Cultivated Sugar Beet Research Articles

Potential of publicly available Beta vulgaris germplasm for sustainable sugarbeet improvement indicated by combining analysis of genetic diversity and historic resistance evaluation

AbstractSugar beet (Beta vulgaris L. ssp. vulgaris Doell.) was originally selected from white fodder beet in the 1780s and was then specifically bred for sucrose production. The relatively recent inception of the crop has led to a narrow genetic base that has bottlenecked sustainable improvement. To evaluate the potential of publicly available germplasm for sugar beet improvement, genetic diversity analysis with SNPs (single‐nucleotide polymorphisms) covering the whole genome of sugar beet was conducted using 1936 publicly available germplasm lines in the United States. The results confirmed the narrow genetic base of sugar beet and identified germplasm accessions with inherently greater diversity that were mostly accessions of wild sea beet (B. vulgaris ssp. maritima (L.) Arcang.), the progenitor species of white fodder beet. These wild accessions displayed a distinct genetic relationship from cultivated sugar beet lines, indicating their high potential for broadening sugar beet genetic diversity. Analysis of historic resistance evaluations also suggested a higher potential of B. vulgaris ssp. maritima accessions to be used as sources of resistance to major diseases and insects of sugar beet. A genome‐wide association study using historic evaluation data identified genomic regions significantly associated with disease and insect resistance. However, genomic regions associated with resistance to nematode, insects, or diseases vectored by insects were of low significance, indicating the need for additional research to allow for a more precise evaluation of germplasm responses to insects. The research confirms that accessions of B. vulgaris ssp. maritima are potentially valuable for improving biotic stress resistance and broadening the genetic base of sugar beet.

Bacterial endophytes as indicators of susceptibility to Cercospora Leaf Spot (CLS) disease in Beta vulgaris L.

The fungus Cercospora beticola causes Cercospora Leaf Spot (CLS) of sugar beet (Beta vulgaris L.). Despite the global importance of this disease, durable resistance to CLS has still not been obtained. Therefore, the breeding of tolerant hybrids is a major goal for the sugar beet sector. Although recent studies have suggested that the leaf microbiome composition can offer useful predictors to assist plant breeders, this is an untapped resource in sugar beet breeding efforts. Using Ion GeneStudio S5 technology to sequence amplicons from seven 16S rRNA hypervariable regions, the most recurring endophytes discriminating CLS-symptomatic and symptomless sea beets (Beta vulgaris L.ssp. maritima) were identified. This allowed the design of taxon-specific primer pairs to quantify the abundance of the most representative endophytic species in large naturally occurring populations of sea beet and subsequently in sugar beet breeding genotypes under either CLS symptomless or infection stages using qPCR. Among the screened bacterial genera, Methylobacterium and Mucilaginibacter were found to be significantly (p < 0.05) more abundant in symptomatic sea beets with respect to symptomless. In cultivated sugar beet material under CLS infection, the comparison between resistant and susceptible genotypes confirmed that the susceptible genotypes hosted higher contents of the above-mentioned bacterial genera. These results suggest that the abundance of these species can be correlated with increased sensitivity to CLS disease. This evidence can further prompt novel protocols to assist plant breeding of sugar beet in the pursuit of improved pathogen resistance.

Assessment of interspecific hybridization between wild beet Beta vulgaris L. subsp. maritima and cultivated sugar beet under Moroccan conditions

