Scientists Engineer Root-Knot Nematode Resistance - UPDATES

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                                  Scientists Engineer Root-knot Nematode Resistance






ScienceDaily
(Sep. 28, 2006)

— University of Georgia professor Richard Hussey has spent 20 years studying a worm-shaped parasite too small to see without a microscope. His discovery is vastly bigger. Hussey and his research team have found a way to halt the damage caused by one of the world's most destructive groups of plant pathogens.

Root-knot nematodes are the most economically important group of plant-parasitic nematodes worldwide, said Hussey, a distinguished research professor in plant pathology at the UGA College of Agricultural and Environmental Sciences.

They attack nearly every food and fiber crop grown, about 2,000 plant species in all.

The nematode invades plant roots, and by feeding on the roots' cells, they cause the roots to grow large galls, or knots, damaging the crop and reducing its yields.

Working with assistant research scientist Guozhong Huang and research technician Rex Allen, Hussey discovered how to make plants resistant to root-knot nematode infection.

Eric Davis at North Carolina State University and Thomas Baum at Iowa State University also collaborated on the research.

The discovery "has the potential to revolutionize root-knot resistance in all crops," Hussey said.

The most cost-effective and sustainable management tactic for preventing root-knot nematode damage and reducing growers' losses, he said, is to develop resistant plants that prevent the nematode from feeding on the roots. Because root-knot nematode resistance doesn't come naturally in most crops, Hussey's group bioengineered their own.

The results of the study were published Sept. 26 in the journal, Proceedings of the National Academy of Sciences.

Four common root-knot nematode species account for 95 percent of all infestations in agricultural land. By discovering a root-knot nematode parasitism gene that's essential for the nematode to infect crops, the scientists have developed a resistance gene effective against all four species.

Using a technique called RNA interference, the researchers have effectively turned the nematode's biology against itself. They genetically modified Arabidopsis, a model plant, to produce double-stranded RNA to knock out the specific parasitism gene in the nematode when it feeds on the plant roots.

This knocked out the parasitism gene in the nematode and disrupted its ability to infect plants.

"No natural root-knot resistance gene has this effective range of root-knot nematode resistance," Hussey said.

The researchers' efforts have been directed primarily at understanding the molecular tools the nematode uses to infect plants. This is a prerequisite for bioengineering durable resistance to these nematodes in crop plants.

Through this research, they've discovered the parasitism genes that make a nematode a plant parasite so it can attack and feed on crops, Huang said.

"Our results of in-plant RNA interference silencing of a parasitism gene in root-knot nematodes provides a way to develop crops with broad resistance to this destructive pathogen," Hussey said. "Equally important, our approach makes available a strategy for developing root-knot-nematode-resistant crops for which natural resistance genes do not exist."

Funding for the project came from the U.S. Department of Agriculture's Cooperative State Research, Education and Extension Service National Research Initiative and the UGA College of Agricultural and Environmental Sciences.


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Adapted from materials provided by University of Georgia.
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 MLA University of Georgia (2006, September 28). Scientists Engineer Root-knot Nematode Resistance. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2006/09/060927100819.htm

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              Genome Of One Of World's Most Common And Destructive Plant Parasites Sequenced






ScienceDaily
(Sep. 25, 2008)
 
— North Carolina State University scientists and colleagues have completed the genome sequence and genetic map of one of the world's most common and destructive plant parasites – Meloidogyne hapla, a microscopic, soil-dwelling worm known more commonly as the northern root-knot nematode.

The research could help lead to a new generation of eco-friendly tools to manage the ubiquitous parasitic worm, which, along with other species of root-knot nematode, causes an estimated $50 billion in crop and plant damage yearly, says Dr. Charles Opperman, professor of plant pathology at NC State, co-director of the Center for the Biology of Nematode Parasitism and the corresponding author on a scientific paper describing the research.

