Halterman Lab Blog


MPMI Interactions EIC

I also just signed on as Editor in Chief of the Interactions publication for International Society of Molecular Plant-Microbe Interactions. The content is online only but will be read by members of the society. It’ll include personal-interest type stories and information that is relevant to the members of the society. I’m looking forward to this challenge and I think it’ll be a great opportunity to me to contribue to the society.

PlantingScience

I recently joined PlantingScience as a mentor. I’m really excited about hte opportunity. The new session starts in February. I’ll have a chance to work with students from all over the world on classroom science projects. I’ve done lots of outreach events before, but this will be a different kind of interaction, as it will go on all semester and I’ll be the only scientist contact for the students. I can’t wait!

How to Build a Better Potato


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On February 21st, Dr. Halterman, along with fellow USDA/ARS scientists Dr. Shelley Jansky and Dr. Paul Bethke and technician Holly Reuss, traveled to Stevens Point, WI to meet with 7th and 8th graders from around Wisconsin for the STEM (Science, Technology, Engineering and Mathematics) Career Day for Girls.  The event showcases STEM career professionals from throughout Wisconsin. Students engage in hands-on workshops (and learn the many career paths available with an education in STEM). The conference includes exhibits, a keynote presentation, and three, one-hour workshops. 


Our presentation was entitled “How to Build a Better Potato” and we discussed a couple of topics that we are very familiar with - disease resistance and potato storage.  While these are only two aspects of breeding that we are interested in, they provided hands-on opportunities for the students.  Dr. Halterman led a discussion of virus resistance in potato and why it is important to be able to identify whether plants are infected with a virus.  Students were able to view plants with and without the Potato Virus Y virus and predicted the presence of PVY in unknowns.  Leaflets of the plants were then used in a rapid diagnostic test kit to determine whether or not the unknowns contained virus and whether their observations correlated with the results.


Drs. Jansky and Bethke led a discussion of potato storage and why it is important to store potatoes under conditions that limit respiration and disease (cold) and how this contrasts with the need to keep sugar levels in the potatoes low (potato starches are converted to sugar under cold conditions).  High sugar levels in potatoes lead to dark colored chips and fries, which are frowned upon by the potato production industry.  Using potatoes that had been stored in warm and cold conditions, the students first used glucose test strips to determine the sugar levels of each potato.  Then, they placed a slice of each potato into hot oil to make chips.  The potatoes with high sugar levels (cold stored) turned dark brown, while the low sugar potatoes (warm stored) stayed a light golden color after frying.  The students were then each given an “unknown” and predicted the potato chip color using the glucose test strips and tested their hypothesis by frying them.

UW scientists probe, attack late blight in potatoes

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This was an article that was written by University Communications writer David Tenebaum and was published online at the UW-Madison

http://news.cals.wisc.edu/agriculture/2012/09/03/uw-scientists-probe-attack-late-blight-in-potatoes/

Monday, September 3rd, 2012









As the annual potato harvest begins, Wisconsin farmers continue to check their fields for late blight, the ferocious plant disease that caused the 1848 Irish potato famine and fueled massive emigration from Ireland.


The cooler, damper conditions that started in August are conducive to late blight in potatoes, says assistant professor Amanda Gevens, who has joint appointments with University of Wisconsin-Extension and the UW-Madison Department of Plant Pathology. She cautions that the latest highly pathogenic strain, called US-23, can destroy a field within a week.


When scouts detect the characteristic lesions — or even when late blight is rumored to be in the area — growers must reevaluate methods for limiting disease, including irrigation and the selection and timing of fungicides. They may harvest early to get the crop out of harm's way.


"Late blight infects any aboveground tissue," says Gevens. "Below ground, it does little damage to true roots, but it can infect the tubers. And it can devastate entire fields."


Her particular nightmare is the potential that two strains of late blight can sexually combine to produce a spore that survives in the soil over the winter. However, those strains have not yet appeared at the same time and place in Wisconsin.


Current outbreaks are seeded by infected seed potatoes, infected volunteer potatoes, infected tomato transplants, or spores that blow in during the growing season.


In 2011, Wisconsin was the nation's No. 4 potato producer, growing 2.2 billion pounds on 62,000 acres. So far, Gevens says, this year's yields are good.


Late blight also affects tomatoes. It is caused by the fungus-like microorganism Phytophthora infestans, a member of a large group of plant pathogens that can infect a wide range of trees, vegetables and fruits.