Obtaining a viable and fertile beet hybrid resulting from wild and cultivated sugar beet crosses under Moroccan conditions is challenging. To deal with hybridization, barriers in sugar beet, such as concordance of flowering period between biannual and annual subspecies, flowering aptitude according to vernalization requirement, genotype incompatibility and hybrid sterility, should be overcome. In our study, interspecific hybrids were obtained from crosses between 17 cultivated sugar beet Beta vulgaris subsp. vulgaris and 17 Beta vulgaris subsp. maritima, collected in different regions of Morocco. Twenty-two agro-morphological traits were used for the evaluation of 208 hybrid plants, under greenhouse conditions. CH and WH hybrids were collected on cultivated and wild parents separately. Most of the hybrids behaved as annual plants, of which 83.17% were able to flower and produce seeds without any vernalization requirements. All WH hybrids and 57.06% of CH hybrids were morphologically similar to their wild parent. However, 24% of CH hybrids were phenotypically similar to their cultivated parent. The remaining CH hybrid plants were behaving as intermediate genotypes between both wild and cultivated parents. Our results showed the success of interspecific beet crosses and emphasized the high variability among hybrid genotypes. This is of great importance for sugar beet improvement and breeding programs and interspecific crosses patterns understanding.

Fodder beet is a reservoir of drought tolerance alleles for sugar beet breeding

Drought leads to serious yield losses and followed by increasing food prices. Thereby, drought tolerance is one of most important, pivotal issues for plant breeding and is determined by the very complex genetic architecture, which involves a lot of genes engaged in many cell processes. Within genomes of currently cultivated sugar beet forms, the number of favourable allelic variants is limited. However, there is a potential to identify genes related to drought tolerance deposited in genomes of wild or fodder relatives. Therefore, the goal of our study, was to identify the source of allelic variants involved in drought tolerance using a large spectrum of sugar or fodder beets and their wild relatives for analyses. Based on the drought tolerance index, calculated for morphophysiological traits, it was demonstrated that some of selected fodder beets showed the highest level of drought tolerance. The most drought tolerant fodder beet genotype did not show differences in the level of expression of genes engaged in osmoprotection and the antioxidative system, between control and drought condition, compared to sugar and wild beets. The genetic distance between selected beet forms was broad and ranged from 18 to 87%, however the most drought tolerant sugar, fodder and wild beets showed high genetic similarity and formed the common clade. Based on obtained results we propose that an adequate broad source of genes related to drought tolerance occurs in fodder beets, the crossing with which is easier, less time-consuming and more cost-effective than with wild forms of beets.

Irrigation and Fertilization Management of Successive Cultivated Sugar Beet and Cotton under Salt-Affected Soil Conditions

Two field trials were carried out at the experimental farm, Sakha agricultural research station, Kafr El-Sheikh, Egypt during two successive growing seasons. The aim of this study was to investigate the impact of applied mineral and organic fertilizers under water stress on the physical, chemical and fertility of the soil properties as well as the productivity of sugar beet and cotton. The main investigated factors included irrigation treatments at 80,100 and120%, respectively evaporation from standard class A evaporation pan. The fertilization treatments included applying N-fertilizer at three rates of 100, 80 and 60 % N from recommended dose in combination with compost. Two levels of potassium humate (i.e., 12and 24kg ha-1) were also applied. The results showed that studied soil chemical, physical properties and its fertility parameters were significantly influenced by the individual treatments and recorded highest values due to the interaction among studied treatments after sugar beet and cotton cultivation. The yield of sugar beet and cotton crops were significantly increased and recorded the highest values at the interaction of highest levels of treatments. Therefore, the irrigation and fertilization management could be considered a proper approach to sustain the soil and water resources in particular under arid and semi-arid regions. Further studies are needed for more and novel approaches in handling the salt-affected soils

Haplotype Variation of Flowering Time Genes of Sugar Beet and Its Wild Relatives and the Impact on Life Cycle Regimes.

