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United States Department of Agriculture

Agricultural Research Service

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

2012 Annual Report

1a. Objectives (from AD-416):
(1) Identify and confirm resistance to soybean rust at multiple locations in the southern U.S.; (2) Characterize relationships among different rust resistance genes and breed soybean lines with various resistance genes singly and in pairs; (3) Assess genetic and virulence diversity within and among domestic populations of the soybean rust fungus.

1b. Approach (from AD-416):
(1) Coordinate field testing of exotic germplasm, improved breeding lines and sets of differentials for resistance to soybean rust (SBR) in the southern U.S., and in greenhouse evaluations in Griffin GA and Urbana IL. Plant Introductions from the USDA Soybean Germplasm Collection will be screened for resistance to SBR at field nurseries in Baton Rouge and Bossier City, LA; Fairhope, AL; and Quincy, FL, to determine which have resistance. Tests will also be conducted at greenhouses in Georgia and Illinois. (2) Use phenotypic, genetic mapping and genomic data to characterize relationships among Rpp genes from germplasm accessions with SBR resistance, and develop breeding and experimental lines that carry Rpp genes singly or in pairs. Experiments will be conducted to determine which resistance genes and pairs of genes are most effective, and these genes will be selected for in soybean breeding lines. (3) Assess genetic and virulence diversity within and among domestic P. pachyrhizi populations, and maintain a collection of representative isolates that will be necessary for identifying and verifying specific resistance. Samples of the soybean rust fungus will be collected in the field, purified, and tested to determine what reactions they provoke on a set of soybean lines with known resistance genes.

3. Progress Report:
(1) Screening of USDA soybean germplasm for rust resistance: In collaboration with colleagues from the University of Georgia, 108 plant introductions (PIs) from the USDA Soybean Germplasm Collection were planted to be evaluated for resistance to soybean rust (Phakopsora pachyrhizi) in the field at the Attapulgus Research and Education Center 2011. Due to high temperatures and severe drought conditions during the growing season, no disease rating data could be collected before a mid-November frost destroyed the plants in the nursery. Screening nurseries were also planted in Quincy, FL (in collaboration with the University of Florida) and in Fairhope, AL (in collaboration with Auburn University). Despite frost damage, disease rating data were obtained from about two-thirds of the plots in Florida, but the plants in Alabama were fatally injured by the early frost before data could be obtained. (2) Soybean germplasm accessions with field resistance to soybean rust in 2009 and in northern Florida in 2011 were screened for resistance to Georgia isolates in greenhouse assays: Soybean PIs with resistance to rust in the field were inoculated with a mixture of isolates collected in Georgia to evaluate seedling resistance. The majority of these accessions were either immune or had developed the reddish-brown type of lesion associated with incomplete resistance when rated two weeks after inoculation. (3) Evaluation of rust resistance in soybean breeding lines and gene mapping populations: Breeding lines derived from PIs with resistance to soybean rust were developed by the University of Georgia and the USDA-ARS in Urbana, IL. About 20 resistant and agronomically promising breeding lines from the ARS program were planted in replicated experiments in Georgia. Colleagues at the University of Georgia have developed and rated lines in mapping populations derived from more than 30 different rust-resistant PIs, and have developed backcross or inbred breeding lines from many of these resistant PIs as well. (4) Collection, purification and maintenance of isolates of the soybean rust fungus (Phakopsora pachyrhizi): Additional isolates of P. pachyrhizi from several different states were collected, purified and archived during FY 2012.

4. Accomplishments

Last Modified: 06/22/2017
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