Liliana Franco-Lara

Detection and identification of phytoplasmas associated with declining Liquidambar styraciflua trees in Colombia

Liquidambar styraciflua was introduced in Bogotá (D. C.) Colombia, in the 1990s as an urban tree. Yellowing and deformation of the tree crowns began to appear in 2007, leading to the hypothesis of a possible phytoplasma infection. To detect and identify phytoplasmas, samples were collected from 21 liquidambar trees from Bogota in 2009, 2010 and 2011 and subjected to nested PCR, RFLP and sequencing analyses of 16S ribosomal DNA. Nested PCR assays with group-specific primers and RFLP analyses identified phytoplasmas belonging to the 16SrI-B (aster yellows), 16SrV-B (jujube witches’ broom), 16SrVII-A (ash yellows), 16SrIX (pigeon pea witches’ broom) and 16SrXII-A (“stolbur”) groups/subgroups, in single or mixed infections. Sequence analysis and phylogenetic evaluation of samples with single phytoplasma infections confirmed the presence of phytoplasmas related to ‘Candidatus Phytoplasma asteris’, ‘Ca. P. fraxini’, and ‘Ca. P. solani’. In 2010 and 2013 two further surveys involving 100 trees each time were carried out to estimate the prevalence of the disease: the average prevalence with severe symptoms was 28%, with mild symptoms, 56%, and with minor symptoms 16% of the trees. No symptomless trees were observed. Phytoplasma presence in liquidambar trees from Bogota carries economic, environmental and epidemiological consequences, and urgent measures should be implemented to avoid the spreading of the disease to other tree species and to the agricultural areas surrounding the city.

Major Phytoplasma Diseases of Forest and Urban Trees

In the northern hemisphere, yellows, witches’ broom, and decline diseases of several forest and urban tree species are widespread and of considerable economic and ecological significance. Elm (Ulmus spp.) and alder (Alnus spp.) are affected by elm yellows (EY) and alder yellows (ALY), respectively. These diseases are mainly associated with the presence of closely related phytoplasmas, the EY agent ‘Candidatus Phytoplasma ulmi’ and the ALY agent, which are members of the EY or 16SrV group, subgroups 16SrV-A and 16SrV-C, respectively. Ash (Fraxinus spp.) is affected by ash yellows, a disease which occurs mainly in North America and is associated with the presence of ‘Candidatus Phytoplasma fraxini’, a member of subgroup 16SrVII-A. Poplar (Populus spp.), sandal (Santalum album), paulownia (Paulownia spp.), and mulberry (Morus spp.) are affected by yellows diseases associated with phytoplasmas of different 16SrI subgroups. Several species of conifers are affected by yellows and witches’ broom diseases associated with phytoplasmas belonging to at least five taxonomic groups (16SrI, 16SrIII, 16SrVI, 16SrIX, and 16SrXXI) and several different subgroups. A number of urban tree species grown in the Sabana de Bogota (Colombia) are affected by decline diseases which are primarily associated with 16SrI and 16SrVII phytoplasmas. This chapter summarizes the current knowledge of major phytoplasma diseases of forest and urban trees grown in the northern hemisphere.