The species Beta vulgaris encompasses wild and cultivated members with a broad range of phenological development. The annual life cycle is commonly found in sea beets (ssp. maritima) from Mediterranean environments which germinate, bolt, and flower within one season under long day conditions. Biennials such as the cultivated sugar beet (B. vulgaris ssp. vulgaris) as well as sea beets from northern latitudes require prolonged exposure to cold temperature over winter to acquire floral competence. Sugar beet is mainly cultivated for sugar production in Europe and is likely to have originated from sea beet. Flowering time strongly affects seed yield and yield potential and is thus a trait of high agronomic relevance. Besides environmental cues, there are complex genetic networks known to impact life cycle switch in flowering plants. In sugar beet, BTC1, BvBBX19, BvFT1, and BvFT2 are major flowering time regulators. In this study, we phenotyped plants from a diversity Beta panel encompassing cultivated and wild species from different geographical origin. Plants were grown under different day length regimes with and without vernalization. Haplotype analysis of BTC1, BvBBX19, BvFT1, and BvFT2 was performed to identify natural diversity of these genes and their impact on flowering. We found that accessions from northern latitudes flowered significantly later than those from southern latitudes. Some plants did not flower at all, indicating a strong impact of latitude of origin on life cycle. Haplotype analysis revealed a high conservation of the CCT-, REC-, BBX-, and PEBP-domains with regard to SNP occurrence. We identified sequence variation which may impact life cycle adaptation in beet. Our data endorse the importance of BTC1 in the domestication process of cultivated beets and contribute to the understanding of distribution and adaption of Beta species to different life cycle regimes in response to different environments. Moreover, our data provide a resource for haplotypes identified for the major floral regulators in beet.

Sugarbeet Germplasm Lines Selected from Crosses between Wild Beta vulgaris subsp. maritima from France, Belgium, and Denmark and Cultivated Sugar Beet

Sugarbeet Germplasm Lines Selected from Crosses between Wild Beta vulgaris subsp. maritima from France, Belgium, and Denmark and Cultivated Sugar Beet

Root rot symptoms in sugar beet lines caused by Fusarium oxysporum f. sp. betae

The soil-borne fungus Fusarium oxysporum can cause both Fusarium yellows and Fusarium root rot diseases with severe yield losses in cultivated sugar beet. These two diseases cause similar foliar symptoms but different root response and have been proposed to be caused by two distinct F. oxysporum formae speciales. Fusarium yellows, caused by F. oxysporum f. sp. betae, presents vascular discoloration, whereas Fusarium root rot, due to F. oxysporum f. sp. radicis-betae, appears as black rot visible on the root surface. The aim of this work was to study the host-pathogen interaction between sugar beet lines and isolates originally characterized as Fusarium oxysporum f. sp. betae. Eight susceptible sugar beet lines, selected by the USDA-ARS (US) and UNIPD (University of Padova, Italy) breeding programs, were inoculated with three different isolates of F. oxysporum f. sp. betae, the causal agent of Fusarium yellows, representing different genetic groups. All inoculated lines developed symptoms, but severity, expressed as area under the disease progress curve (AUDPC), differed significantly (P < 0.05) among lines. Two lines from UNIPD, 6 and 9, were the most susceptible to the disease, whereas the other lines showed similar levels. The three isolates of F. oxysporum f. sp. betae differed significantly (P < 0.05) in disease severity. Five weeks after inoculation the plants were harvested and roots examined. Surprisingly, severe root rot was observed in the susceptible UNIPD lines when inoculated with all three isolates, while this symptom was never observed in the USDA germplasm. The development of this disease symptom obviously depends on the plant genotype.

Characterization of the BETA1 gene, which might play a role inBeta vulgaris subsp. maritima salt tolerance

Salinity stress has a negative impact on plant growth, which affects homeostasis and productivity. The uptake of nonessential salt ions changes the osmotic balance of the cell and causes dehydration. Higher plants develop salt tolerance mechanisms to avoid dehydration. Sea beet (Beta vulgaris subsp. maritima) is a halophytic ancestor of cultivated sugar beet that displays salt stress tolerance. In this study, we screened a B. vulgaris subsp. maritima cDNA library in Saccharomyces cerevisiae strain Ab11c (ena1Δ, nha1/4Δ, nhx1Δ), which is deficient in sodium transport, to find sodium-detoxifying genes. We identified a cDNA construct, named BETA1, providing salt tolerance to yeast cells. This gene had no previously described function. Intracellular sodium measurements demonstrated no significant differences between yeast cells expressing BETA1 or a sham vector, suggesting that sodium was not effluxed in BETA1-expressing cells. Transcriptionally, BETA1 mRNA levels were induced immediately in leaves and later in the root system in response to the salt stress. Our results suggest that the BETA1 gene is part of the salt tolerance network in B. vulgaris subsp. maritima.

