Resistant Sugar Beet Research Articles

Evaluation of Rz2 Gene Expression in Sugar Beet Hybrids Infected with Beet Necrotic Yellow Vein Virus.

Sugar beet hybrids are essential in modern agriculture due to their superior yields, disease resistance, and adaptability. This study investigates the role of the Rz2 gene in conferring resistance to beet necrotic yellow vein virus (BNYVV) in 14 sugar beet hybrids cultivated in Kazakhstan, including local and European varieties. The Rz2 gene, encoding a CC-NB-LRR protein, is a known resistance factor against BNYVV. Using RT-qPCR, we assessed Rz2 expression and detected BNYVV in bait plants inoculated with virus-infested soil. Our findings identified two highly resistant varieties: the Kazakh cultivar 'Abulhair' and the French line 22b5006. Additionally, the Kazakh cultivar 'Pamyati Abugalieva' and the French hybrid 'Bunker' exhibited increased resistance, suggesting involvement of other resistance loci. Notably, the Danish hybrid 'Alando', despite resistance to rhizomania, did not effectively resist BNYVV, highlighting possible evasion of its genetic factors by local virus strains. Our results emphasize the importance of Rz2 in resistance breeding programs and advocate for further research on additional resistance genes and the genetic variability of BNYVV in Kazakhstan. This work pioneers the molecular evaluation of BNYVV resistance in sugar beet in Kazakhstan, contributing to sustainable disease management and improved sugar beet production.

Insights into the molecular basis of beet curly top resistance in sugar beet through a transcriptomic approach at the early stage of symptom development

Curly top disease caused by Beet curly top virus (BCTV) is a limiting factor for sugar beet production. The most economical and sustainable control of BCTV in sugar beet would be via the growth of resistant cultivars, although most commercial cultivars possess only low-to-moderate quantitative resistance. A double haploid line (KDH13) showed a high level of resistance to BCTV infection. However, the mechanism of resistance and response of this line to BCTV infection is unknown. Here, we tested the response of this line to both local and systemic BCTV infections. The virus replicated at a high level in locally infected tissue but lower than in susceptible KDH19 plants. Resistant KDH13 plants systemically infected with BCTV showed only mild enation without leaf curling after 30 days. In contrast, severe leaf curling appeared after 12 days in susceptible plants with higher virus accumulation. Transcriptome analysis of the BCTV-infected KDH13 plants at the early stage of symptom development showed only 132 genes that were exclusively deregulated compared to the regulation of a large number of genes (1018 genes) in KDH19 plants. Pathway enrichment analysis showed that differentially expressed genes were predominantly involved in hormone metabolism, DNA methylation, immune response, cell cycle, biotic stress and oxidative stress. The auxin level in both resistant and susceptible plants increased in response to BCTV infection. Remarkably, exogenous application of auxin caused leaf curling phenotype in the absence of the virus. This study demonstrates the response of resistant and susceptible plants to BCTV infection at both local and systemic infections and highlights the defence-related genes and metabolic pathways including auxin for their contribution towards BCTV symptom development and resistance in sugar beet.

Molecular epidemiology of Cercospora leaf spot on resistant and susceptible sugar beet hybrids

AbstractCercospora leaf spot (CLS), caused by Cercospora beticola, is a major foliar disease impacting sugar beet production worldwide. The development of new resistant sugar beet hybrids is a powerful tool to better manage the disease, but it is unclear how these hybrids affect CLS epidemiology. We used a molecular epidemiology approach to study natural epidemics of CLS affecting two susceptible and two resistant sugar beet hybrids at two field sites. Infected plants were geotagged on a weekly basis. Isolations of C. beticola were made from infected leaves and genotyped using six simple‐sequence repeat loci to identify clones. We determined that CLS epidemics had a later onset in plots planted to resistant hybrids, but once the pathogen established an infection, there was little difference between resistant and susceptible hybrids in the probability of localized spread and dispersal. We found that different clones often infected the same leaf and that clusters of infected plants were often colonized by a mixture of clones. There was little overall difference in genetic diversity of C. beticola collected on resistant and susceptible hybrids; however, genotypic diversity was lower on the resistant hybrid at one site, suggestive of a selection bottleneck. At the end of the epidemic infections were not randomly distributed across the fields and we found that a single clone could spread over a distance of 100 m during a growing season.

