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United States Department of Agriculture

Agricultural Research Service


Location: Foreign Disease-weed Science Research

2012 Annual Report

1a. Objectives (from AD-416):
Identify genomic and phenotypic elements to characterize emerging and foreign fungal plant pathogens. Develop an understanding of the biology, genetics and epidemiology of emerging and foreign fungal plant pathogens. Screen germplasm for resistant sources to emerging and foreign fungal plant pathogens. Per PDRAM for Research on Emerging Fungal Plant Pathogens at Frederick, MD #R07 Objective 4: Develop rapid and reliable diagnostics for new and emerging foreign fungal plant pathogens that can be transferred to regulatory agencies and the private sector.

1b. Approach (from AD-416):
Utilize the Bio-Safety Level 3 Plant Pathogen Containment facilities to investigate and characterize virulence, genetic variability, epidemiology, host range, and survival of foreign and emerging fungal plant pathogens considered to be a threat to the U.S. Establish pathogen collections, compare exotic and endemic isolates for morphology, virulence, and genomics using a variety of scientific methods. Develop detection techniques using PCR and immunological methodologies. Investigate pathogen genomics and host plant resistance using classical and molecular approaches.

3. Progress Report:
Soybean rust: In collaboration with ARS scientists at Stoneville, MS rust resistant soybean germplasm and breeding lines identified in field trials in Paraguay were evaluated further in seedling inoculations with purified isolates of Phakopsora pachyrhizi at the FDWSRU. Several metabolic pathway genes have been cloned and will be evaluated for a role in Rpp-mediated rust resistance using virus-induced gene silencing (VIGS). Wheat blast: One hundred twenty spring wheat lines were inoculated with a single isolate of Magnaporthe oryzae, T-25 isolated in Brazil in 1988. Host range studies have shown that the M. oryzae wheat pathotype can infect and produce sporulating lesions on grains and grasses common to the US, including perennial ryegrass, annual ryegrass, oats, finger millet, green foxtail, green bristle grass, maize, switchgrass, and buffalo grass.

4. Accomplishments
1. Unique proteins identified that are expressed during infection by soybean rust. Phakopsora pachyrhizi, the causal agent of Asian soybean rust, has the potential to spread rapidly and cause substantial yield loss. Soybeans grown in the U.S. are highly susceptible to rust, and fungicides are the only management tool available to growers. Understanding the molecular mechanisms involved in the infection process may lead to alternative control options. Using two-dimensional gels and mass spectrometry, 119 proteins were identified by ARS researchers at Frederick, Maryland from a specialized infection structure know as an appressorium. The identification of these proteins will be useful to government, academic, and private sector researchers for developing resistant soybean cultivars or targeting fungicides to control soybean rust.

2. High temperatures affect development of rust on soybean. Soybean rust, caused by the fungus Phakopsora pachyrhizi, is a serious foliar disease in most countries where soybeans are grown. Understanding environmental effects on the development of soybean rust disease is critical in developing disease models that can assist growers in deciding if and when to apply fungicides. Experiments conducted, by ARS researchers at Frederick, Maryland, in controlled growth chambers determined the effects of temperature on lesion formation and spore production after infection has taken place. No lesions developed when the daily temperature high was 37 degrees C or above. The inhibition of temperature highs on soybean rust development in southeastern states limits disease spread. This information will be for developing soybean rust disease forecasting models.

Review Publications
Luster, D.G., Mcmahon, M.B., Edwards, H.H., Boerma, B.L., Miller, S.A., Dorrance, A.E. 2012. Novel phakopsora pachyrhizi extracellular proteins are ideal targets for immunological diagnostic assays. Applied and Environmental Microbiology. 78(11):3890-3895.

Kim, K., Unfried, J.R., Hyten, D.L., Frederick, R.D., Hartman, G.L., Nelson, R.L., Song, Q., Diers, B.W. 2012. Molecular mapping of soybean rust resistance in soybean accession PI 561356 and SNP haplotype analysis of the Rpp1 region in diverse germplasm. Theoretical and Applied Genetics. 125:1339-1352.

Li, S., Smith, J.R., Ray, J.D., Frederick, R.D. 2012. Identification of a new soybean rust resistance gene in PI 567102B. Theoretical and Applied Genetics. 125:133-142.

Stone, C.L., Mcmahon, M.B., Fortis, L.L., Nunez, A., Smythers, G.W., Luster, D.G., Frederick, R.D. 2012. Gene expression and proteomic analysis of the formation of P. pachyrhizi appressoria. Biomed Central (BMC) Genomics. 13:269.

Bonde, M.R., Nester, S.E., Berner, D.K. 2012. Effect of soybean leaf and plant age on susceptibility to initiation of infection by Phakopsora pachyrhizi. Plant Health Progress. PHP-2012-0227-01-R.

Bonde, M.R., Nester, S.E., Berner, D.K. 2012. Effects of post-dew period temperature on development of phakopsora pachyrhizi on soybean. Phytopathology. 102:761-768.

Last Modified: 2/23/2016
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