Increasing the Marketability of Pacific Northwest Potatoes

View the project final report

Commodities

• Agronomic: potatoes

Practices

• Education and Training: extension
• Farm Business Management: value added
• Production Systems: general crop production

Consumer demand for fresh potato in the U.S. has been steadily decreasing since the 1990s, and this has directly impacted growers’ profitability and has been threatening the economic sustainability of the U.S. potato industry. Although the reasons for declining potato consumption are complex and have no single cause, negative comments from some nutritionists about potato in the diet, such as its association with weight gain, has been detrimental to potato perception by consumers and, therefore, to potato sales. In a 2010 survey conducted by the U.S. Potato Board, 55% of respondents reported various health-related statements as the worst things about potatoes (e.g. “Any good ways to prepare them are unhealthy, or at least have no nutritional value.”). In addition, a survey by the Oregon Potato Commission determined that the three factors that most influence consumers' decisions to purchase potatoes are appearance, flavor and nutritional value. These surveys reveal that health is the biggest challenge for potatoes.

In an effort to remedy negative publicity about potato in the diet, there has been an increased demand from the stakeholders to develop cultivar-specific nutrition profiles with an aim toward advertising positive nutritional attributes and to focus breeding efforts toward enhancing the nutritional value of fresh potatoes in addition to other traditionally targeted traits such as yield potential, biotic and abiotic stress resistance, processing qualities, bruising and shrinkage resistance, storability, and appearance. The Oregon Potato Breeding and Variety Development program plays a key role in the Tri-State (Idaho, Oregon and Washington) potato variety development program, with research focus on the aforementioned traits.

Vitamin B₉ deficiency is one of the most widespread nutritional deficiencies worldwide and is associated with the increased risk of birth defects (e.g., spina bifida, anencephaly), strokes, cardiovascular diseases, anemia, some types of cancers, and impairment of cognitive performance. Good nutrition is the basis of a healthy and productive life, and potatoes should have a prominent role to play since it is part of our diet. Vitamin B₉-enriched potatoes will help sustain the economic viability of potato farms and will enhance the basal intake level of nutrients by consumers.

Thus, the Graduate student’s project focused on (1) exploring the genetic diversity of potato for folate content, and (2) identifying genetic factors that control folate accumulation.

First, 250 individual plants from 77 accessions and 10 Solanum species were screened for their folate content using a tri-enzyme extraction and microbial assay. The screening focused on species that had been previously shown to have individuals with high folate content. These species were Solanum tuberosum subsp. andigenum, Solanum vernei and Solanum boliviense. Other species that had never been analyzed for folate content before, S. stipuloideum, S. chacoense subsp. chacoense, S. candolleanum, S. acaule, S. demissum, S. microdontum, and S. okadae, were also evaluated. There was a 10-fold range of folate concentrations among individuals tested. Certain individuals within the species Solanum tuberosum subsp. andigenum, Solanum vernei and Solanum boliviense have the potential to produce more than double the folate concentrations of commercial cultivars such as Russet Burbank. These results show that exploring the genetic diversity of potato is a promising approach to increase the folate content of this important crop.

Second, to better understand the regulatory mechanisms that control folate accumulation in potato tubers, the expression of genes involved in folate metabolism was determined in high and low folate tuber samples using RNA-sequencing (RNA-Seq) and Real Time Quantitative RT-PCR (qPCR) analyses. RNA-Seq analysis showed that among folate biosynthesis and salvage genes, γ-glutamyl hydrolase 1 (GGH1) was consistently expressed at higher levels in high folate compared to low folate segregants of a Solanum boliviense accession. qPCR analysis was used to determine GGH1 expression in eight additional pairs of folate segregants. Results showed that GGH1 transcripts levels were higher in high folate compared to low folate segregants for seven out of eight pairs of folate segregants analyzed. These results suggest that GGH1 gene expression may be a determinant of folate content in potato tubers and may be considered as a target for folate engineering.

Third, an F2 population of 94 individuals from a cross between a high and a low folate genotype was evaluated for folate content and genotyped for Single Nucleotide Polymorphism (SNP). More than 3,000 high quality SNPs were used to assemble maps for each of the 12 potato chromosomes. SNP-trait association analysis and QTL single marker analysis was performed in order to find SNPs and genomic regions that associate with high folate content. SNPs associated with folate content were located on chromosomes 3, 6, and 7. Future research should focus on validating these SNP markers. 

