Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2014
Publication Date: 6/23/2014
Publication URL: http://handle.nal.usda.gov/10113/58953
Citation: Walker, D.R., Harris, D.K., King, Z.R., Li, Z., Phillips, D.V., Buck, J.W., Nelson, R.L., Boerma, H.R. 2014. Soybean germplasm accession seedling reactions to soybean rust isolates from Georgia. Crop Science. 54(4):1433-1447. Interpretive Summary: Soybean rust is a fungal disease with the potential to cause severe yield losses in soybean grown in the southeastern United States. Resistant soybean varieties would reduce yield losses without the use of fungicides. Previous research to identify sources of soybean rust resistance was done in the field, where environmental conditions and rust pathogen populations are both highly variable, and where results can be inconsistent. This research was done in the greenhouse, where reactions to the disease can be measured more quickly and reliably. We confirmed the resistance of more than 100 soybean lines from the USDA Soybean Germplasm Collection. Seedling resistance in the greenhouse generally agreed with the reactions of adult plants in the field in the years that the fungus spores used in the greenhouse assays were collected. Similarities between seedling reactions and assessments of resistance on adult plants in the field indicate that data from the greenhouse assays can be used to predict field results. The validation of this screening method is important information for all interested in reducing losses from soybean rust.
Technical Abstract: Soybean rust (SBR), caused by Phakopsora pachyrhizi, is a threat to soybean [Glycine max (L.) Merr.] production in regions of the world where winters are not cold enough to completely eliminate the many hosts of the fungus, so resistant soybean cultivars would be useful in managing this disease. Resistant germplasm accessions have been identified, and resistance (Rpp) genes have been mapped to six independent loci, but the high degree of virulence variability among P. pachyrhizi populations and isolates means that the level of resistance to different populations and isolates can vary considerably. Greenhouse assays were conducted from 2008 until 2013 in which seedlings of soybean plant introductions were challenged with bulk P. pachyrhizi isolates collected in the state of Georgia. Accessions were included in the tests either because they carried known Rpp genes, or because they had appeared resistant to SBR in previous field assays. The resistance was assessed on the basis of lesion type, visible urediniospore development, and sometimes lesion density. With a few exceptions, most of the accessions that appeared resistant as adult plants in the field also had resistance reactions as seedlings, and these reactions were generally similar or identical in the different years that the greenhouse assays were conducted. This study demonstrates that greenhouse seedling reactions should usually be reliable indicators of adult plant resistance to related P. pachyrhizi isolates or populations, and confirms the resistance of more than 100 soybean germplasm accessions to fungal isolates and field populations from Georgia.