Phytoplasmas associated with elm yellows
In USA, elm yellows (formerly called elm phloem necrosis – EPPO A1 quarantine pest) is a widespread and serious disease of elm associated with a phytoplasma (Elm yellows phytoplasma). This disease has been observed on Ulmus americana and also on other species, such as: U. alata, U. crassifolia, U. rubra and U. serotina. It is present in central and southern states (from 32° to 46° north latitude) and also in Pennsylvania, New York, New Jersey, Massachusetts. A putative vector is Scaphoideus luteolus (Homoptera: Cicadellidae – EU Annexes). Highly susceptible trees generally die within one growing season after the first symptoms have appeared. Affected trees showed premature yellowing, leaf epinasty, butterscotch discoloration of inner bark accompanied with an odour of wintergreen oil (methyl salicylate). So far, only a phytoplasma belonging to group 16SrV had been found in association with diseased elms. However, phytoplasmas belonging to another group have recently been found in dying elms in Illinois. Since the last 10 years more than 1000 mature elm trees have died near Chicago (first in 1991 in the village of Arlington Heights). Elm yellows was suspected but symptoms observed differed slightly and tests often failed to detect the phytoplasma. PCR and RFLP revealed the presence of a phytoplasma belonging to another group (16SrVI-C). Until this finding, it was thought that in North America, elm yellows was always associated with strains of elm yellows phytoplasma. This new phytoplama has been called Illinois elm yellows phytoplasma.
In Europe, the situation of elm yellows is quite different. Elm species of European and Asiatic origin (and their hybrids) rarely die from the disease. Affected trees may show a general decline, stunting, chlorosis and witches’ brooms. The disease does not spread rapidly and can remain localized for many years. The vector Scaphoideus luteolus does not occur in Europe. Phytoplasmas associated with elm yellows have been reported from France and Italy, most of them are members of 16SrV-A, 16SrI-B and 16SrXII groups (so different from the North American ones). Mixed infections are also reported. Recent studies have showed that phytoplasmal DNA could be detected in flowers and seeds of elm trees infected with elm yellows, but it could not be detected in plant progeny. Preliminary studies have also showed that asymptomatic weeds could harbour the same phytoplasmas.
Bertelli, E.; Tegli, S.; Sfalanga, A.; Surico, G. (2002) Detection of phytoplasmal DNA in flowers and seeds from elm trees infected with Elm Yellows.
Phytopathologia Mediterrannea, 41(3), 259-265.
Jacobs, D.A.; Lee, I.M.; Griffiths, H.M.; Miller, F.D. Jr; Bottner, K.D. (2003) A new member of the clover proliferation phytoplasma group (16SrVI) associated with elm yellow in Illinois.
Phytopathology, 87(3), 241-246.
Sfalanga, A.; Martini, M.; Surico, G.; Bertaccini, A. (2002) Involvement of phytoplasmas in a decline of Ulmus chenmoui in Central Italy.
Forest Pathology, 32, 265-275.
University of Illinois - Extension. Report on Plant Disease, no. 660. May 1998.
Elm yellows or phloem necrosis and its control.