Epidemiological characterization of a disease associated with phytoplasmas in Andean oak, Quercus humboldtii Bonpland, in Bogota-Colombia

Quercus humboldtii is the dominant tree species in oak forest ecosystems in the Colombian Andes, and approximately 15,000 trees have been planted in urban Bogota. In Bogota, Q. humboldtii is affected by phytoplasmas. The management of phytoplasmas relies mainly on control of the insect vectors. The aim of this work was to generate information on phytoplasmas affecting Q. humboldtii and the potential insect vectors involved. Phytoplasmas were detected by nested PCR and identified by restriction fragment length polymorphism or sequencing analysis of the 16S rRNA gene in 238 randomly selected urban trees, from 17 city zones. The prevalence of the disease was 80%, with phytoplasmas detected in 94% of trees. 'Candidatus Phytoplasma fraxini' was found in 54.6%, 'Candidatus Phytoplasma asteris' in 30.7% and mixed infections of both phytoplasmas in 8.8% of the trees. Phytoplasmas were observed in the phloem of infected trees by electron microscopy. 'Ca. P. fraxini' was more common than 'Ca. P. asteris' in both street and parks trees, but correlations between the phytoplasma and disease-associated variables were not observed. The entomofauna of a subsample of 102 of these trees was examined. Representative specimens of seven orders were collected, with Hemiptera the most prevalent. Specimens of 17 Cicadellidae, one Membracidae and one Psyllidae species were collected. Cicadellidae species from subfamilies Aphrodinae, Deltocephalinae, Iassinae, Eurymelinae, Megophthalminae and Typhlocybinae were found, in which phytoplasma vectors have been reported previously. Specimens of two known Cicadellidae vector species were collected: Amplicephalus funzaensis (Deltochephalinae) and Exitianus atratus (Deltochephalinae). Phytoplasmas were assessed in 103 Cicadellidae specimens. 'Candidatus P. asteris' was detected in A. funzaensis (n = 3/16 tested), E. atratus (n = 2/10 tested) and Alebrini sp. 1 (n = 1/11) tested). The possible epidemiological implications of these findings are discussed.