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