Project Number: 8042-22000-286-00-D
Project Type: In-House Appropriated
Start Date: May 14, 2013
End Date: May 13, 2018
The long-term goal of this project is to discover, characterize, and use disease resistance genes to broaden the genetic base of the common bean and to reduce the vulnerability of this crop to several hyper-variable pathogens that include those that cause the devastating rust, anthracnose,and angular leaf spot diseases. These pathogens are known for their extensive virulence diversity that may change from one year or location to another. Thus, one very important target of this project is to identify broad-spectrum disease resistance genes from the Mesoamerican and Andean gene pools of the wild and cultivated common bean. This will be accomplished by inoculating common bean with selected races of the aforementioned pathogens. Studies of the inheritance of disease resistance will be conducted to characterize and map the new disease resistance genes. Simple sequence repeat (SSR) molecular markers linked with the newly discovered disease resistance genes will be identified to expedite the incorporation of these genes into new bean cultivars using marker-assisted selection. Conventional and molecular breeding approaches will be used to develop bean germplasm lines in various market classes that combine several genes with broad-spectrum resistance to the rust, anthracnose, and angular leaf spot pathogens with high yield and other valuable agronomic attributes. The specific objectives of this project are: Objective 1: Evaluate available common bean accessions from various geographic regions to identify potential sources of resistance to various pathogens, characterize new resistance genes, and develop molecular markers for use in introgression. Objective 2: Introgress useful disease resistance genes, combine with good agronomic and quality trait genes in adapted backgrounds, and release germplasm lines or cultivars that can be used to broaden the genetic base of common bean.
To identify disease resistance sources and genes for rust, anthracnose, and angular leaf spot, the emphasis will be on evaluating 77 wild accessions and 55 domesticated landraces from the Mesoamerican and Andean gene pools of the common bean. The Andean Diversity Panel with about 350 bean accessions will also be evaluated. All evaluations will be conducted under greenhouse or field conditions. Evaluations in the field will be in locations where these pathogens occur naturally or where inoculation with local isolates is possible. Similar methodologies will be used for the three aforementioned diseases. Selected races of each of these pathogens known for the virulence spectrum will be used to inoculate all bean accessions. Crosses will be made between selected resistant and susceptible cultivars to determine their inheritance of resistance. F2 populations consisting of at least 120 F2 plants will be inoculated with selected races of the three pathogens. Reactions of each F2 plant to these pathogens will be recorded. Molecular markers including simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) DNA markers are needed for use in marker-assisted selection to develop common bean cultivars with durable resistance. To accomplish this, the parents, the segregating population, and checks will be inoculated with specific races of the three pathogens to which one of the parents is resistant and the other susceptible. The reactions for each F2 plant will be recorded. Genomic DNA will be isolated from the parents, checks, and from each of the F2 plants of the segregating population. Bulked segregant analysis will used to identify DNA markers associated with resistance in those cases when the segregation indicates single gene resistance. The homozygous and susceptible bulks and the resistant and susceptible parents will be analyzed with 5398 SNP DNA markers using the BARCBean6K_3 Illumina Infinium assay. The whole genome sequence scaffold possessing the polymorphic SNPs will be canvassed for SSRs that distinguish the R and S parental lines. The SSRs will be assayed on the recombinant inbred line mapping population, such as BAT 93 x Jalo EEP 558 population, to map the resistance genes to one of the common bean linkage groups. Crosses will be made to combine the newly identified bean rust resistance genes with other already identified rust resistance genes to create bean germplasm lines with broad and durable resistance to this pathogen. A similar approach will be followed to develop cultivars with broad resistance to the anthracnose and angular leaf spot diseases. To combine genes for resistance to rust and other diseases into a single common bean germplasm line or cultivar, crosses will be made between cultivars carrying the newly discovered broad-spectrum rust resistance genes with cultivars having genes for resistance to the anthracnose and angular leaf spot diseases. Races of the pathogens and molecular markers will be used to confirm the presence of the disease resistance genes in the newly created bean plants with genes for resistance to rust, anthracnose, and angular leaf spot.