At UW-Madison, the nation's largest group of potato researchers is seeking a weak link in a ferocious adversary. They are advising farmers of best disease management practices, characterizing new late blight strains, and looking at the fundamental genetics and biochemistry of late blight resistance in the potato.


Amy Charkowski in the Department of Plant Pathology runs the Wisconsin Seed Potato Certification Program, which ensures that seed potatoes are disease-free, and oversees the state seed potato farm near Rhinelander.


Gevens, through UW-Extension, provides expert advice on disease management in potatoes and vegetables and coordinates Blitecast, a prediction model that warns farmers when conditions are ripe for blight. "This system integrates our knowledge of the pathogen and capabilities of fungicides for enhanced late blight control in Wisconsin," says Gevens.


Jiming Jiang, a professor of horticulture, helped identify a resistance gene called "RB" in 2003. RB comes from a distant potato relative that cannot cross-breed with commercial potatoes, so it must be transferred through genetic engineering. Although this process has produced experimental varieties with strong resistance to blight, Jiang says, "Unfortunately, society does not currently accept genetic engineering for potatoes and most vegetable crops, even though we have it almost 100 percent in soy and corn."


Jiang warns that late blight could get bad enough to force another look at genetically modified potatoes. In the meantime, he uses the system "as a model to understand the fundamentals of disease resistance, to understand why a plant that contains a single gene from a wild potato can fend off every strain of the pathogen."


One resistance gene is not a permanent solution to late blight, cautions Dennis Halterman, a U.S. Department of Agriculture geneticist who works in the Vegetable Crops Research Unit in Madison and collaborates with Gevens and Jiang on late blight research. "Late blight has been able to overcome a lot of resistance genes. In the 1950s and '60s, people thought this resistance could solve the problem, but in four or five years, late blight had wiped them out."


"We know strains of Phytophthora in Central America and Mexico can overcome RB already," says Halterman.


Halterman is looking at a molecule called IPI-O in Phytophthora that can turn off RB, and seems to be ubiquitous in late blight. "We believe Phytophthora needs IPI-O to cause disease," Halterman says. "If we can target that molecule, we think that would lead to broad spectrum resistance."


Growers continue to battle late blight through use of varietal tolerance when available and appropriately timed and selected fungicides. However, Phytophthora continues to evolve to survive new threats. The UW potato scientists warn about the future for potatoes. "Genetic engineering provides the best hope for long-term late blight resistance," says Halterman.

Molecular Determinants of Resistance Activation and Suppression by Phytophthora infestans Effector IPI-O

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Our paper was just published online at PLoS Pathogens.  Check it out: 


http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002595


Late Blight - Is Resistance Futile? 2

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This was an article I wrote for the Badger Common’Tater, the trade journal for the Wisconsin Potato and Vegetable Growers.

Friday, July 1, 2011









Every potato and tomato grower has probably lost sleep at some point worrying about the possibility of a late blight epidemic in their state, their county, or (in the worst case scenario) their own fields.  The worries stem from the fact that, unless they are one of the few people growing resistant cultivars, the crop they have in the field looks like an all-you-can-eat buffet to a few hungry late blight spores. 


In places like Central and South America, wild potato populations exist as a mixed collection of plants that aren't all genetically identical to one another.  This allows the population to adapt and survive even under intense pressure from pathogens such as late blight.  Some (or most) individuals in wild populations are susceptible and, when the disease spreads, will die without passing on their genetic information to the next generation.  However, the resistant individuals will flourish and pass on the valuable trait to their progeny. Therefore, the species as a whole will survive.  Growing potato in an agricultural setting is quite different, however.  A field of potatoes contains plants that are all genetically identical to one another, and they will all react in the same way to the environment, including exposure to late blight.


Unfortunately, the vast majority of potato varieties are late blight susceptible.  This is likely due to a breeding "bottleneck" when potato was first introduced to Europe in the second half of the 16th century.  The lack of genetic diversity among potatoes became apparent in the mid-1800's during the Great Irish Famine.  Since then, breeders have been actively pursuing the development of late blight resistant varieties.


