Location:2009 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. Formerly 5354-21220-015-00D (4/08).
3. Progress Report
New genes Rk^r^ and bic which effect seed and flower color, respectively, were discovered and characterized in dry bean. The Rk^r^ gene effects red seed coat color and maps to Phaseolus vulgaris linkage group 1. This work was done in collaboration with researchers from the Center for Tropical Agriculture (CIAT) in Cali, Colombia, and a University of Florida Plant Geneticist who led the study. Secondly, a preliminary comprehensive genetic linkage map of 37 QTL conferring resistance to white mold was constructed. Two-way populations designed to study the effect of combining independent QTL on level of disease resistance were developed. Disease reaction in the greenhouse was obtained and marker assays conducted. Preliminary analysis indicates an improved level of resistance to white mold and common blight may be attained by combining resistance genes. More than 125 biparental crosses were conducted to combine genes for development of multiple stress resistant germplasm releases and cultivars. Eight acres of test plots (~2800) were planted during the summer of 2009 to evaluate, increase and/or advance 850 distinct breeding lines representing six major dry bean market classes: pinto, small red, pink, black, great northern, and cranberry. The pea cultivar strike was assessed for resistance to Pythium ultimum using isolates collected from pea growing regions of the Columbia Basin, WA. The cultivar Strike was determined to not have any partial resistance to Pythium as previously assumed by the pea industry and the contingency plan of testing the pea cultivar Freezer 43 for Pythium resistance will have to be pursued. Pythium isolates from 60 fields in the state of Washington were assessed for resistance to metalaxyl, and isolates from sixteen of the 60 fields were metalaxyl-resistant. Five metalaxyl-resistant and five metalaxyl-sensitive isolates were tested for aggressiveness on peas based on seed rot and pre-emergence seedling rot. Metalaxyl-resistant isolates were determined to be more aggressive than sensitive isolates based on their ability to cause seed and seedling rots. In two field studies, the impact of pea variety, treated seed, compacted soil, and foliar applications of a plant defense-inducing compound (phosphorous acid) on managing pea root rot was assessed. Eight treatments outlined in the project plan, were evaluated at each location for each pea variety tested (Columbian and Aerial). Phosphorous acid applied as a foliar treatment at the 2.5 pint per acre rate was identified as the most economical and effective means of managing root rot, and when coupled with not rolling the soil after planting, the combination of these two treatments consistently was the most effective means to significantly improve dry pea yields in commercial dry pea production areas of Washington. In two separate field studies, the impact of seven fertilizer treatments and five soil amendments, respectively, on pea root rot were assessed in a dry land pea production area located near Milton-Freewater, OR.
1. Quantitative resistance to Bean dwarf mosaic virus in common bean is associated with the Bct gene for resistance to Beet curly top virus. Bean dwarf mosaic virus (BDMV) is a white-fly vectored viral disease that is problematic for dry bean production in the tropics. Genetic resistance can be used to control this disease but sources are lacking. USDA-ARS scientists Prosser, WA led a team of scientists from UC-Davis, in the identification and characterization of a new source of quantitative resistance effective against BDMV. The quantitative resistance is associated with the Bct gene which confers qualitative resistance against a completely different virus disease, Beet curly top (BCTV), which is vectored by a leaf hopper. This work provides breeders with a new source of resistance to combat BDMV. Knowledge generated enables simultaneously breeding for resistance to two disparate viral diseases.
2. Use of Phosphorous Acid and Avoidance of Rolling Soil Improves Dry Pea Production. Aphanomyces root rot caused by Aphanomyces euteiches is considered by dryland pea growers to be the major disease affecting pea production in the states of Washington and Idaho. Current dry pea cultivars lack significant resistance to this pathogen and the disease is so devastating that some growers have lost the ability to plant peas in their crop rotation. The impact of early foliar applications of phosphorous acid and the avoidance of packing soil (rolling) after planting, on root rot and yield of dry peas in commercial pea fields in Washington and Idaho was investigated. ARS scientists at Prosser, WA found that a 2.5 pint foliar application of phosphorous acid applied at the 3rd to 5th node stage of pea development, and avoiding rolling the soil after planting, can significantly reduce root rot caused by Aphanomyces and other root rotting pathogens. Implementing these results could improve the yields of popular dry pea cultivars by 12 to 67% over the standard commercial practice.
Miklas, P.N., Larsen, K.M., Terpstra, K.A., Hauf, D.C., Grafton, K.F., Kelly, J.D. 2007. Qtl analysis of ica bunsi-derived resistance to white mold in a pinto x navy bean cross. Crop Science. 47: 174-179.