Characterization of wild Beta populations in and adjacent to sugar beet fields in the Imperial Valley, California

Populations of wild Beta L. species exist as weeds in commercial sugar beet (Beta vulgaris L. subspecies vulgaris) fields in the Imperial Valley, California. Significant losses to sugar yield and quality result if these wild plants are not removed. In cases of extreme infestation, fields are abandoned without harvest. No selective chemicals are available to differentiate conventional sugar beet from wild relatives and hand removal is labor intensive and expensive. Planting sugar beet varieties with tolerance to glyphosate is a potential solution for infested fields, but risk of gene flow to adjacent wild relatives must be determined. Previous research identified these populations as either Beta vulgaris L. subspecies maritima (L.) Arcang. or Beta macrocarpa Guss. This distinction is critical because B. v. subsp. maritima will readily cross hybridize with cultivated sugar beet while B. macrocarpa rarely will. In April 2011, we collected herbarium samples, mature seed, and leaf tissue from wild Beta populations in 25 infested sugar beet fields throughout the Imperial Valley. Bolting cultivated beets were identified at two locations. Taxonomy of whole plant herbarium samples was unclear due to wild beet stem elongation when under competition with sugar beet plants for canopy light. Morphology of plants from collected seed grown in non-competitive conditions assigned taxonomy of these populations to B. macrocarpa. We used molecular tools to determine the genetic structure of wild Beta populations throughout the Imperial Valley. Extracted DNA was genotyped with 22 simple sequence repeat molecular markers and evaluated for population structure. The bolting beet samples were clearly separated from the majority of B. macrocarpa samples, except for two. The remaining wild populations were further divided into two subgroups suggesting exchange of genetic information or a common ancestor.

Registration of FC305 Multigerm Sugarbeet Germplasm Selected from a Cross to a Crop Wild Relative

FC305 (Reg. No. GP-286, PI 671963) sugarbeet (Beta vulgaris L.) germplasm was developed and released by the USDA–ARS, at Fort Collins, CO, Salinas, CA, and East Lansing, MI, in cooperation with the Beet Sugar Development Foundation, Denver, CO. This germplasm is a diploid, sugarbeet population in normal cytoplasm, segregating for self-sterility (Sf:SsSs), multigermity (M:mm), and hypocotyl color (R:rr). FC305 has moderate resistance to cercospora leaf spot (CLS) (caused by Cercospora beticola Sacc.), aphanomyces root rot (caused by Aphanomyces cochlioides Drechsl.), and beet curly top (Beet curly top virus), as well as resistance to Fusarium yellows [caused by Fusarium oxysporum Schlecht. f. sp. betae (Stewart) Snyd. & Hans.]. This germplasm is segregating for resistance to rhizomania (Beet necrotic yellow vein virus) and contains both Rz1 and Rz2 genes for resistance. There was no resistance to root-rotting strains (AG-2–2) of Rhizoctonia solani Kühn. FC305 could provide an alternate source of resistance to CLS and Fusarium yellows in a diverse genetic background to enrich the cultivated sugarbeet germplasm base. FC305 provides a source from which to select disease-resistant, multigerm pollinator parents. Because monogerm and O-type is within its parentage, it should be possible to select monogerm, O-type, CMS-maintainer lines from FC305 as well.

