15 research outputs found
Phytoplasma Diseases in Ornamental Crops
An extensive and update review of the literature reporting the phytoplasma associated diseases in a number of ornamental plants and their classification is presented with major emphasis to reports in the main floricultural areas. Symptomatology of reported diseases is described in the most relevant traditional species as well as in emerging species used in floriculture and gardening worldwide
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 Bogotà (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
Multilocus genetic characterization of phytoplasmas
Classification of phytoplasmas into 16S ribosomal groups and subgroups
and \u2018Candidatus Phytoplasma\u2019 species designation have been primarily based on
the conserved 16S rRNA gene. However, distinctions among closely related \u2018Ca.
Phytoplasma\u2019 species and strains based on 16S rRNA gene alone have limitations
imposed by the high degree of rRNA nucleotide sequence conservation across
diverse phytoplasma lineages and by the presence in a phytoplasma genome of two,
sometimes sequence heterogeneous, copies of this gene. Thus, in recent years, moderately
conserved genes have been used as additional genetic markers with the aim
to enhance the resolving power in delineating distinct phytoplasma strains among
members of some 16S ribosomal subgroups. The present chapter is divided in two
parts: the first part describes the non-ribosomal single-copy genes less conserved
(housekeeping genes) such as ribosomal protein (rp), secY, secA, rpoB, tuf, and
groEL genes, which have been extensively used for differentiation across the majority
of phytoplasmas; the second part describes the differentiation of phytoplasmas
in the diverse ribosomal groups using multiple genes including housekeeping genes
and variable genes encoding surface proteins