Location:2011 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. B
3. Progress Report
A primary research effort is to develop potatoes with superior phytonutrient amount. A new cultivar (AmaRosa) was released from our program that is a fingerling with red flesh and very high antioxidants. Immature potatoes were found to contain higher amounts of some phytonutrients. Analysis of phenylpropanoid gene expression during tuber development showed that expression was higher in immature tubers and correlated with metabolite levels. Changes in sugars and carbohydrate gene expression during development were characterized to assess relationships between phytonutrients (secondary metabolism) and primary metabolism. Phytonutrients are also affected by environment. An exhaustive analysis of environmental effects of phenylpropanoid and carotenoid metabolites and gene expression was conducted on potatoes grown in Alaska, Texas or Florida and over two-fold differences in some metabolites were observed in the same genotype. A large field trial with ~90 genotypes was conducted to screen for those suitable for use as “baby potatoes” with high yields of small tubers and high phytonutrients. Transgenic approaches are underway that are designed to better understand tuber phenylpropanoid or folate metabolism by silencing or overexpressing target genes. Putative transgenic plantlets are currently in tissue culture. Research continued on the important emerging zebra chip disease of potatoes, caused by a newly described bacterium, Candidatus Liberibacter solanacearum (Lso) that is transmitted by the potato psyllid. A more rapid way to screen psyllids for Lso was developed that showed molecular detection of the bacterium was reliable in pooled insect samples of 29 Lso-free psyllids combined with one Lso-infected psyllids. We developed and validated a standardized protocol that can detect and identify eleven potato viruses and one viroid. We found all important cultivars in the Columbia Basin are susceptible to the potato purple top disease, caused by a phytoplasma found to be transmitted through tubers. Some of these tubers give rise to infected daughter plants, showing this is a risk for potato seed certification efforts. Columbia root-knot nematode is an important pest of potatoes and we have been developing resistant germplasm by utilizing wild species diversity. A resistant line was evaluated in a field trial and compared to Russet Burbank. In the absence of fumigation, this nematode resistant line outperformed Russet Burbank without damage or yield loss, whereas Russet Burbank was severely damaged. We are trying to identify hatching factors and trap crops for control of the potato cyst nematode (PCN). Solanum sisymbriifolium was identified as a potential trap crop and no PCN reproduction was observed in greenhouse assays. We have screened over 125 additional plant species seeking additional potential trap crops.
1. Tuber transmission of potato phytoplasma. The potato purple top phytoplasma is an important pathogen of potatoes and other vegetable crops in the Columbia Basin of Washington and Oregon and was widespread in this region in 2002. This pathogen is transmitted from wild host plants to potatoes by the beet leafhopper but little information was available on the ability of the phytoplasma to be perpetuated in infected potato tubers. Over the course of three years, ARS researchers at Prosser, WA, found that the phytoplasma was indeed transmitted through the tubers and that some of these tubers would give rise to infected daughter plants. This information alerts potato seed certification personnel and potato growers of the potential for tuber-borne infections which could result in a resurgence of purple top disease in this important potato growing region.
2. Standardized test for potato viruses. There are a number of viruses that infect potatoes and these infections reduce the total yield and quality of the potato crop. Accurate identification of the virus or viruses affecting a crop is essential to understanding the epidemiology of the disease(s) and a variety of techniques and materials have been developed for this purpose, but these techniques are often specific for a single virus. ARS researchers at Prosser, WA, have developed and validated a standardized set of reagents and protocols that can be used for detection and identification of eleven viruses and one viroid of potatoes. These standardized methods simplify testing for the various viruses and will be useful for certification agencies, research laboratories, and commercial laboratories that conduct potato virus disease diagnosis.
3. Release of fingerling potato with enhanced phytonutrient content. Potato has a great deal of genetic diversity for phytonutrients that has not been incorporated into modern varieties. Researchers at ARS Prosser along with Northwest State University cooperators have selected a potato with a high level of antioxidant activity. The potato, ”AmaRosa” is a fingerling type with dark red skin and red flesh. The anthocyanin pigments conferring the red color are themselves strong antixoidants and anti-inflammatories. A potato with these properties is a good solution to recent publicity that downgrades the potato to an unhealthy cause of weight gain.
4. Molecular testing of potato psyllids. The potato zebra chip (ZC) disease is an important emerging disease of potatoes in North America, Central America, and New Zealand and is associated with a bacterium, Liberibacter solanacearum (Lso), transmitted to potatoes by the potato psyllid. Efforts to determine the relationship of Lso-infected psyllids to the incidence of ZC in commercial potato fields is hampered by the lengthy DNA extraction procedures necessary on a large number of these insects. ARS researchers at Prosser, WA, determined that composite insect samples of 29 Lso-free psyllids combined with one Lso-infected psyllid provides reliable and reproducible molecular detection of the bacterium. This ability will aid efforts designed to test large numbers of the psyllids in order to improve our understanding of the relationship between numbers of infected psyllids near potato fields and the subsequent development of ZC disease within the crop.
5. Environmental effects on phytonutrients. Potatoes with enhanced nutritional content are desirable, but the factors that govern tuber phytonutrients, including environment, are poorly understood. ARS scientists in Prosser, Washington, and collaborators in Alaska, Texas and Florida analyzed over forty tuber phenylpropanoids or carotenoids in a genotype grown in environmentally diverse locations and correlated concentrations with expression of twenty genes in the pathways. Environment significantly affected the nutritional value of potatoes with over two-fold differences seen for some phytonutrients, showing that environment complicates assessing the nutritional value of a given genotype. This research contributes to understanding mechanisms that regulate tuber nutritional content and suggests additional options may exist to increase tuber phytonutrients.
6. Resistance to Columbia root-knot nematode. Columbia root-knot nematode (Meloidogyne chitwoodi) is an important pest of potatoes in the Western United States, but especially in Washington State. It reproduces on the potato root system and invades tubers producing unacceptable blemishes for fresh market and processing. Resistance to the nematode was introduced by ARS researchers from a Mexican wild species and moved by backcrossing into a commercial oblong russet skinned type of potato. In the absence of fumigation, this new resistant potato significantly outperformed Russet Burbank without damage or yield loss. This is a first demonstration of the strength of this resistance, which could give growers potential savings of $350 per acre in fumigation costs.
7. Phytonutrients during tuber development. High-phytonutrient potatoes are desired by both the potato industry and consumers. ARS scientists at Prosser, WA, found that young tubers contain high levels of some phytonutrients and analyzed gene expression to understand why amounts are higher. To identify potential “baby potato” cultivars ~ninety potato genotypes were grown in a 2010 field trial and evaluated for yield of small tubers and phytonutrient content. Lines were identified that have high levels of antioxidants, good yield, taste and appearance. This work is important step towards creating new opportunities for an industry struggling with declining demand and providing consumers the healthy choices they are increasingly demanding.Karasev, A., Hu, X., Brown, C., Kerlan, C., Nikolaeva, O., Crosslin, J., Gray, S.M. 2011. Genetic diversity of the ordinary strain of potato virus Y (PVY) and origin of recombinant PVY strains. Phytopathology. 101:778-785.