Resistant Sugar Beet Research Articles

Variations in Pathogenicity of Three Different Forms of Rhizoctonia Inoculum and Assessment of Cultivar Resistance of Sugar Beet

Rhizoctonia solani causes pre-emergence and post-emergence damping-off, as well as crown and root rot of sugar beet (Beta vulgaris L.), which significantly affects the yield returns in the USA and Europe. The pathogen overwinters as sclerotia or melanized mycelium. Traditionally, the resistance of cultivars to R. solani is evaluated by scoring disease reactions at the crowns and roots of older seedlings, thus resistance is not evaluated during seed germination. Moreover, earlier studies evaluated cultivars resistance to R. solani using colonized whole barley or wheat grains which, unlike sclerotia, are artificial inocula of the pathogen that require time, space and technical know-how to produce. Moreover, colonized grains are prone to contamination with other pathogens, consumed by rodents/birds while applied in the field, and are often uneconomic. Considering those limitations, a study was undertaken (1) to develop in vitro methods to generate large-scale sclerotia, (2) to compare pathogenic potentials of sclerotia, mycelia, and colonized barley grains for optimization of dampingoff assays, and (3) to evaluate Rhizoctonia resistance of selected commercial cultivars during the seed germination phase. Comparing six different culture media, we found that R. solani had the highest radial growth (8.9 ± 0.04, cm³) at 8-days and the maximum number of sclerotia produced (203 ± 4.6) at 28-days in CV8 medium. We demonstrated significant differences in pathogenicity of the three different forms of R. solani inocula and susceptibility of cultivars to preand post-emergence damping-off. The highest pre-emergence damping-off and root rot were observed with sclerotia, and the highest post-emergence dampingoff was recorded with both sclerotial and colonized barley inocula. In addition, varietal differences in susceptibility to pre- and post-emergence damping-off were noted. The highest pre-emergence damping-off was recorded on cv Crystal 101RR and lowest in Maribo MA 504. The highest post-emergence damping-off was recorded on BTS 8500 and the lowest in Crystal 467. The maximum mean root rot was observed in BTS 8500, BTS 8606, and Crystal 101R. Our studies demonstrated that sclerotia serve as efficient natural inocula, reemphasized that host-pathogen interactions differ at the early vs. late stages of sugar beet growth, and highlighted the need to reevaluate commercial sugar beet cultivars for resistance at the seed germination stage.

Studying of the acid chitinase SE2 gene in sugar beet genotypes

Aim of the work was specific primers (FusA1F/FusA1R) testing to study the SE2 gene controlling acid chitinase effect under stress conditions. Plants of domestic and foreign sugar beet were the material for the investigation. To confirm relationship between the SE2 gene (localized to the chromosome 3) controlling steady effect of acid chitinase and sugar beet resistance to root rot, 10 sugar beet samples were genotyped using the FusA1 molecular marker. DNA-fragments of 600 and 400 b.p.in length were revealed in each of the investigated genotypes except plants of wild beet ( Beta corolliflora Zoss .). As a result of molecular-genetic studies of the SE2 gene, eight single nucleotide polymorphism (3 T/C, 2 C/G, A/G, G/A, C/T) and 3 single nucleotide inserts (nucleotide A) were identified in plants of the breeding sample No. 9 (Sh.1). Plants of this genotype showed symptoms of fusariose infection under field conditions as well. It can be concluded that the SNPs data lead to overcoming of resistance (by changing an amino-acid unit in a polypeptide), and, as consequence, to decrease of plant adaptability.

Screening of sugar beet pre-breeding populations and breeding lines for resistance to Ditylenchus dipsaci penetration and reproduction