Introduction

Potato consumption in the U.S. has been steadily declining since the 1990s. This has had a considerable impact on the economic sustainability of the potato industry, making the business of growing and selling potatoes challenging and less profitable. One of the key consumer trends which are attributed to the downturn in consumer demand for potatoes is the fact that consumers are becoming increasingly interested in making healthier food choices, and they are often dragged down by outdated beliefs that potatoes are unhealthy. Anti-potato advocates include Walter C. Willett at the Harvard School of Public Health who views potatoes as a starch, not as a vegetable, and who recommends to use potatoes sparingly. They are ignoring that the potato is packed full of vitamins, minerals, and nutrients. For instance, a medium-size potato provides 45% of the daily value (DV) for vitamin C, 20% of the DV for potassium, and12% of the DV for dietary fiber. The potato was also found to be the third most important source of vitamin B_9, also known as folate (Figure 1), in the Dutch diet and provided 9-12% of the total vitamin B₉ in a Norwegian study. Therefore, in order to secure increased potato use, promotional campaigns which dispel the myths of potatoes as unhealthy, “empty carbs” should continue to remind consumers that fresh potatoes are ‘vegetables’ and that they are a healthy choice to be included in their diets.

A complementary strategy which aims at increasing potato use, and thereby sustaining the economic viability of potato farms, is to breed potato for increased amounts of micronutrients essential for human health, especially white-fleshed varieties which are the most consumed form in the United States. This is particularly relevant because micronutrient deficiency is responsible for millions of deaths every year, affecting half of the world’s population, especially children, women, and the elderly of not only poor populations but also industrialized countries like the United States. Vitamin B₉ deficiency is a common health issue worldwide and is most often caused by a dietary insufficiency. Vitamin B₉ deficiency is linked to various serious diseases such as neural tube defects (NTDs), cardiovascular diseases, certain types of cancers, stroke, anemia, and impairment in cognitive performance^. NTDs are among the most common congenital and devastating birth defects. The defects occur between the 21^st and 27^th days after conception, a time when many women do not realize they are pregnant. In the United States, despites the implementation of folic acid food fortification programs in staple foods such as rice and pasta since 1998, vitamin B₉ intake remains suboptimal. For instance, the population of women aged 15–44 years who consume more than the Recommended Daily Allowance of 400 μg/day of folate has not yet reached the FDA’s 50% target. Folate-rich diets have been associated with decreased risk of cardiovascular disease, with reported 55% lower risk of an acute coronary event in men who consumed the most dietary folate.

The purpose of this research was to further explore folates’ natural diversity within potato germplasm, better understand the regulation of folate levels, and to begin the development of molecular tools to assist breeding efforts that aim at increasing folate content in commercial potato cultivars.

Objective #1: Exploring folate diversity in wild and primitive potatoes for modern crop improvement

The objective was to identify sources of high folate germplasm for introgression into modern cultivars. Two hundred and fifty individual plants from 77 accessions and 10 species, as well as a Russet Burbank standard, were planted in the greenhouses on OSU’s main campus in May 2014. Samples were harvested in early November of 2014.

Objective #2: Transcriptome analysis in low- versus high-vitamin B9 genotypes

In this objective, gene expression between low and high folate genotypes was compared to identify differentially expressed genes that may control folate content.

Objective #3: Single Nucleotide Polymorphism markers associated with high folate content from wild potato species

The objective was to identify SNPs and regions of the genome that may contribute to high folate levels. A selection from Solanum boliviense PI 597736 that showed high tuber folate content (referred as Fol 1.6) was crossed with the low/medium folate recombinant inbred clone USW4self#3 (labeled USW4s#3) to generate an F1 progeny. Twelve of the resulting F1 seedlings were intermated to produce an F2 population named BRR3. One hundred and fifty of these F2 seeds were planted, but only 94 of the individuals produced tubers for further analysis. These individuals were used for linkage group mapping, SNP genotyping, and QTL single marker anaylsis.

Objective #4: Extension activities.

Hydromania summer camp in the summer of 2015. Poster presentation at Potato Field Day at the HAREC station 2015. Farmtastic extension center day camp for kids 8-12 years old in the summer of 2015. Seminar given to the professional mentoring committee (growers from the area) during the summer 2015. Seminar given in the graduate student competition at the Potato Association of America annual meeting in Portland, ME 2015.