Archive for the ‘Host plant resistance’ Category

From PestNet

Researchers Create Plant that Grows Fast and Defends Itself from Insects

Section: News from Around the World

A team of researchers from Michigan State University (MSU) has developed a plant that can outgrow and outcompete its neighbors for light, and defend itself against insects and disease.

Led by Gregg Howe, MSU Foundation professor of biochemistry and molecular biology, the team modified an Arabidopsis plant by “knocking out” both a defense hormone repressor and a light receptor in the plant. This genetic alteration allowed the plant to grow faster and defend itself from insects at the same time.

In plants, more growth equals less defense, and more defense equals less growth, but Howe said that their “genetic trickery” can get a plant to do both. If the results of this breakthrough can be replicated in crop plants, the work could have direct benefits for farmers trying to feed a world population that is expected to reach nine billion by the year 2050.

For more details, read the news release at MSU Today.

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New York Times


Cherry tomatoes. Researchers found that domesticated tomatoes like these were less resistant to whiteflies than currant tomatoes, a wild species. Credit Dean Fosdick/Associated Press

Whiteflies are the scourge of many farms, damaging tomatoes, peppers, eggplants and other crops. Now, researchers in Britain report that a species of wild tomato is more resistant to the pest than its commercial counterparts.

The wild type, the currant tomato, is closely related to domestic varieties, “so we could crossbreed to introduce the resistance,” said Thomas McDaniel, a biologist and doctoral student at Newcastle University in England and a co-author of the study, published in the journal Agronomy for Sustainable Development. “Another method would be genetic engineering, if we identified the genes.”

The researchers studied Trialeurodes vaporariorum, a species of whitefly that often attacks tomatoes grown in greenhouses. Whiteflies damage tomato plants by extracting the plant’s sap, which contains vital nutrients; by leaving a sticky substance on the plant’s surface that attracts mold; and by transmitting viruses through their saliva.

But currant tomatoes have some sort of mechanism, yet to be understood, that repels whiteflies. “They seemed to move away every time they tried to sample the sap,” Mr. McDaniel said.

The wild plants also produce a chemical reaction that causes the plant sap to gum up the whitefly’s feeding tube.

Growers use a parasitic wasp to control whiteflies. The wasp lays its eggs on young whiteflies, which are eaten by hatching larvae. The treatment is expensive and laborious. As an alternative, farmers use chemical pesticides, but some have been linked to declines in bee populations.

“Genetic diversity is very, very low in domestic crops, so introducing these genes that we’ve lost along the way is probably quite important,” Mr. McDaniel said.

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Chiapas, Mexico, July 25, 2016

Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his maize plants infected with tar spot complex.
Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his maize plants infected with tar spot complex. Photo: J. Johnson/CIMMYT.

In southern Mexico and Central America a fungal maize disease known as tar spot complex (TSC) is decimating yields, threatening local food security and livelihoods. In El Portillo, Chiapas, Mexico, local farmer Felix Corzo Jimenez sadly surveys his maize field.

“It’s been a terrible year. We’ll be lucky if we harvest even 50 percent of our usual yields,” he said, examining a dried up maize leaf covered in tiny black dots, and pulling the husk off of an ear to show the shriveled kernels, poorly filled-in. “Tar spot is ruining our crops.”

Named for the black spots that cover infected plants, TSC causes leaves to die prematurely, weakening the plant and preventing the ears from developing fully, cutting yields by up to 50 percent or more in extreme cases. Caused by a combination of three fungal infections, the disease occurs most often in cool and humid areas across southern Mexico, Central America and South America. The disease is beginning to spread – possibly due to climate change, evolving pathogens and susceptible maize varieties – and was reported in important maize producing regions of central Mexico and the northern United States for the first time last fall. To develop TSC resistant maize varieties that farmers need, the Seeds of Discovery (SeeD) initiative is working to “mine” the International Maize and Wheat Improvement Center’s (CIMMYT) genebank for native maize varieties that may hold genes for resistance against the disease.

The first stage of fungal maize disease TSC, with tiny, black “tar spots” covering the leaf. The spots will soon turn into lesions that kill the leaf, preventing photosynthesis from occurring.

