Diseases
Invisible to the naked eye, cyst nematodes are a major threat to agriculture, causing billions of dollars in global crop losses every year. A group of plant scientists, led by University of Missouri researchers, recently found one of the mechanisms cyst nematodes use to invade and drain life-sustaining nutrients from soybean plants. Understanding the molecular basis of interactions between plants and nematodes could lead to the development of new strategies to control these major agricultural pests and help feed a growing global population.

Soybeans are a major component for two-thirds of the world’s animal feed and more than half the edible oil consumed in the United States, according to the U.S. Department of Agriculture (USDA). Cyst nematodes jeopardize the healthy production of this critical global food source by “hijacking” the soybean plants’ biology.

“Cyst nematodes are one of the most economically devastating groups of plant-parasitic nematodes worldwide,” said Melissa Goellner Mitchum, a researcher in the Bond Life Sciences Center and an associate professor in the Division of Plant Sciences at MU. “These parasites damage root systems by creating a unique feeding cell within the roots of their hosts and leeching nutrients out of the soybean plant. This can lead to stunting, wilting and yield loss for the plant. We wanted to explore the pathways and mechanisms cyst nematodes use to commandeer soybean plants.”

About 15 years ago, Mitchum and colleagues unlocked clues into how nematodes use small chains of amino acids, or peptides, to feed on soybean roots.

Using next-generation sequencing technologies that were previously unavailable, Michael Gardner, a graduate research assistant, and Jianying Wang, a senior research associate in Mitchum’s lab, made a remarkable new discovery – nematodes possess the ability to produce a second type of peptide that can effectively “take over” plant stem cells that are used to create vital pathways for the delivery of nutrients throughout the plant. Researchers compared these peptides with those produced by plants and found that they were identical to the ones the plants use to maintain vascular stem cells, known as CLE-B peptides.

“Plants send out these chemical signals to its stem cells to begin various functions of growth, including the vascular pathway that plants use to transport nutrients,” Mitchum said. “Advanced sequencing showed us that nematodes use identical peptides to activate the same process. This ‘molecular mimicry’ helps nematodes produce the feeding sites from which they drain plant nutrients.” | READ MORE
New genes – showing resistance to the yield-robbing blackleg in canola crops – have been identified in trials.

New South Wales (Australia) Department of Primary Industries senior principal research scientist, Harsh Raman, said the study has unlocked the genetic make-up of canola to characterize major and minor genes resistant to the fungal pathogen Leptosphaeria maculans, which causes blackleg disease.

“Finding new sources of resistance, particularly resistance which is controlled by minor genes, is extremely important to the canola industry,” Dr Raman said. “Blackleg disease can cause up to 80 per cent yield loss in canola - in Australia, France and Canada resistance has been broken down in some canola varieties due to the emergence of new races of the blackleg pathogen.” | READ MORE
Stripe rust could show up with a vengence in Ontario again this year, but that doesn’t mean we’re lacking the tools to control the problem.

Last year was one of the worst stripe rust years that Albert Tenuta, field crop extension plant pathologist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), has seen. Tenuta addressed the latest on where, when, and how often to apply fungicides to a room of farmers and agronomists at the Southwest Agriculture Conference, which took place Jan. 4 and 5 in Ridgetown, Ont. One of the diseases of focus was stripe rust and whether we can expect to see the same levels of the disease as last year.

Stripe rust typically thrives when temperatures sit around 16 C. But last year rust was exploding and multiplying in elevated nighttime temperatures sitting around 21 to 23 C. This may mean that the pathogen is changing in stripe rust.

“We’re seeing more and more races developing, becoming more heat tolerant,” Tenuta says. “They are living organisms that adapt and change, so nothing stays static over time.”

Since stripe rust is an obligate parasite (the disease needs a host to survive), the rust retreats back to the south in the U.S. in the winter, where there is greenery. With the milder winter last year, it’s likely spores are overwintering closer to Ontario, meaning the spores don’t need to travel as far and making it easier for them to reproduce. As millions and millions of spores are created, there are mutants that can develop and bypass resistance (from temperatures, for example) leading to an increase in cases of the disease.

If stripe rust had overwintered in the province, farmers would have seen it much earlier than the first reports in early May. This year, if conditions are right, we could potentially see the disease back in the province; it depends on the direction of wind as well as temperatures.

