Cercospora leaf spot, caused by Cercospora beticola, is the most destructive foliar disease of sugar beet. Management has relied heavily on fungicides, but widespread fungicide resistance emphasized the need for resistant varieties. To assess how varietal resistance shapes C. beticola populations, we conducted a 3-year field experiment at four locations in Germany using sugar beet varieties ranging from susceptible to highly resistant. Infected leaves were collected separately per variety and location to serve as inoculum for the following year, maintaining variety- and location-specific pathogen populations under controlled selective conditions. A total of 900 isolates were subjected to whole-genome sequencing and population genetic analyses. Isolates collected in 2022 showed extensive admixture among locations. Equal mating-type ratios were observed in some populations but skewed in others, suggesting that sexual reproduction may occur locally. Location-specific re-inoculation preserved population continuity but did not produce detectable local adaptation. By contrast, the population was affected to some extent by variety-specific re-inoculation. Populations from one highly resistant variety formed two divergent lineages with reduced diversity and altered allele frequency spectra, consistent with host-driven selection. Genome scans identified 26 candidate genes, including two putative effectors, associated with adaptation to the highly resistant variety. These findings demonstrate rapid C. beticola adaptation to resistant varieties, highlighting the role of host-driven selection in resistance management.

Despite advances in modeling and sensing, no study has previously integrated mechanistic, meteorological and UAV data into a unified predictive framework for Cercospora leaf spot. From 2020 to 2022, field trials with a susceptible variety under contrasting fungicide regimes and artificial inoculation were monitored for disease severity, airborne inoculum, and yield. Significant treatment differences emerged 44 days after sowing, with incubation lasting 7–12 days and spore peaks occurring from day 77, preceding rapid severity increases. Dissemination showed no prevailing direction but was favored by light, variable winds under conducive microclimates. Yield loss reached up to 0.0123 kg root fresh weight per plant per severity point, and both yield and sugar content decreased with earlier onset and higher final severity. Hybrid models were implemented at multiple levels, integrating multisource data. Severity was best predicted by climatic variables with UAV spectral–structural indices; fructification by humidity–temperature thresholds with stress traits; dissemination by wind-variability metrics with sporulation indicators; and yield and sugar content by UAV indices supplemented with mechanistic covariates. High-level hybridization reduced the RMSE to 0.615 (on a 0–10 severity scale), 0.067 ng C. beticola DNA for actual spores, 2.033 ng for cumulative spores, 1.769° for dissemination direction, 0.015 ng day⁻¹ for dissemination magnitude, 0.235% for sugar content, and 0.051 kg plant⁻¹ for root fresh weight, achieving up to a 39% improvement over lower-level configurations. These results enhance disease prediction, improve the understanding of disease epidemiology, and could support more effective plant-disease management.

Sugar beet cultivation in Europe is threatened by two vector-borne diseases: syndrome “basses richesses”, caused by the phloem-limited pathogen ‘Candidatus Arsenophonus phytopathogenicus’, and phytoplasmoses associated with ‘Ca. Phytoplasma solani’ subgroup 16SrXII-A and the related subgroup 16SrXII-P. Infections lead to reduced sugar yield, biomass and growth abnormalities. In Germany, Pentastiridius leporinus represents the main vector. Despite their importance, genetic diversity remains poorly understood. During a two-year survey, barcoded amplicons were generated from infected sugar beet samples from Germany and neighbouring countries using the phytoplasma markers 16S rRNA-ITS-23S rRNA, tuf, and groEL-stamp-nadE, as well as rplO-secY-rpmJ and groEL for ‘Ca. A. phytopathogenicus’. Amplicon pools underwent single-molecule real-time sequencing and amplicon-sequence-variant inference. Additionally, planthopper samples from sugar beet in Germany were analysed and compared to sugar beet data for ‘Ca. A. phytopathogenicus’. No genetic diversity of ‘Ca. A. phytopathogenicus’ was detected, whereas 16SrXII-A and -P showed variation below the subgroup level. 16SrXII-A exhibited higher diversity than 16SrXII-P. In Germany, 16SrXII-A formed a single cluster, while 16SrXII-P comprised two clusters based on 16S rRNA-ITS-23S rRNA. In neighbouring countries, only 16SrXII-A showed diversity, resolving up to four clusters by groEL-stamp-nadE. These results provide a basis for the identification of dominant strains supporting comparative variety evaluation for tolerance.

