Blueberry Floral probiotics: nectar microbes inhibit the growth of Colletotrichum pathogens

Authors: Rering, Caitlin; Lanier, Alexia; PERES, NATALIA - University Of Florida

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2023
Publication Date: 12/8/2023
Citation: Rering, C.C., Lanier, A.M., Peres, N.A. 2023. Blueberry Floral probiotics: nectar microbes inhibit the growth of Colletotrichum pathogens. Journal of Applied Microbiology. 134:12, 1-14. https://doi.org/10.1093/jambio/lxad300.
DOI: https://doi.org/10.1093/jambio/lxad300

Interpretive Summary: Crop flowers are vulnerable to pathogen infection, which if left unmanaged can cause severe losses and food safety concerns. To prevent disease, growers frequently apply fungicides to crop flowers, sometimes on a weekly basis. Prolonged use of fungicides can lead to resistance, where pathogens adapt to withstand fungicides such that the products no longer provide protection. Additionally, when fungicides are applied to flowers, pollinators are exposed to these chemicals. And although fungicides are usually not acutely toxic to bees, meaning they do not cause immediate death, they are harmful. They reduce bees' lifespans and their ability to learn, and they make bees them more susceptible to disease, pests, and other toxic chemicals in their environment. Therefore, a pollinator-safe method to protect crop flowers is needed. One promising approach is microbial biocontrol, a technique where microorganisms that can limit the growth of pathogens are applied to plants in lieu of chemical fungicides. ARS Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, in Gainesville, FL in collaboration with scientists from University of Florida evaluated native floral microorganisms from FL blueberry plants as potential microbial biocontrol products, using laboratory tests to evaluate their ability to limit the growth of a pathogen that infects blueberry flowers. Four promising microbes were selected, each able to inhibit the pathogen’s growth in at least one of the tests. Researchers also examined honey bee feeding of these microbes in an artificial nectar, finding that honey bees readily consumed all microbes tested, which suggests their application to flowers will not deter bees from pollinating crops. Although further testing in plants is needed, results from this study are an important first step in discovering new, sustainable, and pollinator-safe methods for the control of plant diseases.

Technical Abstract: Aims: To identify microorganisms that confer prophylactic protection to crop flowers, we evaluated the antifungal capacity of blueberry nectar-dwelling microbes against various Colletotrichum species and their impacts on nectar sugars and honey bee consumption.Methods and Results: The growth inhibition of Colletotrichum (C. acutatum, C. fioriniae, C. gloeosporioides) was screened with two in vitro assays: an artificial nectar co-culture and a dual culture plate assay. Initially, all nectar microbes were screened for antagonism against a single C. acutatum isolate. We then selected four candidate nectar microbes with the best performance, Neokomagataea thailandica, N. tanensis, Metschnikowia rancensis, and Symmetrospora symmetrica, and evaluated their antagonism against three additional C. acutatum isolates, and a single isolate of both C. fioriniae and C. gloeosporioides. In artificial nectar assays, single and three-species cultures inhibited the growth of two of four C. acutatum isolates by ca. 60%, but growth of the other Colletotrichum species was not affected. In dual culture plate assays, inhibition was observed for all Colletotrichum species for at least three of four selected microbial antagonists (13'53%). Neither honey bee consumption of nectar nor nectar sugar concentrations were affected by any microbe or pathogen tested. Conclusions: Selected nectar microbes inhibited the growth of all Colletotrichum species in vitro, although the degree of inhibition was specific to the assay and pathogen examined. In all microbial treatments, nectar sugars were preserved and honey bee preference was not affected.Impact Statement: Nectar microbes have potential to limit the growth of fungal pathogens that infect blueberry flowers with limited impacts on nectar sugars and honey bee preference.