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United States Department of Agriculture

Agricultural Research Service

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Location: Sunflower Research

2012 Annual Report

1a.Objectives (from AD-416):
The overall goal of the proposed project is to improve Sclerotinia stalk rot resistance in the cultivated germplasm. Specific objectives are to:

1. Pre-breed novel Sclerotinia resistance from wild annual species of H. argophyllus, H. debilis, H. praecox, and H. petiolaris into cultivated sunflower, and develop an advanced backcross population for QTL mapping. 2. Investigate inheritance of Sclerotinia resistance in introgressed lines. 3. Develop, deploy, and validate a SNP marker resource for Sclerotinia stalk rot resistance from the results of our previous project.

1b.Approach (from AD-416):
Our approach has three parts. First, we will develop pre-breeding germplasm populations for genetic mapping and germplasm release. We have already developed eight BC2 populations from the crosses of HA 89 with resistant plants selected from H. argophyllus, H. debilis, H. praecox, and H. petiolaris. We will continue to evaluate Sclerotinia resistance in BC2F1 and BC2F2 populations in greenhouse trials in 2011 and identify resistant introgressed lines. We will also develop an advanced backcross mapping population from a cross of HA 89 (susceptible parent) with H. argophyllus (PI 494573, resistant parent) for molecular genetic mapping of Sclerotinia stalk rot resistance QTL. The BC2F2-derived population will be evaluated for host plant resistance to Sclerotinia stalk rot in the field, and will be interrogated with SSR markers in future years. Second, we will follow donor segment introgressions with genetic markers. Five-hundred sunflower SSR markers selected from sunflower genetic maps will be used to screen the polymorphism between HA 89 and wild annual species in order to monitor the introgressed traits in cultivated sunflower. Markers of introgressed zones of H. argophyllus, H. debilis, H. praecox, and H. petiolaris in the resistant lines are assumed to be good candidates to identify the segments carrying stalk rot-resistant QTLs. Third, we will use SNP markers associated with Sclerotinia resistance, discovered in our previous project, to improve a population of maintainer (B-line) sunflower with marker-assisted recurrent selection. This will also function to validate the utility of the markers. An oligonucleotide pool assay (OPA) will be developed and released based on our previous project’s results. The OPA will be used to conduct 3 cycles of recurrent selection. After the three cycles are complete, we will use field testing for stalk rot resistance to determine progress using markers versus foregoing the use of markers and proceeding using standard pedigree selection.

3.Progress Report:

The goal of the proposed project is to improve Sclerotinia stalk rot resistance in the cultivated germplasm. The selected F1 resistant plants from wild crosses were backcrossed to HA 458, and their BC1s were again backcrossed to HA 89. A total of 575 BC2F1 plants from eight crosses were screened for their reaction to stalk rot in the greenhouse in 2011, and the 68 most resistant plants were advanced to the BC2F2 generation. In the winter 2011 and spring 2012 we screened a total of 4,340 plants from the BC2F2 populations in greenhouse trials, and selected 250 most resistant plants to advance to the BC2F3 generation for field testing to validate the greenhouse results in the 2012 growing season. In order to molecular map Sclerotinia stalk rot QTLs transferred from exotic germplasm, an advanced backcross (AB) population is being developed. A total of 300 plants from the 14 BC2F1 plants were advanced to the BC2F2 generation by single-seed descent in 2011.

We sequenced five candidate genes, believed to associate with Sclerotinia disease resistance, in a set of 104 sunflower genotypes comprised of plant introductions (PIs) and inbred lines. Preliminary results revealed strong association of COI1, EIN1 and ABI1 and ABI2 genes with the Sclerotinia stalk rot resistance. We then developed automated SNP assays for the most significant SNPs in the remaining 156 lines in a larger association mapping population evaluated for Sclerotinia stalk rot resistance in two-year multilocation trials. During this time, we used the preliminary results and field data on the 260 lines in the association mapping population to form a broad-based population, consisting of 35 parents, from pairwise crosses between elite inbred lines from our breeding program and Plant Introductions with interesting levels of Sclerotinia resistance. We are currently random mating the resulting F1s now, which will form a cycle 0 population with which we will validate the significant markers already found using the Marker Assisted Recurrent Selection approach.

Last Modified: 4/22/2015
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