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United States Department of Agriculture

Agricultural Research Service

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Research Project: Multidisciplinary Approaches to Enhanced Sugar Beet Germplasm

Location: Sugarbeet Research

Project Number: 5402-21220-009-00
Project Type: Appropriated

Start Date: Jul 29, 2013
End Date: Jul 28, 2018

Objective:
Objective 1: Evaluate and characterize the genetic diversity for priority agronomic traits within and among sugar beet genetic resources, and incorporate evaluation and characterization data into the GRIN database. Objective 2: Characterize the diversity in isolates of Fusarium and Rhizoctonia species to determine their role in disease development and epidemiology, and apply that new knowledge to mitigate disease losses. Sub-objective 2.A: Determine if homologous gene sequences that have been previously reported to contribute to fungal pathogenicity and virulence in other systems, are present in F. oxysporum f. sp. betae and characterize their genotypic diversity within the F. oxysporum f. sp. betae population. Sub-objective 2.B: Determine if selected candidate pathogenicity/virulence (or effector) genes that occur in F. oxysporum f. sp. betae are expressed and contribute to pathogenicity to sugar beet. Objective 3: Determine the genetic interactions between sugar beet germplasm and the pathogens which incite important diseases, including but not limited to Fusarium yellows and Rhizoctonia crown and root rot. Objective 4: Incorporate genes from the crop progenitor Beta vulgaris ssp. maritima to develop and release improved germplasm with increase disease resistance to major sugar beet pathogens.

Approach:
Objective 1: In order to test how well the current taxonomy adequately describes the genetic diversity in molecular and phenotypic characters, we will examine 15 samples from each of 10 to 15 accessions of each of the three species (Patellifolia patellaris, P. procumbens, and P. webbiana). Where feasible, accessions will be chosen to span the extent of the species geographic distribution. Samples will be grown in the greenhouse for morphological characterization at the individual level and leaf tissue will serve as a DNA source from each individual. Objective 2; Sub-objective 2.A: Non-pathogenic and pathogenic isolates (F. oxysporum & F. o. f.sp. betae) will be chosen to represent the phylogenetic diversity within the U.S. sugar beet production. The DNA sequence(s) for previously reported fungal (or Fusarium spp.) pathogenicity gene and virulence effectors will be used to design primers for each pathogenicity gene. Specific primer pairs are designed for each gene to eliminate paralogs of gene sequences present in our F. oxysporum population. Objective 2; Sub-objective 2.B: Sugar beet cores will be inoculated with a pathogenic F. o f.sp. betae isolate. RNA will be extracted from both the mycelia and the sugar beet cores post inoculation. RT-PCR will be performed to determine if difference in gene expression occurs in planta. Candidate gene sequences will be used to generate knock-out mutations for each candidate gene. Gene replacement constructs (both as gain of function and loss of function) will be created in isolates of F. oxysporum replacing the endogenous gene sequence. All transformed F. oxysporum isolates will be inoculated to a susceptible sugar beet germplasm to determine if they are pathogenic (or have lost pathogenicity). Objective 3: Two isolates from our Fusarium collection have been selected for genomic sequencing. To determine pathogenicity of each isolate, disease severity from the sixth week of scoring will be statistically analyzed with a water control. Each isolate of F. oxysporum will have the entire genome sequenced utilizing an Illumina based sequencing method. Sequence will be compared between the pathogenic and non-pathogenic isolate to provide insight into the mechanism(s) that F. oxysporum f. sp. betae employs to cause disease in sugar beet. Objective 4: The approach of this breeding program is the formation of long range breeding populations through the introgression of resistant germplasm from “exotic” sources of the primary Beta germplasm pool (B. v. subsp. maritima, fodder beet, table beet, Swiss chard, foreign sugar beet landraces from the PI collection, etc.). This breeding scheme provides great flexibility to accommodate the genetic background of the germplasm and the disease resistances being chosen. The development of breeding populations will be accomplished using methods that produce genetically defined sub populations, which are useful for resistance gene mapping, marker development, exploring sugar beet-pathogen interactions, and gene discovery.

Last Modified: 4/19/2014
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