The majority of maize varieties planted in Mexico today are susceptible to TSC, meaning that farmers would have to spray expensive fungicides several times each year to protect their crops against the disease, a huge financial burden that few can afford. Creating varieties with natural resistance to tar spot is an economical and environmentally friendly option that will protect the livelihoods of the region’s smallholder maize farmers.

“This project targets the many farmers in the region with limited resources, and the small local seed companies that sell to farmers at affordable prices,” says Terry Molnar, SeeD maize breeder.

The key to developing maize varieties with resistance to TSC lies in the genetic diversity of the crop. For thousands of years, farmers have planted local maize varieties known as landraces, or descendants from ancient maize varieties that have adapted to their environment. Over centuries of selection by farmers these landraces accumulated specific forms of genes, or alleles, which helped them to resist local stresses such as drought, heat, pests or disease.

These novel genetic traits found in landrace maize can help breeders develop improved maize varieties with resistance to devastating diseases such as TSC. However, it is quite challenging for breeders to incorporate “exotic” landrace materials into breeding programs, as despite their resistance to stresses found in their native environment, they often carry unfavorable alleles for other important traits.

A maize ear with shriveled kernels that are poorly filled, a major side effect of TSC that reduces farmer’s tields.

To help breeders incorporate this valuable genetic diversity into breeding programs, SeeD works to develop “bridging germplasm” maize varieties, which are created by transferring useful genetic variation from landraces held in the CIMMYT genebank into plant types or lines that breeders can readily use to develop the improved varieties farmers need. These varieties are created by crossing landrace materials with CIMMYT elite lines, and selecting the progeny with the genetic resistance found in a landrace without unfavorable traits breeders, farmers and consumers do not want.

“The CIMMYT maize genebank has over 28,000 maize samples from 88 countries, many of which are landraces that may have favorable alleles for disease resistance,” Molnar says. “We all know that there is good material in the bank, but it’s scarcely being used. We want to demonstrate that there are valuable alleles in the bank that can have great impact in farmers’ fields.”

A susceptible maize variety infected with TSC (left) compared to a healthy maize plant , a resistant variety immune to the disease (right).

SeeD scientists began by identifying landrace varieties with genetic resistance to TSC. Trials conducted in 2011, 2012 and 2014 evaluated a “core set” – a genetically diverse subset of the maize germplasm bank – in search of resistant varieties.  Of the 918 landrace varieties planted in 2011 and 2012, only two landraces—Oaxaca 280 and Guatemala 153—were outstanding for tolerance to the disease.  Genotypic data would later confirm the presence of unique resistant alleles not currently present in maize breeding programs that could be deployed into SeeD’s bridging germplasm. This bridging germplasm will be available to breeders for use in developing elite lines and varieties for farmers.

“As a breeder, I’m excited to work with SeeD’s bridging germplasm as soon as it is available,” said Felix San Vicente, CIMMYT maize breeder working with the CGIAR Research Program on Maize and the Sustainable Modernization of Traditional Agriculture (MasAgro) project.

Terry Molnar, maize breeder with SeeD, and Enrique Rodriguez, field research technician with SeeD, evaluate bridging germplasm for resistance to TSC.

Up to this point, most breeders have only used elite lines to develop hybrids, because landraces are extremely difficult to use. This practice, however, greatly limits the genetic diversity breeders employ. Using novel alleles from maize landraces allows breeders to develop improved hybrids while broadening the genetic variation of their elite germplasm. This novel genetic diversity is very important to protect crops from evolving pathogens, as it means the varieties will have several resistant alleles, including alleles that have never been used in commercial germplasm before.

“The more alleles the better,” said San Vicente, “as it protects the line longer. It provides a form of insurance to smallholder farmers as these varieties will have more genes for resistance, which reduces their risk of losing their crop.”

To ensure that farmers can access this improved seed, CIMMYT works with small local seed companies. “The price of seed will be very affordable,” according to San Vicente. “As CIMMYT is a non-profit, we provide our improved materials to seed companies at no cost.”

