2013 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.
During the winter of 2011 and the spring of 2012, we screened a total of 4,288 BC2F2 plants derived from eight original resistant accessions of H. argophyllus, H. debilis, H. praecox, and H. petiolaris, and advanced 302 BC2F3 families from the selected resistant individuals. Seventy-one BC2F3 families from one accession each of the four wild species were evaluated for their resistance to stalk rot in field trials at Carrington, ND, and Crookston, MN, in the summer of 2012. Overall, 17 BC2F3 families had disease incidence lower than 10% at both locations, which were similar or superior to the resistant check, Croplan 305 (13.2%). Out of 71 BC2F3 families tested in the field, 23 derived from H. petiolaris PI 435843 and H. argophyllus PI 494573 were also evaluated for their resistance to stalk rot in the growth chamber in the summer of 2012. Combining field and greenhouse data, the two most resistant lines, 11-256-053 from H. petiolaris and 11-275-037 from H. argophyllus, were identified. Whole genome scans of the resistant line 11-275-037 with sunflower SSR markers revealed the presence of introgressed chromosome segments located on linkage groups 8, 9, 10, and 11, indicating these chromosomes may associate with stalk rot resistance. Additionally, during the winter of 2012 and the spring of 2013, a total of 279 BC2F3 families (24 plants for each family) developed from different accessions of wild species H. argophyllus, H. debilis, and H. praecox were also inoculated with S. sclerotiorum in the greenhouse to screen the resistant lines. Overall, 48 potential resistant lines from these three species were obtained. These lines along with the best resistant lines from last year's testing were further evaluated for their resistance to stalk rot in two locations in the summer of 2013.
We continued to develop an advanced backcross (AB) population to facilitate genetic characterization of novel QTL for stalk rot resistance derived from H. argophyllus PI 494573. A total of 180 plants derived from 14 BC2F1 plants were advanced to the BC2F4 generation by single-seed descent. Our goal is to produce an AB population of BC2F2:6 lines by an additional two cycles of single-seed descent.
A list of significant markers derived from our candidate gene and whole genome association mapping work for Sclerotinia stalk rot have been included in two publications, one currently in draft and the other in final stages of review with Theoretical and Applied Genetics. The significant markers are currently being applied to our validation population derived from 34 highly resistant or agronomically elite B-lines of sunflower. Recurrent selection based on these markers has been applied once with each marker weighted by its effect estimate and a selection intensity of 15%. Another round of selection will occur on new random mated progeny this summer.