Impact of soil salinity on fungal vector of rhizomania virus infecting beta vulgaris

Polymyxa betae Keskin is the only natural transmitting vector of the Beet necrotic yellow vein virus (BNYVV) among the cultivated sugar beet. This work aims to study the impact of salt stress on fungus-virus-host relationships. The fungal infected fine roots of sugar beet plant naturally infected with BNYVV were collected and treated with different salt concentrations (0, 2000, 4000, 6000 and 8000 ppm) of NaCl for one day prior to mixing it with a sterile soil. After virus symptoms appeared on leaves, disease severity has been determined, leave and roots tissues were collected for BNYVV detection. It was found that severe symptoms on sugar beet inoculated with treated roots by low salt concentrations (2000 and 4000 ppm) while at high salt concentrations, 8000 ppm less injury approximately as control treated with H2O. On the other hand it was found the cystosorial colonization was increased in low salt concentrations (2000 and 4000 ppm) while decrease in high salt concentrations (6000 and 8000 ppm) especially in 8000 ppm. The same trend results were observed in virus concentration in roots where as the BNYVV concentration was increased in low salt concentrations (2000 and 4000 ppm) while decrease in high salt concentrations (6000 and 8000 ppm). So the relation between capacity of fungal vector to infect the plant by virus and salinity concentration are antagonistic. Soil salinity extremes most often lead to decrease infection of BNYVV via effect on fungal zoospore. Key words: Polymyxa betae, sugar beet, rhizomania, beet necrotic yellow vein virus (BNYVV), salinity.

The Evolutionary History of Beet necrotic yellow vein virus Deduced from Genetic Variation, Geographical Origin and Spread, and the Breaking of Host Resistance

Beet necrotic yellow vein virus (BNYVV) is an economically important pathogen of sugar beet and has been found worldwide, probably as the result of recent worldwide spread. The BNYVV genome consists of four or five RNA components. Here, we report analysis of sequence variation in the RNA3-p25, RNA4-p31, RNA2-CP, and RNA5-p26 genes of 73 worldwide isolates. The RNA3-p25 gene encodes virulence and avirulence factors. These four sets of gene sequences each fell into two to four groups, of which the three groups of p25 formed eight subgroups with different geographical distributions. Each of these subgroup isolates (strains) could have arisen from four original BNYVV population and their mixed infections. The genetic diversity for BNYVV was relatively small. Selection pressure varied greatly depending on the BNYVV gene and geographical location. Isolates of the Italy strain, in which p25 was subject to the strongest positive selection, were able to overcome the Rz1-host resistance gene to differing degrees, whereas other geographically limited strains could not. Resistance-breaking variants were generated by p25 amino acid changes at positions 67 and 68. Our studies suggest that BNYVV originally evolved in East Asia and has recently become a pathogen of cultivated sugar beet followed by the emergence of new resistance-breaking variants.

Susceptibility of intercrops to infection with Rhizoctonia solani AG 2‐2 IIIB and influence on subsequently cultivated sugar beet

The susceptibility of intercrop species (Raphanus sativus, Brassica juncea, B. rapa, Sinapis alba and Phacelia tanacetifolia) to the sugar beet pathogen Rhizoctonia solani was investigated in vitro, in the greenhouse and in the field with artificial inoculation. Disease severity in subsequently cultivated sugar beet was monitored in the field. Differences in susceptibility between species were found to be consistent in all experimental systems. All intercrop species were susceptible to R. solani. Brassica rapa and R. sativus were less susceptible than P. tanacetifolia. Compared to fallow, the cultivation of B. rapa and R. sativus reduced disease severity in subsequently grown sugar beet (median ratings of up to 3·0 and 3·5, respectively, depending on environmental conditions). This resulted in higher white sugar yield compared to fallow (up to 210% and 157% for B. rapa and R. sativus, respectively). This study demonstrates that in vitro and greenhouse resistance tests are suitable systems to predict the effects of intercrop species susceptibility in the field on disease severity and white sugar yield in subsequently grown sugar beet. Intercrop breeding programmes might profit from fast and efficient screening tests to provide Rhizoctonia‐resistant intercrops as an additional control measure against R. solani in sugar beet.