Improving genomic prediction of rhizomania resistance in sugar beet (Beta vulgaris L.) by implementing epistatic effects and feature selection

Background Rhizomania counts as the most important disease in sugar beet Beta vulgaris L. for which no plant protection is available, leaving plant breeding as the only defence strategy at the moment. Five resistance genes have been detected on the same chromosome and further studies suggested that these might be different alleles at two resistance clusters. Nevertheless, it was postulated that rhizomania resistance might be a quantitative trait with multiple unknown minor resistance genes. Here, we present a first attempt at genomic prediction of rhizomania resistance in a population that carries resistances at the two known resistance clusters. The sugar beet population was genotyped using single nucleotide polymorphism (SNP) markers. Methods First, genomic prediction was performed using all SNPs. Next, we calculated the variable importance for each SNP using machine learning and performed genomic prediction by including the SNPs incrementally in the prediction model based on their variable importance. Using this method, we selected the optimal number of SNPs that maximised the prediction accuracy. Furthermore, we performed genomic prediction with SNP pairs. We also performed feature selection with SNP pairs using the information about the variable importance of the single SNPs. Results From the four methods under investigation, the latter led to the highest prediction accuracy. These results lead to the conclusion that more than the two known resistance clusters are involved in rhizomania resistance and that genetic interactions affect rhizomania resistance. Finally, we have analysed which SNPs were repeatedly detected in the feature selection process and discovered four SNPs, two of which are located on chromosomes that were previously not associated with rhizomania resistance.

Genomic characterization of bZIP gene family and patterns of gene regulation on Cercospora beticola Sacc resistance in sugar beet (Beta vulgaris L.).

Sugar beet (Beta vulgaris L.) is one of the most important sugar crops, accounting for nearly 30% of the world's annual sugar production. And it is mainly distributed in the northwestern, northern, and northeastern regions of China. However, Cercospora leaf spot (CLS) is the most serious and destructive foliar disease during the cultivation of sugar beet. In plants, the bZIP gene family is one of important family of transcription factors that regulate many biological processes, including cell and tissue differentiation, pathogen defense, light response, and abiotic stress signaling. Although the bZIP gene family has been mentioned in previous studies as playing a crucial role in plant defense against diseases, there has been no comprehensive study or functional analysis of the bZIP gene family in sugar beet with respect to biotic stresses. In this study, we performed a genome-wide analysis of bZIP family genes (BvbZIPs) in sugar beet to investigate their phylogenetic relationships, gene structure and chromosomal localization. At the same time, we observed the stomatal and cell ultrastructure of sugar beet leaf surface during the period of infestation by Cercospora beticola Sacc (C. beticola). And identified the genes with significant differential expression in the bZIP gene family of sugar beet by qRT-PCR. Finally we determined the concentrations of SA and JA and verified the associated genes by qRT-PCR. The results showed that 48 genes were identified and gene expression analysis indicated that 6 BvbZIPs were significantly differential expressed in C. beticola infection. It is speculated that these BvbZIPs are candidate genes for regulating the response of sugar beet to CLS infection. Meanwhile, the observation stomata of sugar beet leaves infected with C. beticola revealed that there were also differences in the surface stomata of the leaves at different periods of infection. In addition, we further confirmed that the protein encoded by the SA signaling pathway-related gene BVRB_9g222570 in high-resistant varieties was PR1, which is closely related to systemic acquired resistance. One of the protein interaction modes of JA signal transduction pathway is the response of MYC2 transcription factor caused by JAZ protein degradation, and there is a molecular interaction between JA signal transduction pathway and auxin. Despite previous reports on abiotic stresses in sugar beet, this study provides very useful information for further research on the role of the sugar beet bZIP gene family in sugar beet through experiments. The above research findings can promote the development of sugar beet disease resistance breeding.

