Introduction of Aureobasidium pullulans to the Phyllosphere of Organically Grown Strawberries with Focus on Its Establishment and Interactions with the Resident Microbiome

Abstract

Currently, there is little knowledge of the establishment of repeatedly applied biological control agents (BCAs) in the phyllosphere of plants and, in particular, their interactions with the resident microbiome. Under field conditions, the BCA Aureobasidium pullulans was applied as a model organism to organically grown strawberries during two subsequent years (2011, 2012), either as single strain treatment or with the co-application of the entomopathogenic fungus Beauveria bassiana. Fungal and bacterial communities of strawberry leaves were investigated by means of plate counts and 454 pyrosequencing. The establishment of the introduced A. pullulans strains considerably differed between the two years, presumably due to distinct environmental conditions. Short-term and long-term effects of BCA applications on the composition and diversity of fungal communities could be observed as a result of successful establishment of A. pullulans, in 2011, showing, for instance, reduced diversity of fungal communities by competitive displacement shortly after BCA introduction. Due to considerable dynamics in untreated resident microbial communities in the phyllosphere in general, however, we suggest that even the effects caused by the applied BCA preparations in 2011 are negligible under practical conditions

Resilience of the Natural Phyllosphere Microbiota of the Grapevine to Chemical and Biological Pesticides

“…Thus, indigenous communities of the phyllosphere in fields seem to be more stable than those on leaves under controlled conditions, suggesting that exogenous microbes should compete strongly with indigenous communities to occupy leaf niches. The biocontrol agents introduced could compete with indigenous microorganisms for nutrients and space (21,67), and successful colonization could be affected by the resilience of the leaf community. AZ78 treatment increased the abundance of Xanthomonadaceae (which comprises AZ78 reads) on the leaves of plants of SM2, but not in the vineyard in a very closed location (SM1), suggesting a different level of AZ78 immigration based on pyrosequencing analysis.…”

“…In particular, AZ78 treatment decreased the abundance of the Enterobacteriaceae family and increased the abundance of the Sphingobium genus on plants of SM2. Negligible changes in microbial composition have been also observed after the introduction of fungal and bacterial biocontrol agents on strawberry leaves in field conditions (18,21). Likewise, treatments with Bacillus thuringiensis and a parathyroid insecticide only minimally altered the leaf microflora of Brassica oleracea in field conditions (66).…”

“…Successful colonization of the phyllosphere by immigrating microorganisms may be highly dependent on the competitiveness of biocontrol agents, and competitive biocontrol agents might eventually harm not only pathogenic microorganisms but also nontarget organisms (17,18). However, the nontarget effects of biocontrol agents have mainly been investigated on soil microbial communities (17,19), and the impact on indigenous leaf microbiota has only recently been analyzed (18,20,21). Therefore, chemical and biological treatments could potentially affect taxonomic structures and functional properties of the phyllosphere microbiota, and deeper knowledge of different crops and environmental conditions is required to better understand the impact on indigenous leaf communities.…”

“…In terms of safety, biocontrol agents should not have any effects on nontarget organisms (16). Successful colonization of the phyllosphere by immigrating (17,19), and the impact on indigenous leaf microbiota has only recently been analyzed (18,20,21). Therefore, chemical and biological treatments could potentially affect taxonomic structures and functional properties of the phyllosphere microbiota, and deeper knowledge of different crops and environmental conditions is required to better understand the impact on indigenous leaf communities.…”

Control of Botrytis cinerea in strawberries by biological control agents applied as single or combined treatments

“…Despite these positive results, the use of phyllosphere applied BCAs against B. cinerea is still challenging (Alabouvette et al 2006;Elad and Stewart 2004;Prokkola and Kivijärvi 2007). Inconsistent treatment effects apparently arise from the complex interactions between the BCAs and the multiple factors determining their establishment in the phyllosphere, such as fluctuating abiotic conditions (Andrews 1992;Lindow and Brandl 2003), morphological and physiological plant properties (Hunter et al 2010;Whipps et al 2008) and inconsistent phyllosphere microbiomes (Jacobsen 2006;Monier and Lindow 2005;Sylla et al 2013b). …”