Ditylenchus dipsaci is an economically important plant-parasitic nematode affecting European sugar beets. To date, no sugar beet cultivars carrying resistance against D. dipsaci are available to farmers. To find potentially resistant sugar beet lines restricting reproduction and penetration of D. dipsaci, three consecutive in vivo bioassays were carried out. The first experiment determined the penetration rate of D. dipsaci in 79 breeding lines and 14 pre-breeding populations. Based on these results, D. dipsaci penetration and reproduction resistance of eight genotypes was intensively investigated. It could be demonstrated that none of the genotypes showed resistance towards D. dipsaci. However, a high variation of the penetration rate by D. dipsaci was observed among the genotypes. The breeding line ‘DIT_119’ effectively reduced D. dipsaci penetration (34.4 ± 8.8 nematodes/plant at 22 days post-planting) compared to the susceptible control (109.0 ± 16.9) while ensuring a yield comparable to non-inoculated plants. However, the breeding line ‘DIT_119’ did not reduce D. dipsaci reproduction. The paternal line of the cultivar BERETTA KWS, demonstrating a high tolerance to D. dipsaci crown rot symptoms, did not reduce penetration and reproduction. Thus, no correlation can be established between reduced penetration rates, reproduction, and tolerance to D. dipsaci. This study provides an essential basis for the development of resistant sugar beet cultivars to D. dipsaci. The variations observed among genotypes now need to be confirmed with larger-scale screenings.

Virulence and pathogenicity of four Ditylenchus dipsaci populations on sugar beet

The stem nematode, Ditylenchus dipsaci, is a severe pest in European sugar beet production. In France, Germany, and Switzerland, D. dipsaci damage in sugar beet varies among specific geographic areas. In this study, the reproduction potential of four geographically distinct D. dipsaci populations was determined using sterile carrot disc cultures. In addition, virulence and pathogenicity were investigated in-vivo using sugar beet. No difference was found in the reproduction potential on carrot discs, as well as penetration rate in sugar beet seedlings. The reproduction rate in sugar beet tissue was significantly affected by the D. dipsaci population used. The population from Seeland (CH) showed the highest number of nematodes per plant at 60 dpi (21,071.8 ± 5340.0), compared to the three other populations contained 3588.6 ± 3858.3, 5136.9 ± 4950.8, and 3579.7 ± 5174.2, respectively. Furthermore, the reproduction rate of D. dipsaci was negatively correlated with fresh biomass of sugar beets at 60 dpi. Based on these results, the D. dipsaci population “Seeland” is suitable for breeding programs to detect resistance in sugar beet. After selecting candidate genotypes/varieties, these should be further evaluated for their field resistance in their targeted growing regions.

The Beta vulgaris-derived resistance gene Rz2 confers broad-spectrum resistance against soilborne sugar beet-infecting viruses from different families by recognizing triple gene block protein 1.

Sugar beet cultivation is dependent on an effective control of beet necrotic yellow vein virus (BNYVV, family Benyviridae), which causes tremendous economic losses in sugar production. As the virus is transmitted by a soilborne protist, the use of resistant cultivars is currently the only way to control the disease. The Rz2 gene product belongs to a family of proteins conferring resistance towards diverse pathogens in plants. These proteins contain coiled‐coil and leucine‐rich repeat domains. After artificial inoculation of homozygous Rz2 resistant sugar beet lines, BNYVV and beet soilborne mosaic virus (BSBMV, family Benyviridae) were not detected. Analysis of the expression of Rz2 in naturally infected plants indicated constitutive expression in the root system. In a transient assay, coexpression of Rz2 and the individual BNYVV‐encoded proteins revealed that only the combination of Rz2 and triple gene block protein 1 (TGB1) resulted in a hypersensitive reaction (HR)‐like response. Furthermore, HR was also triggered by the TGB1 homologues from BSBMV as well as from the more distantly related beet soilborne virus (family Virgaviridae). This is the first report of an R gene providing resistance across different plant virus families.

Evaluation of Silicon and Proline Application on the Oxidative Machinery in Drought-Stressed Sugar Beet.

