Location:2010 Annual Report
1a. Objectives (from AD-416)
Objective 1. Identify superior germplasm for potato disease and pest resistance, phytonutrients, minerals and vitamins, using high-throughput methods to determine the extent of natural variation in diverse potato germplasm of select phytonutrients/metabolites. These traits will be incorporated into the cultivated breeding pool using traditional breeding and molecular approaches. Sub-objective 1.A. Identify germplasm with a range of expression of phytonutrients, study inheritance, identify associated markers, and produce superior parents. Sub-objective 1.B. Develop germplasm with resistance to pests and diseases, establishing effective and efficient screening protocols, determining range of expression, inheritance, heritability, and discover molecular markers, while mapping genetic factors where possible and useful. Sub-objective 1.C. Use metabolic profiling of multiple chemical constituents to identify sources of high expression and genotypes possessing desirable combinations. Objective 2. Determine host resistance options, epidemiological parameters and develop diagnostic tests for emerging pests and pathogens of potato. Sub-objective 2.A. Determine the impact, distribution, and importance of the soil-borne viruses tobacco rattle virus (TRV) and potato mop top virus (PMTV) on Pacific Northwest potato production. Assist in evaluating advanced germplasm for resistance to the viruses as materials become available. Sub-objective 2.B. Develop and improve diagnostic procedures for insect transmitted viruses (potato virus Y [PVY] and potato leafroll virus [PLRV]) and phytoplasmas (purple top phytoplasma and aster yellows) in potatoes. Evaluate advanced potato lines for resistance to diverse viruses. Objective 3: Elucidate genetic, molecular and biochemical factors governing host disease resistance and accumulation of select phytonutrients and vitamins. Sub-objective 3.A. Elucidate genetic, molecular and biochemical processes governing accumulation of select phytochemicals and vitamins with respect to improving potato as a food. Sub-objective 3.B. Elucidate genetic, molecular and biochemical processes involved in plant host resistance.
1b. Approach (from AD-416)
Germplasm will be surveyed for expression of disease and pest resistance, and nutraceuticals. High performing genotypes will be intercrossed to with suitable commercial materials to introduce new traits into the potato breeding pool. Inheritance and genomic location will be studied using nucleic acid markers. Transgenics designed to enhance or knock out gene expression will be used to test hypotheses on gene function. Field testing will identify agronomically superior genotypes for use as parents and submission to regional yield trials.
3. Progress Report
Potato genes were cloned to allow metabolic engineering of tuber phenolic phytonutrients, including anthocyanins, phenolic acids and flavonols. Available transformation vectors only allow constitutive expression of genes in potato; we constructed several plasmids that allow tuber specific overexpression or silencing and are selecting for transformants. We are trying to increase tuber protein by overexpressing systemin, or folate by overexpressing endogenous genes that would allow an intragenic approach; previously we used heterologous genes to increase folate. Complimentary non-transgenic approaches are simultaneously being used for all phytonutrient targets by screening for naturally high germplasm or breeding lines. We expanded the types of tuber phytonutrients we can evaluate by developing a liquid chromatography-mass spectrometry method to identify and quantitate anthocyanins. We determined “baby potatoes” have higher levels of some phytonutrients and in a large field trial, planted 90 genotypes to screen for those with high yields of small tubers and phytonutrients. Two molecular markers in the carotenoid biosynthetic pathway were identified that segregate with very high carotenoid levels. Work continued on the important emerging zebra chip disease of potatoes, caused by a newly described bacterium, Candidatus Liberibacter solanacearum. Various diagnostic methods are being tested to improve the reliability of test procedures for this bacterium in both plants and vector insects. We completed and published the complete genomic sequence of an isolate of tobacco rattle virus (TRV) from Michigan that is only the second North American isolate of TRV published. We found that younger potato plants are more susceptible, and that all important cultivars in the Columbia Basin are susceptible to the potato purple top disease, caused by a phytoplasma. Resistance to Columbia root-knot nematode was verified in breeding line 82-4; despite fields not being fumigated, 82-4 remained processable. Other lines were tested for yield under heavy inoculation pressure from black dot and powdery scab, and high-yielding, resistant material was identified, including Yukon Gem and Sage Russet. Resistance to black dot has been identified in the South American varieties in the taxon Solanum tuberosum Group Andigena. Several clonal selections from two accessions from Colombia and Ecuador were identified and used to introduce a new source of resistance. A study of resistance to Spongospora subterannea determined several breeding lines show stable resistance in four different environments. A new source of resistance to PVY from high carotenoid diploid South American potato varieties was further characterized. High levels of resistance, but not extreme resistance can be bred into advanced breeding lines to the major strains of PVY. We are working on identifying hatching factors and trap crops for control of the potato cyst nematode.
