Location: Crop Germplasm Research
2019 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
Work under this project in FY 2019 generated important new information on sorghum disease organisms that have actual or potential adverse impact on U.S. sorghum farmers. Under Objective 1, cooperative work with scientists from other ARS locations, and academia, evaluated more than 200 sorghum lines from the U.S. Sorghum Collections, converted sorghum lines, and commercial hybrids for resistance to anthracnose, grain mold, and head smut. In addition, 456 sorghum types known as recombinant inbred lines or RILs, were tested for disease resistance. These RILs were derived from crosses of the anthracnose resistant lines SC265 and SC1103 with the susceptible parent RTx430; the offspring were evaluated in the field for resistance against the anthracnose and downy mildew pathogens in Texas, and promising lines for enhanced resistance were identified. Under Objective 2, greenhouse evaluations were conducted to establish the virulence patterns of 15 isolates each of the anthracnose and head smut pathogens; results documented a wide range of virulence patterns. Work is also underway at two Texas locations to establish the efficacy of fungicides (Proline, Propulse, and Headline) and an experimental biocontrol agent (LP16S) on anthracnose and grain mold response and on yield of one commercial sorghum hybrid (DKS67-66).
Accomplishments
1. New sources of anthracnose, grain mold, head smut, 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 in controlling these fungal diseases would be development of new disease-resistant sorghum varieties. ARS scientists at College Station, Texas, and Mayaguez, Puerto Rico, working with collaborators from Texas A&M University, evaluated a number of sorghum lines drawn from various sources, with focus on identifying resistance to anthracnose, grain mold, 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 work is a significant advancement in sorghum disease research in that it provides sorghum breeders and other researchers critical new germplasm that will be foundational in developing new, disease-resistant sorghum varieties for productive use in world agriculture.
2. Potential new biocontrol agent for sorghum diseases. Bacillus velezensis is a bacterium that is known in some cases to promote plant growth and also to express antifungal activity. ARS scientists at College Station, Texas, working with Texas A&M University collaborators, identified a bacterium that was designated as LP16S; the bacterium exhibited high antifungal activity against some sorghum fungal disease organisms. Genome sequencing of LP16S was accomplished, confirming it to be a B. velezensis type. The current work has established that LP16S has significant inhibitory activity against the fungal pathogens that cause anthracnose and grain mold in sorghum. Work is ongoing to test the organism under field conditions and conduct efficacy comparisons with conventional fungicides. LP16S as a biological control agent may represent an effective alternative in some cases to conventional fungicides in sorghum production.
Review Publications
Radwan, G., Prom, L.K., Odvody, G., Magill, C. 2019. Mating type a locus alleles and genomic polymorphism in Sporisorium reilianum: Comparison of sorghum isolates to those from maize. Australasian Plant Pathology. 48(2):119-129. https://doi.org/10.1007/s13313-018-0607-3.
Prom, L.K., Ahn, E., Isakeit, T., Magill, C. 2019. GWAS analysis of sorghum association panel lines identifies SNPs associated with disease response to Texas isolates of Colletotrichum sublineola. Theoretical and Applied Genetics. 132(5):1389-1396. https://doi.org/10.1007/s00122-019-03285-5.
Pugh, N., Han, X., Collins, D., Thomasson, A., Cope, D., Chang, A., Jung, J., Isakeit, T., Prom, L.K., Carvalho, G., Gates, I., Vree, A., Bagnall, G., Rooney, W. 2018. Estimation of plant health in a sorghum field infected with anthracnose using a fixed-wing unmanned aerial system. Journal of Crop Improvement. 32(6):861-877. https://doi.org/10.1080/15427528.2018.1535462.
Prom, L.K., Cuevas, H.E., Isakeit, T., Perumal, R., Erathaimuthu, S. 2018. Mycoflora analysis and other measured parameters of sorghum seeds collected from Puerto Rico and Mexico. Plant Pathology Journal. 17(2):80-86. https://doi.org/10.3923/ppj.2018.80.86.
Prom, L.K., Cisse, N., Perumal, R., Cuevas, H.E. 2018. Response of sorghum lines and hybrids from the United States to long smut and grain mold. Journal of Agriculture and Crops. 4(11):152-156. https://doi.org/10.32861/jac.411.152.156.
Prom, L.K., Cuevas, H.E., Perumal, R., Isakeit, T., Magill, C. 2018. Inheritance of resistance of three sorghum lines to pathotypes of Colletotrichum sublineola, causal agent of anthracnose. Plant Pathology Journal. 17(2):75-79. https://doi.org/10.3923/ppj.2018.75.79.
Ahn, E., Prom, L.K., Odvody, G., Magill, C. 2018. Responses of Johnsongrass against sorghum anthracnose isolates. Journal of Plant Pathology & Microbiology. 9:442. https://10.4172/2157-7471.1000442.
Cuevas, H.E., Prom, L.K., Copper, E.A., Knoll, J.E., Ni, X. 2018. Genome-wide association mapping of anthracnose (Collectotrichum sublineolun) resistance in the U.S. sorghum association panel. The Plant Genome. 11:170099.
Ahn, E., Prom, L.K., Odvody, G., Magill, C. 2019. Defense responses against the sorghum anthracnose pathogen in leaf blade and midrib tissue of johnsongrass and sorghum. Physiological and Molecular Plant Pathology. 106:81-86. https://doi.org/10.1016/j.pmpp.2018.12.008.
