Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/7/2010
Publication Date: 3/1/2011
Citation: Walker, D.R., Boerma, H.R., Harris, D.K., Phillips, D.V., Schneider, R.W., Hartman, G.L., Miles, M.R., Weaver, D.B., Sikora, E.J., Moore, S.H., Buckley, J.B., Shipe, E.R., Mueller, J.D., Wright, D.L., Marois, J.J., Nelson, R.L. 2011. Evaluation of USDA soybean germplasm accessions for resistance to soybean rust in the southern United States. Crop Science. 51:678-693. Interpretive Summary: Accessions from the USDA Soybean Germplasm Collection were evaluated in the field for resistance to soybean rust at seven locations in five states between 2006 and 2008. From 96 to 422 accessions per year were rated for disease severity in all locations, and for disease incidence, sporulation, lesion type or uredinia density in some. Accessions carrying the soybean rust resistance genes Rpp1 through Rpp4 were included in the evaluations and of these, Rpp1 provided the highest level of resistance in most year-location environments. Altogether, 64 accessions were resistant in at least two environments, but nearly all were susceptible in some other environments. Of the accessions with uncharacterized resistance genes, PI 567104B had the highest overall resistance. These evaluations provide useful information to soybean breeders about which germplasm accessions should be effective sources of resistance to soybean rust in North America.
Technical Abstract: Soybean [Glycine max (L.) Merr.] resistance to soybean rust (SBR) caused by Phakopsora pachyrhizi would reduce reliance on fungicides to manage this disease. Field evaluations of accessions from the USDA Soybean Germplasm Collection for resistance to SBR were conducted at seven locations in the southern United States between 2006 and 2008. Late summer planting dates and sometimes artificially extended photoperiods were used to better synchronize flowering of maturity group (MG) 000 to X accessions with each other and with autumn SBR epidemics. The numbers of accessions tested in at least one location each year were 347 in 2006, 422 in 2007, and 96 in 2008. Cultivars from each MG except X were included as susceptible checks, and entries were rated for disease severity in all location-year environments, and for disease incidence, fungal sporulation, lesion type, and/or uredinia density in certain environments. While none of the accessions were immune in all environments, 64 were resistant in two or more locations each year that they were tested, often appearing to be more resistant in certain environments than in others. Of the original four Rpp genes described in the literature, Rpp1 provided the highest level of resistance. Among the accessions with uncharacterized Rpp genes, PI 567104B had the highest overall resistance across environments. The plant introductions confirmed to have resistance in these evaluations may be useful sources of genes conferring resistance to at least some North American populations of P. pachyrhizi.