The resulting sequence data has been deposited in public databases, so other researchers interested in the root-knot nematode – how it develops, establishes a host-parasite interaction or evades host defenses, for example – are now able to use the map of the parasite's genes as a tool to discover more specific information about the parasite.

The northern root-knot nematode is the smallest multicellular animal genome completely sequenced, says Dr. David McK. Bird, professor of plant pathology at NC State, co-director of the Center for the Biology of Nematode Parasitism and a co-author of the paper.

The study is published online this week in Proceedings of the National Academy of Sciences. Researchers from the University of California, Davis; the University of California, Berkeley; and the Joint Genome Institute also contributed to the research.

The northern root-knot nematode has been developed into a key model species in the study of plant-parasitic nematodes, and the completion of the genome sequence will further empower researchers to ask highly specific questions about the evolution and nature of parasitism. "A key facet to making M. hapla the premier model species for plant-parasitic nematodes is the development of a genetic map by our colleague, Dr. Valerie Williamson, at the University of California-Davis. The combination of a complete genome sequence with the genetic map makes this a unique and powerful system for the in-depth study of nematode-host interaction" Opperman says.

Besides being extremely important for the development of new and effective management strategies, the researchers say that the information gleaned from the genome sequence and genetic map will help scientists learn more about what they call the "themes of parasitism."

"All parasites have to do the same things to infect their hosts, whether the hosts are plants, animals or humans," Bird says. "Plants offer an advantage over those systems because they are easier to manipulate experimentally, and enable us to perform detailed experiments not easily done in animals, and not possible in humans."

The study shows that M. hapla has a somewhat smaller genome when compared with other microscopic worms like Caenorhabditis elegans, one of the models of scientific studies of animals. The northern root-knot nematode genome might be smaller, the researchers say, because the inside of the host plant's root provides an isolated environment compared to the soil.

"Having 99 percent of the genome sequenced allows you to not only know what's there, but to compare it to other nematodes to see what's missing from this genome," Bird says. "Finding potential Achilles' heels, what the nematode is getting from the plant and how is it really interacting with the plant are all more possible now."

The genome's reduced size made it easier to assemble the sequence, Opperman says. "In combination with an extensive database of plant parasitic nematode expressed genes from a previous project led by our Center for the Biology of Nematode Parasitism, this system provides a powerful platform for study of these important parasites," he added.

Although M. hapla was previously not known to be as widespread as other species of root-knot nematode, the cool-climate worm is now taking root in warmer climes, perhaps due to global climate change. The worm has been detected recently in Ugandan soils and other tropical and subtropical regions, for example. The expansion of range to new climates makes finding ways of controlling it even more critical, the researchers say.

The study was funded by a grant from the Microbial Genome Sequencing Project of the Cooperative State, Research, Education and Extension Service in the U.S. Dept. of Agriculture.


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Journal reference:



1.Opperman et al. Sequence and genetic map of Meloidogyne hapla: A compact nematode genome for plant parasitism. Proceedings of the National Academy of Sciences, Published online Sept. 22, 2008 DOI: 10.1073/pnas.0805946105
Adapted from materials provided by North Carolina State University.
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 MLA North Carolina State University (2008, September 25). Genome Of One Of World's Most Common And Destructive Plant Parasites Sequenced. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2008/09/080923104412.htm

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                                                   Outwitting Pesky Parasites






ScienceDaily
(July 18, 2007)

— Across the southern United States, an invisible, yet deadly parasite known as the root-knot nematode is crippling soybean crops. While plant breeders are racing to develop cultivars resistant to the root-knot nematode, they are being slowed down by current time-consuming and expensive methods of screening for resistant plants. Now, researchers believe they have found a shortcut for screening resistant soybean crops.

Researchers at the University of Georgia report the discovery of several molecular markers that will help soybean breeders to accurately screen for root-knot resistant plants at a fraction of the time and cost of current screening techniques in the July issue of The Plant Genome.

