such modifications of roots include increased length and branching and have been observed in both dicots and monocots (Delaplace et al ., ; Gutiérrez‐Barranquero et al ., ) (Figure f). VOCs produced by root‐colonizing mycorrhizal fungi were suggested to play equally important roles on root morphology (see below) (Figure f).…”

Airborne signals from Trichoderma fungi stimulate iron uptake responses in roots resulting in priming of jasmonic acid‐dependent defences in shoots of Arabidopsis thaliana and Solanum lycopersicum

“…For example, exposure to VCs produced by certain rhizobacteria led to significant changes in root architecture and shoot biomass (Ryu et al ; Blom et al ; Meldau et al ; Zamioudis et al . ; Delaplace et al ) or to enhanced resistance against pathogen infection (Ryu et al ; Chung et al . ).…”

“…Bacterial VCs can be detected by neighbouring plants, leading to adjustments in plant growth and defensive status (Wenke et al 2010). For example, exposure to VCs produced by certain rhizobacteria led to significant changes in root architecture and shoot biomass (Ryu et al 2003;Blom et al 2011;Meldau et al 2013;Zamioudis et al 2013;Delaplace et al 2015) or to enhanced resistance against pathogen infection (Ryu et al 2004;Chung et al 2016). In most of the studies, complete plant seedlings were exposed to bacterial VCs.…”

Developmental plasticity ofBrachypodium distachyonin response to P deficiency: modulation by inoculation with phosphate-solubilizing bacteria

“…Four bacterial strains were selected for their potential plant growth promotion and phosphorus solubilization capacities: Bacillus velezensis GB03 (BveGB03), Bacillus velezensis FZB42 (BveFZB42), Pseudomonas fluorescens 29ARP (Pfl29ARP) and Azotobacter vinelandii F0819 (AviF0819). The Bacillus strains were selected for their plant growth promotion activities on Poaceae (Delaplace et al 2015; Myresiotis et al 2015; Zhang et al 2014), as well as their ability to solubilize different forms of P (Giles et al 2014; Idris et al 2007; Idriss et al 2002; Liu et al 2015). Pseudomonas fluorescens also exhibited P solubilizing activities and promoted wheat (Shaharoona et al 2008) and maize growth (Li et al 2017).…”

“…Azotobacter vinelandii , a free diazotrophic bacteria, exhibited P solubilization activity (Nosrati et al 2014) and PGP traits (Taller and Wong 1989). Escherichia coli DH5α 99B829 (Eco99B829), was selected as a negative control for plant growth promotion (Delaplace et al 2015; Wu et al 2016; Zhou et al 2016). The strains BveGB03 and Eco99B829 were kindly provided by Dr Paul W. Paré and Dr John McInroy (Texas Tech University, Lubbock, TX, USA), Pfl29ARP by Dr Alain Sarniguet (Institut National de la Recherche Agronomique, Rennes, France), AviF0819 by the Katholieke Universiteit Leuven (Leuven, Belgium), and BveFZB42 by Pr Rainer Borriss (Nord Reet UG, Greifswald, Germany).…”