Location:2010 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
Molecular data and phenotypic disease reactions were partially obtained for new dry bean genetic populations segregating for resistances to halo bacterial blight, common bacterial blight, and peanut mottle virus (PeMoV). Segregation of the Pse-2 gene (pending) and linked marker (completed) is being used to confirm Mendelian ratios. Advanced progeny lines used to study the interaction between two QTL (SAP6 and SU91) conferring resistance to common bacterial blight, indicate an effect for SAP6 QTL to a Puerto Rican strain of the pathogen but not against a South African strain. Two inbred populations phenotyped for reaction to PeMoV indicate association of resistance to the bc-1^2^ locus for resistance to bean common mosaic virus. Ten populations were generated but not yet phenotyped for testing association of the newly discovered PeMoV resistance gene with existing genes. A comparative genetic linkage map of 35 QTL conferring resistance to white mold was constructed and submitted for publication. Seventy-five bi-parental crosses were conducted to enhance bean germplasm for multiple stress resistance. Thirteen acres of field trials representing 2500 test plots were planted during the summer of 2010 to evaluate dry bean lines for disease reaction, biological nitrogen fixation, and yield performance. The ED-50 concentration for metalaxyl, and growth rates at three temperatures of five metalaxyl-resistant and five metalaxyl-sensitive isolates of Pythium ultimum were determined in laboratory and growth chamber tests to assess differences in fitness and aggressiveness between these isolates. Metalaxyl-resistant isolates were determined to be more aggressive than sensitive isolates based on more rapid growth rates. In three separate field studies, the impact of nine fertilizer treatments on pea root rot were assessed in one dryland and two irrigated pea production areas located in growers’ fields in Washington and Oregon. A pea mapping population consisting of 183 pea lines, two parents and two commercial standards was screened in replicated trials for white mold resistance under controlled growth chamber conditions. Pea lines showing promising resistance to white mold from the mapping population were maintained in a greenhouse until seed could be harvested for further evaluations.
1. Metalaxyl-resistant Pythium ultimum isolates are more aggressive than sensitive isolates. Pythium seed rot caused by Pythium ultimum is a major problem for both conventional and organic pea growers worldwide. Metalaxyl is currently the only compound used by vegetable growers to successfully protect seed from seed rot by this pathogen, but one-third of the crop fields in WA State tested have metalaxyl-resistant isolates. ARS researchers in Prosser, WA identified metalaxyl-resistant isolates, and that cyazofamid was the most effective compound in managing resistant isolates. Research directs farmers to use combinations of metalaxyl and cyazofamid for effective management of Phythium seed rot.
2. Bean yield is enhanced by deployment of genes for resistance to bacterial blight disease. Common bacterial blight limits dry bean production worldwide. Genetic resistance can provide effective control, but the genes derive from exotic sources, thus may actually limit yield when the disease is absent. This condition is referred to as ‘yield drag’ or ‘linkage drag’. ARS researchers in Prosser, WA, transferred two exotically-derived genes into adopted dry bean lines. Extensive yield testing of these lines across three locations and two years indicated the genes could be deployed without harming yield potential in environments which lacked disease. This finding gives dry bean breeders the green-light to widely deploy these resistance genes to effectively combat common bacterial blight disease worldwide.
3. New genes and linked markers discovered for resistance to devastating virus disease in common bean. Beet curly top virus is a problematic disease of common bean in the Western U.S. Genetic resistance provides effective control but can be difficult to discern in early generations. Scientists at ARS, Prosser, WA, have characterized genes conditioning resistance to this virus and generated markers for rapid identification of the genes. A marker linked with a newly discovered resistance gene from a landrace cultivar was developed. The discovered gene, first from the Andean gene pool, represents an important gene for broadening the genetic basis of resistance to this virus. The markers facilitate breeding enhanced bean germplasm with higher levels of resistance to the virus.
5. Significant Activities that Support Special Target Populations
Organic seed treatments to manage Pythium seed rot will benefit small-scale organic vegetable growers.
Talukder, Z.I., Anderson, E., Miklas, P.N., Blair, M.W., Osorno, J., Dilawari, M., Hossain, K.G. 2010. Genetic diversity and selection of genotypes to enhance Zn and Fe content in common bean. Canadian Journal of Plant Science. 90: 49-60.