Location: Tropical Crops and Germplasm Research
2022 Annual Report
Objectives
1. Phenotype exotic sorghum germplasm for important agronomic traits to identify the most valuable accessions for sorghum breeding programs.
1a. Genetically-characterize sorghum accessions from the West-Central African diversity panel (WCADP).
1b. Phenotypically-characterize highly genetically diverse sorghum accessions from the WCADP.
1c. Phenotypically-characterize accessions from NPGS sweet sorghum germplasm.
2. Identify new sources of anthracnose and grain mold resistance through the evaluation of exotic sorghum germplasm from the National Plant Germplasm System (NPGS) sorghum germplasm collection for further introgression breeding.
2a. Identify new sources of host-plant resistance to anthracnose in the WCADP.
2b. Identify new sources of host-plant resistance to grain mold in the WCADP.
Approach
The focus of this research is to use genotypic and phenotypic characterization of National Plant Germplasm System (NPGS) sorghum germplasm to identify new sources of resistance to anthracnose and grain mold in exotic germplam. A total of 396 accessions from West-Central Africa countries will be characterized for host-plant resistance to both diseases followed by genetic characterization through genotype-by-sequence analysis. This information will be combined with phenotypic and genotypic characterization data from sorghum association panels and core subsets from the NPGS Ethiopian and Sudan collections to conduct a large genome wide association analysis. The results will discover new sources of disease resistance and identify novel molecular markers for breeding programs seeking disease resistance. Presently, sweet sorghum varieties utilized as a biofuel source have a narrow genetic base. Therefore, evaluation of sweet sorghum accessions present in the NPGS 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. For this purpose, a subset of NPGS sweet sorghum germplasm with high Brix values will be characterized for biofuel related traits in conjunction with a subset of the sorghum bioenergy association panel.
Progress Report
The phenotypic characterization of 564 accessions from West-Central Africa Diversity Panel (WCADP) was completed. Results from the 3-year evaluation of WCADP showed that 312 accessions were resistant to anthracnose. This high frequency of resistant germplasm was associated with the population structure observed in this germplasm. The WCADP is composed of nine ancestral populations and each one encloses resistant accessions. Nevertheless, a higher frequency of resistant accessions was found in three of the populations indicating accessions belonging to these populations underwent anthracnose pressure and fixed resistance genes. In parallel, a 2-year rust evaluation study using 375 accessions from WCADP found that 47 accessions were highly resistant, 54 moderately-resistant and 274 susceptible. A total 45 accessions were resistant to both anthracnose and rust. Remarkably, one population of the WCADP enclose a higher frequency of both rust and anthracnose-resistant accessions. The screening of this population against other fungal foliar diseases is likely to identify resistant germplasm.
The complex inheritance of grain mold resistance makes difficult the introgression of resistance genes from tropical germplasm. The evaluation of 29 pre-breeding lines derived from tropical germplasm in Texas, Georgia, Florida and Puerto Rico showed grain mold resistant response. These lines had seed germination rates similar to those observed in nine temperate-adapted lines (Kansas Orange, Rox Orange, Red Amber, Keller, 6550 Summac, Summac, SC609, SC15 and SC13) previously identified as grain mold resistant. The inclusion of these lines in sorghum breeding programs will assist to develop new grain mold resistant varieties.
Sugarcane aphid [Melanaphis sacchari (Zehntner)] is a destructive pest that has had an economic impact on sorghum production in North America since 2013. The temperate-adapted line SC112-14 is resistant to anthracnose and sugarcane aphid (SCA) but the genetic control for its SCA resistance response was unknown. During this fiscal year, the SCA evaluation of 103 recombinant inbred lines derived from SC112-14 was completed and the analysis found that a genomic region on chromosome 6 control the observed resistance response. Remarkably, this genomic region is in proximity to those observed in two other SCA resistant lines (Henong 16 and Tx2783). Therefore, line SC112-14 is an additional SCA resistance source that can be combined or strategically used with other resistant sources to ensure a more robust host plant resistance to SCA.
Genome-wide association studies (GWAS) were completed for anthracnose and grain mold resistance using NPGS tropical germplasm from Ethiopia, Sudan, and Yemen. The genetic and grain mold characterization of NPGS core collections from Ethiopia and Sudan were combined to increase the statistical power of the GWAS. The genome scan using 599 accessions found two genomic regions in chromosome 4 and 7 associated with germination rate, and four genomic regions in chromosome 1, 3, 6, and 7 associated with seed deterioration. These genomic regions provide an insight of the molecular mechanism involved in the resistant response; however, they only explain a limited portion of observed variation. Further development of segregating populations from these resistant accessions could lead to untapping other resistance loci. The GWAS for anthracnose resistance response observed in the Yemen core collection detected a genomic region at the top of chromosome 2. Remarkably, this genomic region encloses genes that encode proteins associated with the plant immune system.
The sugar content (Brix) variation observed among 233 NPGS sweet sorghum accessions evaluated in Puerto Rico and Georgia for two years was used to perform GWAS. This genome scan found two genomic regions in chromosome 1 and 8 associated with the observed Brix variation. Further validation of these genetic loci in segregating populations will allow scientists in this project to increase the efficiency of selection based on marker assisted selection.
Accomplishments
1. Identification of sugarcane aphid (SCA) resistance locus in SC112-14. The identification, development, and use of resistant sorghum germplasm is the most feasible strategy to control SCA. In collaboration with ARS scientist in Georgia, ARS researchers in Mayaguez, Puerto Rico, determined that the SCA resistance observed in SC112-14 is controlled by a genomic region in chromosome 6. This genomic region is in proximity to those observed in two other SCA resistance lines (Henong 16 and Tx2783), and similar to one genomic region found in a Haitian sorghum breeding population. This research allows breeders in sorghum improvement programs to immediately use line SC112-14 to develop new resistant germplasm to ensure robust control of the SCA.
Review Publications
Cuevas, H.E., Cruet-Burgos, C.M., Prom, L.K., Knoll, J.E., Stutts, L.R., Vermerris, W. 2021. The inheritance of anthracnose (Colletotrichum sublineola) resistance response in sorghum differential lines QL3 and IS18760. Scientific Reports. 11. Article 20525. https://doi.org/10.1038/s41598-021-99994-3.
Cuevas, H.E., Vermerris, W. 2022. Linkage map construction using limited parental genotypic information. Euphytica. 218, 18. https://doi.org/10.1007/s10681-022-03005-z.
Prom, L.K., Cuevas, H.E., Ahn, E., Isakeit, T., Magill, C. 2022. Response of sorghum accessions from three African countries to anthracnose, grain mould, and rust. Plant Pathology Journal. 21(1):12-23. https://doi.org/10.3923/PPJ.2022.12.23.
Xin, Z., Wang, M.L., Chen, J., Harrison, M.L., Morris, G., Cuevas, H.E., Pugh, N.A. 2021. Sorghum genetic, genomic, and breeding resources. Planta. 114:254. https://doi.org/10.1007/s00425-021-03742-w.
