Assessing the Risk of Biological Control Agents on the Indigenous Microbial Communities: Serratia plymuthica HRO-C48 and Streptomyces sp. HRO-71 as Model Bacteria

Abstract

The phytopathogenic fungus Verticillium dahliae Kleb. causes high yield losses in strawberry production. As effective chemical control of this fungus is no longer available, biological control based on natural antagonists might provide new control strategies. The aim of this study was to assess the impact of the two biological control agents S. plymuthica HRO-C48 and Streptomyces sp. HRO-71 on the rhizosphere community of the Verticillium host plant strawberry in field trials at two different sites in Germany. Therefore, we determined the abundances of culturable bacteria and investigated the community structure of the total rhizosphere microbiota by PCR-single strand conformation polymorphism analysis of the 16S rRNA and fungal ITS1 region. The abundances of culturable rhizobacteria on R2A medium as well as the proportion of in vitro Verticillium antagonists did not differ significantly. Additionally, no treatment specific differences were obtained in the composition of species of the non-target antagonistic bacteria in the rhizospheres. The culture-independent analysis revealed only transient differences between the bacterial communities not due to the treatments rather than to the plant growth stage. Fungal and bacterial community fingerprints showed the development of a microbiota, specific for a field site. However, no sustainable impact of the bacterial treatments on the indigenous microbial communities was found using culture-dependent and -independent methods.

Effect of sorghum seedlings, and previous crop, on soil fluorescent Pseudomonas spp.

“…It is generally and reasonably believed that for changes in microorganism populations to be biologically significant, differences in numbers need to be at least by a power of 10 (Curl and Truelove 1986;Briones et al 2002). However, trends also have drawn notice (Gu and Mazzola 2003;McSpadden-Gardener 2007) and, especially in field studies, even statistical significance may have been difficult to demonstrate (Schwerinski et al 2007). Additionally, relative totals may not demonstrate huge changes but may reflect changes in specific groups of organisms (Curl and Truelove 1986).…”

Biological control in the microbiome era: Challenges and opportunities

“…Several studies evidenced that factors like soil properties, experimental conditions and physiological state had a deeper and more durable effect on the rhizosphere microbiota than BCA application (Chowdhury et al, 2013;Grosch et al, 2006;Kröber et al, 2014;Scherwinski et al, 2007;Schreiter et al, 2014b). The effect of a BCA can also depend on its interaction with other factors: amplicon sequencing analysis revealed significant modifications of the bacterial community composition of lettuce rhizosphere following application of the BCA P. jessenii RU47 in alluvial loam, but not in diluvial sand or loess loam (Schreiter et al, 2014a).…”

“…The disease status of plants needs to be clearly stated in publications comparing the impact of a BCA and of a pathogen on microbial communities. Several publications identified a transient modification of the plant microbiota after BCA application (Buddrus-Schiemann et al, 2010;Chen et al, 2013;Chowdhury et al, 2013;Scherwinski et al, 2007;Yin et al, 2013). However, microbial community composition returned to a similar state to the untreated control over time.…”

Risikofolgeabschätzung für den Einsatz mikrobieller Antagonisten: Gibt es Effekte auf Nichtzielorganismen?

“…und Rhizoctonia solani Kühn wurden spezifische mikrobielle Antagonisten selektiert (Kalbe et al 1996;Faltin et al 2004;Berg et al 2005a), deren krankheitsunterdrückende Wirkung wiederholt unter Feldbedingungen beobachtet wurde Grosch et al 2005a, b;Kurze et al 2001;Scherwinski et al 2007a).…”