Drought stress deleteriously affects growth, development and productivity in plants. So, we examined the silicon effect (2 mmol) and proline (10 mmol) individually or the combination (Si + proline) in alleviating the harmful effect of drought on total phenolic compounds, reactive oxygen species (ROS), chlorophyll concentration and antioxidant enzymes as well as yield parameters of drought-stressed sugar beet plants during 2018/2019 and 2019/2020 seasons. Our findings indicated that the root diameter and length (cm), root and shoot fresh weights (g plant−1) as well as root and sugar yield significantly decreased in sugar beet plants under drought. Relative water content (RWC), nitrogen (N), phosphorus (P) and potassium (K) contents and chlorophyll (Chl) concentration considerably reduced in stressed sugar beet plants that compared with control in both seasons. Nonetheless, lipid peroxidation (MDA), electrolyte leakage (EL), hydrogen peroxide (H2O2) and superoxide (O2●−) considerably elevated as signals of drought. Drought-stressed sugar beet plants showed an increase in proline accumulation, total phenolic compounds and up-regulation of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activity to mitigate drought effects. Si and proline individually or the combination Si + proline considerably increased root and sugar yield, sucrose%, Chl concentration and RWC, MDA and EL were remarkably reduced. The treatments led to adjust proline and total phenolic compounds as well as CAT and SOD activity in stressed sugar beet plants. We concluded that application of Si + proline under drought stress led to improve the resistance of sugar beet by regulating of proline, antioxidant enzymes, phenolic compounds and improving RWC, Chl concentration and Nitrogen, Phosphorus and Potassium (NPK) contents as well as yield parameters.

Development of a new in vivo protocol through soil inoculation to investigate sugar beet resistance towards Ditylenchus dipsaci penetration

Summary The stem nematode, Ditylenchus dipsaci, causes severe damage in sugar beet. To date, nematode inoculation through the leaf axil has been used as the standard method to investigate D. dipsaci interaction with sugar beet under in vivo conditions. To get as close as possible to field conditions, we established a new screening mechanism to perform soil inoculation. The most suitable inoculation time point, inoculum level and positioning on sugar beet, as well as rearing process on carrots, were determined. At a 15:8°C day:night temperature regime, penetration rates of D. dipsaci were at maximum following soil inoculation at plant emergence. Up to 115 nematodes penetrated sugar beet seedlings 22 days post-planting with an inoculum level of 1000 nematodes into the soil at plant emergence. Ditylenchus dipsaci penetration rate was higher in plants with soil inoculation than with inoculation on to the leaf axil. High soil moisture increased nematode migration into seedlings when D. dipsaci inoculation was carried out in four holes 1 cm from the plant base. Rearing the nematodes for 35 days at 20°C on carrot discs resulted in an infective inoculum containing up to 50% eggs. We recommend a soil inoculation of 1000 freshly extracted nematodes per pot at plant emergence. The nematode suspension has to be previously reared for 35 days on carrot discs to obtain active D. dipsaci inoculum. This system will allow for the selection of suitable sugar beet genotypes that suppress nematode penetration, in support of breeding for resistance against D. dipsaci.

Determination of Reactions of Some Resistant Sugar Beet Varieties against Rhizoctonia spp.

Şeker pancarında fide ve kök çürüklüklerine sebep olan fungal hastalıklar, bu bitkide önemli verim ve kalite kayıplarına sebep olmaktadır. Ülkemizde Konya bölgesi, şeker pancarı üretim alanlarının yaklaşık %35.5'ini elinde tutan önemli bir şeker pancarı üretim alanıdır. Son yıllarda Konya bölgesinde kök çürümesi ve çökertenin meydana getirdiği verim kayıplarında önemli artışlar meydana gelmiştir. Çeşit reaksiyon çalışmaları, 2015-2017 büyüme dönemlerinde, Konya bölgesinde şeker pancarı taç ve kök çürüklüğüne neden olan Rhizoctonia spp.’lerden tespiti yapılan AG-2-2-IIIB, AG-4-HGI, AG-4-HGII, AG-4-HGIII, AG-A ve AG-K izolatlarına karşı denenmiştir. Bu çalışmada, 10 dirençli şeker pancarı çeşidi ve izolatların anastomosis grupları belirlenen ve tüm AG'leri temsil eden %50'nin üzerinde en yüksek virülansa sahip izolatlarından birer adet seçilerek, saksı denemelerinde inokulum tabaka tekniği kullanılarak denemeye tabi tutulmuştur. Dayanıklı şeker pancarı çeşitleri, Rhizoctonia kök çürüklüğü ile entegre bir yönetimin parçasıdır. Denemeler sonucunda çok çekirdekli Rhizoctonia izolatlarında inokulum seviyesinin ve patojenin yüksek olan virülensliğinin de etkisi sonucu, çeşitlerde bir dayanıklılık tespit edilmemiştir.Virülensliği daha düşük olan iki çekirdekli Rhizoctonia’lar da ise AG-A için Iguana, Valentina, Eldorado, Rodeo, Lider ve 5K614 çeşitleri, AG-K için ise Lider ve Valentina çeşitleri yüksek dayanıklı olarak belirlenmiştir.