Ecological characteristics of sugar beet plant and rhizosphere soil in response to high boron stress: A study of the remediation potential

High boron (B) stress degrades the soil environment and reduces plant productivity. Sugar beet has a high B demand and potential for remediation of B-toxic soils. However, the mechanism regarding the response of sugar beet plants and rhizosphere soil microbiome to high B stress is not clear. In the potted soil experiment, we set different soil effective B environments (0.5, 5, 10, 30, 50, and 100 mg kg−1) to study the growth status of sugar beets under different B concentrations, as well as the characteristics of soil enzyme activity and microbial community changes. The results showed that sugar beet growth was optimal at 5 mg kg−1 of B. Exceeding this concentration the tolerance index decreased. The injury threshold EC20 was reached at an available B concentration of 35.8 mg kg−1. Under the treatment of 100 mg kg−1, the B accumulation of sugar beet reached 0.22 mg plant−1, and the tolerance index was still higher than 60%, which had not yet reached the lethal concentration of sugar beet. The abundance of Acidobacteriota, Chloroflexi and Patescibacteria increased, which was beneficial to the resistance of sugar beet to high B stress. In summary, under high B stress sugar beet had strong tolerance, enhanced capacity for B uptake and enrichment, and changes in soil microbial community structure. This study provides a theoretical basis for clarifying the mechanism of sugar beet resistance to high B stress and soil remediation.

Histopathological Investigation of Varietal Responses to Cercospora beticola Infection Process on Sugar Beet Leaves.

Cercospora leaf spot (CLS) is the most destructive foliar disease in sugar beet (Beta vulgaris). It is caused by Cercospora beticola Sacc., a fungal pathogen that produces toxins and enzymes which affect membrane permeability and cause cell death during infection. In spite of its importance, little is known about the initial stages of leaf infection by C. beticola. Therefore, we investigated the progression of C. beticola on leaf tissues of susceptible and resistant sugar beet varieties at 12-h intervals during the first 5 days after inoculation using confocal microscopy. Inoculated leaf samples were collected and stored in DAB (3,3'-diaminobenzidine) solution until processed. Samples were stained with Alexa Fluor-488-WGA dye to visualize fungal structures. Fungal biomass accumulation, reactive oxygen species (ROS) production, and the area under the disease progress curve were evaluated and compared. ROS production was not detected on any variety before 36 h postinoculation (hpi). C. beticola biomass accumulation, percentage leaf cell death, and disease severity were all significantly greater in the susceptible variety compared with the resistant variety (P < 0.05). Conidia penetrated directly through stomata between 48 to 60 hpi and produced appressoria on stomatal guard cells at 60 to 72 hpi in susceptible and resistant varieties, respectively. Penetration of hyphae inside the parenchymatous tissues varied in accordance with time postinoculation and varietal genotypes. Overall, this study provides a detailed account to date of events leading to CLS disease development in two contrasting varieties.

Temporal and species-specific resistance of sugar beet to green peach aphid and black bean aphid: mechanisms and implications for breeding.

