Leaf Microbiota of Strawberries as Affected by Biological Control Agents

Abstract

The increasing use of biological control agents (BCAs) against Botrytis cinerea in strawberry raises the question of whether there are any undesirable impacts of foliar applications of BCAs on nontarget microorganisms in the phyllosphere. Therefore, our objective was to investigate this issue within a field study. Strawberry plants were repeatedly sprayed with three BCAs-namely, RhizoVital 42 fl. (Bacillus amyloliquefaciens FZB42), Trianum-P (Trichoderma harzianum T22), and Naturalis (Beauveria bassiana ATCC 74040)-to suppress Botrytis cinerea infections. Microbial communities of differentially treated leaves were analyzed using plate counts and pyrosequencing and compared with the microbial community of nontreated leaves. Plate count results indicate that the applied Bacillus and Trichoderma spp. survived in the strawberry phyllosphere throughout the strawberry season. However, no significant impacts on the leaf microbiota could be detected by this culture-dependent technique. Pyrosequencing of internal transcribed spacer ribosomal RNA and 16S RNA sequences revealed a change in fungal composition and diversity at class level after the introduction of T. harzianum T22 to the phyllosphere, whereas the bacterial composition and diversity was not affected by either this Trichoderma preparation or the other two BCAs. Our results suggest that pyrosequencing represents a useful method for studying microbial interactions in the phyllosphere.

Biological control in the microbiome era: Challenges and opportunities

“…These results show that a BCA has an impact on the plant microbiome. Two recent publications compared the results obtained using NGS and low-throughput approaches (Schmidt et al, 2014b;Sylla et al, 2013). They both showed that classical techniques failed to detect alterations in microbial communities found when using NGS technologies.…”

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

“…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.…”

“…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).…”

“…In terms of safety, biocontrol agents should not have any effects on nontarget organisms (16). 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).…”

“…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.…”