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ARS Home » Southeast Area » Mayaguez, Puerto Rico » Tropical Crops and Germplasm Research » Research » Research Project #435128

Research Project: Uncovering Novel Sources of Anthracnose Resistance in Populations of Genetically Diverse Sorghums [Sorghum bicolor (L.) Moench]

Location: Tropical Crops and Germplasm Research

Project Number: 6090-21000-058-02-I
Project Type: Interagency Reimbursable Agreement

Start Date: Sep 15, 2018
End Date: Sep 14, 2021

Objective:
The main objectives of this proposal are to use community genotypes and germplasm mapping populations as well as to strategically genotype and phenotype the National Plant Germplam System (NPGS) sorghum collection to uncover anthracnose resistant loci present in Sorghum Association Panel (SAP), mine the NPGS sorghum collection for resistance alleles not present in SAP, validate resistance genes in susceptible sweet sorghum germplasm, and understand the sorghum immune system against anthracnose based on the newly identified resistance genes.

Approach:
Two sets of recombinant inbred lines (RILs) (>200 lines per population) from sorghum Nested Association Mapping (NAM) populations segregating for anthracnose resistant response will be evaluated against multiple C. sublineolum pathotypes from Puerto Rico, Texas, Georgia and Florida through a two-year replicated field trial. High-density recombination linkage maps previously constructed based on genotyping-by-sequencing (GBS) of the lines will be used to delimit genomic regions associated with resistant response based on linkage analysis. It is evident that this family-based approach will not uncover all resistant sources present in the SAP. Therefore, to increase frequency of resistance alleles in the SAP, NPGS exotic accessions belonging two four major sorghum races will be genotyped and characterized for anthracnose resistance response. A total of 400 NPGS exotic accessions belonging to Guinea and Kafir sorghum races will be genotyped and characterized to complement the previous efforts for NPGS Ethiopian (Durra), SAP , sweet sorghum and Sudan (Caudatum). Principal component analysis (PCA) and neighbor-joining trees will be used to investigate the population structure of this diverse panel of >1300 accessions. GWAS analysis using a mixed linear model (MLM) approach and logistic regression (i.e. resistant or susceptible) will be completed to identify novel anthracnose resistance loci. Comparative analysis among anthracnose resistant loci identified based on GWAS and family approach will complement our understanding of host/pathogen relationships present in different sorghum races. Four resistance genes (three on chromosome 5, one on chromosome 9) will validate and investigate the molecular mechanisms leading to anthracnose resistance. Given the regulatory function of these genes, we will perform expression profiling of infected and mock-inoculated tissue over time and identify coordinately expressed genes. In addition, by resequencing these four genes from a representative subset of 384 accessions selected based on the previous phylogenetic analysis, we can associate the presence of particular alleles with anthracnose resistance, and determine how this correlates with expression profiles. In parallel, the four genes will be validated based on introgression to highly susceptible sweet sorghum germplasm. Seven resistant lines (SC15, SC110, SC1330, SC17, SC1321, SC155, SC13) that contain multiple resistance alleles for the different loci will be crossed with the highly susceptible sweet sorghum line ‘Early Honey’. Genetic markers (e.g. KASP) based on single nucleotide polymorphism (SNPs) will be developed and used to select for resistance alleles in the BC1F1 to BC3F1 generation and to later fix them in the BC3F2 generation. Selected plants will be advanced until BC3F4 and evaluated for anthracnose resistant response in a replicated trial in Georgia, Florida and Puerto Rico.