Wild potato species have provided natural rich resistance sources against late blight.  Solanum demissum is a Mexican species from which 11 genes for resistance have been identified and used in potato breeding.  In the 1930's there was great optimism that the incorporation of these genes would completely eliminate late blight in North America.  Unfortunately, their optimism was misplaced.  Because of the popularity of the new cultivars, there was an intense selective pressure on late blight to evolve and overcome resistance. New strains of late blight rapidly overcame the resistance genes from S. demissum in most potato growing regions.  Even the combination of multiple genes, called "pyramiding", into a single cultivar proved ineffective.  The cultivar ‘Pentland Dell’, which contained three different genes for resistance was released for production in 1963.  By 1967, new late blight strains arose that could overcome the resistance.  Despite this, breeders have continued to incorporate novel sources of late blight resistance.  Some recent US cultivars include ‘Defender’ (Rich Novy, ID), ‘Missaukee’ and ‘Jacquelline Lee’ (David Douches, MI).  The genes involved in resistance in these cultivars are currently unknown, so we will have to wait and see how well they withstand late blight’s rapid evolution.


A great deal of work has also been done using resistance from the wild species S. bulbocastanum. This species contains three different resistance genes - RB (also called Rpi-blb1), Rpi-blb2, and Rpi-blb3.  All three are very effective at providing resistance to many different strains of late blight.  However, since S. bulbocastanum cannot be crossed with cultivated potato, their integration and deployment has been impeded.  Somatic fusions (non-sexual recombination of two plant cells) can be used, but this process brings with it a lot of "wild" potato traits that are difficult to remove.  Somatic fusions between S. bulbocastanum and cultivated potato were made in the mid-1990's by Dr. John Helgeson (USDA/ARS, UW-Plant Pathology).  In collaboration with Dr. Shelley Jansky (USDA/ARS, UW Horticulture), the Halterman Lab is continuing to work with the somatic fusion derivatives to integrate other valuable traits, such as early blight resistance, in order to develop useful germplasm for breeders.  In the mean time, late blight continues to evolve and there is no guarantee that new cultivars released years from now will continue to be resistant.  A speedier process is to integrate resistance using genetic modification, which allows introduction of a single gene - or pyramiding of multiple genes in the same amount of time.  This process is not only fast (it takes about 6 months), but avoids the introduction of undesirable traits from wild potato.  The result is a potato or tomato that grows and produces just like the original, but is now resistant to late blight.  The only hurdle at this point is public acceptance of crops that have been genetically improved in this way.  This method also does nothing to stop late blight from overcoming resistance within a few years. 


Why is late blight able to overcome resistance so quickly?  The answer lies within the genome of Phytophthora infestans, which contains all the information needed for this pathogen to grow and reproduce.  The entire genome of P. infestans has now been sequenced, revealing all the factors that are potentially involved in causing disease.  In order to cause disease, all plant pathogens (bacteria, fungi, nematodes, etc.) produce molecules that enter plant cells and make modifications to create a better living environment.  It's kind of like someone breaking into your house, turning off the alarm system, resetting the thermostat, doing laundry, making dinner, watching TV, and eating all your food - all on your bill! These pathogen molecules are called "effectors" because their presence results in some effect on the plant.  It is estimated that there are about 500-600 effectors secreted by P. infestans in order to modify potato or tomato to make it a better living environment (imagine 600 people breaking into your house).  Compared to other pathogens, this is an enormous number of effectors and is most likely the reason why late blight has proven so adaptable.


The Halterman lab has recently been most interested in late blight effectors that directly affect the activity of plant resistance genes - specifically the RB gene.  RB acts as a sentry within the plant and, when it recognizes the presence of a pathogen effector, it flips a molecular switch that turns on the plant's defense system.  What is somewhat troubling (but not unexpected), is that some P. infestans strains contain an effector that functions to sabotage RB and render it useless.  We have been very successful in understanding the mechanism that P. infestans uses to accomplish this.  Our work is now focused on identifying RB-like genes from wild species of potato or engineering new RB variants that are invulnerable to the activity of P. infestans effectors in order to try to stay one step ahead of late blight.


In the end, resistance to late blight is probably not futile, but it can sometimes feel like it.  When you consider that it takes 10-15 years to develop a potato cultivar and that late blight can overcome resistance in 5 years or less, the math doesn't seem to add up.  However, advanced technologies are now available to speed up the breeding process, and our ongoing efforts to understand how late blight causes disease will make us prepared to identify and deploy resistance quickly and effectively.


Biotech Potatoes - Are we prepared for the future?

