Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 26, 2002
Publication Date: N/A
Interpretive Summary: More than 1,000 mature American elms have died during the last ten years in a suburb west of Chicago, IL. The disease outbreak was first noted in 1991 when ten trees died in the town of Arlington Heights, where nearly 10,000 mature elms line residential parkways. The cause of death was unknown, but disease symptoms clearly differed from those of Dutch elm disease (DED). Elm yellows (EY), caused by a leafhopper-transmitted phytoplasma, was suspected. However, EY was historically absent from the northern third of Illinois. We have employed a DNA-based diagnostic procedure for detection and identification of phytoplasmas, and have detected a phytoplasma in almost all symptomatic trees tested. We have identified the phytoplasma as representative of a new subgroup (16SrVI-C) first report of a phytoplasma, other than elm yellows phytoplasma, causally linked to an elm yellows disease. The information will be useful to extension workers and diagnosticians, and to regulatory agencies for implementation of new quarantine regulations.
Technical Abstract: An outbreak of a disease appearing similar to elm yellows (EY) began in the early 1990s in the Chicago suburb of Arlington Heights, Illinois, U.S.A. Over one thousand mature American elm (Ulmus americana) trees have since died from the disease. Unreliable symptomology and negative results from commercial phytoplasma detection tests in 1997, led us to more systematically sample trees for the presence of EY phytoplasma. Nested PCR using universal primer pairs previously designed for detection of phytoplasma revealed that thirteen of the fourteen trees growing in the outbreak region were positive for phytoplasma, regardless of the magnitude of symptoms. All fourteen trees died from the disease during the course of the study, and phloem scraped from trunk bark samples was superior to wood shavings or foliage for detecting the phytoplasma. All control elms tested negative for phytoplasma. Restriction fragment length polymorphisms (RFLP) and DNA sequence analyses of 16S rDNA of representative samples indicated that the Illinois phytoplasma is not related to the phytoplasma causing EY disease elsewhere (taxonomic group16SrV-A), but is most closely related to clover proliferation phytoplasma (group 16SrVI). We have identified the phytoplasma as representative of a new subgroup (16SrVI-C) of clover proliferation (CP) phytoplasma group (16SrVI). Neither the traditional EY, nor the newly designated Illinois elm yellows(ILEY), phytoplasmas were detected in local leafhopper populations trapped daily between May and September in the year 2000. This is the first report of a phytoplasma related to CP phytoplasma causing an elm yellows disease.