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United States Department of Agriculture

Agricultural Research Service

Research Project: SOYBEAN DISEASE AND PEST MANAGEMENT

Location: Soybean/maize Germplasm, Pathology, and Genetics Research

Title: Characterizing resistance to Phakopsora pachyrhizi in soybean

Authors
item Miles, Monte
item Hartman, Glen
item Bonde, Morris
item Nester, Susan
item Frederick, Reid

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2011
Publication Date: May 1, 2011
Citation: Miles, M.R., Hartman, G.L., Bonde, M.R., Nester, S.E., Frederick, R.D. 2011. Characterizing resistance to Phakopsora pachyrhizi in soybean. Plant Disease. 95:577-581.

Interpretive Summary: Soybean rust is one of the most important disease constraints to soybean production worldwide. Resistance to soybean rust has been characterized by the presence of reddish-brown (RB) lesions or an immune reaction, and four independently inherited single genes have been identified. However, this resistance has not always been durable and strains of the fungus are known to overcome resistance. Partial resistance, expressed as a reduced rate of disease development that is cumulative over time, may be more durable than the single gene resistance, but is a poorly defined trait to characterize resistance. The objective of this research was to identify components of partial resistance to the fungus causing soybean rust by evaluating 34 soybean accessions each inoculated with four P. pachyrhizi isolates. Differences in latent period, disease development over time, fungal sporulation, and infection frequency were identified. Isolate specificity and interactions between isolates and accessions were identified for many of the disease resistance traits analyzed. Two of the most resistant accessions had a RB phenotype. Other accessions had a susceptible reaction but had components of partial resistance. These results identify lines with partial resistance that may be used as sources to develop high yielding soybean cultivars with partial resistance to soybean rust. This research is important to soybean researchers that are interested in developing resistance to soybean rust.

Technical Abstract: Resistance to Phakopsora pachyrhizi has been characterized by the presence of reddish-brown (RB) lesions or an immune reaction, and four independently inherited genes have been identified. However, this resistance has not been durable once utilized in a breeding program. Partial resistance, expressed as a reduced rate of disease development that is cumulative over time, may be more durable than the single gene resistance, but is poorly defined with soybean rust. The objective of this research was to identify components of partial resistance to P. pachyrhizi in soybean by evaluating 34 soybean accessions inoculated with four P. pachyrhizi isolates. Differences in latent period, measured as area-under-disease-progress-curve (AUDPC) for sporulating uredinia, and infection frequency, measured as severity, were identified. Low AUDPC and low severities were observed on the accessions that had a susceptible tan phenotype as well as accessions that had a resistant RB phenotype. There were few differences among accessions with tan phenotypes for number of uredinia per lesion and uredinia diameter, but accessions with RB phenotypes produced smaller and fewer uredinia per lesion. Interactions between isolates and accessions were identified with AUDPC for number of sporulating uredinia, uredinia per lesion and uredinia diameter as well as sporulation levels with RB lesions, but not with severity. PI 594538A and PI 561356 were among the most resistant of the accessions with RB phenotypes.

Last Modified: 7/25/2014
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