Registration of Seven Sugarbeet Germplasms Selected from Crosses between Cultivated Sugarbeet and Wild Beta Species

Seven sugarbeet (Beta vulgaris L.) germplasm lines, F1017 (GP‐265, PI 656591), F1018 (GP‐266, PI 658401), F1019 (GP‐267, PI 656592), F1020 (GP‐268, PI 656593), F1021 (GP‐269, PI 658402), F1022 (GP‐270, PI 656594), and F1023 (GP‐271, PI 656595), were released 23 Feb. 2009 by the USDA‐ARS and the North Dakota Agricultural Experiment Station. These lines were developed to introduce genetic diversity into the narrow base of sugarbeet. The original populations were produced by crossing male‐sterile plants of a cultivated line with wild relatives of sugarbeet. The pollinators for F1017, F1018, F1019, and F1020 were B. v. subsp. maritima accessions originally collected in Denmark, Belgium, Ireland, and the Middle East, respectively. The pollinators for F1021, F1022, and F1023 were based on species (F1021, B. atriplicifolia Rouy; F1022, B. macrocarpa Guss.; F1023, B. patula Aiton). Six‐year mean root yield of the germplasm lines was 32.63 Mg ha−1 or 63% of the yield of an adapted hybrid. Average sucrose concentrations of the lines ranged from 114 to 122 g kg−1, compared with 136 g kg−1 for a commercial hybrid. These lines will contribute to the broadening of the genetic diversity of the crop, and the infusion of genes from these and other exotic sources may result in unique gene combinations that expand the limits of improvement through selection and enhance combining ability.

Evaluation of Beta corolliflora for Resistance to Curly Top in Idaho

Curly top of sugarbeet is caused by Beet severe curly top virus (BSCTV) or closely related curtovirus species which are vectored by the beet leafhopper (Circulifer tenellus). Beta corolliflora, shown in 1969 to impart a very high level of curly top resistance to sugarbeet into the BC 2 generation, is a wild relative of cultivated sugarbeet that has not been utilized in breeding programs. The nature of curly top resistance from B. corolliflora seems to be reduced symptoms and resistance to viral accumulation. Field screening of 14 B. corolliflora accessions for resistance to curly top followed by PCR detection of BSCTV did not identify any accessions with phenotypic symptoms of curly top and 9 accessions did not have detectable virus. Clip cage inoculations followed by PCR detection of BSCTV and of related species, Beet mild curly top and Beet curly top viruses, were difficult to interpret due to small sample size but indicated that accessions BETA 408, BETA 414, BETA 528, BETA 690, and BETA 805, from Genebank Gatersleben, Foundation Liebniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany had no visible curly top symptoms or evidence of virus accumulation. Results of a preference test showed that beet leafhoppers did not

Genetic structure and gene flow in wild beet populations: the potential influence of habitat on transgene spread and risk assessment

Summary The consequences of the movement of transgenes from genetically modified (GM) crops into wild populations of plants continues to be of concern to ecologists and conservationists because of the possible threat posed to those populations in terms of their continued survival and because of the further knock‐on effects that might occur to habitats in which they occur. We examined five UK sea beet Beta vulgaris ssp. maritima populations from each of two major habitat types, cliff top and drift line. We assessed population genetic parameters, genetic diversity, gene flow, population differentiation and isolation by distance, to enable determination of the likelihood and consequences of spread to wild populations of genes from cultivated sugar beet group Beta vulgaris ssp. vulgaris, which could in the future be transgenic. Drift line populations were more diverse than cliff top populations and also showed greater levels of gene flow. Isolation by distance was identified in both habitats, but the relationship between genetic and geographical distance was detectable over longer distances for drift line populations. However, clear indications of vicariance (the subdivision of a population into distinct taxa by the appearance of a geological barrier) between cliff and drift line populations were also evident, because of the restriction of gene flow between the two habitats occurring more in one direction than the other. Synthesis and applications. The likelihood of transgene spread from crop to wild populations is habitat dependent and conservation management decisions could therefore vary from one population to another, for example water courses were found to facilitate seed dispersal. This should be taken into account when estimating isolation distances for GM beet, and when predicting transgene frequencies (exposure estimates) for environmental risk assessments of GM beet.