1. High-phytonutrient “baby potatoes.” High-phytonutrient potatoes are desired by both the potato industry and consumers. ARS scientists at Prosser, WA found that young potato tubers contain high levels of some phytonutrients. In order to bring such potatoes to the market, genotypes with the required traits must be identified or developed. Ninety potato genotypes were grown in a field trial and evaluated for numerous traits including yield of small tubers and phytonutrient content. Lines were identified, including some from the Tri-state breeding program, which have very high levels of antioxidants and good yield, taste and appearance. This work is important step towards bringing high-phytonutrient baby potatoes to the market, can create new opportunities for an industry struggling with declining demand and provide consumers with the healthy choices they are increasingly demanding.
2. Molecular markers assist with a hard to breed trait - ultra high total carotenoids. High carotenoids is a difficult trait to transfer from South American diploid varieties to the cultivated tetraploid potatoes used in the United States. Our group at the USDA/ARS Prosser, WA was able to attribute a majority of genetic variation associated with ultra-high carotenoid production to two marker genes. The lack of genetic transmission of high carotenoids is explained by the total absence of one gene allele in the tetraploid potato gene pool. The production potatoes with high levels of carotenoids should promote eye health by providing high concentrations of lutein and zeaxanthin in the diet.
3. Many viruses infect potatoes and plants closely related to potatoes resulting in substantial economic losses. Some of these potato relatives possess characteristics that can be useful in potato breeding programs, such as resistance to frost, pests, or diseases. One of these plants, Solanum acaule, has been used in potato breeding programs, but APHIS detected a virus that had been introduced into the United States in seed of S. acaule. Scientists at USDA-ARS, Prosser, WA identified the virus as a new variant of cherry leaf roll virus and alerted personnel involved in potato breeding programs that the virus posed a threat. The development of methods for rapid detection and identification of the virus provides a means for potato breeding programs to test for this new pathogen in their breeding materials, limit its spread and minimize the negative impact on the industry.
4. Identification of phytonutrient rich potatoes. An industry survey found that consumer’s least favorite thing about potatoes was a perceived lack of nutrition or healthfulness, while conversely nutritional value, taste and appearance were the most important three traits. Increasing the nutritional value of potatoes is a major objective of ARS scientists at Prosser, WA who are using both breeding, germplasm mining and transgenic approaches. High-throughput screening methods were used to evaluate phytonutrients in over a hundred diverse genotypes to identify potatoes with naturally high amounts and better utilize potato genetic diversity. Genotypes high in phytonutrients and antioxidants were identified, and when compared to 15 other vegetables, potatoes from a mature purple-flesh cultivar had the highest amount of antioxidants on a fresh-weight basis (34 micromoles trolox equivalents per gram). These results show that the phytonutrient content of such potatoes can compare favorably to other vegetables and suggest that increasing the phytonutrients in this staple crop would significantly increase phenolic dietary intake.
5. Significant Activities that Support Special Target Populations
This project has a program that provides planting materials to the Makah Native Americans of Neah Bay Washington. This includes teaching several classes in the biology curriculum and having a yearly extension meeting with community members.