Location: Crop Improvement and Protection Research2011 Annual Report
1a. Objectives (from AD-416)
The long-term objective of this project is to develop sugarbeet (Beta vulgaris L. subsp. vulgaris) breeding lines and populations with resistance to specific diseases and pests. Genes and gene pools from wild beet relatives will be evaluated, characterized, and introgressed into adapted germplasm. Progeny lines and specific breeding materials will be genotyped and phenotyped to determine inheritance patterns and to search for molecular genetic markers. Markers will be validated for usefulness in marker-assisted selection. The efficacy of resistance genes will be evaluated in biological evaluations and replicated trials. The breeding and population improvement program will be continued to accumulate numerous favorable alleles and combine broadly based host plant resistance and high productivity. Over the next 40 months the program will focus on the following objectives: Objective 1: Analyze the inheritance of disease resistance mechanisms to pathogens common in the United States, especially in the Western growing regions, through mapping sources of disease resistance and identifying phenotypic variation for disease resistance. Objective 2: Identify novel sources of disease resistance within sugarbeet and its wild relatives to broaden the sugarbeet germplasm base. Objective 3: Improve sugarbeet germplasm and develop genetic resources through utilization of traditional and molecular breeding tools for release to international sugarbeet seed companies for improved agronomic, quality, disease resistance, and tolerance to abiotic stresses.
1b. Approach (from AD-416)
Develop populations and genetic stocks for mapping qualitative and quantitative sources of disease resistance in sugarbeet. Identify regions of the Beta vulgaris genome associated with phenotypic variation for disease resistance and select advantageous alleles to facilitate marker-assisted selection. Evaluate wild and ancestral relatives of sugarbeet both phenotypically and genotypically for novel sources of disease resistance. Characterize and introgress genetically diverse resistance alleles into enhanced sugarbeet germplasm. Continue a sugarbeet pre-breeding, population, and breeding line improvement program. Integrate genomic tools to develop new germplasm with improved agronomic and quality characteristics and resistance to biotic and abiotic stresses.
3. Progress Report
Under Objective 1A, 31 crosses were made to develop genetic stocks and mapping populations. Of these, ten crosses were to study the inheritance of rhizomania resistance, six for powdery mildew resistance, five for sugarbeet cyst nematode (SBCN) resistance, and eight for high sucrose content. One cross was made for determinate growth and one for inter-species hybridization. Under Objective 2A, we progressed with the evaluation of wild sugarbeet relatives for unique sources of disease resistance. Pools of extracted DNA from Beta vulgaris subsp. maritima (Bvm) accessions were developed: 1. a pool of all four individuals for a single accession, 2. a pool of 12 individuals from different accessions, and 3. a single individual from one accession. We ran 162 (simple sequence repeats) SSR molecular markers on these pools to identify polymorphisms. 159 markers were selected and run on Beta vulgaris subsp. maritima (Bvm) accession individuals. These polymerase chain reaction (PCR) products were analyzed on an Applied Biosystems 3500 genetic analyzer and eight markers were selected to run on all accessions. Under Objective 2B, genetic stocks from crosses made between recurrent parent, 8747, and 11 C79 rhizomania resistant-lines were selfed to advance the generation of mapping populations. Each line has a different Bvm accession donor parent. Literature and field trials have confirmed that these lines are resistant to the wild type-rhizomania virus strain. We tested the C79 lines to determine which confer resistance to the resistance breaking-rhizomania virus strain. Of the eleven lines, only three were resistant to the resistance breaking-rhizomania virus strain: C79-2, C79-3, and C79-7. Under Objective 3A, continued progress was made on the sugarbeet pre-breeding, population, and breeding line improvement program. At our Salinas locations, we evaluated 5805 plots comprising 785 lines for traits including stand count, powdery mildew resistance, rhizomania resistance, cercospora leaf spot resistance, tons roots harvested per acre, and percent soluble solids. We evaluated 1280 plots of 288 lines in our Brawley location for stand count and sugarbeet cyst nematode resistance. In addition, in collaboration with researchers at Michigan State University, Fort Collins, CO and the University of Minnesota a comprehensive multigene evaluation of the phylogenetic relationships among the intersterility groups of Rhizoctonia solani AG 2-2 is in progress. This will provide a strong foundation for classification of isolates (currently this is done by temperature growth and is not always reflective of discrete biological species). In collaboration with researchers at Michigan State University and the University of Minnesota an evaluation of the population structure of Rhizoctonia solani AG 2-2 intersterility groups (IIIB and IV) in Michigan and Minnesota is in progress using SSR and sequence based markers. A culture collection of California isolates of Polymyxa betae, the obligate vector for several sugarbeet viruses, is under establishment.
1. New sources of resistance to beet necrotic yellow vein virus (BNYVV) strains of rhizomania. BNYVV incites the soilborne disease rhizomania, the most serious disease of sugarbeet worldwide. An ARS researcher at Salinas, CA screened the entire U.S. National Plant Germplasm System Beta vulgaris subsp. maritima collection (424 accessions) for resistance to the wild type and Rz1 resistance-breaking strains of BNYVV, and identified 150 accessions resistant to both the wild type and Rz1 resistance-breaking BNYVV strains. Twenty-one of the 150 accessions were also resistant to powdery mildew and bolting (data are available at the Germplasm Resources Information Network (GRIN) website). This research benefits both sugarbeet growers in the Western U.S. and seed producers in the global market. Resistance to both diseases is critical for production in the Imperial Valley, CA. Long term impact will include release and registration of advanced resistant germplasm and eventual variety release by industry.
2. Source of resistance to the Rz1 resistance-breaking strain of BNYVV. Beet necrotic yellow vein virus (BNYVV) incites the soilborne disease rhizomania, the most serious disease of sugarbeet worldwide. Eleven near-isogenic sugarbeet lines released from the Salinas breeding program in 1994, named the C79 lines, were developed from 11 different sources of resistance to BNYVV. ARS researcher at Salinas, CA found one of the lines, C79-7, to be resistant to the Rz1 resistance-breaking strain of BNYVV. Resistance in C79-7 was derived from the commercial hybrid Rima and is genetically uncharacterized. C79-7, and populations derived from it, will aid in determining the genetic mechanisms behind Rz1 breaking-resistance and the inheritance of resistance genes.