The TSC resistant bridging germplasm developed by SeeD has been tested in on-farm trials in TSC-prone sites in Chiapas and Guatemala, with promising results, and will be publicly available to breeders in 2017. In the meantime, local farmers look forward to seeing the results of this research in their own fields. “A variety with the disease resistance of a landrace and the yield and performance of a hybrid is exactly what we need,” says Corzo Jimenez.

Corzo Jimenez in his maize field infected with TSC. Varieties made from SeeD bridging germplasm would allow him to protect his crop without applying expensive fungicides.

Corzo Jimenez in his maize field infected with TSC. Varieties made from SeeD bridging germplasm would allow him to protect his crop without applying expensive fungicides. CIMMYT/Jennifer Johnson.

SeeD is a multi-project initiative comprising: MasAgro Biodiversidad, a joint initiative of CIMMYT and the Mexican Ministry of Agriculture (SAGARPA) through the MasAgro (Sustainable Modernization of Traditional Agriculture) project; the CGIAR Research Programs on Maize (MAIZE CRP) and Wheat (WHEAT CRP); and a computation infrastructure and data analysis project supported by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC). To learn more about the Seeds of Discovery project, please go to http://seedsofdiscovery.org/.


More news from: CIMMYT (International Maize and Wheat Improvement Center)


Website: http://www.cimmyt.org

Published: July 26, 2016


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From the Ohio State University Vegetable Newsletter

Matt Kleinhenz, Department of Horticulture and Crop Science, The Ohio State University

Many articles, including one in the June 21 edition of VegNet, have stated that grafted fresh market tomato plants can out-yield ungrafted ones by up to 50% or more depending on the circumstances. Those circumstances appear to include abiotic and biotic stresses that also occur in processing tomato production in Ohio and elsewhere. In some tests, grafted fresh market tomato plants have also out-yielded ungrafted ones when lower rates of fertilizer were used.

So, at first glance, it seems obvious that grafted plants will also be useful in processing tomato production. However, that has not been proven. Clearly, more information is needed to understand the value of grafted plants in processing tomato production. Their value is increasing in fresh market production and their potential to enhance processing production is real. That said, differences between fresh market and processing tomato production, including their economics and varieties, requires the value of grafted plants in processing production to be validated separately. Grafting effects on processing tomato yield, quality, and profit potential must be tested thoroughly.

Growers, researchers, and others must do the testing. Teams in California and Ohio have started. Currently, as described in Figure 1, plots at the OARDC in Wooster, OH contain plants representing thirty rootstock-scion variety combinations and ungrafted plants of the fruiting (scion) varieties. We are tracking crop development and we will record fruit yield and quality, including color and soluble solids. Our work is supported by The Ohio Vegetable & Small Fruit Research & Development Program (OVSFRDP), the USDA-SCRI program, The OSU-OARDC, and the Department of Horticulture and Crop Science. We will be happy to assist growers with tests on their farms. Contact Matt Kleinhenz (ph. 330.263.3810; kleinhenz.1@osu.edu) for more information. Also, see resources at http://www.vegetablegrafting.org/ for additional information.



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Copyright: Flickr/IITA
Speed read

Researchers studied the genetic components of cultivated and wild cassava

They unravelled cassava genome that could aid creation of good varieties

But an expert says the findings should not be linked to better traits of cassava

Researchers have sequenced the genome of the cassava — enabling them to better understand the genetic basis the plant’s disease resistance, quality and crop maturity.

A research team in Kenya spent four years decoding the DNA, the genetic material, of the cassava plant, which is widely farmed and eaten across the tropics.

“Cassava is the main food security crop of [Africa], so providing a high yield in poor soils with minimal water can be crucial when other crops fail.”

The researchers identified the order of the genetic letters of 53 cultivated and wild cassava plant materials from Africa, Asia, South America and Oceania — a process called genome sequencing. They also sequenced five cassava-related plants such as M. glaziovii and identified the genetic components of 268 African cassava varieties.

The study which started in 2012, was aimed at increasing the genomic resources for cassava, says Morag Ferguson, a co-author of the study and a molecular geneticist at the International Institute of Tropical Agriculture (IITA), Kenya. The research was published in the journal Nature Biotechnology last month.