While previous studies of soybean crops helped researchers to locate genes associated with root-knot nematode resistance, University of Georgia scientists recently identified single nucleotide polymorphisms (SNPs), slight variations in the DNA, nearby genetic regions that code root-knot nematode resistance. After linking the identified SNPs to root-knot nematode resistance, scientists developed a marker assisted screening test that used SNPs to determine whether or not plants were resistant to root-knot nematode.

"The basic objective of any breeding scheme is to identify elite individuals that can pass on their desirable characteristics," explained Bo-Keun Ha, lead author of study. While Ha says most conventional breeders rely on phenotypic evaluations of plants to select the plant with most desirable traits, this process takes time and money.


For example, if a breeder wants to select plants with resistance to root-knot nematode based upon a phenotypic evaluation alone, he or she must grow a large population of plants, inoculate plants with nematode eggs, wait until the growth of the nematode and evaluate the damage before selecting the most resistant plants.

Instead of relying on the time-consuming phenotypic screening to determine whether or not the root-knot resistance genes are present in soybean crops, "marker assisted selection can inform breeders about the presence of the resistance gene in individual plants," said Ha. Also, because marker assisted selection involves the screening of a few markers across thousands of plants Ha pointed out that the marker assisted selection is rather inexpensive and time efficient.

"Our results found SNPs linked to two root-knot nematode resistance genes and developed the resources for a relatively high throughput method of selection for the two genes," said Ha. "The SNP assays that we have reported will empower soybean breeders to efficiently incorporate root-knot resistance genes into new productive cultivars."



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Adapted from materials provided by Crop Science Society of America, via EurekAlert!, a service of AAAS.
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 MLA Crop Science Society of America (2007, July 18). Outwitting Pesky Parasites. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2007/07/070716133100.htm

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Root-knot nematodes, recently confirmed in southern Indiana, can cause extensive damage to soybeans, corn and watermelon, three of the main cash crops in that area of the Midwest.

Purdue plant pathologist Andreas Westphal and his research team have identified several commercial varieties of soybeans that grow well in the area and are resistant or tolerant to this type of nematode and also to soybean cyst nematode.

In the photo, Westphal is holding a tomato plant infected with root-knot nematodes, evidenced by the knobby growths on the roots.



(Credit:
Purdue Agricultural Communication photo/
Tom Campbell)

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                 Soybean Varieties Viable In Southern Indiana, Resistant To Root-knot Nematode






ScienceDaily
(Mar. 25, 2008)

— Purdue University researchers have identified several soybean varieties that grow well in areas of the Midwest like southern Indiana and are resistant to root-knot nematodes, a plant-destroying parasite with a recently confirmed presence in that part of the state.

The researchers verified that resistance in soybeans to one nematode parasite doesn't predict how well the plant will fight off another nematode species, said Andreas Westphal, assistant professor of plant pathology. Some of the varieties also were resistant to soybean cyst nematode.

"We were trying to identify soybean lines that will grow in Indiana and are root-knot nematode  resistant," said Westphal, who is senior author of the report published online in the journal Crop Science and will be published in the March-April print issue.

The research team recently published a paper in Plant Health Progress that details the distribution of root-knot nematodes on soybeans in southwestern Indiana.

"We also wanted to find varieties that are nematode-tolerant," Westphal said. "In other words, the nematode is present in the soil, but the plant doesn't suffer a lot of damage."

Root-knot nematodes, including the species Meloidogyne incognita, infect soybeans in sandy loam soil and also reproduce on corn and the highly root-knot nematode-sensitive watermelon, two other major cash crops in the southern part of Indiana. The area, along with additional parts of the state, also suffers from other nematodes, including the soybean cyst nematode (Heterodera glycines). Root-knot nematodes are responsible for a loss of 93,000 tons of soybeans annually in the United States.

Other than resistant and tolerant plants, available methods to rid fields of the destructive organisms are not always practical or economically feasible, Westphal said. For example, chemicals that are effective against nematodes can be dangerous to the environment, people and animals.