If the disease shows up again this year, there are two main ways for farmers to protect their crops. The first is well-timed application of fungicide. According to Martin Chilvers, assistant professor at Michigan State University and co-speaker at the session, in 2016 the most successful applications were the T2, or prior to flowering, applications. With applications at this stage, researchers were able to protect 20 bushels. Strobilurins and triazole compounds are best if applied as a preventative measure for stripe rust, although triazole also shows some post-infection functions as well.

Choosing a stripe-resistant variety is also important – even if it’s a moderately resistant variety. “Although you still see some disease developing, those lesions are often smaller, so they don’t produce as many spores,” Tenuta says. Therefore, spore production is reduced and successive generations decrease substantially.

But, Tenuta cautions, it’s still important to choose a variety that protects against Fusarium first and foremost. “Remember, Fusarium head blight is a risk you have every year. Stripe rust may occur – it may not.” Keep a lookout for stripe rust in your crops starting in May.
Kansas State University researchers recently announced a significant breakthrough in controlling the spread of the soybean cyst nematode, a parasitic roundworm that has caused anywhere from five to 100 per cent yield losses in Ontario.

Plant geneticist Harold Trick said the university has received a patent for the technology that “silences” specific genes in the nematode, causing it to die or, at the least, lose the ability to reproduce.

“We have created genetically engineered vectors [or DNA molecules], and put those into soybeans so that when the nematodes feed on the roots of the soybeans, they ingest these small molecules,” said Trick, who has worked closely with plant pathologist Tim Todd on this project.

So far, the scientists have found the technology has reduced the nematode population in greenhouse studies by as much as 85 percent. | READ MORE
A team of U.S. Department of Agriculture (USDA) and university scientists has developed a sensitive new assay method for detecting the fungus that causes wheat blast, a disease of wheat in South America and, most recently, Bangladesh.
"Ug99” might not mean much to the world outside agriculture, but few wheat diseases have so much potential to devastate production – and ultimately, consumer access to a basic staple – around the world.
Manitoba Pulse and Soybean Growers has revealed the most prevalent races of Phytophthora sojae found in Manitoba. | READ MORE
Nine high school students will study the effects of potassium supplementation on canola plants infected with blackleg fungal disease at the Canadian Light Source (CLS) in Saskatoon. The students will use the CLS beamlines to conduct elemental and molecular analysis on the infected plants. | READ MORE
Root rot was rampant in pulse crops this year, due to the wet conditions. Dr. Bruce Gossen, research scientist with Agriculture and Agri-Food Canada, says root rot has become more prevalent on the prairies as the popularity of pulse crops continues to increase. | READ MORE
The warning bells rang loud and clear in 2013 when a shift in clubroot pathotypes overcame clubroot-resistant canola varieties on the market. Tests found the pathotypes present were capable of overcoming most of the clubroot-resistant canola hybrids. Because this breakdown in resistance wasn’t unexpected, plant breeders have continued to look for alternate sources of resistance that can be bred into new varieties to help manage the multiple pathotypes that have been identified in Alberta.
In Western Canada, clubroot in canola is a serious problem. In Alberta alone, infestations have been identified in more than 2000 fields across several municipalities. Although clubroot represents a potentially serious threat to canola production in Saskatchewan, so far only a few isolated infestations have been identified. Industry approached researchers to see if there might be an option for controlling clubroot in these small areas and limiting the spread of this soilborne disease to other fields.
Spraying barley crops with RNA molecules that inhibit fungus growth could help protect the plants against disease, according to a new study published in PLOS Pathogens.
Over the past 15 years, ergot has shifted from being a sporadic, localized problem to a widespread disease issue for Prairie cereal growers. As a result, ergot research has become a rising priority for researchers and producer-driven research funding agencies. A key part of the current research focuses on developing crop varieties that are less susceptible to ergot.
In Saskatchewan, leaf blotch disease complex has become more prevalent in oat fields in recent years, but very little is known about the impact of these diseases on oat production. In infected fields, oat yield and grain quality, including test weights, are often reduced, which can impact milling quality and reduce returns.
For years, scientists have bred clubroot resistant canola varieties to combat issues with the disease, but researchers have found some new virulent clubroot pathotypes that can overcome resistance. Swift Current Online reports. | READ MORE
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