“The study includes 97 per cent of the estimated genes,” Ferguson tells SciDev.Net. “The large amount of DNA sequence information provides insights into the origin of cassava and resources for the improvement of cassava”.

For example, the genome holds information on resistances to cassava brown streak disease, a devastating viral disease affecting cassava in southern, eastern and central Africa.

Sequence information, according to Ferguson, revealed that some disease-resistant cassava varieties in Tanzania, including Namikonga and Muzege, contain sections of genomes of M. glaziovii.

“Cassava is the main food security crop of [Africa]”, so providing a high yield in poor soils with minimal water can be crucial when other crops fail, says Ferguson.

The study was conducted by researchers from countries as varied as Fiji, Kenya, Micronesia, Nigeria, Tanzania and United States.

Paul Kimani, a plant breeder from Kenya’s University of Nairobi says the main contribution of the findings is a clear demonstration of the genetic relationships among the various species, including cultivated cassava, its wild relatives and others in the secondary or even tertiary gene pool.

“What it does not do is link the genes with any economically important traits such as disease resistance, nutritional quality or agronomic traits,” he says.

Kimani explains that because cassava breeders often have little genetic variety among their crop, an epidemic can easily cause severe damage, leading to rapid spread of diseases such as cassava mosaic disease and brown streak disease in Africa.

“The key issue is whether the wild cassava has genes for economically important traits such as resistance to diseases, which can be transferred to commercial varieties,” Kimani tells SciDev.Net.

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.
Jessen V. Bredeson and others Sequencing wild and cultivated cassava and related species reveals extensive interspecific hybridization and genetic diversity (Nature Biotechnolgy, 18 April 2016)
– See more at: http://www.scidev.net/global/biotechnology/news/cassava-genome-mapped-boost-qualities-2.html?utm_medium=email&utm_source=SciDevNewsletter&utm_campaign=international%20SciDev.Net%20update%3A%209%20May%202016#sthash.co9ylka7.dpuf

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  • Fungus-resistant gene found in rice


Scientists in Japan have found a way to create high-yielding rice with long-lasting resistance to the devastating rice blast fungus.

Sufficient rice to feed 60 million people is destroyed by the blast fungus, Magnaporthe grisea — also known as Magnaporthe oryzae — every year.

Some rice is naturally resistant but is often also of lower yield. Now a team led by Shuichi Fukuoka from the National Institute of Agrobiological Sciences in Japan has engineered good quality rice that is both resistant to blast disease and high-yielding.

Their research was published in Science last week (21 August).

By comparing japonica rice that is resistant to blast disease with rice that succumbs to infection, Fukuoka found that a change in a key gene called Pi21 can mean the difference between devastating infection and mild disease.

Fukuoka says even plants with the resistant form of the gene become infected, but “The damage they suffer is not so serious, making it possible to reduce the amount of fungicide used by 50 per cent.”

He says his team’s findings will be particularly useful in mountainous areas where blast disease is a serious threat.

There have been many previous attempts to engineer resistant rice strains by making specific adjustments to plant immunity to allow the plants to recognise and resist the fungus.

But according to Nick Talbot, professor of molecular genetics at Exeter University in the UK, many of these modifications have a field life of just 2–3 years, as the fungus is quick to find ways to circumvent them and avoid being recognised.

Having the resistant form of Pi21, however, means a plant increases its defences against infection in general, making it much harder for the blast fungus to find a way to take hold, says Talbot.

He says the Japanese researchers have made a big discovery with universal applicability. When this is combined with other methods of engineering rice, scientists may be in a position to “exclude blast infections in a durable manner”.

Fukuoka has also managed to isolate the resistant form of Pi21, meaning it can be separated from other genes associated with poor yield. Previously this has been difficult because when scientists have tried to transfer the resistant Pi21 gene into new strains of rice, the genes affecting quality have also hitched a ride.

Fukuoka says the fact that his research has shown the exact location of the Pi21 gene means scientists can ensure it is not replaced by a more vulnerable form when breeding new rice strains.

Link to full article in Science


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