A major concern for farmers is that soybeans, corn and watermelon are all susceptible to root-knot nematodes. Most farmers in southern Indiana plant crops in a soybean-corn-watermelon rotation. If the parasites infect the soybeans, then the organisms will be in the soil and can damage the subsequent crops planted in the same field.

"The availability of nematode-resistant varieties is important, not only for soybean production, but also for the whole rotation sequence because a resistant soybean crop will reduce the number of nematodes in the soil," Westphal said.

The study involved planting eight soybean strains in a commercial field near Vincennes, Ind. These were plant varieties that already were known to grow well in soil and weather similar to that found in southern Indiana. The field had a history of root-knot and soybean cyst nematode infestations. Westphal and his team also tested some of the same soybean lines in a field in which they introduced the nematodes and in a greenhouse where they used similar soil containing the root-knot nematodes.

Using plants known to be resistant to soybean cyst nematode, the researchers confirmed resistance to that nematode doesn't predict how resistant the plant will be to root-knot nematodes.

Although Indiana farmers previously were aware of the damage to their crops from soybean cyst nematode, it was only recently that they learned about root-knot infection of soybeans. They now know how to identify both nematodes and how these parasites damage crops.

Damage by plant-parasitic nematodes usually appears in patches in fields because where nematodes are introduced determines the infestation area. The type of soil and environmental conditions also play a role in the parasite's survival.

Both the soybean cyst and root-knot nematode feed on roots, robbing the plant of needed nutrients and water. The lemon-shaped soybean cyst nematode is easy to spot on the root because it stays on the outside. These pinhead-sized nematodes are white, then yellow, and finally become brown as they mature. The nematode-induced cysts are much smaller than the so-called "nodules," which are structures induced by the beneficial bacterium rhizobium. Rhizobium association aids the plant in nutritional nitrogen absorption.

The root-knot nematode induces big clumps, or galls, on the root that look a bit like a wart or a tree knot, and the deformations are much bigger than the signs caused by the soybean cyst nematode. The nematode galls have irregular tumorlike shapes, in contrast to the spherical shape of nodules caused by rhizobium association.

Next the researchers will try to determine varieties of cover crops that are nematode-resistant. Cover crops are used over the winter to control erosion but can provide a habitat for the parasites. This means that larger populations of the parasites are present when crops are planted in the spring.

"We hope that we can improve nematode suppression in the entire crop sequence to improve the yield of the cash crops," Westphal said.

The other authors on this paper were graduate student Greg Kruger and postdoctoral researcher Lijuan Xing, both of the Purdue Department of Botany and Plant Pathology, and Allen LeRoy, Purdue Department of Agronomy soybean breeding and genetics professional.

The Indiana Soybean Alliance; Indiana Crop Improvement Association; AG Spectrum; Purdue departments of Botany and Plant Pathology, and Agronomy; and the Purdue College of Agriculture provided support for this research.


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Adapted from materials provided by Purdue University.
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 MLA Purdue University (2008, March 25). Soybean Varieties Viable In Southern Indiana, Resistant To Root-knot Nematode. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2008/03/080320173605.htm

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                                    New Peanut Variety Resistant To Nematodes, Virus






ScienceDaily
(May 23, 2008)

— A new peanut variety developed by Agricultural Research Service (ARS) scientists may help farmers in their battle against two key peanut problems.

Peanuts are a very popular commodity, with annual U.S. production well above 2 billion pounds. But peanut varieties are plagued by pests like the peanut root-knot nematode and diseases like tomato spotted wilt virus (TSWV).

While certain peanut varieties exhibit resistance to either the microscopic worms or the TSWV pathogen, Tifguard is the first variety that has resistance to both. It is the product of research by plant geneticist C. Corley Holbrook in the ARS Crop Genetics and Breeding Research Unit at Tifton, Ga.; plant pathologist Patricia Timper in the ARS Crop Protection and Management Research Unit, also at Tifton; and University of Georgia collaborators Albert Culbreath and Craig K. Kvien, in the College of Agriculture and Environmental Sciences.

