Publications

4983

Abstract Members of the verrucomicrobial clade ‘ Candidatus Udaeobacter’ rank among the most dominant bacterial phylotypes in soil. Nevertheless, despite this global prevalence, in‐depth analyses with respect to pH preferences of ‘ Ca . Udaeobacter’ representatives are still lacking. Here, we utilized a recently designed primer pair, specifically targeting ‘ Ca . Udaeobacter’, to investigate links between soil pH and the abundance as well as phylotype composition of this largely unexplored verrucomicrobial clade. Based on 150 forest and 150 grassland soils, comprising a broad pH range, we determined the highest total abundance of ‘ Ca . Udaeobacter’ in strongly acidic soil (pH, ~5.1) and, noteworthy, in ultra‐acidic soil (pH < 3.5) and at a pH ≥ 7, its abundance drastically declined. When we analysed the six most dominant amplicon sequence variants affiliated with ‘ Ca . Udaeobacter’ separately, their abundances peaked within a pH range of approximately 4.7–5.2, and only in one case at slightly acidic soil pH (pH, 6.1). Our study benefits from a combination of quantitative real‐time PCR and high‐throughput amplicon sequencing, enabling for the first time a highly specific abundance analysis of representatives affiliated with ‘ Ca . Udaeobacter’, which revealed that this globally abundant verrucomicrobial clade shows preferences for acidic soil.

A protocol to successfully transmit the huanglongbing (HLB) pathogen, ‘Candidatus Liberibacter asiaticus’, between citrus plants by using the Asian citrus psyllid (ACP) and an alternative way to help growers control ACP are proposed. Best results were obtained when pathogen acquisition by adults reared on fully symptomatic ‘Ca. Liberibacter asiaticus’-positive plants, latency, and inoculation occurred at ambient air temperatures ranging from 24 to 28°C and when a single infective adult ACP was confined for 7 days on soft, newly developing vegetative shoots (stages v2 to v4). No infection resulted from confinement of infective ACP adults on mature leaves (stage v6). Under the described conditions, single ACP adults could successfully transmit ‘Ca. Liberibacter asiaticus’ to an average of 56.5% (35 to 83%) of plantlets with v2 to v4 shoots growing in 0.3-liter tubes and to 80.5% (76 to 86%) of plants with v2 to v4 shoots growing in 4.7-liter pots. The use of single insects and plantlets reduces labor, space, and other resources necessary to undertake transmission tests. It also reduces time needed for transmission studies and should help accelerate research on HLB. The results were used to develop an index for favorability to infection (IFI) to determine orchard vulnerabilities to ‘Ca. Liberibacter asiaticus’. The IFI is based on the heterogeneous population of new shoots that occurs on tree canopies and may offer alternative or complementary alternatives to the laborious and costly insect surveys currently used in most instances to determine threshold levels for insecticide applications.

Abstract Background Rickettsia spp. are human pathogens that cause a number of diseases and are transmitted by arthropods, such as ixodid ticks. Estonia is one of few regions where the distribution area of two medically important tick species, Ixodes persulcatus and I. ricinus, overlaps. The nidicolous rodent-associated Ixodestrianguliceps has also recently been shown to be present in Estonia. Although no data are available on human disease(s) caused by tick-borne Rickettsia spp. in Estonia, the presence of three Rickettsia species in non-nidicolous ticks has been previously reported. The aim of this study was to detect, identify and partially characterize Rickettsia species in nidicolous and non-nidicolous ticks attached to rodents in Estonia. Results Larvae and nymphs of I.ricinus (n = 1004), I. persulcatus (n = 75) and I.trianguliceps (n = 117), all removed from rodents and shrews caught in different parts of Estonia, were studied for the presence of Rickettsia spp. by nested PCR. Ticks were collected from 314 small animals of five species [Myodes glareolus (bank voles), Apodemus flavicollis (yellow necked mice), A.agrarius (striped field mice), Microtus subterranius (pine voles) and Sorex araneus (common shrews)]. Rickettsial DNA was detected in 8.7% (103/1186) of the studied ticks. In addition to identifying R.helvetica, which had been previously found in questing ticks, we report here the first time that the recently described I.trianguliceps-associated Candidatus Rickettsia uralica has been identified west of the Ural Mountains. Graphical Abstract

AbstractIn recent years, empty or poor grain bearing corn plants with leaf reddening symptoms have been observed in some commercial maize production areas in the Adana province of Turkey. The disease is increasing and causing economic losses. To verify the possible presence of phytoplasmas, leaf samples were tested with P1/Tint and R16F2n/R2 phytoplasma‐specific primer pairs after DNA extraction. The 16S ribosomal gene sequence analysis followed by sequence in silico enzyme digestions and phylogenetic analyses allowed the identification of ‘Candidatus Phytoplasma solani’, subgroup of 16SrXII‐A related‐strain in all symptomatic samples. The positive samples were characterized using tuf and vmp1 genes. In silico restriction fragment length polymorphism and sequence analyses allowed the inclusion of all the positive samples into tuf‐type b and V15 molecular types. The sequence analysis indicated the presence of a single genotype in all the tested samples (n = 12). This is the first molecular characterization of a ‘Ca. P. solani’ strain infecting maize plants in Turkey. The identified pathogen is listed in the EPPO A2 list.