Potato research tackles starch content and pests

New research projects aim to modify potato starch content to improve nutritional benefits and to reduce the effect of the crop's major pathogenic threat. Sean Ottewell reports.

World production of potatoes stands at about 320mt/y, but late blight remains an ongoing challenge. Caused by a fungus-like microbe, this disease is difficult and economically challenging to eradicate. It was largely responsible for the Irish potato famine of the mid-19th century.

Today the cost of the disease is estimated at more than EUR5b/y, easily enough to drive farmers out of business and increase food prices.

Howard Judelson at the University of California, Riverside, has received a US$9m (EUR6.2m), five-year grant from the United States Department of Agriculture, National Institute of Food and Agriculture USDA-NIFA to research late blight and ensure a sustainable and long-term control of this devastating disease.

"Late blight is a global problem," said Judelson who will lead a multidisciplinary team of extension faculty and researchers - plant pathologists, molecular biologists, epidemiologists, plant breeders, sociologists and economists - at universities, government labs and a non-profit research institution. "To manage this disease, which is favoured by cool, moist weather, we need a multipronged approach. In this research project, we will develop an integrated plan of research, education and extension that includes developing diagnostic tools, resistant plants through breeding and biotechnology, and systems to provide improved management guidelines to growers," he added.

"More than 40 per cent of current crop production among the top ten food crops is lost to pests and diseases annually and that is a huge loss for farmers," said Cathie Woteki, USDA under secretary for research, education and economics. "USDA is funding this project to help agricultural producers win the future by ensuring our country can keep producing the food needed to meet rising global demand in a sustainable way."

Late blight symptoms include the appearance of dark lesions on leaf tips and plant stems. In humid conditions, white mold appears under the leaves. Infected potatoes show grey or dark patches outside; inside, such potatoes show reddish brown lesions. A threat to home gardeners and commercial farmers, the disease can wipe out potato fields within a week.

The disease is caused by Phytophthora infestans, the most significant pathogen of potato. Spores of the pathogen primarily travel in air, eventually landing on plants where the spores colonise leaves and cause them to die. Spores also can enter the soil, reach potato tubers, and destroy them. Available fungicides tend to be expensive and have potentially adverse environmental effects. Moreover, some strains of the pathogen are resistant to some fungicides.

"This grant to Dr Judelson builds on historic UC Riverside strengths in research on this pathogen and is one more acknowledgement that UC Riverside is a leader in agricultural research," said Donald Cooksey, divisional dean for agriculture and natural resources in UCR's College of Natural and Agricultural Sciences. "By leading research on managing late blight, we will help protect the productivity of potato farmers worldwide."

The research project will focus on providing growers with better tools for managing the disease. These include better systems for making disease management decisions, plant varieties that are more resistant, tools for rapid identification of the pathogen, and tools for characterising pathogen strains. The researchers also will test and expand the use of social media and smartphone technology to communicate with growers.

In the US, late blight is seen predominantly on potato in eastern states such as Maine, New York and Pennsylvania, and outbreaks also occur in the Midwest and West. In California, late blight is mostly seen in the central valley in the early season, when conditions are moist and cool.

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New starches

Potato starch, with its low protein and fat content, is favoured in many industrial processes including the manufacture of food, paper, plastics, medicines and more.

The starch molecule itself is made up of two carbohydrates, amylose and amilopectin. If the starch branching enzyme (SBE) involved in their formation can be inactivated, a whole new set of starches with different physicochemical properties more suited to industrial and food processing could be generated.

Neiker-Tecnalia, the Basque Institute of Agricultural Research and Development, is carrying out just such a project using molecular and genetic tools in order to obtain high-quality starch in potato tubers of the species Solanum tuberosum.

The aim of the research is to produce starches which have better physicochemical characteristics for industrial use, as well as for producing healthier and more functional foodstuffs. Techniques such as allele mining, inverse genetics, mapping by association and in vitro assays will be used to evaluate the different starches produced.

Allele mining is used to identify allelic variations for the relevant traits within a collection of genetic resources. It has already been used with a number of other commercial varieties of potatoes and with germplasm of the Solanum genus in order to analyse the variability of alleles of genes that code for SBE with reduced or zero activity.

In a complementary manner, mutated dihaploid potatoes were produced through inverse genetics in order to study the mechanisms of the genes involved. Moreover, an in vitro test was used for the rapid analysis of the enzymatic activity of the SBE alleles, in such a way that it was not necessary to obtain homozygotic plants for these alleles and only the alleles of interest form part of the enhancement process.

A drastic reduction of the content of amylopectin means a reduction of the total content of starch. This is an obstacle for genetic improvement, as the greater the dose of SBE alleles induced, the less will be the starch yield. To eliminate this problem, clones were selected with more effective capacity for the biosynthesis of starch. This is achieved with the help of gene-mapping by association. With this technique, alleles with better performances were detected in the starch biosynthesis route. In this way, DNA molecular markers with diagnostic value are sought for the genetic enhancement of varieties of high-yield potatoes.

New types of starch will make it possible to obtain transparent gels without disagreeable odours and, moreover, which have optimum conditions of adhesiveness and reactivity, as well as good qualities for the formation of films. For example, starches with a high content of amylose have better viscosity characteristics and are useful in the manufacture of paper, adhesives, or in the textile industry. Starches with a high content of phosphate can be used to produce synthetic polymers.

As regards the production of healthier foods, the improvement in the amylose content will optimise nutritional content and give varieties of potato that can be used as functional foods. For example, being fibre-enriched such starches have a lower calorific value (Fig. 1).

The R&D activities are being undertaken within the umbrella of a European ERA-NET project within the plant genomics section. The project is co-financed by the Spanish Ministry of Science and Innovation within the framework of the Euroresearch (EU2009-04028) programme.

Neiker-Tecnalia is working on the project with a number of Spanish and German private companies and research centres, including: German potato breeding company Bioplant; the IME-Fraunhofer Institute of Plant Biochemistry and Biotechnology, also in Germany; Spanish potato breeding company Appacale; and the the Max Planck Institute for Plant Breeding Research in Germany

New potatoes to satisfy demand for crisps

Researchers at US company Cornell have released two new varieties of potato, both ideal for being made into crisps.

Called Waneta and Lamoka, the new potatoes are aimed at New York growers and are especially appealing to potato crisp manufacturers because they fare well in storage and produce a nice colour when cut. This is important because such potatoes are harvested in the autumn, but may not be used until the following spring.

Lamoka has a high level of starch, a trait that is desirable for chipping because it soaks up less oil when fried. Waneta has less starch, but is also less likely to bruise, a characteristic that may appeal to farmers in New York, where fields are stony.

Both varieties are resistant to the golden nematode, a pathogen present in some New York soil that attacks potato roots, and common scab, another soil-borne pathogen present nationwide that can cause pits in potatoes.

According to Cornell, this gives them a distinct advantage over Snowden potatoes, the crisp industry standard, which are susceptible to both diseases

Nationally, 28 per cent of the domestic potato crop is sold fresh; 13 per cent become potato crisps and 35 per cent become frozen fries. The average American eats 126 pounds (57 kg) of potatoes each year, according to the US Department of Agriculture.

Almost half of the 20,500 acres of potatoes grown in New York by 150 commercial farmers are made into crisps.

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