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This was an article that I wrote with collaborators for the proceedings of Wisconsin’s Annual Potato Meeting

by Dr. Dennis Halterman, Dr. Shelley Jansky, and Dr. Jiming Jiang








US and Global Historical Perspective

Since the introduction of the first genetically modified (GM)/biotech crops in the mid-1990s, the agriculture industry has seen a steady increase in the acreage of biotech crops planted and harvested each year. In 2009, a record 14 million farmers in 25 countries planted 330 million acres of biotech soybean, maize, cotton, canola, zucchini squash, papaya, alfalfa, poplar, sugar beet, tomato, and sweet pepper. This represents an 80-fold increase in usage between 1996 and 2009. This increase is largely due to the economic, environmental, and productivity benefits derived from the use of GM crops. Biotech crops are accepted for import for food and feed use and for release into the environment in 57 countries, including major food importing countries like Japan, which do not plant biotech crops. Of these, Japan tops the list for the number of biotech crops accepted, followed by the US, Canada, South Korea, Mexico, Australia, the Philippines, the European Union, New Zealand and China.


But what about potato? Are we being left behind? The answer is most decidedly “no,” but the history of biotech potato has curtailed its reintroduction into the world food market somewhat. However, as you will see below, the acceptance of new GM crops continues to increase and, with the introduction of new technologies to introduce important traits using biotechnology, it seems to be only a matter of time before biotech potatoes are approved not only for cultivation but also for human consumption.

In 1995, Monsanto introduced the NewLeaf Potato, its first bioengineered crop. NewLeaf was engineered to express a bacteria-derived toxin (Bt) that protected against feeding by the Colorado potato beetle (CPB). Although NewLeaf never captured more than 5% of the market, it was quite effective at preventing CPB damage. At its peak in 1999, NewLeaf potatoes were planted on about 55,000 acres in North America. However, in 2001, Monsanto quietly stopped production of NewLeaf potatoes, bowing to pressure from food companies that were against the use of bioengineered food. They instead decided to focus on the production of crops with far bigger markets. The release of NewLeaf potatoes into the market without approval from the US Environmental Protection Agency and the Food and Drug Administration led to a much larger debate regarding the use of biotechnology in food crops and, since then, the release of biotech crops that are directly consumed by people (corn and soybean are primarily used for animal feed) has been difficult and rare.


Estimates place the cost of deregulating a new GM crop for human consumption at around $1 million, which makes it very difficult for researchers to develop new crops for release without industry support and a large market for the biotech crops. In some cases, where a devastating disease threatens crops, we have seen the release and acceptance of biotech crops containing resistance.  For example, papaya is susceptible to the incurable papaya ring spot virus (PRSV) and infected plants are severely affected.  PRSV was first detected in Hawaii in the 1940s and in the 1950s had all but eliminated the papaya crop on the island of Oahu.  Although production was moved to another island and was successful for decades, it was expected that PRSV would eventually spread to new production areas. Therefore, in the late 1980s, researchers with the USDA and the University of Hawaii began to develop a papaya cultivar resistant to PRSV. To do this, parts of the virus itself were transferred to the papaya genome. The production of the non-infectious virus particles elicited a type of immune response in the plants. Therefore, the new genetically modified plants are no longer susceptible to PRSV infection. The first virus resistant papayas were commercially grown in Hawaii in 1999 and now transgenic papayas account for more than 60% of the total Hawaiian papaya crop. China has been growing biotech papaya since 2006 and it now accounts for more than 88% of China’s papaya production. Genetically modified papayas are approved for consumption not only in the US, Canada, and China, but were also approved recently for import and consumption in Japan. 


Another disease for which there has been great interest recently in developing biotech-derived resistance is Huanglongbing (HLB), also called citrus greening or yellow dragon disease of citrus crops. The disease is caused by a bacteria-like organism called a Liberibacter, and is spread by the Asian citrus psyllid. The disease causes yield losses, reduces the economic value of the crop, and can kill trees. Like PRSV, once a plant is infected, there is no way to cure the plant of the disease. New biotech citrus plants have been developed by Texas AgriLife Research of Texas A&M University that contain resistance to HLB using a gene derived from spinach. There is a projected timeline of six years for these plants to prove themselves and to be accepted as safe by all state and federal agencies. If they are accepted, general release and production will likely follow.