Molecular insights into the compatible and incompatible interactions between sugar beet and the beet cyst nematode

BackgroundSugar beet (Beta vulgaris subsp. vulgaris) is an economically important crop that provides nearly one third of the global sugar production. The beet cyst nematode (BCN), Heterodera schachtii, causes major yield losses in sugar beet and other crops worldwide. The most effective and economic approach to control this nematode is growing tolerant or resistant cultivars. To identify candidate genes involved in susceptibility and resistance, the transcriptome of sugar beet and BCN in compatible and incompatible interactions at two time points was studied using mRNA-seq.ResultsIn the susceptible cultivar, most defense-related genes were induced at 4 dai while suppressed at 10 dai but in the resistant cultivar Nemakill, induction of genes involved in the plant defense response was observed at both time points. In the compatible interaction, alterations in phytohormone-related genes were detected. The effect of exogenous application of Methyl Jasmonate and ET-generator ethephon on susceptible plants was therefore investigated and the results revealed significant reduction in plant susceptibility. Genes putatively involved in the resistance of Nemakill were identified, such as genes involved in phenylpropanoid pathway and genes encoding CYSTM domain-containing proteins, F-box proteins, chitinase, galactono-1,4-lactone dehydrogenase and CASP-like protein. Also, the transcriptome of the BCN was analyzed in infected root samples and several novel potential nematode effector genes were found.ConclusionsOur data provides detailed insights into the plant and nematode transcriptional changes occurring during compatible and incompatible interactions between sugar beet and BCN. Many important genes playing potential roles in susceptibility or resistance of sugar beet against BCN, as well as some BCN effectors with a potential role as avr proteins were identified. In addition, our findings indicate the effective role of jasmonate and ethylene in enhancing sugar beet defense response against BCN. This research provides new molecular insights into the plant-nematode interactions that can be used to design novel management strategies against BCN.

Variability in Reaction to Root and Crown Rot Caused by Rhizoctonia Solani Among Table Beet Cultivars, Breeding Lines, and Plant Introductions in Controlled Environment Conditions

Table beet (Beta vulgaris ssp. vulgaris) is adversely affected by the soilborne fungus, Rhizoctonia solani, which greatly decreases root quality. There are no reports of breeding efforts designed to improve resistance to this fungus in table beet. A collection of table beet PIs, cultivars, and publicly available inbreds were characterized for their response to inoculation with R. solani in three replicated greenhouse experiments conducted between 2017 and 2019. An isolate of AG 2-2 IIIB was used to inoculate 8-week old plants, and both susceptible and resistant sugar beet genotypes were used for comparison. Plants were evaluated for internal and external disease characteristics 3 and 5 weeks postinoculation. Compared with uninoculated controls, PI accessions ranged from 2% to 44% infection, whereas cultivars and inbred lines ranged from 16% to 53% and 22% to 52%, respectively. No commercial cultivar outperformed the resistant sugar beet genotype; however, several PI accessions exhibited lower mean diseased tissue percentages than the resistant sugar beet. This suggests that resistance to R. solani may exist in table beet germplasm. PI accessions exhibited greater resistance on average than did cultivars. Inbred lines exhibited the least amount of variation. Ordinal regression allowed for prediction of infection response, which may be helpful in future selection efforts. ‘Badger Flame’, Ames 22164, PI 502294, PI 169015, ‘Long Season’, ‘Red Cloud’, and ‘Albina Vereduna’ were some of the most resistant accessions in our screens. The findings from this study can be used to inform decisions for breeding for host plant resistance in table beet.

Field evaluation for rhizomania resistance of transgenic sugar beet events based on gene silencing

Rhizomania is one of the most damaging and widespread diseases in the major sugar beet (Beta vulgaris L. subsp. vulgaris) growing regions worldwide. The causal agent, Beet necrotic yellow vein virus, is transmitted by a plasmodiophorid vector, Polymyxa betae Keskin. In this study, the inhibition of BNYVV multiplication was evaluated, under field conditions, in six sugar beet transgenic events generated based on gene silencing of the major coat protein gene (CP21). Phenotypic criteria, including scoring for disease symptoms and an immunoassay for viral accumulation, indicated that the transgenic events were less susceptible to rhizomania and had lower virus titre rates than non-transgenic plants of the susceptible cultivar ‘9597’. Disease severity and virus titres were comparable to the resistant cultivar ‘Dorothea’, which carries the Rz1-resistance gene and was bred through traditional means. This study provides a proof of concept for the effectiveness of the gene-silencing mechanism for introducing rhizomania resistance in sugar beet at the field level.

