Bacterial species recognized for the first time for its biocontrol activity against fire blight (Erwinia amylovora)

Abstract

This study included eight bacterial isolates originating from the apple phyllosphere or soil environment that were previously selected using the pear fruitlet test (Mikiciński 2017). Identification of these isolates based on phenotypic assays and DNA analysis showed that five of them belonged to species for which an antagonistic activity against Erwinia amylovora and the protective capacity of apple and pear against fire blight were not previously demonstrated. These were L16 identified as Pseudomonas vancouverensis, 3 M as Pseudomonas chlororaphis subsp. aureofaciens, 35 M-Pseudomonas congelans, 43 M-Enterobacter ludwigii, and 59 M-Pseudomonas protegens. Investigation of the biotic relationships between the tested strains and E. amylovora showed that 3 M, 35 M and 59 M inhibited the growth of the pathogen on five out of six media used (NAS, KB, LB, R2A, NAG), but 43 M did not do so on any of these media. Strain L16 did not inhibit the growth of the pathogen on LB or R2A medium. In contrast, all strains grown on medium 925 stimulated the growth of the pathogen, which showed no growth without cocultivation with these strains. The experiments on apple trees and detached apple branches showed the ability of the tested bacteria to protect flowers at medium to high levels, depending on the experiment (55-93%). In some cases, this protection was even higher than that of the copper product used for comparison. In studies assessing the bacterial ability to protect shoots of M.26, the highest efficacy was observed for strains 35 M (96%) and 43 M (93%) but on 'Gala Must' all tested strains showed 100% of efficacy.

Plant‐associatedmicrobiota as a source of antagonistic bacteria against the phytopathogenErwinia amylovora

“…3), with the VA isolates leading to the lowest percentages of incidence and severity of infection (ANOVA, P < 0.001 for incidence and severity). The different levels of efficacy observed may depend on the antagonistic abilities of isolates, either by the competition in the colonization of plant surface or by the production of substances with activity against E. amylovora, all leading ultimately to the appearance of necrosis to varying degrees (Paternoster et al, 2010;Rosell o et al, 2013;Mikici nski et al, 2020). Some plant bacterial isolates also showed in vitro antagonism against E. amylovora…”

“…In fact, numerous Enterobacter species are endophytic bacteria (Davin-Regli et al, 2019) reported as potential biocontrol agents (Kim et al, 2020). Competition can be established by the secretion of antibacterial proteins in the periplasm of the bacterial target, as this species contains loci for type VI secretion system (T6SS) (Navarro-Garcia et al, 2019). The isolate T3-27 was identified as Curtobacterium flaccumfaciens, a bacterial species able to inhibit the in vitro growth of other pathogens, such as Xylella fastidiosa or Acidovorax citrulli (Lacava et al, 2007;Horuz and Ayssan, 2018), and to drastically reduce the incidence of crown gall caused by Agrobacterium tumefaciens (Tolba and Soliman, 2013).…”

Diversity of pathogenic Pseudomonas isolated from citrus in Tunisia

“…P. congelans was first described as non-pathogenic from the phyllosphere of grasses (Behrendt et al 2003 ) and actually potentially included strains of the PG02c phylogroup. These strains have been described previously as dominated by pathogenic strains isolated sometimes from plants and frequently from environmental substrates linked to the water cycle (Berge et al 2014 ) or having a biocontrol activity against fire blight (Mikicińskiet al 2020 ). At the opposite of the other strains from the P. syringae phylogroup PG02 having the canonical Type Three Secretion System (T3SS) used to secrete proteins that help the bacteria infect plant cells, PG02c strains have an atypical T3SS similar to S-PAI of P. viridiflava (Clarke et al 2010 ).…”

Control of Erwinia amylovora Growth by Moringa oleifera Leaf Extracts: In Vitro and in Planta Effects

“…The limitations in the control of this pest and the need to reduce antibiotics use in agriculture highlighted the urge for new, safe, and efficient control strategies. In response to this, one of the most studied fields in the last years is the identification of bacteriophages and antagonistic bacteria [ 10 , 11 ], and the application of essential oils and natural antimicrobial compounds [ 12 ].…”