Sugar beet (Beta vulgaris ssp. vulgaris), a key crop for sugar production, faces significant yield losses caused by the black bean aphid Aphis fabae (Scop.) and the green peach aphid Myzus persicae (Sulzer), which also transmits viruses. The restriction on neonicotinoid usage in Europe has intensified this problem, emphasizing the urgent need for breeding resistant crop varieties. This study evaluated 26 sugar beet germplasms for resistance against both aphid species by using performance and feeding behavior assays. Additionally, whole plant bioassays and semi-field experiments were carried out with Myzus persicae. Our findings demonstrate the presence of temporal resistance against both aphid species in the primary sugar beet gene pool. Beet yellows virus (BYV) carrying aphids showed enhanced performance. Different levels of plant defense mechanisms were involved including resistance against Myzus persicae before reaching the phloem, particularly in sugar beet line G3. In contrast, resistance against Aphis fabae turned out to be predominately phloem-located. Furthermore, a high incidence of black inclusion bodies inside the stomach of Myzus persicae was observed for approximately 85% of the plant genotypes tested, indicating a general and strong incompatibility between sugar beet and Myzus persicae in an initial phase of interaction. Sugar beet resistance against aphids involved different mechanisms and is species-specific. The identification of these mechanisms and interactions represents a crucial milestone in advancing the breeding of sugar beet varieties with improved resistance. © 2023 Julius Kühn-Institut and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Cultivar and Fungicide Evaluations for Cercospora Leaf Spot Control in Organic and Conventional Table Beet Production

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive foliar disease of table beet (Beta vulgaris ssp. vulgaris) in Wisconsin, USA, and globally. Under conducive conditions, symptomatic lesions on the leaf expand and coalesce forming large necrotic areas that can ultimately lead to complete defoliation. This damage reduces productivity and threatens the ability to mechanically harvest. CLS damage also detracts from the visual appeal of fresh market bunched beets to such an extent that growers risk buyer rejection if CLS severity is observed to be greater than 5%. Fungicide use for CLS control is threatened by the emergence of resistant C. beticola strains, and the application of host resistance is constrained by limited knowledge of cultivar reaction to CLS in table beet. This study aimed to address the knowledge gaps of fungicide efficacy and cultivar reaction by conducting replicated field trials in multiple table beet growing environments across Wisconsin. Broad variation for resistance to CLS was observed among the 10 included cultivars. The mean area under disease progress curve (AUDPC) across environments for the most susceptible cultivar was 267% greater than the most resistant cultivar. Spearman correlations between environments for mean cultivar AUDPC value ranged from 0.71 to 0.99, revealing consistent cultivar CLS reactions across environments. Although susceptible cultivars surpassed 5% severity in all environments, the resistant cultivars remained below this threshold in six of the 10 environments. By comparison with resistant sugar beet (Beta vulgaris ssp. vulgaris) cultivars, however, all tested table beets appeared susceptible to CLS, highlighting the potential for a CLS breeding effort in table beet. Neither of the evaluated Organic Materials Review Institute–listed treatments were effective at limiting CLS disease progress, whereas both tested conventional fungicides significantly reduced disease severity over the nontreated plots. These findings may provide helpful guidance to table beet growers affected by CLS in Wisconsin and beyond.

The arms race between beet necrotic yellow vein virus and host resistance in sugar beet.

Beet necrotic yellow vein virus (BNYVV) causes rhizomania disease in sugar beet (Beta vulgaris), which is controlled since more than two decades by cultivars harboring the Rz1 resistance gene. The development of resistance-breaking strains has been favored by a high selection pressure on the soil-borne virus population. Resistance-breaking is associated with mutations at amino acid positions 67-70 (tetrad) in the RNA3 encoded pathogenicity factor P25 and the presence of an additional RNA component (RNA5). However, natural BNYVV populations are highly diverse making investigations on the resistance-breaking mechanism rather difficult. Therefore, we applied a reverse genetic system for BNYVV (A type) to study Rz1 resistance-breaking by direct agroinoculation of sugar beet seedlings. The bioassay allowed a clear discrimination between susceptible and Rz1 resistant plants already four weeks after infection, and resistance-breaking was independent of the sugar beet Rz1 genotype. A comprehensive screen of natural tetrads for resistance-breaking revealed several new mutations allowing BNYVV to overcome Rz1. The supplementation of an additional RNA5 encoding the pathogenicity factor P26 allowed virus accumulation in the Rz1 genotype independent of the P25 tetrad. This suggests the presence of two distinct resistance-breaking mechanisms allowing BNYVV to overcome Rz1. Finally, we showed that the resistance-breaking effect of the tetrad and the RNA5 is specific to Rz1 and has no effect on the stability of the second resistance gene Rz2. Consequently, double resistant cultivars (Rz1+Rz2) should provide effective control of Rz1 resistance-breaking strains. Our study highlights the flexibility of the viral genome allowing BNYVV to overcome host resistance, which underlines the need for a continuous search for alternative resistance genes.

