Location: Crop Germplasm Research
2021 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 2021 under Objective 1, cooperative work with scientists from ARS and academia evaluated more than 200 sorghum lines from U.S. Sorghum Collections, converted sorghum lines, and commercial hybrids for resistance to anthracnose, grain mold, head smut, and downy mildew. In addition, 42 grain mold resistant lines derived from crossing seven photosensitive accessions with the RTx430 sorghum parental line are currently being evaluated in the field for resistance in Texas. Under Objective 2, greenhouse evaluations were conducted to establish the virulence patterns of six and eight isolates of the anthracnose and head smut pathogens, respectively. Deoxyribonucleic acid extraction and sequencing of several anthracnose and head smut isolates were performed and the data are being analyzed and evaluated. Work is also underway at the Texas A&M AgriLife Research Farm, Burleson County, Texas, to determine the efficacy of fungicides (Azoxystrobin and Pyraclostrobin) and an experimental biocontrol agent (Bacillus velezensis LP16S) on anthracnose and grain mold response and yield of the commercial sorghum hybrid, BH 4100. Results from these fungicide and biocontrol agent studies will validate the effectiveness of this Bacillus species in sorghum disease management.
Accomplishments
1. New sources of grain mold resistance in sorghum. Grain mold on sorghum causes economic losses totaling hundreds of millions of dollars per year in yield and seed quality. The most effective control strategy for this disease complex is the use of resistant sources. ARS researchers at College Station, Texas, and Mayaguez, Puerto Rico, working with collaborators at Texas A&M University, evaluated the Sorghum Association Panel lines for resistance against three grain mold fungi, individually and in combination, and also used a genome-wide association study to identify annotated gene(s) that may play a role in grain mold resistance. The work identified 18 sorghum lines, including PI533962, PI642998, PI 566819, PI576130, and PI656051 that exhibited grain mold resistance response against the fungi either individually or in combination. Molecular tools known as 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 accomplishment is significant because the top-scoring SNPs in this study were mapped to the nearest, or a nearby annotated gene(s) in the nine sorghum chromosomes and will in turn provide a platform for testing the effectiveness of each gene listed for sorghum defense against these fungal pathogens.
2. New sources of anthracnose, head smut, and downy mildew resistance in sorghum. Anthracnose, head smut, and downy mildew cause annual global economic losses in sorghum yield and seed quality amounting to hundreds of millions of dollars. The most appropriate strategy for controlling these fungal diseases is development of new disease-resistant sorghum varieties. ARS researchers at College Station, Texas, and Mayaguez, Puerto Rico, working with collaborators at Texas A&M University, evaluated dozens of sorghum lines drawn from various sources, with focus on identifying resistance to anthracnose, head smut, and downy mildew. The work established that a number of these lines are highly resistant to one or more of the diseases. This accomplishment represents 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 and profitable use in world agriculture.
Review Publications
Prom, L.K., Sarr, M., Diatta, C., Ngom, A., Aidara, O., Cisse, N., Magill, C. 2021. The occurrence and distribution of sorghum diseases in major production regions of Senegal, West Africa. Plant Pathology Journal. 20(1):1-10. https://doi.org/10.3923/ppj.2021.1.10.
Prom, L.K., Isakeit, T., Cuevas, H.E., Erattaimuthu, S., Jacobsen, R. 2020. Sorghum seed fungal community and their association with grain mold severity, seed weight, and germination rate. Journal of Agriculture and Crops. 7(1):14-19. https://doi.org/10.32861/jac.71.14.19.
Prom, L.K., Perumal, R., Isakeit, T., Erattaimuthu, S., Magill, C. 2021. Response of sorghum accessions against newly documented pathotypes 5 and 6 of head smut pathogen, Sporisorium reilianum. American Journal of Plant Sciences. 12:432-443. https://doi.org/10.4236/ajps.2021.123028.
Isakeit, T., Labar, S., Rooney, W.L., Prom, L.K. 2021. Effect of Bacillus velezensis and fungicides on sorghum anthracnose in Burleson County, Texas, 2020. Plant Disease Management Reports. 15. Article CF076.
Prom, L.K., Ahn, E.J., Magill, C.W. 2021. SNPs that identify alleles with highest effect on grain mold ratings after inoculation with Alternaria alternata or with a mixture of Alternaria alternata, Fusarium thapsinum, and Curvularia lunata. Journal of Agricultural and Crop Research. 9(3):72-79.
Ahn, E., Prom, L.K., Hu, Z., Odvody, G., Magill, C. 2021. Genome-wide association analysis for response of Senegalese sorghum accessions to Texas isolates of anthracnose. The Plant Genome. Article e20097. https://doi.org/10.1002/tpg2.20097.
