2012 Annual Report
1a.Objectives (from AD-416):
The major and long-term objectives of this project are.
1)to identify and characterize disease resistance genes in common bean for the management of the soybean rust pathogen (Phakopsora pachyrhizi), (2) to identify and characterize disease resistance genes in common bean for the management of common bean rust (Uromyces appendiculatus), and.
3)to use newly discovered and other disease resistance genes to develop common bean germplasm lines with multiple resistances to common bean and soybean rusts and other highly variable pathogens.
1b.Approach (from AD-416):
To identify and characterize disease resistance genes for soybean rust (SBR) control in common bean, a sub sample of the common bean core collection will be evaluated. This core collection will have about 250 bean accessions from the Andean (five countries) and Mesoamerican (six countries) gene pools. Soybean accessions will be included as checks. Several isolates of the SBR pathogen from different countries in Africa, Asia, and South America, and from the United States, will be used to inoculate the common bean accessions. SBR resistant and susceptible accessions will be crossed to characterize the inheritance of SBR resistance and to search for molecular markers linked to the SBR resistance genes. Appropriate populations (F2, RILs, etc.) for these types of studies will be developed and inoculated with selected isolates of the SBR. Leaf tissue from each F2 plant or other appropriate progeny plant will be collected for DNA extraction and the identification of molecular markers linked to SBR resistance genes. To determine yield reduction on common bean caused by SBR, dry bean plots will be established under field conditions in collaboration with scientists from the United States and Brazil. Two locally adapted dry bean cultivars will be used. Locally adapted soybean cultivars will also be included for comparison. Similar methodologies and approach will be used for the identification and characterization of resistance genes in common bean for the control of common bean rust. All the newly discovered genes for resistance to both rusts will be used in the development of new bean cultivars with commercial bean seed type and broad resistance to rusts and other important common bean pathogens.
Progress was made on a project that aims to identify new dry bean lines in different U.S. market classes with resistance to the rust disease. This is significant because a new strain of the bean rust pathogen that appeared recently in the United States renders susceptible many dry bean varieties that previously were resistant to rust. Hundreds of dry bean lines developed by bean breeders in state universities and industry were evaluated under field and greenhouse conditions at Beltsville, MD. This is the sole location in the United States where rust evaluations are conducted. Much progress was been made in identifying under field conditions many advanced dry bean lines in the Pinto and Great Northern market class that combine broad resistance to rust and other highly desirable attributes, such as high yield and upright architecture. These evaluations also included dry beans lines from other market classes where progress was also being made in determining reaction to the rust pathogen.
Progress was made in studying a new and very important gene for resistance to the highly variable pathogen that causes the rust disease of common bean. This new gene, which was identified in common bean accession PI 310762, confers broad resistance to all but one of the 90 races of the rust pathogen maintained at the USDA-ARS bean project at Beltsville, MD. The resistance spectrum of this gene is different from that conferred by the other 10 known and named rust resistance genes in common bean. Progress was made in studying the inheritance of resistance of this gene as well as is in the search for molecular genetic markers linked to this gene. These markers will facilitate the transfer of this resistance gene to new common bean cultivars in different market classes and will therefore have significant value to U.S. bean producers.
A study of the inheritance of resistance results in a genetic solution for the control of two major diseases of common bean. Among the major diseases of common bean in the world, anthracnose and angular leaf spot are very severe and recurrent. ARS researchers at Beltsville, MD and collaborators studied the inheritance of resistance to these diseases in a black-seeded bean named Ouro Negro. The analysis of a genetic population developed using Ouro Negro as a parent to determined that the resistance to the two diseases is conferred by two separate genes located very close to each other. Because of their proximity, these two genes are inherited together. We identified two molecular markers that are located in close proximity to the two resistance genes. Consequently, when crosses are made to transfer the anthracnose and angular leaf spot disease resistance genes from Ouro Negro to other bean cultivars, the molecular markers can be used to identify the progeny having the two disease resistance genes without the need to conduct the complex process of inoculating the progeny with the disease organisms. This genetic solution reduces the costs of dry bean production and the possible harmful environmental impact that pesticides have when used to control diseases. The results of this study are very useful to plant breeders in ARS, state universities, and industry wishing to develop common bean cultivars with resistance to the anthracnose and angular leaf spot diseases. These molecular markers will significantly reduce the time and cost associated with the simultaneous transfer of the two genes for resistance to the anthracnose and angular leaf spot diseases into new common bean cultivars.
Brick, M.A., Ogg, J.B., Schwartz, H.F., Johnson, J.J., Judson, F., Miklas, P.N., Singh, S.P., Pastor Corrales, M.A., Kelly, J.D. 2011. Registration of “Croissant” pinto bean. Journal of Plant Registrations. 5(3):299-303.