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

Abstract

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 Bogotá. In Bogotá, 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.

Insects and phytoplasmas in urban trees in a mega-city: a case study in Bogotá, Colombia

“…Grass is the main host of these two species, so it is possible that they visit Andean oak trees occasionally when the grass is tall or the trees have low branches. Our observations suggest that these species are not the main phytoplasma vectors of Andean oaks, but they may play a marginal role in transmitting phytoplasmas to and from the grass, as has been hypothesized previously(Lamilla et al 2022). Some species of Cicadellidae and Psylloidea were collected in Andean oak trees and neighbouring plants; therefore, we propose that in addition to the movement of insect vectors from grass to trees and vice versa(Lamilla et al 2022), different species of Cicadellidae move to and from trees or shrubs dispersing phytoplasmas.…”

“…'Candidatus Phytoplasma fraxini' (group 16SrVII) was detected in 54.6% (n = 130), 'Candidatus Phytoplasma asteris' (group 16SrI) in 30.7% (n = 73) and mixed infections of both phytoplasmas in 8.8% (n = 21) (Lamilla et al 2022).…”

“…P. asteris' and 'Ca. P. fraxini' infect at least eleven urban tree species in the Sabana de Bogotá (Franco-Lara 2019), including Andean oak trees (Lamilla et al 2022).…”

“…Considering the overall results, the most abundant orders were Diptera, Hymenoptera, Thysanoptera and Hemiptera. In the work of Lamilla et al (2022), Hemiptera was the most abundant taxon, although the abundance and richness varied at different sampling sites. In this work, Hemiptera was dominant in the three sampling sites with direct sampling but was less abundant with indirect sampling.…”

Ectomycorrhizal fungal communities in natural and urban ecosystems: Quercus humboldtii as a study case in the tropical Andes

“…), it grows well under urban conditions. Lamilla et al ( 2022 ) found an 80% prevalence of phytoplasma infection in Bogotá’s oaks, but without having lethal or severe consequences to the tree, suggesting a high level of resistance in these environments. The ECM communities associated with this species have not yet been studied in urban ecosystems.…”