HLB: The Microbiome’s Role

Ernie NeffHLB Management

HLB
Orange groves and lab work
(Credit: Nichole Ginnan)

Researchers Caroline Roper and Nichole Ginnan at the University of California, Riverside led a large research collaboration that sought to explore the microbiome’s role in HLB disease progression. Their recent article in Phytobiomes Journal, “Disease-Induced Microbial Shifts in Citrus Indicate Microbiome-Derived Responses to Huanglongbing,” moves beyond the single-snapshot view of the microbial landscape typical of microbiome research.

Their holistic approach to studying plant-microbe interactions captured several snapshots across three years and three distinct tissue types (roots, stems and leaves). What is so interesting about this research is the use of amplicon (16S and ITS) sequencing to capture the highly intricate and dynamic role of the microbiome (both bacterial and fungal) as it changes over the course of HLB disease progression.

The researchers surmised that HLB created a disease-induced shift of the tree’s microbiome. Specifically, the researchers showed that as the disease progresses, the microbial diversity increases. They further investigated this trend to find that the increase in diversity was associated with an increase in putative pathogenic (disease-causing) and saprophytic (dead tissue-feeding) microbes. They observed a significant drop in beneficial microbes in the early phases of the disease. Arbuscular mycorrhizal fungi were one such beneficial group that the authors highlighted as showing a drastic decline in relative abundance.

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The depletion of key microbial species during disease might be opening the door for other microbes to invade. Certain resources may become more or less available, allowing different microbes to prosper. Roper and Ginnan hypothesize that when HLB begins, this depletion event triggers a surge of beneficial microbes to come to the aid of the citrus tree. They suspect that the microbes are initiating an immune response to protect the host.

As the disease proliferates, the citrus tree and its microbiome continue to change. Ginnan, the lead author on this study, found that there was an enrichment of parasitic and saprophytic microorganisms in severely diseased roots. The enrichment of these microbes may contribute to disease progression and root decline, one side effect of HLB.

Survivor trees, or trees that did not progress into severe disease, had a unique microbial profile as well. These trees were enriched with putative symbiotic microbes like Lactobacillus sp. and Aureobasidium sp. This discovery led the researchers to identify certain microbes that were associated with slower disease progression.

Learn more about their research here.

Source: American Phytopathological Society

 

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