Virus yellows (VY), caused by beet chlorosis virus (BChV), beet mild yellowing virus (BMYV) and beet yellows virus (BYV), is a serious disease affecting sugar beet, leading to significant yield losses. The main vector is the green peach aphid Myzus persicae . Beet mosaic virus (BtMV) is often associated with VY due to the shared vector. Different host plants of VY-associated viruses can play an important role in the aphid's life cycle and the VY-epidemiology. This study evaluated the susceptibility of 25 cover crops and flower strip plants to VY-associated viruses as well as their attractiveness to M. persicae . None of the tested plants were susceptible to BYV or BtMV, while Gypsophila elegans tested positive for BChV and 13 species tested positive for BMYV. Seven of these, including important cover crops and flower strip plants such as Linum usitatissimum , Trifolium resupinatum , T. incarnatum and Centaurea cyanus , were identified as new BMYV hosts. Plant attractiveness to M. persicae varied widely. Under field conditions, only a few species, such as Sinapis alba or Raphanus sativus var. oleiferus , showed high levels of natural infestation by M. persicae . However, a field choice experiment revealed that BMYV infection can occur in different plants, even at low levels of M. persicae infestation. Field trials also confirmed that M. persicae can transmit BMYV from infected cover crops to sugar beet. The findings emphasise the potential importance of cover crops and flower strip plants as green bridges in VY-epidemiology and highlight the need for research in large-scale field studies.

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive foliar disease in sugar beet. Although CLS is traditionally managed through fungicide applications, integrated management is recommended in practice due to increased fungicide resistance and loss of fungicide efficacy. The implementation of varieties that are resistant to CLS is important for integrated pest management. Currently, resistant varieties have been reported to show delayed disease onset and reduced disease development in the field. However, studies that investigating the resistance phenotype of varieties under greenhouse conditions are limited. In this study, we evaluated, under greenhouse conditions, the resistance properties of three sugar beet varieties that had previously been tested in the field. To identify incubation conditions that allow discrimination between varieties with different levels of resistance, inoculated plants were incubated for varying lengths of time after inoculation. As in field trials, differentiation between susceptible and resistant varieties was possible based on disease development under greenhouse conditions. The variety that performed best in field trials was also the best in greenhouse trials, with high reproducibility. In contrast, a second resistant variety that showed less resistance in field trials also performed more variably in greenhouse trials, depending on the incubation time. A higher overall disease development was closely associated with longer incubation, but no single treatment consistently discriminated all three tested varieties across two independent experiments. Therefore, assessing disease resistance to CLS in a greenhouse can provide additional information but cannot replace field trials under natural infection conditions.

Accurate monitoring of insect vectors is critical for managing Syndrome ‘basses richesses’ (SBR), a disease affecting sugar beet crops in Europe. This study presents a deep learning (DL) approach for the automated identification of Cixiidae planthoppers, the primary SBR vectors. Several DL architectures, including convolutional neural networks (CNN) and vision transformers, were benchmarked, leading to the selection of Inception-v3. This architecture was then used to develop two complementary models: the first to distinguish Cixiidae from other insect groups, and the second to classify species within Cixiidae, namely Pentastiridius leporinus, Hyalesthes obsoletus, and Reptalus spp. Discrimination among these species is essential, as they differ in their efficiency and role in transmitting SBR. The models were trained and validated on over 40,000 high-resolution insect images collected from sticky traps deployed in sugar beet and grapevine fields across Germany and Serbia between 2022 and 2024. Species labels were based on morphological identification and verified via DNA barcoding, and the resulting dataset was made publicly available. Statistical and visual model evaluation confirmed high performance and biological relevance. The first model achieved 94

