Abstract
Biocontrol microorganisms are emerging as an effective alternative to pesticides. Ideally, biocontrol agents (BCAs) for the control of fungal plant pathogens should be selected by an in vitro method that is high-throughput and is predictive of in planta efficacy, possibly considering environmental factors, and the natural diversity of the pathogen. The purpose of our study was (1) to assess the effects of Fusarium strain diversity (N = 5) and culture media (N = 6) on the identification of biological control activity of Streptomyces strains (N = 20) against Fusarium pathogens of wheat in vitro and (2) to verify the ability of our in vitro screening methods to simulate the activity in planta. Our results indicate that culture media, Fusarium strain diversity, and their interactions affect the results of an in vitro selection by dual culture assay. The results obtained on the wheat-based culture media resulted in the highest correlation score (r = 0.5) with the in planta root rot (RR) inhibition, suggesting that this in vitro method was the best predictor of in planta performance of streptomycetes against Fusarium RR of wheat assessed as extension of the necrosis on the root. Contrarily, none of the in vitro plate assays using the media tested could appropriately predict the activity of the streptomycetes against Fusarium foot rot symptoms estimated as the necrosis at the crown level. Considering overall data of correlation, the activity in planta cannot be effectively predicted by dual culture plate studies, therefore improved in vitro methods are needed to better mimic the activity of biocontrol strains in natural conditions. This work contributes to setting up laboratory standards for preliminary screening assays of Streptomyces BCAs against fungal pathogens.
Highlights
The use of biocontrol agents (BCAs) against major plant pathogens is becoming a valuable alternative to chemical control of plant diseases and represents an important resource for the future of agriculture (Bardin et al, 2015)
In an effort to identify quick and effective methods of selecting Streptomyces strains against Fusarium diseases in wheat, we evaluated the effect of Fusarium strains, one F. culmorum and four F. graminearum characterized by different chemotypes, and culture media on the activity of streptomycete strains
The flour was obtained from wheat seeds inoculated with a mixture of agar-mycelium plugs derived from colonies of F. culmorum (FcUK) and F. graminearum (PH1) incubated at 24 C in 250 mL Erlenmeyer flasks in the dark at 100% humidity
Summary
The use of biocontrol agents (BCAs) against major plant pathogens is becoming a valuable alternative to chemical control of plant diseases and represents an important resource for the future of agriculture (Bardin et al, 2015). Streptomyces, a taxonomically wide genus of the phylum Actinobacteria, are gram-positive bacteria ubiquitous in soil as free-living microorganisms and as symbionts of plants, animals, and fungi (reviewed in Seipke, Kaltenpoth & Hutchings, 2012). In most cases, these interactions are positive, as they combine in planta endophytic behavior (Sardi et al, 1992) with the ability to produce an array of specialized metabolites with biological activities (reviewed in Barka et al, 2016). They have been studied for their antibacterial and antifungal effects (Wei et al, 2017), as well as their plant growth promoting capabilities (reviewed in Viaene et al, 2016), and they can be exploited in agriculture
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