A combined method to study gene flow from cultivated sugar beet to ruderal beets in the glasshouse and open field

Gene flow from transgenic plants to compatible wild relatives is one of the major impediments to the development of the culture of genetically engineered crop plants. In this work the flow of two linked transgenes, EPSPs (conferring resistance to glyphosate) and gus genes of sugar beets, toward the ruderal beets in greenhouse conditions, in an open field (1 ha) and in normal seed multiplication conditions for sugar beet were studied. The data relate to only the 1999 summer season on one location of southwest of France. Care was taken as to the quality of the plant material and the efficiency of the analytical methods. Moreover, pollen dispersal and fertilization of the target plants were favorised and a detailed analysis of the hybrid offspring was performed. Greenhouse studies show that emasculated ruderal plants can be fertilized by the transgenic pollen of crop beets as easily as the male sterile isogenic line (near 100%). Only a part of the seedballs sown gave plantlets, the rest remains non-germinated in the soil. Both the hybrid progeny plantlets and the non-germinated embryos were analyzed. An efficient competition existed between the transgenic and the ruderal beet pollens, which hampers the production of a large transgenic hybrid progeny. In field, such a protection effect was also clearly operating when ruderal plants were implanted in groups (six plants) inside the transgenic donor source. The proportion of transgenic hybrids in receptor plots (containing 60 ruderal beets plus 20 male sterile beets) decreased rapidly with the distance from the transgenic source and was about 0.5% for ruderal beets and 1.5% for male sterile beets, at 200 m from the source. Moreover, the overall values were always higher in the east plots (under prevailing wind) than in the other directions, emphasizing the important role played by the wind in transgene dispersal. Male sterile receptor plots (80 × 2 plants) implanted one km from the transgenic donor source show a transgenic progeny. So even at this distance, pollen was still capable of fertilization. However, the percentage of the transgenic progeny of these male sterile plants was low (about 0.15%) and would be lower in the case of ruderal beets, owing to pollen competition. However, because non-germinated transgenic embryos have also been recovered indicating that care would have to be taken in rotation cultures involving genetically engineered beets.

Construction of a BAC Library Covering a Common Region between Two Sugar Beet Translocation Lines with Two Cyst Nematode Resistance Genes

Resistance against the beet cyst nematode (BCN) has been introduced into cultivated sugar beet from wild beet by conventional breeding. The first gene effective against the BCN, Hs1pro-1, was isolated from the sugar beet translocation line A906001. It is assumed that a second nematode resistance gene, Hs1pro-1, is present in the translocation line PRO3, which does not carry Hs1pro-1 but still imparts complete resistance against the nematode and resides in the overlapping region between the two lines. The overall goal of this study was to construct a bacterial artificial chromosome (BAC) library to facilitate the cloning of Hs1pro-1. A BAC library from PRO3 was constructed containing 45,041 clones with an average insert size of 108.36 kb. Screening of the library with organelle specific probes indicated less than 1% mitochondrial and 4% chloroplast DNA content. The library covers 6.17 genome equivalents which provides a 99.76% probability of recovering any specific sequence present in the genome.

Identification of a putative cation transporter gene from sugar beet ( Beta vulgaris L.) by DDRT-PCR closely linked to the beet cyst nematode resistance gene Hs1pro-1

The beet cyst nematode ( Heterodera schachtii Schm.) is a widespread pest that causes agronomic losses in sugar beet cultivation. Since no nematode resistance genes have been found in Beta vulgaris L. cultivars, a chromosomal fragment from Beta procumbens has been bred into cultivated sugar beet in order to provide resistance to Heterodera schachtii. The introgressed translocation carries the nematode resistance gene Hs1 pro-1 and may also contain genes that are linked to the defense response and/or signal transduction. A novel cDNA designated Bp23 was isolated from the translocation in this work by comparing resistant and susceptible sugar beets of a segregating F 2 population by differential display. Bp23 shows similarity to Arabidopsis thaliana BAC clones and to diverse plant ESTs with similarity to the Escherichia coli cation transporter ChaC. The open reading frame could encode a hydrophilic protein of 25 kDa that is similar to cation transporters and has a presumptive K + selective motif at the N-terminus.