Comparison of Promoter Sequences of Flowering Control Genes, FT1 and Three Versions of VIN3, in Susceptible and Resistant Sugar Beet Genotypes to Bolting

Comparison of Promoter Sequences of Flowering Control Genes, FT1 and Three Versions of VIN3, in Susceptible and Resistant Sugar Beet Genotypes to Bolting

Application of a Reverse Genetic System for Beet Necrotic Yellow Vein Virus to Study Rz1 Resistance Response in Sugar Beet.

Beet necrotic yellow vein virus (BNYVV) is causal agent of rhizomania disease, which is the most devastating viral disease in sugar beet production leading to a dramatic reduction in beet yield and sugar content. The virus is transmitted by the ubiquitous distributed soil-borne plasmodiophoromycete Polymyxa betae that infects the root tissue of young sugar beet plants. Rz1 is the major resistance gene widely used in most sugar beet varieties to control BNYVV. The strong selection pressure on the virus population promoted the development of strains that can overcome Rz1 resistance. Resistance-breaking has been associated with mutations in the RNA3-encoded pathogenicity factor P25 at amino acid positions 67–70 (tetrad) as well as with the presence of an additional RNA component (RNA5). However, respective studies investigating the resistance-breaking mechanism by a reverse genetic system are rather scarce. Therefore, we studied Rz1 resistance-breaking in sugar beet using a recently developed infectious clone of BNYVV A-type. A vector free infection system for the inoculation of young sugar beet seedlings was established. This assay allowed a clear separation between a susceptible and a Rz1 resistant genotype by measuring the virus content in lateral roots at 52 dpi. However, mechanical inoculation of sugar beet leaves led to the occurrence of genotype independent local lesions, suggesting that Rz1 mediates a root specific resistance toward BNYVV that is not active in leaves. Mutation analysis demonstrated that different motifs within the P25 tetrad enable increased virus replication in roots of the resistant genotype. The resistance-breaking ability was further confirmed by the visualization of BNYVV in lateral roots and leaves using a fluorescent-labeled complementary DNA clone of RNA2. Apart from that, reassortment experiments evidenced that RNA5 enables Rz1 resistance-breaking independent of the P25 tetrad motif. Finally, we could identify a new resistance-breaking mutation, which was selected by high-throughput sequencing of a clonal virus population after one host passage in a resistant genotype. Our results demonstrate the feasibility of the reverse genetic system for resistance-breaking analysis and illustrates the genome plasticity of BNYVV allowing the virus to adapt rapidly to sugar beet resistance traits.

Genetic and biochemical variations among sugar beet cultivars resistant to Cercospora leaf spot

The goal of the study was to construct a reliable molecular and biochemical tool for the selection of resistant sugar beet cultivars to minimize the loss in productivity caused by Cercospora leaf spot disease. Three PCR marker systems: inter simple sequence repeats (ISSR), and sequence-related amplified polymorphisms (SRAP), and random amplified polymorphic DNA (RAPD) were used to assess the genetic diversity among eight cultivars of sugar beet and to detect the molecular markers linked to resistance to Cercospora beticola. Molecular tools successfully differentiated resistant from susceptible cultivars and detected 10 specific DNA markers in the resistant cultivars. Euclidean distance analysis based on physiological traits grouped the eight cultivars into two main clusters. Protein and isozyme patterns of peroxidase, polyphenol oxidase, chitinase, super oxide dismutase, glutamate oxalo-acetate transaminase and esterase were validated as quick means to select resistant cultivars of sugar beet. Specific protein and isozyme bands were lacking or were induced in cultivars based on their resistance phenotype. Our Results show that molecular markers and isozyme patterns are powerful tools for distinguishing resistant sugar beet cultivars resistant against Cercospora leaf spot.

