Location: Tropical Crops and Germplasm Research
Project Number: 6090-21000-058-001-I
Project Type: Interagency Reimbursable Agreement
Start Date: Sep 1, 2015
End Date: Sep 14, 2018
Identify new anthracnose resistance sources in diverse sorghum germplasm, identify which loci are responsible for tolerance against anthracnose pathotypes, and determine the disease resistance mechanism of at least one of these loci, with the ultimate goal of providing plant breeders with a tool kit that can be used to identify maximum levels of resistance for an intended area of production.
Three sets of recombinant inbred lines (RILs; ~120 individual lines each) derived from the cross of three sorghum differential lines with resistance to different anthracnose pathotypes (SC112-14, QL3 and IS18760) and a highly susceptible line PI609251 have already been developed as a tool to map anthracnose resistance response against multiple pathotypes. These lines are originally from Ethiopia, India, and Sudan, respectively, and contain different sources of resistance against some anthracnose pathotypes. The anthracnose resistance response of these lines against pathotypes from Puerto Rico, Florida, Georgia, and Texas will be determined through a two-year replicated field trial employing the screening methodology from Prom et al. 2009. High-density recombination linkage maps will be constructed based on genotyping by sequencing (GBS) of the lines, and genomic regions associated to anthracnose resistant response identified by linkage analysis. In order to facilitate this effort, a reduced sample of RILs from each population will be selected based on complementary recombination breakpoints spaced evenly throughout the genome [i.e. selective mapping (Vision et al. 2000) for subsequent greenhouse evaluation against subsets of pathotypes from Puerto Rico, Florida, Georgia, Arkansas, and Texas. This approach will be useful to identify multiple anthracnose resistant loci within a region averaging ~10 cM, which can later be reduced to 1-5 cM intervals by the evaluation of other specific recombinant events present in the RILs populations. The complementary results of both approaches will result in the identification of multiple anthracnose resistant loci, and the genomic information necessary to make adequate use of these resistance sources through marker-assisted selection. In a parallel set of experiments, the molecular mechanism controlling anthracnose resistance response will be investigated by identification of candidate genes underlying a recently identified QTL for anthracnose resistance against pathotypes common in Florida, originating from the resistant cultivar Bk7 (Vermerris, unpublished). Through a combination of fine-mapping, expression analysis, and virus-induced gene silencing with Brome mosaic virus, we will identify and validate individual candidate genes, with complementary histochemical studies providing information on the mechanism of resistance. The identification of anthracnose resistant sources present in the NPGS sweet sorghum germplasm collection will expedite the development of new resistant sweet sorghum varieties by avoiding time-consuming introgression breeding approaches (Cuevas et al. 2014). We will evaluate the approximately 2,180 accessions present in U.S. National Plant Germplasm Sysem (NPGS) for Brix values to develop a diversity panel of ~200 genetically and geographically diverse accessions with high sugar content (>15.0 Brix). This panel will be later evaluated for anthracnose response in Puerto Rico, Florida, Georgia, and Texas. GBS analysis od the panel will be used to do genome-wide association analysis (GWAS) using mixed linear model (MLM) approach to identify novel anthracnose resistant loci.