While the majority of GM crop production is comprised of soybean, maize, and cotton, other biotech crops, including some vegetables, have recently been approved for production and are being grown.  In 2009, an estimated 95% of the 485,000 hectares of sugar beets planted in the US were devoted to varieties improved through biotechnology (Roundup-Ready).  Canadian growers planted approximately 15,000 hectares of biotech varieties in 2009, representing about 96% of the nation’s sugar beet crop.  In October 2009, India’s Genetic Engineering Approval Committee recommended the commercial release of insect resistant brinjal (eggplant).  Biotech brinjal is expected to be the first biotech food crop to be commercialized in India.  India has several other biotech food crops in field trials, including biotech Bt rice.  GM potato for starch production has been approved in the European Union and will be discussed below.


Biotechnology Challenges

The development and utilization of biotech potatoes involves some biological hurdles. The first is the ability to grow plants in tissue culture and regenerate them after they have been genetically modified.  Fortunately, compared to many crops, potato is relatively easy to manipulate in tissue culture.  Some cultivars are more amenable to the system than others, but with appropriate protocol modifications, most are capable of transformation.  Another potential hurdle is the availability of genes to introduce into cultivars via transformation, especially if the public or industry requires that the genes originate from potato. Again, potato is an exceptional crop for transformation due to the tremendous amount of genetic diversity in wild and cultivated relatives.  For example, genes from wild potato relatives can contribute resistance to late blight, Verticillium wilt, potato virus Y, and cold sweetening. 


After GM cultivars have been created, two potential safety issues arise. The first is the potential for pollen flow from the transgenic cultivars to either weeds or other potato cultivars after their release into the field. In US potato production regions, no weeds are cross compatible with potato, so transgenic weeds will not be created. In addition, unlike grain crops, the product of pollination in potato is not harvested and is not used for propagation of a new crop.  Consequently, it is simply not possible for genes to move from biotech cultivars to conventional ones. A second potential safety concern is that biotech crops contain modifications that alter the structure of the genome in an unpredictable way.  There is some worry that these modifications could have unforeseen consequences.  However, if the gene being introduced originates from a wild potato relative, then the amount of genetic modification is actually less than if traditional breeding is used to introduce the gene. The biotech plant will contain only the segment of DNA inserted during transformation, while a plant developed by breeding will contain 50% exotic germplasm after the first cross, 25% after the second cross, and so on.  The introduction of a gene within a crop (e.g. a wild potato gene into cultivated potato) is termed “intragenics” and differs from transgenics because the final product does not contain any foreign DNA.  Finally, some GM plants are created by knocking out the function of existing genes, so they do not rely on the introduction of new genes. 


It can be argued that potato is the crop that can benefit most by biotechnology. Breeding progress is slow because cultivars are tetraploid and genetic variability in existing cultivars is low. Potato is easy to transform, genes are available from wild species, and gene flow is not an issue. Since disease and storage losses are significant in the potato crop and control is expensive and not always effective, significant productivity gains could be realized through the use of biotech cultivars.


What does the future hold for biotech potato in the US?

The European Union has set the stage for the acceptance of biotech potato with a cultivar intended for industrial use. The BASF chemical company has been granted approval to produce the cultivar Amflora, which will be used as a source of starch in industrial processes such as the manufacture of paper. The company is moving ahead with plans to grow biotech processing cultivars containing resistance genes for late blight and other disease. The decision made on the Amflora potato was the first approval for the planting of a biotech crop in the EU since 1998. 


In the US, perhaps low acrylamide potatoes will provide the next test case for acceptance of GM potatoes. Acrylamide, a neurotoxin and a potential carcinogen, is produced in all starch-rich foods processed under high temperatures. Potato chips and french fries have especially high acrylamide levels. This has raised a worldwide food safety concern that has resulted in lawsuits against major potato and fast food companies. Developing methods to reduce acrylamide in fried potato products has become an urgent requirement for the potato processing industry. The substrates for the production of acrylamide are reducing sugars (glucose and fructose) and the amino acid asparagine. Consequently, one biotech strategy has focused on suppressing the accumulation of reducing sugars by knocking out (silencing) the production of the enzyme acid invertase, which cleaves sucrose into glucose and fructose. This strategy has been very successful in transforming standard chip cultivars into clones with high levels of resistance to cold sweetening. Another strategy that is being evaluated is knocking out the expression of the two genes that are required for the synthesis of asparagine. Biotech cultivars would provide a mechanism to quickly respond to industry needs. Potato cultivars with the acid invertase and asparagine synthase genes silenced could be ready for commercial production in 3-5 years. It would take at least 15-20 years to breed new cultivars with low acrylamide characteristics similar to the silencing lines.


Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating potato disease worldwide. Control of late blight in the US relies almost exclusively on fungicide application. During an average epidemic year, the fungicide cost to control late blight is about $200-300 per acre in Wisconsin, which equates to a total fungicide cost in the range of $4-8 million per season in Wisconsin plus at least $4 million to cover the cost of application.  Due to constant genetic shifts of P. infestans populations and decreases in fungicide effectiveness, late blight can cause a complete loss of the crop. The most effective and environmentally friendly way to prevent widespread devastation by late blight is to incorporate host plant resistance. 


Potato breeders have incorporated many late blight resistance genes (R genes) from wild Solanum species into cultivated potato. Unfortunately, most of these R genes provided resistance against only specific races of P. infestans. Such race-specific resistance is often short-lived and can be rapidly overcome by new strains of P. infestans. Solanum bulbocastanum is a Mexican wild potato species that has co-existed in the same habitat as the late blight pathogen for centuries. S. bulbocastanum is not immune to late blight, but instead shows a marked delay in both the onset of symptoms and the development of lesions. Such rate-limiting resistance may put less selection pressure on the P. infestans populations and protect the durability of the resistance genes. In 2003, we isolated and cloned a resistance gene, RB, from S. bulbocastanum. Susceptible potato varieties were subsequently transformed with RB. They have shown a high level of resistance over a broad-spectrum of various P. infestans strains, with a marked delay in both the onset of symptoms and the development of lesions. Most remarkably, the transgenic lines have exhibited a high level of resistance in the Toluca Valley in Mexico, which is the most late blight infested region in the world. Among the numerous disease resistance genes cloned from various plant species, few have shown a resistance spectrum as broad as RB.  However, it is no surprise that new races of late blight are emerging that are able to overcome RB resistance.  Therefore, in order to keep up with the rapid evolution of the pathogen, it will be critical to be able to rely on a mechanism to rapidly deploy new R genes derived from wild potato species, pyramid multiple R genes together, or engineer new genes to recognize new pathogen strains.  The use of GM potatoes will prove to be an invaluable resource in our fight against this disease.


In the near future, we expect to create biotech potatoes with resistance to Verticillium wilt and potato virus Y. In several wild potato relatives, we have identified a gene that is analogous to the Ve gene that has been used as a source of Verticillium wilt resistance in tomato for several decades. Efforts are underway to create plants containing this gene and then test for resistance. We have not yet isolated a PVY resistance gene, but have the resources to do so and expect to be able to clone a gene from the wild species S. chacoense in the near future. That will lead the way to the development and testing of potato containing PVY resistance.



Fighting Potato Diseases by Enhancing Germplasm

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This was an article published in the 2010 May/June issue of Agricultural Research - a magazine highlighting research done by USDA/ARS scientists.  I’m pictured with Shelley Jansky while looking at late blight inoculated plants.










Geneticists Dennis Halterman and Shelley Jansky, with ARS’s Vegetable Crops Research Unit in Madison, Wisconsin, are hunting for wild potatoes that contain resistance to important diseases plaguing potato growers nationwide.


One wild potato Halterman has identified, Solanum verrucosum, contains a gene with resistance to late blight. Efforts are under way to cross S. verrucosum with cultivated potato and integrate the late blight resistance gene.


The researchers are looking to produce germplasm useful for develop- ing a potato cultivar with resistance to both late blight and early blight, which also affects tomatoes. Early blight, a fungal disease, mainly affects the potato plant’s leaves and stems but, if left uncontrolled, can also reduce yield. To create the multi-disease-resistant cultivar, the scientists crossed S. verrucosum with another wild potato species that has resistance to early blight, and then crossed the resulting wild potato hybrid with cultivated potato. They currently have seedlings in the greenhouse waiting to be field tested.


Halterman and Jansky are also looking for resistance to Verticillium wilt, another fungal disease that can remain in the soil for up to 10 years. Halterman developed a molecular marker to screen germplasm for resistance to this disease, saving the scientists time and effort. They found resistance in the wild potato species S. chacoense and produced cultivated potato hybrids that contain the important gene. According to Halterman, this is a good, durable gene that should hold up in the long term.


The scientists are also targeting the potato diseases potato virus Y and common scab.—By Stephanie Yao, ARS.