Rhysomania is a dangerous object the evaluating phytosanitary state of sugar beet seeds in Ukraine

The results of many years of research of beet necrotic yellow vein virus, which causes rhizomania, and is a quarantine object, are analyzed. The molecular-biological properties, features of its genome and dependence of pathogenesis on genetic variations of the virus are described. Diversity of virus pathotypes and disease circulation in the world and in Ukraine and ways of its spread are shown. Natural genes of sugar beet resistance to rhizomania were also analyzed.

In Vitro Cell Selection of Sugar Beet for Resistance to Culture Filtrate of the Fungus Fusarium oxysporum

A multistep in vitro cell selection was carried out on a well-proliferating callus tissue of sugar beet capable of morphogenesis. A 20-day culture filtrate of the fungus Fusarium oxysporum was used as a selective agent. The general features of the behavior of sugar beet callus cells cultivated under stress conditions on increasing concentrations of the culture filtrate, 5, 10, 15, and 20%, have been established. It was found that a low concentration of CF (culture filtrate) of the pathogen (5%) significantly stimulated the process of callusogenesis, while high concentrations (10–20%) had an inhibitory effect. As a result of cell and tissue selection, calluses that retained the ability for normal growth in the presence of sublethal concentrations of the selective agent were selected. By the method of multistep selection, 82 callus lines characterized by resistance to the toxic effects of CF were selected. From selected callus lines, 47 regenerated plants adapted to the soil were obtained. Only 24 plants passed the test for resistance to the fungus Fusarium oxysporum under in vivo conditions.

Modeling growth, development and yield of Sugarbeet using DSSAT

Sugarbeet (Beta vulgaris) is considered as one of the most viable feedstock alternatives to maize for biofuel production since herbicide resistant sugarbeet was deregulated by the United States Department of Agriculture in 2012. So far, only a few sugarbeet simulation models have been developed and these models are limited to application for local regions. The Decision Support System for Agrotechnology Transfer (DSSAT) provides a common framework for a cropping system study and currently has crop modules for >40 crops. However, DSSAT currently does not include a model for sugarbeet. In this study, the Crop and Environment REsource Synthesis (CERES) Beet model was modified and incorporated into the current version of the Cropping System Model (CSM) to simulate growth, development, and yield of sugarbeet. The PEST optimizer was used for parameter estimation, transferability evaluation, and predictive uncertainty analysis. The sugarbeet model was evaluated with two sets of experimental data collected in two different regions and under different environmental conditions; one in Romania (Southeastern Europe) during 1997–1998 and the other in North Dakota, US (North America) during 2014–2016. After model calibration for specific cultivars, the CSM-CERES-Beet model performed well for the simulation of leaf area index, leaf number, leaf or top weight, and root weight for both datasets (NSE = 0.144–0.976, rRMSE = 0.127–1.014). Uncertainty analysis revealed that the calibrated CSM-CERES-Beet consistently over-predicted leaf number with false confidence, although measured leaf number also showed a significant variability. The model was successfully applied for predicting yield for six different sugarbeet cultivars grown in North Dakota during the 2014 to 2016 growing seasons. CSM-CERES-Beet could be applied for predicting sugarbeet yield for different soil and climatic conditions and various management scenarios for the Red River Valley in the US and other regions with environmental conditions favorable for sugarbeet production.

Production of a Beet chlorosis virus full-length cDNA clone by means of Gibson assembly and analysis of biological properties.

Beet chlorosis virus (genus Polerovirus, family Luteoviridae), which is persistently transmitted by the aphid Myzus persicae, is part of virus yellows in sugar beet and causes interveinal yellowing as well as significant yield loss in Beta vulgaris. To allow reverse genetic studies and replace vector transmission, an infectious cDNA clone under cauliflower mosaic virus 35S control in a binary vector for agrobacterium-mediated infection was constructed using Gibson assembly. Following agroinoculation, the BChV full-length clone was able to induce a systemic infection of the cultivated B. vulgaris. The engineered virus was successfully aphid-transmitted when acquired from infected B. vulgaris and displayed the same host plant spectrum as wild-type virus. This new polerovirus infectious clone is a valuable tool to identify the viral determinants involved in host range and study BChV protein function, and can be used to screen sugar beet for BChV resistance.