The disease syndrome "basses richesses" (SBR) leads to a significant reduction in sugar beet biomass and sugar content, negatively affecting the sugar economy. The mechanistic understanding regarding growth and photoassimilates distribution within the sugar beet taproot diseased with SBR is currently incomplete. We combined two tomographic methods, magnetic resonance imaging (MRI) and positron emission tomography (PET) using 11C as tracer, to non-invasively determine SBR effects on structural growth and photoassimilates distribution within the developing taproot over six weeks. MRI analysis revealed a deformed cross-sectional anatomical structure from an early stage, as well as a reduction in taproot volume and width of inner cambium ring structures of up to 26 and 24 ​%, respectively. These SBR disease effects were also confirmed by post-harvest analysis of the taproot. PET analysis revealed a heterogeneous distribution of labeled photoassimilates for diseased plants: sectors of the taproot with characteristic SBR symptoms showed little to very low 11C tracer signal. The heterogeneity of SBR disease effects is most likely due to a partial inoculation of leaves leading to an uneven distribution of the SBR pathogen in the taproot through the strong vascular interconnection between shoot and root. Also, the pathogen needs to spread non-uniformly within the taproot to explain the observed marked increase of the SBR disease effects over time. Our results indicate that SBR affects photoassimilates sink capacity at an early stage of taproot development. Co-registration of MRI and PET may support an early judging of susceptibility and selection of promising genotype candidates for future breeding programs.

Intermolecular recombination is a critical process in the evolution of plant viruses, including geminiviruses. In this study, we investigated the impact of geminiviral factors on the homologous recombination frequency (HRF) in a model system involving replicons of the beet curly top virus (BCTVRepl) and the cotton leaf curl Multan betasatellite (CLCuMB), which lacks the βC1 gene. BCTVRepl-cGFP and CLCuMB-nGFP replicated together and exhibited intermolecular recombination, which was monitored by reconstituted GFP fluorescence. Mutation of the C2, C3, and C4 genes in BCTVRepl-cGFP led to a significant decrease in HRF. Accumulation of BCTVRepl-cGFP was reduced in the C3 mutant but not in the C2 and C4 mutants. These findings suggest that C4 and, to a greater extent, C2 play a role in homologous recombination (HR) between BCTV and CLCuMB replicons. Furthermore, the BCTV large intergenic region (LIR) sequence to which the C1 (Rep) protein binds to initiate viral replication was introduced into the nGFP construct (referred to as LnGFP). This resulted in a low level of HR (5%) compared to the control nGFP construct, where HR did not occur. Subsequent mutational analysis of the iteron and stem-loop sequences within the LIR of LnGFP revealed the role of these sequences and the C1 (Rep) in the process of DNA recombination. This study presents a new model for assessing HRF in BCTV, which can be applied to other geminiviruses. It also highlights the roles of the C2, C4, C1, and LIR structural sequences in intermolecular recombination and replication in the BCTV replicon.IMPORTANCEIntermolecular recombination is a critical process in the evolution, adaptability, and pathogenicity of plant viruses, including geminiviruses. This study developed a visible and quantifiable system to measure the frequency of homologous recombination between beet curly top virus (BCTV) and cotton leaf curl Multan betasatellite (CLCuMB) replicons based on the reconstitution of GFP fluorescence. Furthermore, mutation analysis of complementary-sense genes in the BCTV replicon indicated that C4 and, to a greater extent, C2 play a role in the recombination between the BCTV and CLCuMB replicons. Subsequent mutational analysis of the iteron and stem-loop sequences within the large intergenic region of BCTV revealed the possible role of these structural sequences in the recombination process.

