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.
3. Progress Report
Progress was made in the development and evaluation of novel snap beans combining genetic resistance to the rust disease and tolerance to high ambient temperatures (heat tolerance). Following a process of crosses between beans with resistance to rust and heat tolerance, subsequent evaluations permitted the identification of two snap bean lines having two genes for rust resistance and tolerance to heat. One of the rust resistance genes was from a bean of the Middle American gene pool and the other gene from a bean of the Andean gene pool. These complementary resistance genes provided broad and effective resistance to all known strains of the hyper-variable rust pathogen under greenhouse conditions. These two lines, check cultivars, and 12 snap bean cultivars adapted to different geographical regions were evaluated during 2009 for their reaction to rust and yield at six field locations in Eastern Africa and for heat tolerance under field conditions in Puerto Rico. The two new selected snap bean lines were resistant to rust in all locations in Eastern Africa, while some of the cultivars were very susceptible. These lines also had stable yields at the same sites with contrasting mean ambient temperatures and were superior to the cultivars presently grown in this region. This research will contribute to the improvement of snap beans for various environments where rust and high ambient temperatures are important constraints to snap bean production. Progress was made in the characterization of the virulence spectra of two new races of the rust pathogen and of their possible impact on bean production in the United States. These races appeared at the end of the 2007 and 2008 in Michigan and North Dakota, respectively. Both new races infected the widely grown dry bean varieties with the Ur-3 rust resistance gene that were previously resistant to the rust disease. However, all dry bean germplasm lines from different market classes developed at Beltsville with two or more rust resistance genes were resistant to these races. Similarly, many new bean cultivars developed in collaboration with scientists at state universities at North Dakota, Michigan, Nebraska, and Colorado were also resistant to these new races. Progress was made in the discovery, characterization, and use of novel sources of resistance to the highly variable bean rust pathogen. New sources of resistance identified include domesticated beans from the Andean and Middle American gene pools and wild beans also from both gene pools of common bean. The sources of resistance will provide new and important rust resistance genes that are germane to the cost-effective and sound management of the rust pathogen that recurrently produces new strains or races as it did in 2007 and 2008 in Michigan and North Dakota, that can overcome the resistance in previously resistant cultivars.
Urrea, C., Steadman, J.R., Pastor Corrales, M.A., Lindgren, D.T., Venegas, J.P., Coyne, D.P. 2009. Registration of Great Northern Common Bean Cultivar NE1-06-12 with Enhanced Disease Resistance to Common Bacterial Blight and Bean Rust. Journal of Plant Registrations. 3:219-222.