2013 Annual Report
1a.Objectives (from AD-416):
1. Genetically-characterize sorghum accessions from Ethiopia and other nations and apply the genetic marker data to select core subsets of accessions for evaluation for host-plant resistance to anthracnose and grain mold.
2. With ARS cooperators, conduct multi-locational evaluations of selected sorghum accessions to identify potential new sources of host-plant resistance to anthracnose and grain mold pathotypes predominant in Puerto Rico and in Texas.
3. With ARS cooperators, develop experimental populations for identifying, characterizing, and mapping the genes that confer host-plant resistance to anthracnose and grain mold pathotypes and for identifying genetic markers closely linked to those resistance traits.
3a. Employ genome-wide association studies (GWAS) to identify genes that confer host-plant resistance to anthracnose.
3b. Employ GWAS to identify genes that confer host-plant resistance to grain mold pathotypes.
4. Evaluate selected sweet sorghum germplasm accessions to identify lines with robust culms, superior sugar content, dry matter production, and host-plant resistance to anthracnose.
1b.Approach (from AD-416):
The focus of this research is to determine the genetic control of anthracnose and grain mold, to identify molecular markers for breeding programs seeking disease resistance, and to discover new sources of resistance present in exotic germplasm. Genome-wide association studies will be employed to understand the genetic control and locate the genome regions of the anthracnose and grain mold resistance genes. The genetic and morphological characterization of sorghum collection from Ethiopia and Sudan will be applied to develop core subsets for further association studies, and to identify new sources of host resistance. Presently, sweet sorghum varieties utilized as a biofuel source have a narrow genetic base. Therefore, evaluation of sweet sorghum accessions present in the US sorghum collection will be carried out to help to identify new germplasm to broaden genetic variability available for the development of new biofuel varieties of sorghum.
This research project initiated in June 2013 and replaces project 6635-21000-049-00D. During the fiscal year, germplasm from Ethiopia was requested from the National Plant Germplasm System (NPGS) and planted in the field for evaluation for host plant disease resistance. The U.S. sorghum association panel (377 lines) are being evaluated for anthracnose and grain mold resistance. A total of 1,000 sweet sorghum accessions are being evaluated for sugar content (Brix) and lodging. A sweet sorghum diversity panel of 270 accessions is being evaluated for sugar content.
Germplasm from the former USDA-ARS sorghum conversion program (terminated 20 years ago) have not been introduced into the sorghum germplasm collection maintained by NPGS. In this regard, 65 lines were indentified in our seed storage facilities, and regenerated to increase seed numbers and viability. These lines are being evaluated for disease resistance, agronomical traits, and photoperiod sensitivity.
A stratified sample of 380 accessions based on sorghum races present in the Ethiopian sorghum collection was planted in the greenhouse for DNA isolation. The DNA from each accession was effectively isolated and its quality tested for use in Genotype by Sequence analysis.
The genetic control of an anthracnose resistance gene present in PI533918 was determined by the analysis of observed segregation in a F2 population. This gene has been mapped to the distal region of chromosome five, flanked by two simple sequence repeat markers, and not associated with the anthracnose resistance gene present in SC748. This information will be valuable in order to introgress and pyramid these genes with other resistance genes.
Rescue of converted sorghum germplasm. ARS scientists in Mayaguez, Puerto Rico identified and seed regenerated sixty five converted lines of sorghum that were not present in the NPGS sorghum collection and sent these to Griffin, Georgia for long-term storage. This germplasm is novel and could serve as a valuable genetic resource for public and industry breeders.
Genome mapping of anthracnose resistance gene present in PI533918. The anthracnose resistance gene present in PI533918 was delimited to a 9.2 cM region at the distal region of sorghum chromosome five. Simple sequence repeats markers within this region were developed and evaluated by ARS scientists in Mayaguez, Puerto Rico, in order to provide a molecular tool to be used in sorghum breeding programs directed to introgress and pyramid multiple resistance genes. The incorporation of this gene, with previously identified resistance gene, will prolong and broaden the control of anthracnose disease.