Exploring Rain as Source of Biological Control Agents for Fire Blight on Apple

Abstract

Poor survival on plants can limit the efficacy of Biological Control Agents (BCAs) in the field. Yet bacteria survive in the atmosphere, despite their exposure to high solar radiation and extreme temperatures. If conditions in the atmosphere are similar to, or more extreme than, the environmental conditions on the plant surface, then precipitation may serve as a reservoir of robust BCAs. To test this hypothesis, two hundred and fifty-four rain-borne isolates were screened for in vitro inhibition of Erwinia amylovora, the causal agent of fire blight, as well as of other plant pathogenic bacteria, fungi and oomycetes. Two isolates showed strong activity against E. amylovora and other plant pathogenic bacteria, while other isolates showed activity against fungal and oomycete pathogens. Survival assays suggested that the two isolates that inhibited E. amylovora were able to survive on apple blossoms and branches similarly to E. amylovora. Pathogen population size and associated fire blight symptoms were significantly reduced when detached apple blossoms were treated with the two isolates before pathogen inoculation, however, disease reduction on attached blossoms within an orchard was inconsistent. Using whole genome sequencing, the isolates were identified as Pantoea agglomerans and P. ananatis, respectively. A UV-mutagenesis screen pointed to a phenazine antibiotic D-alanylgriseoluteic acid synthesis gene cluster as being at the base of the antimicrobial activity of the P. agglomerans isolate. Our work reveals the potential of precipitation as an under-explored source of BCAs, whole genome sequencing as an effective approach to precisely identify BCAs, and UVmutagenesis as a technically simple screen to investigate the genetic basis of BCAs. More field trials are needed to determine the efficacy of the identified BCAs in fire blight control.

Isolation of Nine Bacteriophages Shown Effective against Erwinia amylovora in Korea

“…Antagonistic bacteria such as Pseudomonas, Pantoea, Enterobacter, Serratia, and Bacillus genera were reported for control of fire blight to suppress E. amylovora. For example, Pantoea agglomerans, B. subtilis, Bacillus amyloliquefaciens, and Pseudomonas fluorescens were registered bacteria products and commercially available (Dagher et al, 2020;Mechan Llontop et al, 2020;Mikiciński et al, 2016;Sharifazizi et al, 2017). Recently, use of phage therapy as biological control has been emphasized, in which bacteriophages are expected to prevent bacterial infections.…”

Characterization of the biocontrol activity of three bacterial isolates against the phytopathogen Erwinia amylovora

“…agglomerans isolate against E . amylovora (Mechan Llontop et al, 2020). Our data are also consistent with the literature and the emerging view of the antimicrobial activity of AGA against the phytopathogen E .…”

“…Interestingly, AGA itself is toxic to P. agglomerans Eh1087, and the phz pathway encodes a special phenazine-binding protein, EhpR, that prevents self-poisoning of the producer (Giddens et al, 2003;Mavrodi et al, 2010). Very recently, Mechan et al ( 2020) also have pointed to, using a UV-mutagenesis screen, the AGA synthesis gene cluster as being at the base of the antimicrobial activity of the P. agglomerans isolate against E. amylovora (Mechan Llontop et al, 2020).…”

Are microbes growing on flowers evil? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae)

“…Higher humidity due to these treatments might have enhanced growth of these bacteria. In agriculture, it has often been reported that high humidity or precipitation enhance activities of pathogenic Erwinia and Pseudomonas, and increase damage by diseases [49][50][51].…”

“…Besides, we found significant negative associations between the proportion of the ASVs of Cluster 5 and fruit set based on the GLMM analysis, while we did not for seed set. Since Erwinia and Pseudomonas include plant pathogens that trigger abortion of flowers and fruits [51][52][53], some of these bacteria might have negatively affected fruit development by infecting a reproductive organ. However, we cannot rule out other potential explanations about the correlation.…”