The role of Bacillus megaterium and other bio-agents in controlling root-knot nematodes infecting sugar beet under field conditions

A micro-plot field experiment was conducted in loamy soil naturally infested with Meloidogyne spp. to assess the potential of bio-agents namely bio-arc (Bacillus megaterium), nemastrol (a mixture of active ingredients), humisun (humic acid), and dried sweet basil callus to suppress nematodes’ population and induce resistance in sugar beet. Results indicated that integration of two or more components of such bio-agents gave better results in sugar beet growth parameters than did single ones. Hence, nemastrol and humisun in concomitant with bio-arc, sweet basil callus, and oxamyl (half recommended dose) induced significant (P ≤ 0.05) and maximum improvement in total plant fresh weight and shoot dry weight. Similar trend was also noticed in root diameter and number of leaves of sugar beet infected with Meloidogyne spp. Additionally, the greatest suppression in nematodes’ population (95.7%), root galling (83.0%), and number of egg masses (100%) was also sustained at the soil amended with nemastrol + humisun + bio-arc + sweet basil callus + oxamyl since incorporation of such organic materials into soil might enhance B. megaterium activity that initiates antibiotics towards nematode population. However, single application of dried sweet basil callus showed better performance than did the dried leaves in terms of female fecundity and total nematodes’ population. Thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) indicated the presence of higher content of triterpenoides that belong to three groups, i.e., lupane, ursane, and oleanane, in dried sweet basil callus compared to native dried leaves powder. Concomitant treatment with nemastrol + humisun + bio-arc + sweet basil callus + oxamyl exhihited significantly increased in sucrose (17.1%), total sugar solids (21.8%), and purity (79.0%). The activities of both peroxidase (PO) and polyphenol oxidase (PPO) showed detectable fluctuations at the end of the experiment compared to untreated plants.

Long Term Management of Rhizomania Disease-Insight Into the Changes of the Beet necrotic yellow vein virus RNA-3 Observed Under Resistant and Non-resistant Sugar Beet Fields.

Rhizomania disease, caused by the Beet necrotic yellow vein virus (BNYVV), is considered as one of the major constraints for sugar beet production, worldwide. As a result of the introgression of major resistance genes (Holly, Rz2) in commercially available sugar beet varieties, the virus has endured strong selection pressure since the 90s'. Understanding the virus response and diversity to sugar beet resistance is a key factor for a sustainable management of only few resistance genes. Here we report rhizomania surveys conducted in a rhizomania hot spot, the Pithiviers area (France) during a 4-year period and complementary to the study of Schirmer et al. (2005). The study aimed at evaluating the intra- and inter-field BNYVV diversity in response to different sources of resistance and over the growing season. To follow rhizomania development over the sugar beet growing season, extensive field samplings combined with field assays were performed in this study. The evolution of the BNYVV diversity was assessed at intra- and inter-field levels, with sugar beet cultivars containing different resistance genes (Rz1, Rz1 + Heterodera schachtii resistance and Rz1Rz2). Intra-field diversity was analyzed at the beginning and the end of the growing season of each field. From more than one thousand field samples, the simultaneous presence of the different A, B and P types of BNYVV was confirmed, with 21 variants identified at positions 67–70 of the p25 tetrad. The first variant, AYHR, was found most commonly followed by SYHG. Numerous mixed infections (9.93% of the samples), mostly of B-type with P-type, have also been evidenced. Different tetrads associated with the A- or B-type were also found with a fifth RNA-genome component known to allow more aggressiveness to BNYVV on sugar beet roots. Cultivars with Rz1+Rz2 resistant genes showed few root symptoms even if the BNYVV titre was quite high according to the BNYVV type present. The virus infectious potential in the soil at the end of the growing season with such cultivars was also lower despite a wider diversity at the BNYVV RNA3 sequence level. Rz1+Rz2 cultivars also exhibited a lower presence of Beet soil-borne virus (BSBV), a P. betae-transmitted Pomovirus. Cultivars with Rz1 and nematode (N) resistance genes cultivated in field infected with nematodes showed lower BNYVV titre than those with Rz1 or Rz1+Rz2 cultivars. Overall, the population structure of BNYVV in France is shown to be different from that previously evidenced in different world areas. Implications for long-term management of the resistance to rhizomania is discussed.