Lee Panella

Evolutionary Conservation of the FLOWERING LOCUS C-Mediated Vernalization Response: Evidence From the Sugar Beet (Beta vulgaris)

In many plant species, exposure to a prolonged period of cold during the winter promotes flowering in the spring, a process termed vernalization. In Arabidopsis thaliana, the vernalization requirement of winter-annual ecotypes is caused by the MADS-box gene FLOWERING LOCUS C (FLC), which is a repressor of flowering. During the vernalization process, FLC is downregulated by alteration of its chromatin structure, thereby permitting flowering to occur. In wheat, a vernalization requirement is imposed by a different repressor of flowering, suggesting that some components of the regulatory network controlling the vernalization response differ between monocots and dicots. The extent to which the molecular mechanisms underlying vernalization have been conserved during the diversification of the angiosperms is not well understood. Using phylogenetic analysis, we identified homologs of FLC in species representing the three major eudicot lineages. FLC homologs have not previously been documented outside the plant family Brassicaceae. We show that the sugar beet FLC homolog BvFL1 functions as a repressor of flowering in transgenic Arabidopsis and is downregulated in response to cold in sugar beet. Cold-induced downregulation of an FLC-like floral repressor may be a central feature of the vernalization response in at least half of eudicot species.

A greenhouse test for screening sugar beet (Beta vulgaris) for resistance to Rhizoctonia solani

Rhizoctonia solani Kühn is a serious plant pathogenic fungus, causing various types of damage to sugar beet (Beta vulgaris L.). In Europe, the disease is spreading and becoming a threat for the growing of this crop. Plant resistance seems to be the most practical and economical way to control the disease. Experiments were carried out to optimise a greenhouse procedure to screen plants of sugar beet for resistance to R. solani. In the first experiment, two susceptible accessions were evaluated for root and leaf symptoms, after being grown in seven different soil mixtures and inoculated with R. solani. The fungus infected all plants. It was concluded that leaf symptoms were not reliable for the rating of disease severity. Statistically significant differences between the soil mixtures were observed, and there were no significant differences between the two accessions. The two soil mixtures, showing the most severe disease symptoms, were selected for a second experiment, including both resistant and susceptible accessions. As in the first experiment, root symptoms were recorded using a 1–7 scale, and a significant expression of resistance was observed. The average severity of the disease in the greenhouse experiment generally was comparable with the infection in field experiments, and the ranking of the accessions was the same in the two types of experiments. It was concluded that evaluation procedures in the greenhouse could be used as a rapid assay to screen sugar beet plants for resistance to R. solani.

Sugar Beet as an Energy Crop

The combination of volatility in the oil market and finite oil resources and the effect on global climate change from the addition of CO2 to the atmosphere as a result of burning fossil fuels has increased the interest in sustainable energy generation from renewable biofuels. Most 1st generation biofuels in current production are liquid with bioethanol the product of fermentation. Sugar beet provides an abundance of sucrose, which is easily fermented by many microbes and on a per hectare basis; sugar beet is one of the most efficient sources of ethanol, however storage of harvested roots is problematic. Most studies have indicated sustainable biofuels have reduced greenhouse gas emissions (GHG) when compared to petroleum based fuels. Bioethanol from sugar beet reduces GHG comparably or superiorly to maize or sugarcane. There also are other biofuels from fermentation, including biomethanol, biobutanol ETBE, biomethane, and biohydrogen, many of which are more energy dense than ethanol. Storage of sugar beet is a problem that could be solved by ensilage and anaerobic digestion producing a biogas, which could yield more energy per hectare than bioethanol. As the global economy moves away from fossil fuels, sugar beet will play an increasing role in the adoption of more sustainable energy generation.

Availability of Germplasm for Resistance Against Rhizoctonia Spp.

Farr and co-workers (1989) list over 500 genera of plants in Fungi on Plants and Plant Products in the United States that are hosts to Rhizoctonia solani Kuhn or any of 21 other species of Rhizoctonia that are phytopathogenic. Agricultural, horticultural, ornamental, and some tree species are affected. Twenty-five years ago, Leach and Garber (1970) reviewed resistance to Rhizoctonia infection and concluded, “In general, while it has been possible to identify differences among cultivars or selections in susceptibility to Rhizoctonia infection, it is extremely rare that a high degree of resistance has been found or produced by selection or breeding within a susceptible host species. ” Today, the use of resistant cultivars provides effective and adequate protection against the various diseases caused by Rhizoctonia spp. In some cases, the use of a cultivar with a moderate level of resistance can be coupled with reduced fungicide applications to provide a sufficient level of disease management. A survey of Crop Science revealed a list of 59 cultivar, parental line, and germplasm registrations in nine crop species during last 10 years that have some resistance to diseases caused by Rhizoctonia spp. These are included with cultivar releases from other sources in Table 1. All of this information attests to the importance of germplasm with resistance to Rhizoctonia spp.

