Publications

4934

During field surveys conducted in 2024 and 2025 in pepper production areas in Altunhisar distinct of Niğde province, Türkiye, plants showing phytoplasma-like symptoms were observed. A total of 25 symptomatic pepper samples were collected, and total nucleic acids were extracted using the CTAB method. The samples were analyzed for phytoplasma infection by PCR amplification of the 16S rRNA gene region. In addition, two asymptomatic pepper plants were included as negative controls. PCR analysis revealed that all samples showing symptoms produced amplicons of the expected size, while no amplification was obtained from the asymptomatic plants. Sequencing and phylogenetic analyses revealed that the detected phytoplasma belonged to the 16SrVI-A subgroup, corresponding to ‘Candidatus Phytoplasma trifolii’. The subgroup assignment was further confirmed by in silico (virtual) RFLP analysis of the 16S rRNA gene. The representative 16S rRNA gene sequence of one strain obtained in this study was deposited in the GenBank database (GenBank accession number PX885052). Based on the available literature, this study provides the first molecular evidence of ‘Candidatus Phytoplasma trifolii’ infection in pepper plants grown in Niğde province, Türkiye. The findings contribute to the current knowledge on the distribution of pepper-infecting phytoplasmas in Türkiye and emphasize the need for further epidemiological and vector-related studies.

Abstract Syndrome Basses Richesses (SBR) is a phloem-limited disease of sugar beet caused by ‘ Candidatus Arsenophonus phytopathogenicus’ (ARSEPH), a bacterium currently considered a facultative endosymbiont of its insect vector, Pentastiridius leporinus . Due to increasing disease incidence and the need for reliable vector-free resistance screening methods, this study evaluated alternative ARSEPH transmission routes using chip grafting and the parasitic plant dodder ( Cuscuta campestris ). Given that Arsenophonus species are unculturable and their insect vectors have complex life cycles so laboratory propagation is labor intensive, the development of vector-independent systems is desirable for controlled pathogen transmission and host–pathogen interaction studies. Chip grafting enabled successful ARSEPH transmission to sugar beet, though with low efficiency (~ 9.6%) and delayed pathogen detection. While C. campestris acquired and maintained high ARSEPH titers, it failed to transmit the bacterium to healthy plants, indicating limited systemic movement. In contrast, vector-mediated transmission via P. leporinus achieved 100% efficiency within 25 days, confirming a strong biological compatibility. These findings underscore the limitations of non-vector-based approaches for phloem-restricted pathogens and highlight the need for methodological optimization. The study provides key insights into ARSEPH’s complex transmission biology and supports a functionally specialized association with its insect vector.

Abstract Huanglongbing (HLB), primarily induced by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas), poses a significant threaten to citrus production worldwide. CLas deploys Sec-dependent effectors (SDEs) to manipulate host cellular processes, yet the underlying virulence mechanisms remain incompletely understood. Here, we identify SDE4580, a conserved CLas effector localized to the plant plasma membrane, as a key virulence factor that promotes pathogen proliferation and suppresses host immunity across citrus and Arabidopsis. Transcriptomic analysis reveals that SDE4580 reprograms membrane-associated biological processes and defense responses. Through yeast two-hybrid screening and biochemical validation, we demonstrate that SDE4580 physically interacts with the citrus vesicle trafficking regulator CsPRA1.E, a Prenylated Rab Acceptor 1 family protein. Functional assays establish CsPRA1.E as a positive regulator of immunity that promotes apoplastic secretion of defense-related proteins and enhances resistance to Xanthomonas citri subsp. citri. Crucially, SDE4580 antagonizes CsPRA1.E-mediated resistance by suppressing defense protein secretion without inducing target degradation. These findings uncover a novel pathogenic strategy whereby CLas subverts host endomembrane trafficking to disarm plant immunity. Targeting the SDE4580-CsPRA1.E interface may offer a promising avenue for developing durable HLB control strategies.

‘Candidatus Liberibacter solanacearum’ (Lso) haplotype D, transmitted by the carrot psyllid Bactericera trigonica, is a major threat to carrot production, particularly in the Mediterranean Basin and the Middle East. We investigated the impact of plant age at the time of inoculation on symptom development and yield under greenhouse and outdoor conditions. In greenhouse trials, 1- and 2-month-old plants were inoculated with psyllids harboring Lso. Both age groups showed reduced taproot weight compared with controls, but younger plants were more severely affected, exhibiting 90% yield reduction, while 2-month-old plants showed a 30% reduction. Witches’ broom symptoms appeared earlier in plants inoculated at 1 month (5 weeks postinoculation); however, within 2 weeks, plants inoculated at 2 months reached comparable levels of symptom incidence and severity. Additional greenhouse experiments using Lso-free psyllids confirmed that yield losses and disease symptoms were specifically due to Lso infection and not psyllid feeding. In outdoor trials, we tested the effects of inoculation at 7, 11, 15, and 19 weeks postsowing (wps) on disease incidence and yield. Significant yield losses occurred only in plants inoculated at 7 and 11 wps, with up to 45% reduction by harvest time. Symptoms began to appear at 20 wps in plants inoculated at 7 and 11 wps. At 23 wps, symptoms also appeared in plants inoculated at 15 wps, with a similar incidence to that observed in the earlier inoculation groups. Molecular detection of Lso at harvest (23 wps) confirmed that all plants inoculated at 19 wps or earlier were infected. These results demonstrate that carrots are highly susceptible to Lso-induced yield losses at the earlier stages of growth and highlight the importance of managing early season vector pressure to minimize economic damage.

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.