Suppression of plant defence response by a mycorrhiza helper bacterium

Abstract

Summary• The aim of the present study was to determine whether the mycorrhiza helper bacterium Streptomyces sp. AcH 505 could serve as a biocontrol agent against Heterobasidion root and butt rot.• Bacterial influence on mycelial growth of Heterobasidion sp. isolates, on the colonization of wood discs and Norway spruce ( Picea abies ) roots was determined. The effect of AcH 505 on plant photosynthesis, peroxidase activity and gene expression, and needle infections were investigated.• AcH 505 was antagonistic to 11 of 12 tested fungal Heterobasidion isolates. The antagonism resulted in a suppression of fungal colonization of Norway spruce roots and wood discs. Mycelial growth rate of the 12th strain, Heterobasidion abietinum 331 was not affected by AcH 505, and colonization of roots by this fungal strain was promoted by AcH 505. Bacterial inoculation led to decreased peroxidase activities and gene expression levels in roots.• AcH 505 promotes plant root colonization by Heterobasidion strains that are tolerant to antifungal metabolites produced by the bacterium. This may result from unknown bacterial factors that suppress the plant defence response.

Friends and foes: streptomycetes as modulators of plant disease and symbiosis

“…According to literature, the infection of Norway spruce with Heterobasidion annosum is associated with a plant defence-related increase in peroxidase activity and PaSpi2 peroxidase and PaChi4 chitinase gene expression levels (Asiegbu et al 1993;Fossdal et al 2001;Hietala et al 2004). Instead, we observed decreased expression of these defence markers after AcH 505 inoculation of the plant (Lehr et al 2007). This indicates that AcH 505 suppresses important components of the plant defence response against Heterobasidion.…”

“…This indicates an important application for MHB such as AcH 505: the simultaneous growth promotion of mycorrhizal as well as growth suppression of pathogenic fungi (Schrey et al 2005). To investigate this possibility, Lehr et al (2007) conducted a screening of 12 plant pathogenic isolates of Heterobasidion in dual culture with AcH 505. All but one of the Heterobasidion strains were suppressed by AcH 505.…”

“…The only AcH 505-insensitive strain, H. abietinum 331, showed a high tolerance against WS-5995 B. Since H. abietinum 331 was neither suppressed nor promoted in co-culture with AcH 505, this strain was used to show that AcH 505 had a direct positive influence on plant colonisation (Table 1, Lehr et al 2007). According to literature, the infection of Norway spruce with Heterobasidion annosum is associated with a plant defence-related increase in peroxidase activity and PaSpi2 peroxidase and PaChi4 chitinase gene expression levels (Asiegbu et al 1993;Fossdal et al 2001;Hietala et al 2004).…”

Effects of Plant Growth Promoting Rhizobacteria (PGPR) on <i>In Vitro</i> Bread Wheat (<i>Triticum aestivum</i> L.) Growth Parameters and Biological Control Mechanisms

“…Streptomycetes soil produce hydroxamate-type siderophore, could inhibit plant pathogens growth and thus reduce their action by competing for the phenomenon for iron [27]- [29]. Or by stimulation of plant defenses [30]- [33]. Thus, the results obtained in this study on Fusarium soft wheat will contribute positively to the improvement of biocontrol process against these diseases.…”

Rhizospheric streptomycetes as potential biocontrol agents of Fusarium and Armillaria pine rot and as PGPR for Pinus taeda

“…Although several authors have shown the effectiveness of these microorganisms as biological plant disease control agents (Shekhar et al 2006;Lehr et al 2008), very few reports involve forest species (Lehr et al 2007).…”