Virus yellows disease (VY) is a major threat to sugar beet production in Europe. Beet chlorosis virus (BChV) and beet mild yellowing virus (BMYV) are of particular economic importance and are both persistently transmitted by the aphid vector Myzus persicae. As part of integrated pest management strategies, M. persicae influx into sugar beet fields is recorded weekly using yellow water pan traps. To date, only ELISA and RT-PCR assays have been described for BChV and BMYV detection in individual aphids. In this study, we describe for the first time two one-step TaqMan® RT-qPCR assays designed for the specific detection of BChV and BMYV in M. persicae after 7d incubation in water pan trap medium. Both viruses were reproducibly detected in individual aphids. After 7d incubation in trap medium, both viruses were reproducibly detected in individual aphids, as well as in one viruliferous aphid in a pool of 99 non-viruliferous aphids. Significant correlations can be shown between different mixing ratios of viruliferous to non-viruliferous aphids and Ct values of total RNA templates, allowing the percentage of viruliferous aphids in yellow water pan traps to be estimated using a standard curve. The described methodology provides a high sensitivity combined with a high sample throughput and can be used, after evaluation in the field, for practical monitoring, risk modelling and development of decision support systems for VY.

Beet mosaic virus (BtMV) is one of several viruses infecting sugar beets and was previously managed by controlling the vector Myzus persicae with neonicotinoid seed treatment. Following the ban of this measure in 2019 in Europe, alternative control strategies needed to be researched. One alternative might be the use of RNA interference as a major antiviral defense system. Here, we report the selection of target regions using small RNA high-throughput sequencing of BtMV-infected Beta vulgaris subsp. vulgaris and Nicotiana benthamiana plants, the production of double-stranded RNA (dsRNA), and the effective use of dsRNA in inducing resistance against the mechanically inoculated virus under greenhouse conditions. In Escherichia coli HT115, the dsRNAs produced for BtMV P1 and nuclear inclusion body b (NIb) induced a high level of resistance when sprayed before mechanical BtMV inoculation, resulting in an 80% reduction of symptomatic B. vulgaris and N. benthamiana plants. Stem-loop RT-qPCR showed the systemic distribution of dsRNA-derived small interfering RNA molecules, but the applied dsRNA remained at the site of application and did not spread within the plant. However, when the virus was inoculated on the next upward leaf to the dsRNA application site, no protective effect was observed. Despite this limitation, the results demonstrate the potential of dsRNA as an effective tool for viral protection in sugar beets, thereby establishing a basis for future developments in systemic delivery and broader field applications. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

BACKGROUND:Cercospora leaf spot (CLS), caused by Cercospora beticola, is the most destructive foliar disease in sugar beet. CLS is conventionally controlled with fungicide, but the emergence of fungicide-resistant populations reinforces the importance of developing and cultivating resistant varieties. Understanding the dynamics of CLS in different varieties is hence essential for sustainable CLS management. RESULTS:Field experiments (2022 and 2023) with four sugar beet varieties possessing different resistant properties were conducted to describe the relationship between the variety resistance and the disease epidemiology of C. beticola. For this purpose, spore flight and disease progression were assessed on a weekly basis. Disease severity (DS) and disease incidence (DI) were delayed in resistant varieties compared to the susceptible and moderately susceptible ones. This finding was further confirmed by a model-based analysis of DS and DI for all varieties. Weekly spore flight monitoring during the vegetation period showed a similar tendency of reduced spore quantity by the resistant varieties. This was probably due to the lower DS, as no differences were found when the amount of fungal DNA was determined in individual lesions from the different varieties. Analysis of relative yield loss further confirmed the advantage of growing resistant varieties. CONCLUSION:Our results highlight that resistant varieties delay disease onset resulting in less severe symptoms and reduced spore flight. We also proved that aerial spore flight intensity could reflect the resistant property of each variety. These results provide a deeper insight into the interaction between variety resistance and CLS epidemiology, emphasizing variety-specific CLS management. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phytoplasmas were detected in potato tubers and sugar beet roots in neighbouring fields in Southern Germany using quantitative PCR. Infected potato plants showed phytoplasma-associated symptoms including yellowing, upward leaf rolling, aerial tubers and early senescence. Sugar beet plants showed similar symptoms to those of syndrome 'basses richesses' (SBR) disease, including proliferation, yellowing and necrosis of older leaves. The genetic diversity of the phytoplasmas in the symptomatic potato and sugar beet plants was investigated through sequence analysis of 16S rRNA and stamp, vmp1, tuf and secY genes. The RFLP profiles and sequences of 16S rRNA were identical among all the sugar beet-positive samples and aligned with subgroup 16SrXII-P, whereas the potato phytoplasma strains were identified as belonging to subgroup 16SrXII-A. Sequence analysis of the non-ribosomal genes showed that the potato strains belonged to the b1 group of the tuf gene, the V4 and V17 groups of the vmp1 gene and the secY3 and secY4 groups of the secY gene. However, the sugar beet strain was clearly distinct from the potato strains. Together with strain 916/22 from sugar beet in eastern Germany, they formed a new group of tuf, secY, vmp and stamp genes. RFLP assays and multilocus sequence analysis of non-ribosomal genes of the phytoplasma strains confirmed that the potato phytoplasma strains were molecularly different from the sugar beet phytoplasma strains. In addition, this is the first report on the multilocus sequence analysis of 'Candidatus Phytoplasma solani' strains in potato plants in Germany, suggesting differences in source plants other than sugar beet or interactions with insect vectors specific to each crop.

