Publications

4877

The spread of the reed planthopper Pentastiridius leporinus and its associated pathogens Candidatus Arsenophonus phytopathogenicus (ARSEPH) and Candidatus Phytoplasma solani (PHYPSO) increasingly threatens sugar beet production in Central Europe. Current surveillance systems rely mainly on vector monitoring, visual field assessments and molecular diagnostics of individual vectors and plants, all of which provide valuable but spatially limited information. This study evaluated sugar beet pulp samples generated during routine factory quality assessment as a large- scale surveillance resource for PHYPSO. During the 2025/26 campaign, 4887 pulp samples representing 1954 delivery field locations were collected, of which 1237 samples of individual field locations with consistent beet quality parameters were analyzed by direct PCR. PHYPSO was detected in 214 samples (17.3%). The molecular workflow was not subgroup-specific and did not include genotyping; therefore, PHYPSO-positive samples could not be assigned to individual 16SrXII subgroups. Comparison with visual field assessments showed that 85.7% of positive molecular detections originated from fields without visible symptoms. A carry-over experiment demonstrated that pathogen-derived DNA may persist across consecutive samples under worst-case conditions and must therefore be considered during data interpretation. In contrast, ARSEPH was detected by direct PCR in only six of 1237 samples (0.5%), all originating from the Euskirchen growing region. Comparison with qPCR, single-beet diagnostics and the carry-over experiment indicated insufficient sensitivity of the current ARSEPH direct-PCR assay; therefore, the observed detection rate should not be interpreted as true pathogen prevalence. Nevertheless, the observed spatial distribution patterns of monitoring sites indicate that industrial pulp sample monitoring substantially expands surveillance coverage beyond conventional symptom-based approaches and can help identify regions warranting further epidemiological investigation.

ABSTRACT Phytoplasmas significantly reduce crop yields across different plant species, as exemplified by coconut lethal yellowing disease (CLY), which affects coconut palms in the American continent. These pathogens encode in the genome the ability to produce effectors that target important proteins in the plant host, inducing morphology alterations, plant sterility and attractiveness to insect vectors. This attractiveness is crucial for the transmission and spread of phytoplasmas to other plant species. Understanding how these effectors function is essential for comprehending the mechanisms of action of phytoplasmas. However, only a few effectors coding genes have been identified in phytoplasmas, and no effector responsible for CLY has been reported. In this study, an in silico identification of two effectors of ‘ Candidatus Phytoplasma palmae’ associated with CLY in the Americas was conducted. The predicted effectors encoded two proteins of 124 aa (secretory protein 7) and 128 aa (secretory protein 10) with 73% identity between them. These proteins were classified as classical effectors, characterised by small size, signal peptide, nuclear localisation signal and absence of a transmembrane domain. Furthermore, gene expression of SP10 was detected in samples from leaves and stems of infected palms.