Location: Crop Germplasm Research
2022 Annual Report
Objectives
The primary objectives of this project are enhancement of sorghum productivity by identifying lines with multiple disease resistance genes and utilization of genomic DNA sequence information to assess variability in new and emerging fungal pathogens. Over the next 5 years we will focus on the following objectives.
Objective 1: Evaluate national and international sorghum germplasm resources for resistance to anthracnose, grain mold, and head smut diseases.
Subobjective 1.A. Identify new sources of resistance to anthracnose within converted and exotic sorghum.
Subobjective 1.B. Identify sources of resistance to grain mold.
Subobjective 1.C. Identify sources of resistance to pathotypes (P5 and P6) of Sporisorium reilianum, causing sorghum head smut.
Objective 2: Determine the population structure of diverse anthracnose (Colletotrichum sublineolum) and head smut (Sporisorium reilianum) isolates utilizing genomic DNA sequencing and phenotypic expression patterns of virulence on host differentials to characterize resistance to these diseases.
Subobjective 2.A. Determine the variability of C. sublineolum isolates based on genomic DNA sequencing.
Subobjective 2.B. Monitor changing populations and identify new pathotypes of C.
sublineolum present in the U.S. and Puerto Rico.
Subobjective 2.C. Determine genetic variability among diverse isolates of S. reilianum using genomic DNA sequence information.
Subobjective 2.D. Identify pathotypes of S. reilianum among head smut isolates collected from different sorghum growing regions in the U.S. and Puerto Rico.
Approach
Sorghum productivity and profitability in the U.S. are limited by several biotic constraints, most notably plant pathogens causing anthracnose, grain mold, and head smut. Presently, there is limited information on host-plant resistance to these pathogens within sorghum collections obtained from the center of origin (Ethiopia, Mali, and Sudan) or from other available sorghum germplasm. The focus of this project will be to mitigate the impact of these diseases by identifying host resistance in diverse sorghum germplasm. Germplasm that will be included in the evaluations will be collections or subsets of collections from Africa, newly converted, hybrids, parental, and elite lines. The goal will be to select accessions with host resistance to anthracnose, grain mold, and newly documented head smut pathotypes. All germplasm will also be evaluated for ten priority agronomic traits in order to provide breeders with new disease resistant, agronomic lines that will broaden the genetic base for hybrid development. Sorghum also has great potential as a biofuel source. However, biofuel crops require high plant densities that will increase the vulnerability of the crop to foliar and stalk diseases such as the hypervariable anthracnose pathogen, Colletotrichum sublineolum. Pathotypes of C. sublineolum and Sporisorium reilianum will be identified and characterized using genomic DNA sequencing to enhance our knowledge of the genetic potential for pathogenicity of these organisms. Determination of pathogen variability and identification of molecular markers associated with geographic distribution of pathotypes will provide researchers and breeders with tools needed to guide the deployment of appropriate resistant host varieties across the U.S. and abroad.
Progress Report
In fiscal year (FY) 2022, project work evaluated hundreds of national and international sorghum germplasm resources for resistance to anthracnose, grain mold, and head smut diseases to identify resistant lines (Objective 1). The work was done in cooperation with scientists from ARS and academia. Work under Objective 2 in FY 2022 established the population structure of diverse anthracnose (Colletotrichum sublineolum) and head smut (Sporisorium reilianum) isolates, utilizing genomic DNA sequencing and phenotypic expression patterns of virulence on host differentials to characterize resistance to these diseases. Deoxyribonucleic acid extraction and sequencing of several anthracnose and head smut isolates were performed. Over the life of this project, significant progress was made in identifying new sources of germplasm that are resistant to the damaging effects of a number of sorghum diseases of both national and international importance. Modern molecular tools were applied to the work to help identify/localize the genetic origin of resistance mechanisms. Work overall during the life of the project provided important new information and technology for use by sorghum researchers and breeders in improving the crop for U.S. farmers. This project expired in FY 2022 and was replaced by 3091-22000-039-000D which is continuing and expanding upon the work.
Accomplishments
1. New sources of grain mold resistance in sorghum. Grain mold on sorghum causes economic losses totaling hundreds of millions of dollars in yield and seed quality. The most effective control strategy for this disease complex is the use of resistant sources. ARS scientists at College Station, Texas, and Mayaguez, Puerto Rico, working with university collaborators, evaluated hundreds of Sorghum Association Panel lines, exotic lines from Africa, and commercial hybrids for resistance against grain mold pathogens. The work also used a modern research technique known as genome-wide association to identify genes that may play a role in grain mold resistance. A number of sorghum lines, including PI514449, PI514466, SC725, SC218, and SC19 exhibited resistance response against the individual fungus, Alternaria alternata, or in combination with Fusarium thapsinum and Curvularia lunata. Single-nucleotide polymorphisms (SNPs) with high probability of contribution to the scores for grain mold response also were tracked to the specific chromosome location based on the sorghum genome sequence. This work is significant because the top-scoring SNPs in this study were mapped to the nearest or a nearby annotated gene(s) in the nine chromosomes and will in turn provide a platform for testing the effectiveness of each gene listed for sorghum defense against grain mold fungi.
2. New sources of anthracnose, head smut, rust, and downy mildew resistance in sorghum. Globally, these four diseases cause economic losses in sorghum yield and seed quality amounting to hundreds of millions of dollars each year. The most appropriate strategy for controlling these fungal diseases would be discovery or development of new disease-resistant sorghum varieties. ARS scientists at College Station, Texas, and Mayaguez, Puerto Rico, working with university collaborators, evaluated hundreds of sorghum lines drawn from various sources, with focus on identifying disease resistance. The work established that a number of lines, including PI514453, PI514472, PI514318, PI514538, PI514279, and PI514316 were highly resistant to one or more of the diseases. This work is a significant advancement in sorghum disease research in that it provides sorghum breeders and other researchers with critical new germplasm that will be foundational in developing new, disease-resistant sorghum varieties for productive use in U.S. agriculture.
Review Publications
Prom, L.K., Ahn, E., Isakeit, T., Magill, C. 2021. Correlations among grain mold severity, seed weight, and germination rate of sorghum association panel lines inoculated with Alternaria alternata, Fusarium thapsinum, and Curvularia lunata. Journal of Agriculture and Crops. 8(1):7-11. https://doi.org/10.32861/jac.81.7.11.
Prom, L.K., Isakeit, T. 2021. Diversity and frequency of fungal genera from sorghum lines inoculated with Alternaria alternata alone and in combination with Curvularia lunata and Fusarium thapsinum in a field infected with anthracnose. Journal of Agricultural and Crop Research. 9(11):264-267. https://doi.org/10.33495/jacr_v9i11.21.166.
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.
Prom, L.K., Isakeit, T. 2021. Incidence of zonate leaf spot on sorghum accessions under disease-conducive growing conditions Burleson County, Texas. Journal of Agriculture and Crops. 8(1):35-38. https://doi.org/10.32861/jac.81.35.38.