The genus Beta encompasses economically important root crops such as sugar and table beet. A Beta diversity set including the wild relative B. vulgaris ssp. maritima was grown in the field, and a large phenotypic diversity was observed. The genomes of 290 accessions were sequenced, and more than 10 million high-quality SNPs were employed to study genetic diversity. A genome-wide association study was performed, and marker-trait associations were found for nine phenotypic traits. The candidate gene within the M locus controlling monogermity on chromosome 4 was previously unknown. The most significant association for monogermity was identified at the end of chromosome 4. Within this region, a non-synonymous mutation within the zinc-finger domain of the WIP2 gene co-segregated with monogermity. This gene plays a regulatory role in AGL8/FUL in Arabidopsis. Intriguingly, commercial hybrids are in a heterozygous state at this position. Thus, the long-sought gene for monogermity was identified in this study. Red and yellow pigmentation due to betalain accumulation in shoots and roots is an important characteristic of table and leaf beets. The strongest associations were found upstream or downstream of two genes encoding Cytochrome P450 and anthocyanin MYB-like transcription factor proteins involved in betalain biosynthesis. Significant associations for Cercospora leaf spot resistance were identified on chromosomes 1, 2, 7, and 9. The associated regions harbor genes encoding proteins with leucine-rich repeats and nucleotide binding sites whose homologs are major constituents of plant-pathogen defense.

The syndrome “bassess richesses” is a vector-borne disease of sugar beet in Germany. The gammaproteobacterium ‘Candidatus Arsenophonus phytopathogenicus’ causes reduced sugar content and biomass, growth abnormalities, and yellowing. Co-infection with the 16SrXII-P stolbur phytoplasmas often leads to more severe symptoms and a risk of complete economic loss. This yellowing agent of the Mollicutes class had not been described before, so its differences from other stolbur phytoplasmas remained unanswered. The genome of strain GOE was sequenced, providing a resource to analyze its characteristics. Phylogenetic position was revised, genome organization was compared, and functional reconstructions of metabolic and virulence factors were performed. Average nucleotide identity analysis indicates that GOE represents a new ‘Ca. Phytoplasma‘ species. Our results show that GOE is also distinct from other stolbur phytoplasmas in terms of smaller genome size and G+C content. Its reductive evolution is reflected in conserved membrane protein repertoire and minimal metabolism. The encoding of a riboflavin kinase indicates a lost pathway of phytoplasmas outside the groups 16SrXII and 16SrXIII. GOE shows a complete tra5 transposon harboring orthologs of SAP11, SAP54, and SAP05 effectors indicating an original phytoplasma pathogenicity island. Our results deepen the understanding of phytoplasma evolution and reaffirm the heterogeneity of stolbur phytoplasmas.

