Location:2009 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
We found that by overexpressing two genes involved in folate biosynthesis we could make tubers with at least an eight-fold higher amount of folate than any existing genotype we have (over 80 genotypes). We continue to screen diverse germplasm for phenolic phytonutrients and carotenoids and identified promising genotypes with high phytonutrient content. Screening potato wild species identified genotypes with exceptionally high levels of phenolics. A higher throughput Oxygen Radical Absorbance Capacity (ORAC) assay was developed and used to show these wild species have very high levels of hydrophilic antioxidants, which preliminary results suggest can exceed levels found in spinach or kale. Purple potatoes with anthocyanin concentrations of 50 mg/100 g fresh weight were identified, and in a human feeding study by collaborators showed anti-inflammatory effects. Approaches to improve iron content in tubers included transgenic efforts and screening existing germplasm. Ferritin was overexpressed in tubers, and more replications are needed to confirm that this may double iron content. Screening diverse germplasm found existing cultivars with 3-fold higher than average amounts of iron. In our efforts to improve disease resistance in potatoes, doubly resistant germplasm to powdery scab and black dot were identified in breeding materials in both greenhouse and field evaluations, and a source of potato virus Y (PVY) resistance from a South American variety was found to be due to a single dominant gene. We are trying to identify factors secreted by potato roots that stimulate potato cyst nematode eggs to hatch. Thus far using liquid chromatography mass spectrometry (LCMS) and fractionation we have eliminated over 50% of the compounds secreted from being hatching factors. We have a project component working on emerging diseases of potatoes. Continuing work on the zebra chip disease by our group and others has indicated the involvement of a bacterium “Candidatus Liberibacter solanacearum” with the disease. This bacterium is transmitted to potato by the tomato-potato psyllid. We have been testing populations of psyllids for presence of the bacterium and similarly tested various cultivars of potatoes for susceptibility to the disease. We were involved in making the first report of the disease and bacterium on potatoes in California and Mexico and of the bacterium in diseased tomatoes and peppers in Mexico. Another emerging problem appears to be tomato spotted wilt virus on potatoes. We made the first report of this virus causing symptoms on potatoes in Texas. The purple top phytoplasma is another important pathogen of northwest potatoes. We are continuing to study the effects of this pathogen on major commercial cultivars of potatoes and to access the rate of transmission of the phytoplasma in daughter tubers.
1. Development of high folate potatoes. Folate deficiency is one of the world's most severe nutritional deficiencies and a leading cause of major birth defects and is also implicated in some heart attacks and strokes. ARS scientists at Prosser, WA have developed transgenic potatoes that over express two heterologous folate biosynthetic genes 4-amino-4-deoxychorismate synthase ( ADCS) and GTP-cyclohydrolase (GCHI) under tuber specific promoters identified transgenic plants. The transgenic plants had as much as an 8-fold increase in folate and could contain over 60% of the folate recommended daily allowance in a 6 ounce serving. We are hoping to replace these transgenes with potato cisgenes (to make a cisgenic potato) and have cloned the potato ADCS and GCHI. This research shows that it is possible to make a high-folate potato, which, as a staple crop capable of growing in very diverse habitats, could be a key player in combating global folate deficiency.
2. Identification of corky ringspot in the Midwest. Corky ringspot is a disease of potatoes caused by infection with tobacco rattle virus which is transmitted by soil-inhabiting nematodes. If a sufficiently high percentage of potato tubers show internal symptoms of the disease, the potatoes may not be salable and substantial financial losses can result. The disease has been known to occur in the Pacific Northwest, Florida, and Colorado. Cooperating with researchers at Michigan State University and North Dakota State University, ARS scientists at Prosser, WA achieved the first detection and subsequent identification of corky ringspot disease and tobacco rattle virus on potatoes grown in Michigan, Minnesota, and Wisconsin. This information alerts plant health specialists in these states to this new threat to potato production.
3. Assessing the effect of cooking on potato phytonutrients. To better understand which potato phytonutrients should be targeted for enhancement, it is important to determine the extent they survive cooking. ARS scientists at Prosser, WA have determined that “baby potatoes” contain higher amounts of some phytonutrients and found with high performance liquid chromatography (HPLC) analysis that microwaving, baking, sautéing, boiling and steaming did not significantly decrease total phenolics, chlorogenic acid, flavonols or vitamin C when cooked under optimal conditions with the skin on. This further establishes the phytonutrient potential of “baby potatoes” and shows that these phytonutrients are legitimate targets to further increase in potatoes, as they can substantially survive cooking. This work is important to our efforts to develop high-phytonutrient potatoes that can positively impact public health and improve industry sustainability.
5. Significant Activities that Support Special Target Populations
On an annual basis our unit develops virus free Ozette cuttings or tubers and hand delivers them to the Makah Nation, Neah Bay, Washington. The delivery coincides with Potato Day during which we meet with Tribal Members to discuss this potato which they have grown for more than two hundred years. In 2009 this visitation was augmented with lectures and laboratory exercises in the Makah High School Biology classes. This included evaluations of the Ozette potato for resistance to Rhizoctonia solani.
Nitzan, N., Cummings, T., Johnson, D., Miller, J., Batchelor, D., Olsen, C., Brown, C.R. 2008. Resistance to Root Galling Caused by the Powdery Scab Pathogen Spongospora subterranea in Potato. Plant Disease. 92:1643-1649.