High-throughput RAD-SNP genotyping for characterization of sugar beet genotypes

High-throughput single-nucleotide polymorphism (SNP) genotyping provides a rapid way of developing resourceful sets of markers for delineating genetic structure and for understanding the basis of the taxonomic discrimination. In this paper, we present a panel of 192 SNPs for effective genotyping in sugar beet using a high-throughput marker array technology, QuantStudio 12K Flex system, coupled with Taqman OpenArray technology. The selected SNPs were evaluated for genetic diversity among a set of 150 individuals representing 15 genotypes (10 individuals each) from five cytoplasmic male steriles (CMSs), five pollinators, and five commercial varieties. We demonstrated that the proposed panel of 192 SNPs effectively differentiated the studied genotypes. A higher degree of polymorphism was observed among the CMSs as compared to pollinators and commercial varieties. PCoA and STRUCTURE analysis revealed that CMSs, pollinators, and varieties clustered into three distinct subpopulations. Our results demonstrate the utility of the identified panel of 192 SNPs coupled with TaqMan OpenArray technology as a wide set of markers for high-throughput SNP genotyping in sugar beet.

Identification and Validation of a SNP Marker Linked to the Gene HsBvm-1 for Nematode Resistance in Sugar Beet

The beet-cyst nematode (Heterodera schachtii Schmidt) is one of the major pests of sugar beet. The identification of molecular markers associated with nematode tolerance would be helpful for developing tolerant varieties. The aim of this study was to identify single nucleotide polymorphism (SNP) markers linked to nematode tolerance from the Beta vulgaris ssp. maritima source WB242. A WB242-derived F2 population was phenotyped for host-plant nematode reaction revealing a 3:1 segregation ratio of the tolerant and susceptible phenotypes and suggesting the action of a gene designated as HsBvm-1. Bulked segregant analysis (BSA) was used. The most tolerant and susceptible individuals were pooled and subjected to restriction site associated DNA sequencing (RAD-Seq) analysis, which identified 7,241 SNPs. A subset of 384 candidate SNPs segregating between bulks were genotyped on the 20 most-tolerant and most-susceptible individuals, identifying a single marker (SNP192) showing complete association with nematode tolerance. Segregation of SNP192 confirmed the inheritance of tolerance by a single gene. This association was further validated on a set of 26 commercial tolerant and susceptible varieties, showing the presence of the SNP192 WB242-type allele only in the tolerant varieties. We identified and mapped on chromosome 5 the first nematode tolerance gene (HsBvm-1) from Beta vulgaris ssp. maritima and released information on SNP192, a linked marker valuable for high-throughput, marker-assisted breeding of nematode tolerance in sugar beet.

Targeted Next-Generation Sequencing Identification of Mutations in Disease Resistance Gene Analogs (RGAs) in Wild and Cultivated Beets

Resistance gene analogs (RGAs) were searched bioinformatically in the sugar beet (Beta vulgaris L.) genome as potential candidates for improving resistance against different diseases. In the present study, Ion Torrent sequencing technology was used to identify mutations in 21 RGAs. The DNA samples of ninety-six individuals from six sea beets (Beta vulgaris L. subsp. maritima) and six sugar beet pollinators (eight individuals each) were used for the discovery of single-nucleotide polymorphisms (SNPs). Target amplicons of about 200 bp in length were designed with the Ion AmpliSeq Designer system in order to cover the DNA sequences of the RGAs. The number of SNPs ranged from 0 in four individuals to 278 in the pollinator R740 (which is resistant to rhizomania infection). Among different groups of beets, cytoplasmic male sterile lines had the highest number of SNPs (132) whereas the lowest number of SNPs belonged to O-types (95). The principal coordinates analysis (PCoA) showed that the polymorphisms inside the gene Bv8_184910_pkon (including the CCCTCC sequence) can effectively differentiate wild from cultivated beets, pointing at a possible mutation associated to rhizomania resistance that originated directly from cultivated beets. This is unlike other resistance sources that are introgressed from wild beets. This gene belongs to the receptor-like kinase (RLK) class of RGAs, and is associated to a hypothetical protein. In conclusion, this first report of using Ion Torrent sequencing technology in beet germplasm suggests that the identified sequence CCCTCC can be used in marker-assisted programs to differentiate wild from domestic beets and to identify other unknown disease resistance genes in beet.

Long term preservation of a collection of Rhizoctonia solani, using cryogenic storage.

1 USDA-ARS, Sugarbeet Research Unit, Fort Collins, CO 80526, USA 2 Current address: Department of Plant Pathology, The Ohio State University, Columbus, OH 43210, USA 3 USDA-ARS, National Center for Genetic Resources and Preservation, Fort Collins, CO 80521, USA 4 Current address: US Forest Service, Fort Collins, CO 80526, USA 5 USDA-ARS, Sugarbeet and Bean Research Unit, East Lansing, MI 48824, USA