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

Phytoplasmas: an update

A summary of the research carried out on phytoplasma-associated diseases 50 years after their discovery is presented. The great majority of the research was devoted to classification and differentiation of these prokaryotes by molecular and bioinformatic tools applied to specific phytoplasma genes. The availability of a robust classification system has greatly facilitated phytoplasma identification leading to an increased knowledge of plant diseases worldwide. Scientific knowledge on phytoplasma biology still needs to be improved to allow better management solutions to reduce the impact of these diseases in agricultural and natural environments

Phytoplasma diseases of medicinal crops

Phytoplasma diseases of medicinal plants occur worldwide and are of great concern. So far 19 different phytoplasma ribosomal groups encompassing various subgroups have been reported. The subgroup 16SrI-B phytoplasmas are the prevalent agents mainly detected in Europe, North America and Asia. Phytoplasma diseases of medicinal plants severely reduce yield and quality of crops along with the longevity of the plants. Changes in the composition of secondary metabolites are induced, while the levels of valuable phytochemicals are greatly affected. In contrast, an accumulation of pharmaceutically important compounds such as vinblastine and vincristine is reported in periwinkle upon phytoplasma infections. Important phytoplasma diseases of several medicinal plants with special reference to their impact on active biological constituents and secondary metabolites are reviewed. General information on geographic distribution, diagnostics, genetic diversity, natural transmission and management aspects of phytoplasmas infecting medicinal plants are also discussed