&amp;lt;i&amp;gt;In Vitro &amp;lt;/i&amp;gt;and&amp;lt;i&amp;gt; in Vivo &amp;lt;/i&amp;gt;Management of &amp;lt;i&amp;gt;Sclerotium rolfsii&amp;lt;/i&amp;gt; the Cause of Sugar Beet Root Rot Disease

Management of sugar beet damping off and root rot diseases caused by <i>Sclerotium rolfsii</i> is urgently needed. Therefore, antifungal activities of 13 materials including 2 bio agents, 2 seaweeds, 3 chemical inducers and 6 fungicides were evaluated. Required inoculum potential of either fungal mass or sclerotia to reach more than 50% of disease incidence was firstly investigated. Fungal mass inoculation (40-500g/10kg of soil) provided 70-100% damping off and 100% root rot. Meanwhile, 6.7-36.7% of damping off and no or negligible root rot were obtained using 300-500 sclerotia /10kg of soil. On the other hand, <i>S. rolfsii</i> mycelial growth was completely suppressed <i>in vitro</i> by all tested materials. However, various antifungal activities of these materials were shown <i>in vivo</i> after seed soaking in the 1^st (2020/2021) trail or seed soaking followed by soil drenching in the 2^nd (2021/2022) trail. Tipo top (Tebuoconazole 25.9%: 1cm/L) fungicide was the most effective material in the 1^st trail since the seedling survival was up to 80%, followed by potassium silicate (1cm/L) and Score (Difenoconazole 25%: 1cm/L) fungicide. Seed soaking followed by soil drenching with Tipo top in the 2^nd trail were protected sugar beet from sowing to harvest and enhanced the root weight. Additionally, this study illustrated that both of sugar beet root weight and sucrose content were decreased as root rot severity increased. In conclusion, chemical fungicides are unfortunately still the fast and potent way for <i>S. rolfsii</i> management, especially with the limitation of resistant sugar beet cultivars.

Improving genomic prediction of rhizomania resistance in sugar beet (Beta vulgaris L.) by implementing epistatic effects and feature selection

Background: Rhizomania counts as the most important disease in sugar beet Beta vulgaris L. for which no plant protection is available, leaving plant breeding as the only defence strategy at the moment. Five resistance genes have been detected on the same chromosome and further studies suggested that these might be different alleles at two resistance clusters. Nevertheless, it was postulated that rhizomania resistance might be a quantitative trait with multiple unknown minor resistance genes. Here, we present a first attempt at genomic prediction of rhizomania resistance in a population that was genotyped using single nucleotide polymorphism (SNP) markers. Methods: First, genomic prediction was performed using all SNPs. Next, we calculated the variable importance for each SNP using machine learning and performed genomic prediction by including the SNPs incrementally in the prediction model based on their variable importance. Using this method, we selected the optimal number of SNPs that maximised the prediction accuracy. Furthermore, we performed genomic prediction with SNP pairs. We also performed feature selection with SNP pairs using the information about the variable importance of the single SNPs. Results: From the four methods under investigation, the latter led to the highest prediction accuracy. These results lead to the following conclusions: (I) The genotypes that were resistant at all known resistance genes, provided the highest possible variation of virus concentrations that the machine can measure. Thus, it can be assumed that more genes must be involved in the resistance towards rhizomania. (II) We show that prediction models that include SNP interactions increased the prediction accuracy. Conclusions: Altogether, our findings suggest that rhizomania resistance is a complex quantitative trait that is affected by multiple genes as well as their interaction.

