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Individual Highlight

Identification of a clover proliferation group phytoplasma as the probable cause of American elm Ttee mortality

Photo of 1: Two American elm trees tree on left healthy with dark green foliage while tree on right is diseased and exhibiting light yellow foliage.  
 
2: Variability in American elm leaf color associated with infection by Candidatus. Phytoplasma trifolii  with leaves on left collected from an infected tree while leaves on right were collected from a healthy tree. 
1: Two American elm trees tree on left healthy with dark green foliage while tree on right is diseased and exhibiting light yellow foliage. 2: Variability in American elm leaf color associated with infection by Candidatus. Phytoplasma trifolii with leaves on left collected from an infected tree while leaves on right were collected from a healthy tree. Snapshot : Forest Service scientists observed premature canopy decline symptoms in elm trees within their research plantations in midsummer 2016. They attributed canopy decline symptoms to a phytoplasma in the clover proliferation group previously not reported to impact forest trees. Mitigation approaches are currently being undertaken.

Principal Investigators(s) :
Flower, Charles E. Hayes-Plazolles, Nancy
Slavicek, Jim 
Research Location : Delaware
Research Station : Northern Research Station (NRS)
Year : 2017
Highlight ID : 1255

Summary

During late July 2016, Forest Service scientists observed the widespread appearance of canopy yellowing, foliage wilt, phloem discoloration, and a strong odor of methyl salicylate in elm trees across two elm research plantations in Ohio. Because of the myriad of symptoms exhibited by the diseased elms, the pathogenic agent was suspected to be a phytoplasma, as the elm yellows phytoplasma (Candidatus Phytoplasma ulmi) is known to impact mature elms. The scientists utilized genetic approaches to identify the causal agent. No evidence was found for the specific elm yellows phytoplasma, but researchers detected the presence of a phytoplasma in the clover proliferation yellows group (Candidatus. Phytoplasma trifolii). This represents the first observance of a clover proliferation group phytoplasma impacting elm trees. Phytoplasmas represent an understudied suite of pathogens capable of causing rapid and widespread plant mortality in both herbaceous and woody plants. The scientists are undertaking further research to study the biology of the pathogen and to mitigate its impacts.

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