Location:2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Identify, characterize, and tag genes/QTL conditioning resistance to diseases and abiotic stresses of economic importance in edible legume production. Subobjective 1A: Generate molecular markers in beans and peas with application for MAS of resistance to bacterial, fungal, and viral diseases and tolerance to drought and low soil fertility. Subobjective 1B: Develop dry bean germplasm with enhanced disease and/or abiotic stress resistance using MAS in combination with traditional breeding approaches. Objective 2: Develop improved disease management practices for several soilborne and emerging diseases of edible legumes, and determine environmental host – pathogen relationships. Subobjective 2A: Identify integrated pest management strategies to manage root rot in peas. Subobjective 2B: Investigate effects of environmental factors on edible legume host-pathogen relationships and pathogen biology.
1b. Approach (from AD-416)
Diseases and abiotic stresses (drought, low soil fertility) affecting edible legumes, such as beans, chickpeas, lentils, and peas, result in costly losses to farmers exceeding $100 million annually. Management of soilborne diseases is extremely challenging, because the same pathogens can affect several legumes grown in the same rotation, and the pathogens persist in the soil over many years. Resistant cultivars provide growers with a cost-effective, safe and environmentally friendly way to control most disease and abiotic stress problems. Breeding for resistance, however, is difficult due to the paucity of resistance sources, specifically for soilborne diseases, and lack of information concerning inheritance. Improved management of problematic soilborne diseases is predicated upon a better understanding of the ecology and epidemiology of each pathogen. The objectives of this research are to integrate marker-assisted (MAS) selection with traditional breeding approaches to develop bean germplasm with enhanced levels of disease and abiotic stress resistance, and to improve disease management practices for several soilborne diseases of edible legumes. Novel disease and abiotic stress resistance genes/QTL will be identified, characterized across environments, validated in different genetic backgrounds, and molecular markers with application for MAS of such resistance will be developed and used to breed edible legume germplasm with enhanced resistance. A basis for the improvement of sustainable disease management strategies will be formed through the integration of genetic resistance, chemical and cultural tactics, and improved understanding of the epidemiology and population biology of several economically important pathogens of edible legumes.
3. Progress Report
Seventeen acres of field trials representing 2800 test plots were planted during the summer of 2011 to evaluate dry bean for response to drought, soil compaction, disease, and low soil fertility. Dry bean lines (215 lines) were tested for resistance to bean common mosaic virus in the greenhouse and 175 bi-parental hybridizations were developed to generate dry beans with enhanced disease resistance. Marker-assisted selections in the laboratory for resistance to one bacterial (common blight) and two fungal diseases (anthracnose, rust) were performed on 300 individual plants to facilitate breeding for multiple disease resistance in the pinto bean market class. Thirty-advanced red, pink, great northern, and pinto dry bean breeding lines were tested for yield and general agronomic performance across the United States including Idaho, Michigan, Nebraska, and North Dakota. Twenty-five pinto beans with slow-darkening trait were developed and tested in advanced yield trials in Washington and North Dakota. With researchers from ARS Beltsville and University of Saskatoon, genetic populations segregating for slow dark gene were developed and used to generate linked markers to facilitate molecular breeding for the desirable trait which preserves seed quality under prolonged storage conditions. Progress was made toward discovery of the genes underpinning partial resistance to white mold disease using next generation RNA sequencing. Five mefenoxam-resistant and five mefenoxam-sensitive isolates of Pythium ultimum were assessed for growth at 7.2 and 10°C on corn meal agar to determine the aggressiveness of these seed-rotting pathogens at temperatures normally experienced when green peas are seeded. Sexual reproduction of five mefenoxam-resistant and five sensitive isolates of Pythium ultimum were assessed at five temperatures to determine reproductive capabilities of isolates that have developed fungicide resistance. Two pea mapping populations consisting or 183 and 355 lines, respectively, were screened for resistance to white mold in repeated trials based on lesion expansion, time of disease onset and nodal resistance. From the screenings of these population, 109 individual plants demonstrating excellent partial resistance to white mold were retained, grown in a greenhouse to maturity, and the seed collected for further evaluations. In a collaborative research project with French scientists, a pea mapping population (178 lines) including the parents, was screened for resistance to Fusarium solani in greenhouse trials and resistant lines were identified. In field trials in Oregon and Washington, the effectiveness of fifteen different pea seed treatments in preventing seed rot, reducing root rot, and improving yield was determined.
1. Advances in marker-assisted breeding for resistance to white mold in dry bean. White mold is rated the number one disease problem of dry bean in the United States. Markers linked with resistance to white mold are needed to facilitate marker-assisted breeding efforts because resistance is complex and quantitatively inherited. USDA-ARS (Prosser, Washington) led a team of researchers from the International Center for Tropical Agriculture, in Cali, Colombia, in generating markers linked with white mold resistance traits in two common bean populations. Six of 21 distinct genomic regions affecting resistance most suitable for marker-assisted breeding were highlighted. The new markers and comparative linkage map represent a useful resource for breeding and interpreting past, present, and future genetic studies concerning partial resistance to white mold in common bean.
2. Release of Fusarium wilt and root rot resistant green pea breeding lines. Fusarium root diseases are currently a major concern of the green and dry pea industries worldwide and limited resistant material to these diseases with agronomically acceptable characteristics have been made available to pea breeders. Six advanced breeding lines containing both high levels of field resistance to Fusarium root rot and Fusarium wilt races 1 and 2 were developed and released by a USDA-ARS scientist at Prosser, WA. These breeding lines reduced mean root rot severity in field trials by 38 to 50% compared to the susceptible commercial standard, Bolero. In an artificial inoculation study in a greenhouse, these lines were also resistant to Fusarium wilt race 5. In addition to Fusarium disease resistance, these lines have desirable agronomic traits such as double or triple pods per node and four of the six lines have the afila leaf-type which is in high demand by breeders in the pea industry since it promotes the development of uniform seed coat color and improves anti-lodging characteristics which facilitates harvest. These lines are currently being used by private breeders as a resource for developing root-rot-resistant cultivars serving the canning, freezer, and dry pea industries.
Leavitt, S., Fankhauser, J., Leavitt, D., Porter, L., Johnson, L., St. Clair, L. 2011. Complex patterns of speciation in cosmopolitan "rock posy" lichens - an integrative approach to discovering and delimiting fungal species in the lichen-forming Rhizoplaca melanophthalma speciescomplex. Molecular Phylogenetics and Evolution. 59:587-602.