Plants are constantly challenged by viral pathogens that can limit growth and reduce yield. A key component of the plant innate immunity is RNA silencing, in which viral double-stranded RNA (dsRNA) intermediates are recognised and processed into virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs direct the degradation of viral genomes, thereby restricting infection. Sugar beet (Beta vulgaris subsp. vulgaris) is a crop of major economic importance, where the virus yellows (VY) complex represents a serious threat to production. Here, we profiled and compared vsiRNAs generated during infection of the natural host plant B. vulgaris and the experimental host plant Nicotiana benthamiana with three taxonomically distinct viruses: beet yellows virus (BYV, Closterovirus), beet mild yellowing virus (BMYV, Polerovirus), and beet mosaic virus (BtMV, Potyvirus). High-throughput sequencing of small RNAs revealed characteristic size distributions and strand biases that differed among viruses and host species. Comparative analysis highlighted no host plant-specific pattern of vsiRNA accumulation. This comparative approach provides a detailed view of vsiRNA processing and offers novel insights that are not apparent from coverage profiles alone. Distinct vsiRNA hotspots were detected for each viral genome, and these hotspots did not differ between host plants, pinpointing potential target regions for RNA interference-based control approaches. The identification of such regions provides a basis for the design of synthetic dsRNAs that can be applied exogenously as protective sprays, an emerging, non-transgenic strategy to mitigate VY infections, while advancing understanding of vsiRNA biogenesis in sugar beet and N. benthamiana in general.

Pentastiridius leporinus (Hemiptera: Cixiidae) is the main vector of an emerging and fast spreading sugar beet disease, the syndrome ‘basses richesses’ (SBR), in different European countries. The disease is caused by the γ-3-proteobacterium ‘ Candidatus Arsenophonus phytopathogenicus’ and the phytoplasma ‘ Candidatus Phytoplasma solani’ which are exclusively transmitted by planthoppers and can lead to a significant loss of sugar content and yield. Monitoring of this insect vector is important for disease management. However, the morphological identification is time consuming and challenging as two additional cixiid species Reptalus quinquecostatus and Hyalesthes obsoletus with a very close morphology have been reported in sugar beet fields. Further, identification of females and nymphs of P. leporinus at species level based on taxonomic key is not possible. In this study, an isothermal nucleic acid amplification based on recombinase polymerase amplification (RPA) was developed to specifically detect P. leporinus. In addition, real-time RPA was developed to detect both adults (male and female) and nymph stages using pure or crude nucleic acid extracts. The sensitivity of the real-time RPA for detection of P. leporinus was comparable to real-time PCR, but a shorter time (< 7 min) was required. This is a first report for real-time RPA application for P. leporinus detection using crude nucleic acid templates which can be applied for fast and specific detection of this vector in the field.

This study investigates the potential of high-resolution (<0.5 cm/pixel) aerial imagery and convolutional neural networks (CNNs) for disease incidence scoring in sugar beet, focusing on two important aphid-transmitted viruses, beet mild yellowing virus (BMYV) and beet chlorosis virus (BChV). The development of tolerant sugar beet cultivars is imperative in the context of increased disease management concerns due to the ban on neonicotinoids in the European Union. However, traditional methods of disease phenotyping, which rely on visual assessment by human experts, are both time-consuming and subjective. Therefore, this study assessed whether aerial multispectral and RGB images could be harnessed to perform automated disease ratings comparable to those performed by trained experts. To this end, two variety trials were conducted in 2021 and 2022. The 2021 dataset was used to train and validate a CNN model on five cultivars, while the 2022 dataset was used to test the model on two cultivars different from those used in 2021. Additionally, this study tests the use of transformed features instead of raw spectral bands to improve the generalization of CNN models. The results showed that the best CNN model was the one trained for BMYV on RGB images using transformed features instead of conventional raw bands. This model achieved a root mean square error score of 11.45% between the model and expert scores. These results indicate that while high-resolution aerial imagery and CNNs hold great promise, a complete replacement of human expertise is not yet possible. This research contributes to an innovative approach to disease phenotyping, driving advances in sustainable agriculture and crop breeding.