Novel QTL associated with Rhizoctonia solani Kühn resistance identified in two table beet × sugar beet F2:3 populations using a new table beet reference genome

AbstractThe necrotrophic fungus Rhizoctonia solani Kühn is a major concern for table beet (Beta vulgaris L. ssp. vulgaris) producers across the United States causing upward of 75% losses in severe instances. Thus far, there have been minimal efforts to incorporate host resistance to R. solani in table beet germplasm. To investigate the genetic control of R. solani resistance in table beet, we developed two mapping populations. Parents of the two populations were a Rhizoctonia‐susceptible table beet inbred W357A and a resistant sugar beet germplasm FC709‐2 (sugar beet resistance population, SBRP) and a Rhizoctonia‐resistant table beet inbred W364B and a susceptible sugar beet inbred FC901/C817 (table beet resistance population, TBRP). In Spring 2020, F2:3 families were evaluated for response to artificial inoculation with R. solani AG 2‐2 IIIB isolate R1 in replicated greenhouse experiments. This work also represents the first use of the W357B table beet reference genome, utilized here to align genotyping‐by‐sequencing reads to identify polymorphic markers. Using interval linkage mapping, we identified one quantitative trait locus (QTL) in each of the two populations, each accounting for 30% of the phenotypic variation. The QTL in both the SBRP and TBRP were found on chromosome 2 and contained several putative resistance genes in annotations of the Beta vulgaris and Arabidopsis thaliana genomes. This is the first report of a QTL on chromosome 2 for resistance to R. solani in B. vulgaris ssp. vulgaris and the first identification of QTL for disease resistance in table beet. The newly developed table beet reference genome and markers identified in this study may be of value for marker‐assisted selection in breeding for resistance to R. solani in both sugar beet and table beet breeding programs.

Identification and prediction of functions for drought-responsive microRNAs in sugar beet (Beta vulgaris)

Context Drought is a common abiotic stress affecting crop yield and quality worldwide. Sugar beet (Beta vulgaris L.) is a temperate crop that contributes greatly to world sucrose production and is affected by frequent drought. MicroRNAs (miRNAs) have been demonstrated to play an important role in plant abiotic stress responses. Protein-coding genes associated with drought resistance have been identified in sugar beet; however, studies on miRNAs involved in drought stress response are lacking. Aims The present study focused on analysing miRNAs in sugar beet and their roles in drought stress response. Method Small-RNA libraries were constructed from leaves of plants subjected to drought stress and well-watered conditions. High-throughput sequencing and bioinformatics analysis were used to investigate the genome-wide quantity of miRNAs and identify possible drought response regulatory effects. Key results Deep sequencing identified 49 known miRNAs and 59 new miRNAs. According to the Kyoto Encyclopaedia of Genes and Genomes (KEGG), the sulfur relay system was significantly enriched under drought stress. Co-regulated pairs between miR156a-5p, novel_18 and novel_41, and their target genes BVRB_6g136190, BVRB_009610 and BVRB_6g136680 were observed, suggesting a negative feedback modulation involved in the miRNA pathways. Conclusions Our results indicate that certain metabolic pathways such as the sulfur relay system are activated under drought conditions. Implications The results aid understanding of the mechanisms of drought response at the molecular level and may enable tools to be devised that enhance drought resistance in sugar beet.

The effect of mature plant resistance in sugar beet (Beta vulgaris spp. vulgaris) on survival, fecundity and behaviour of green peach aphids (Myzus persicae).

