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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED RESISTANCE TO SOYBEAN PATHOGENS AND PESTS

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

Title: Use of quantitative traits to assess aggressiveness of Phakopsora pachyrhizi isolates from Nigeria and the United States

Authors
item Twizeyimama, Mathias -
item Ojiambo, Peter -
item Bandyopadhyay, Ranajit -
item HARTMAN, GLEN

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 13, 2014
Publication Date: May 29, 2014
Repository URL: http://handle.nal.usda.gov/10113/59014
Citation: Twizeyimama, M., Ojiambo, P., Bandyopadhyay, R., Hartman, G.L. 2014. Use of quantitative traits to assess aggressiveness of Phakopsora pachyrhizi isolates from Nigeria and the United States. Plant Disease. http://dx.DOI.org/10.1094/PDIS-12-13-1247-RE.

Interpretive Summary: Soybean rust is one of the most important foliar diseases of soybean worldwide. In this study, isolates of soybean rust from Nigeria and the U.S. were compared for six quantitative traits to assess aggressiveness on two soybean genotypes. The number of days after inoculation to first appearance of lesions, uredinia, and sporulation, along with the number of lesions and sporulating uredinia per cm of leaf tissue, and the number of uredinia per lesion, were significantly different among the isolates within each soybean genotype within each country. By defining and understanding the traits used to measure aggressiveness, comparisons among fungal isolates can be used to determine if geographic or environment differences aere associated with quantitative aspects of aggressiveness. This research will be useful to soybean pathologists, mycologists, and other scientists interested in knowing more about aggressiveness traits in fungal pathogens.

Technical Abstract: Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important foliar diseases of soybean worldwide. The soybean-P. pachyrhizi interaction is often complex because of the genetic variability in host and pathogen genotypes. In a compatible reaction, soybean genotypes produce tan colored lesions, whereas in an incompatible reaction, soybean genotypes produce an immune response (complete resistance) or reddish brown lesions (incomplete resistance). In this study, isolates of P. pachyrhizi from Nigeria and the U.S. were compared for six quantitative traits to assess aggressiveness on two soybean genotypes. One soybean genotype, plant introduction (PI) 462312, produced reddish brown lesions to all isolates and the other soybean genotype, TGx 1485-1D, produced tan lesions to all isolates. The number of days after inoculation to first appearance of lesions, uredinia, and sporulation, along with the number of lesions and sporulating uredinia per cm2 leaf tissue, and the number of uredinia per lesion, were significant (P < 0.001) among the isolates within each soybean genotype within each country. The number of days to first appearance of lesions, uredinia, and sporulation was greater on PI 462312 than on TGx 1485-1D among isolates within each country. The number of lesions and sporulating uredinia per cm2, and the number of uredinia per lesion was less on PI 462312 than on TGx 1485-1D among isolates within each country. The number of sporulating uredinia per cm2 regressed to the number of lesions per cm2 increased significantly (P = 0.0001) among isolates on both soybean genotypes. When comparing the slopes of these regression lines, the increase among Nigerian isolates was greater (P < 0.0001) than the U.S. isolates on TGx 1485-1D, but the slopes did not differ (P > 0.0675) between Nigerian and U.S. isolates on PI 462312. This is the first study that used a large number of P. pachyrhizi isolates from two continents that assessed aggressiveness using multiple traits in soybean genotypes that differed in reaction type.

Last Modified: 9/10/2014
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