The complete genome of "Candidatus Phytoplasma solani" GOE was obtained from the infected vector Pentastiridius leporinus by single-molecule real-time sequencing. This 16SrXII-P phytoplasma is associated with the economically important sugar beet disease "syndrome basses richesses." The genome sequence is an essential resource for diagnosis and understanding pathogen-host interaction.

Beet chlorosis virus (BChV), beet mild yellowing virus (BMYV) and beet yellows virus (BYV) transmitted by Myzus persicae cause virus yellows (VY) disease in sugar beet. M. persicae also transmits beet mosaic virus (BtMV), which is often associated with VY. So far, field trials to determine the effect of infection time point on yield have used 100% inoculation density and little is known about the yield effect of BtMV in mixed infections with VY species under field conditions. Therefore, we conducted sugar beet field trials using a new inoculation protocol with densities of 3%–10% in combination with different infection time points; we also tested the effect of BtMV/VY species mixed infections on white sugar yield (WSY). We observed a wide range of WSY losses for BChV (3.6%–26.8%), BMYV (1.7%–22.0%) and BYV (3.7%–37.0%) depending on infection time point, with no further significant losses after BBCH Stages 18/19, 35 and 39, respectively. Both the time of infection and area under disease progress curve showed excellent correlation with WSY losses for all VY species. BtMV had no significant effect on WSY losses either as a single infection or in mixed infections with BChV or BYV compared to control or single infections of these viruses. However, BMYV/BtMV mixed infection showed significantly increased WSY loss (+13.6%) compared to single BMYV infection. Our results can be used to predict yield losses in practical fields and to develop economic control thresholds for decision support systems.

Syndrome ‘basses richesses’ (SBR) disease in sugar beet caused by two phloem-limited pathogens, 'Candidatus Arsenophonus phytopathogenicus' and 'Candidatus Phytoplasma solani' is a fastspreading disease in Central Europe. The planthopper vector, Pentastiridius leporinus (Cixiidae), has recently expanded its host range to potato in Germany. However, the genetic diversity of 'Ca P. solani' in potato and possible association to SBR phytoplasma is unknown. In this study we charachterized ‘Ca. P. solani’ infecting sugar beet and potato plants in close distance fields in Southern Germany. Initially, the pathogen was detected in the potato tubers (18.7%) and sugar beet roots (60%) using TaqMan Real-Time PCR. Then, the sequences of 16S rRNA and other informative genes (stamp, vmp1, tuf and secY) were analysed in a number of infected potato and sugar beet plants. The phytoplasma strain infecting sugar beet in Southern Germany was classified into 16SrXII-P subgroup, a novel subgroup recently reported from sugar beet in Eastern Germany. While, the potato related strains were close to 16SrXII-A, which is a common subgroup for potato stolbur reported in Europe. The multilocus sequence analysis (MLSA) of non-ribosomal genes of the phytoplasma strains showed that the potato strain is clearly different from the sugar beet associated strain in this region. The presence and prevalence of 16SrXII-P in sugar beet in Southern and Eastern Germany suggests that this subgroup is dominant in sugar beet in Germany. In addition, this study elucidates for the first time, the genetic diversity of ‘Ca. P. solani’ strains in potato in Germany with a possible different source rather than sugar beet. Further investigation is required to investigate genetic variation of ‘Ca. P. solani’ in all sugar beet and potato-growing regions including weeds host in Central Europe to better understand the epidemiology of both sugar beet SBR and potato stolbur disease.