Tifguard was developed by hybridizing a TSWV-resistant cultivar with a nematode-resistant cultivar. Field tests for resistance to peanut root-knot nematode were conducted at two Georgia farms in Tift County that were heavily infested. In testing for TSWV-resistance, Tifguard plants were grown in plots at one of the Tift County farms that also displayed severe TSWV problems.

Not only did Tifguard exhibit higher resistance to TSWV, it also produced higher yields than standard check cultivars when grown in fields with little or no nematode pressure. And because of its high level of resistance to both TSWV and root knot nematode, Tifguard had significantly higher yields than all other varieties when grown in two locations with high pressure from both pathogens.

For these reasons, Tifguard should be particularly valuable to peanut growers who have to deal with both root-knot nematodes and TSWV. It was released in 2007 and is currently in seed production. Seed for farmers should be available by the 2009 planting season.


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Adapted from materials provided by US Department of Agriculture.
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 MLA US Department of Agriculture (2008, May 23). New Peanut Variety Resistant To Nematodes, Virus. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2008/05/080521101458.htm

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Researchers work to improve bell pepper
resistance to Root-knot nematodes

(Credit:
Photo by Stephen Ausmus)









                         Parasite-resistant Peppers Green Alternatives To Chemical Pesticides






ScienceDaily
(Nov. 17, 2008)

— Root-knot nematodes are extreme parasites. These microscopic, omnipresent worms cause major damage to horticultural and field crops in sub-tropical regions, resulting in significant financial losses to growers and gardeners.

Until recently, fumigation of the soil with methyl bromide before planting was the primary method for controlling root-knot nematodes in valuable vegetable crops. Methyl bromide (MeBr) is an odorless, colorless gas that has been widely used as a plant pesticide. Since the discovery that the substance has severe negative effects on the environment—it depletes the stratospheric ozone layer—the use of methyl bromide has been phased out in the U.S.

To combat parasites like root-knot nematodes without the use of chemical pesticides, scientists are focusing more research on developing new, parasite-resistant varieties of vegetables. Dr. Judy Thies, a research plant pathologist at the U.S. Department of Agriculture's Agricultural Research Service, was part of a team of scientists who developed the Charleston Belle variety of bell pepper, the first nematode-resistant bell pepper.

In a study published in the February issue of the American Society for Horticultural Science's journal HortScience, Dr. Thies and her colleagues tested the stability of two types of bell peppers, Charleston Belle and Carolina Wonder. Thies explained, "These two types of pepper cultivars are the only nematode-resistant varieties available to commercial growers and home gardeners. Since a large percentage of bell pepper production in the U.S. occurs in the Southeastern U.S., and in particular Florida, we tested the peppers for resistance to nematodes in sub-tropical climates to determine if the cultivars were stable when grown in Florida under high soil temperatures. It is important to know whether the peppers' resistance to parasites breaks down when peppers are grown in hot climates."

Good news for growers and gardeners: study results showed that nematode-resistant varieties such as Charleston Belle and Carolina Wonder are viable alternatives to methyl bromide for managing southern root-knot nematode in bell pepper in sub-tropical environments. To increase the availability of parasite-resistant vegetables, commercial seed companies are currently developing nematode-resistant hybrid bell peppers using both Charleston Belle and Carolina Wonder.


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Journal reference:

1.Thies, Judy A., Dickson, Don W., Fery, Richard L. Stability of Resistance to Root-knot Nematodes in 'Charleston Belle' and 'Carolina Wonder' Bell Peppers in a Sub-tropical Environment. HortScience, 2008 43: 188-190 [link]
Adapted from materials provided by American Society for Horticultural Science.
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 MLA American Society for Horticultural Science (2008, November 17). Parasite-resistant Peppers Green Alternatives To Chemical Pesticides. ScienceDaily. Retrieved July 11, 2009, from



http://www.sciencedaily.com­ /releases/2008/11/081112113603.htm