| Přispěvatelé: |
Ciznar, Ivan, Hršak, Dubravka, Kovacz, Kornel L., Kubicek, Kristian P., Minarovits, Janos, Niller, Hans Helmut, Pigac, Jasenka, Raspor, Peter, Spizek, Jaroslav, Storman, Alenka, Szkaradkiewicz, Andrzej, Tyski, Stefan |
| Popis: |
Phytoplasmas are wall-less prokaryotes present as endocellular parasites in the plant phloem and phloem-feeding insects like leafhoppers (Cicadomorpha) and planthoppers (Fulgoromorpha). These unique bacteria, belonging to a monophyletic clade within the class Mollicutes, have the smallest known self-replicating genome. It consists of only 580-1350 kbp organized mainly in one circular chromosome and it lacks some genes previously considered to be essential for life. In some phytoplasmas, the existence of extrachromosomal elements has been confirmed. Every attempt to obtain axenic phytoplasma pure cultures has failed which impedes most aspects of their research. However, much progress has been done in the last two decades due to the application of various molecular biology-based methods. The most important tools for phytoplasma detection and classification are PCR and RFLP analyses of highly conserved 16S rRNA gene. Lately, other gene regions have been used for finer phytoplasma distinction in order to study their molecular variability and epidemiology. Even though the complete genome of one Candidatus Phytoplasma species is known, the combination of information on 16S rRNA gene and phytoplasma biological properties (plant host range, symptoms, insect vector species) remains to be the basis for the latest phytoplasma classification. Phytoplasmas cause hundreds of plant diseases worldwide and many of them affect economically important crops. On the other hand, insects that harbor and vector these prokaryotes in nature do not necessarily suffer such consequences. The occurrence of phytoplasmas causing grapevine yellows (GY) disease in Croatia was first recorded in 1997. Severely affected vines mostly show the presence of phytoplasmas from the ribosomal subgroup 16SrXII-A (stolbur or bois noir) while atypical and milder GY symptoms have been observed in Croatian indigenous vines that were infected with phytoplasmas of ribosomal subgroup 16SrI-B (aster yellows). By studying several genes of phytoplasmas found in Croatian vineyards, their insect vectors and alternative herbaceous hosts (vineyard weeds) we hope to decipher molecular and ecological factors discriminating this pathosystem from similar ones in Europe. Insight into the molecular epidemiology of GY should also enable devising more effective ways to control these phytoplasma-associated diseases. |