Several studies have shown the negative effects of mature plant resistance (MPR) on aphids in sugar beet, which is correlated to the formation of black deposits in their stomach. However, the underlying mechanism of MPR still needs to be elucidated, by understanding the toxicity effects of MPR on aphids and the role of the plant phenological stage and the environment. Here, we report that MPR in sugar beet does not only affect Myzus persicae mortality rate and the formation of a black deposit in the aphid stomach, but also aphid fecundity and behaviour. In addition, experiments in climate-controlled and field settings showed quantitative variation in MPR to M. persicae between six genotypes of sugar beet. Our results indicate that environmental effects, such as temperature, play a major role in MPR and underscore the importance of proper climate-controlled experiments for investigating MPR. In climate-controlled experiments, 83.3% of aphids on old leaves developed a black deposit, in contrast to only 16.8% of aphids on young leaves. This shows that not only plant age, but also leaf age plays a major role in the intensity of MPR. Further research will be needed to identify the underlying mechanism, before MPR can be used as a viable and sustainable solution to aphid pests in sugar beet.

Nucleotide substitutions in the resistance gene to root-knot nematodes in sugar beet

Here we are testing the specific primers NEM06FWD2/NEM06REV2 and nem06FWD1/ nem06REV1 for the R6m-1 resistance gene to root-knot nematodes Meloidogyne spp. in breeding samples of sugar beet. Sugar beet plants of domestic and foreign breeding lines were the object of the study. To identify the relationship between R6m-1 gene, which is localized on the chromosome 1 and controls the stable level of the kinase activity signal, with sugar beet resistance to phytopathogens, PCR-analysis of 10 sugar beet samples were carried out using 2 pairs of molecular genetic markers. DNA amplification revealed a fragments ~500 bp and ~100 bp in length and as a result of sequencing of nucleotide sequences of R6m-1 gene region with subsequent alignment by Geneious Prime program, 3 single nucleotide substitutions (A/G, G/C, and G/A) in the resistant MS11018 genotype and one nucleotide substitution (A/G) and 3 deletions in a foreign hybrid Humber were identified. It can be assumed that these SNPs can form resistance by amino acid substitutions in the polypeptide chain. Finally, possibility to differentiate homozygous and heterozygous genotypes for this allele was shown.

Regulatory Roles of Small Non-coding RNAs in Sugar Beet Resistance Against Beet curly top virus

Beet curly top virus (BCTV) mediated yield loss in sugar beets is a major problem worldwide. The circular single-stranded DNA virus is transmitted by the beet leafhopper. Genetic sources of BCTV resistance in sugar beet are limited and commercial cultivars rely on chemical treatments versus durable genetic resistance. Phenotypic selection and double haploid production have resulted in sugar beet germplasm (KDH13; 13 and KDH4-9; 4) that are highly resistant to BCTV. The molecular mechanism of resistance to the virus is unknown, especially the role of small non-coding RNAs (sncRNAs) during early plant–viral interaction. Using the resistant lines along with a susceptible line (KDH19-17; 19), we demonstrate the role of sugar beet microRNAs (miRNAs) in BCTV resistance during early infection stages when symptoms are not yet visible. The differentially expressed miRNAs altered the expression of their corresponding target genes such as pyruvate dehydrogenase (EL10Ac1g02046), carboxylesterase (EL10Ac1g01087), serine/threonine protein phosphatase (EL10Ac1g01374), and leucine-rich repeats (LRR) receptor-like (EL10Ac7g17778), that were highly expressed in the resistant lines versus susceptible lines. Pathway enrichment analysis of the miRNA target genes showed an enrichment of genes involved in glycolysis/gluconeogenesis, galactose metabolism, starch, and sucrose metabolism to name a few. Carbohydrate analysis revealed altered glucose, galactose, fructose, and sucrose concentrations in the infected leaves of resistant versus susceptible lines. We also demonstrate differential regulation of BCTV derived sncRNAs in the resistant versus susceptible lines that target sugar beet genes such as LRR (EL10Ac1g01206), 7-deoxyloganetic acid glucosyltransferase (EL10Ac5g12605), and transmembrane emp24 domain containing (EL10Ac6g14074) and altered their expression. In response to viral infection, we found that plant derived miRNAs targeted BCTV capsid protein/replication related genes and showed differences in expression among resistant and susceptible lines. The data presented here demonstrate the contribution of miRNA mediated regulation of metabolic pathways and cross-kingdom RNA interference (RNAi) in sugar beet BCTV resistance.

Development of an SNP Assay for Marker-Assisted Selection of Soil-Borne Rhizoctonia solani AG-2-2-IIIB Resistance in Sugar Beet.

Rhizoctonia solani, causing Rhizoctonia crown and root rot, is a major risk to sugar beet (Beta vulgaris L.) cultivation. The development of resistant varieties accelerated by marker-assisted selection is a priority of breeding programs. We report the identification of a single-nucleotide polymorphism (SNP) marker linked to Rhizoctonia resistance using restriction site-associated DNA (RAD) sequencing of two geographically discrete sets of plant materials with different degrees of resistance/susceptibility to enable a wider selection of superior genotypes. The variant calling pipeline utilized SAMtools for variant calling and the resulting raw SNPs from RAD sequencing (15,988 and 22,439 SNPs) were able to explain 13.40% and 25.45% of the phenotypic variation in the two sets of material from different sources of origin, respectively. An association analysis was carried out independently on both the datasets and mutually occurring significant SNPs were filtered depending on their contribution to the phenotype using principal component analysis (PCA) biplots. To provide a ready-to-use marker for the breeding community, a systematic molecular validation of significant SNPs distributed across the genome was undertaken to combine high-resolution melting, Sanger sequencing, and rhAmp SNP genotyping. We report that RsBv1 located on Chromosome 6 (9,000,093 bp) is significantly associated with Rhizoctonia resistance (p < 0.01) and able to explain 10% of the phenotypic disease variance. The related SNP assay is thus ready for marker-assisted selection in sugar beet breeding for Rhizoctonia resistance.

High stability of genotypic differences in puncture resistance of sugar beet (Beta vulgaris) roots under various growing conditions

AbstractMechanical properties of sugar beet roots are related to their damage susceptibility and storability. For selection in breeding, it is beneficial to identify stable traits that can be measured in young plants. Ten genotypes, nine sugar beet and one fodder beet, were grown in the field (harvest in August and November) and in the glasshouse for 14 weeks. The puncture resistance was measured using a texture analyser. Furthermore, the dry matter content was determined. Genotypic differences in puncture resistance of sugar beet roots could be determined in early growth stages and showed no relevant interaction to environment/growing conditions. The puncture resistance was closely related to the dry matter content of the root. Genotypic differences in puncture resistance are independent of growing conditions (field/glasshouse) and age of the plants (harvest date/growth stage). Puncture resistance is thus a potential trait for selection of genotypes with a high tissue strength. The dry matter content was identified as an easy‐to‐measure parameter for the preselection of genotypes.

Decision Strategies for Absorbance Readings from an Enzyme-Linked Immunosorbent Assay—A Case Study about Testing Genotypes of Sugar Beet (Beta vulgaris L.) for Resistance against Beet Necrotic Yellow Vein Virus (BNYVV)

The Beet necrotic yellow vein virus (BNYVV) causes rhizomania in sugar beet (Beta vulgaris L.), which is one of the most destructive diseases in sugar beet worldwide. In breeding projects towards resistance against BNYVV, the enzyme-linked immunosorbent assay (ELISA) is used to determine the virus concentration in plant roots and, thus, the resistance levels of genotypes. Here, we present a simulation study to generate 10,000 small samples from the estimated density functions of ELISA values from susceptible and resistant sugar beet genotypes. We apply receiver operating characteristic (ROC) analysis to these samples to optimise the cutoff values for sample sizes from two to eight and determine the false positive rates (FPR), true positive rates (TPR), and area under the curve (AUC). We present, furthermore, an alternative approach based upon Bayes factors to improve the decision procedure. The Bayesian approach has proven to be superior to the simple cutoff approach. The presented results could help evaluate or improve existing breeding programs and help design future selection procedures based upon ELISA. An R-script for the classification of sample data based upon Bayes factors is provided.