Diseases

A virologist with Agriculture and Agri-Food Canada (AAFC), in collaboration with breeders, has developed a way to speed up marker-assisted selection in the effort to identify potato virus Y (PVY) resistant material. The method – known as high-resolution melting markers, or HRM markers – has been used in other breeding programs, but Xianzhou Nie, a research scientist at the Fredericton Research and Development Centre, has perfected it so it can be used to select genetic material that is extremely resistant to PVY infections.

As most growers know, PVY infection can devastate a crop, making the choice of seed important. Severe PVY pressure can cause as much as a 90 per cent yield reduction. Choosing seed that is PVY free, therefore, is the first step towards minimizing losses. However, aphids can also transfer the disease, which adds to the workload and cost of production when growers have to spray mineral oil to ensure the spread of aphid-transmitted PVY is minimized. The best solution from economic and environmental perspectives would be to have potato varieties that are resistant to PVY, which would also eliminate the spread of the disease. Nie hopes this research and development of a faster method to identify PVY-resistant and susceptible parent material and progeny will vastly improve and fast-track potato breeding.

“Using HRM markers, we are identifying efficiently and accurately, markers associated with genes controlling PVY resistance in potatoes,” he explains. “If a potato inherits the resistance gene, it will not develop the disease. This will be very useful for breeders making selections in breeding programs.”

Conventional breeding programs can screen thousands of crosses; it isn’t until the most promising are faced with PVY pressure that breeders know for sure if they have a potential disease-resistant variety. Traditional screening for PVY resistance is carried out mainly in the greenhouse by inoculating each and every offspring/progeny plant with the virus and then waiting for symptoms to develop and laboratory detection of PVY to be completed. By using the HRM marker technique (a procedure carried out in a laboratory as well), breeders will not only be able to identify and select parental material that is PVY-resistant or has “extreme resistance” prior to making crosses, but they will also be able to screen for progeny/offspring inheriting the resistance efficiently in the laboratory setting.

Nie estimates that if 200 plants are bred using traditional selecting methods involving PVY inoculation in the greenhouse, it can take two to three months to determine which progeny, if any, are resistant to PVY.

“Using the HRM marker method, we can screen for PVY-resistant plants in two to three days,” he says.

By determining the value of using HRM markers in PVY screening, Nie says that in the future the method could be used to identify other diseases, or to isolate desirable traits. He says using HRM marker technology allows a researcher to run 96 samples in three to four minutes after amplification of the DNA pieces containing the markers. There’s no question the potential for breeding programs in the future is enormous.

“In our breeding program at Agriculture and Agri-Food Canada, we anticipate the method being implemented for screening for disease resistance to speed up the selection process,” Nie says. Because the method was perfected at a public institution, it is not protected by copyright, which makes it accessible to any breeding program in the world. “We have provided the technology and now anyone can choose to use it.”

Early in 2016, this new form of PVY resistance identification was tested on some of the latest clones bred at AAFC. The presence of the HRM markers that indicate PVY resistance was detected, which signals the potential varieties will be PVY-resistant. The breeders are now looking for germplasm that would have extreme resistance to PVY because those markers are present. Nie envisions a day when PVY-resistant potato varieties will be common, giving growers one less disease to worry about.

    

There’s no current technology to detect acrylamide precursors quickly and without destroying the spud, but a new technique developed by Lien Smeesters from the University of Brussels might help weed out potentially toxic potatoes before they even go to market. In Smeesters’ design, a laser uses infrared light to detect acrylamide, which scatters the light in a unique pattern, instructing the machine to knock the toxic potato out of circulation. | READ MORE

With planting season just around the corner, researchers at Agriculture and Agri-Food Canada are reminding home gardeners to take precautions to prevent the infection and spread of late blight. Planting clean and disease-resistant seeds is the best way to prevent the spread of late blight to other gardens and potato farms.

What is late blight?
Late blight is a disease caused by an organism that produces a white fuzz on the underside of leaves which releases millions of spores that float through the air to infect other plants. The spores land on a susceptible leaf, germinate, and cause brown oily lesions. The spores splash on the ground and infect potato tubers, which become brown and rusty looking, with a granular texture. Crop losses due to late blight can cost the Canadian potato industry tens of millions of dollars annually.

Protecting the potato industry
AAFC late blight specialist Rick Peters says taking steps to prevent the disease from infecting potato crops is important to help protect the health of the industry. He advises home gardeners to ensure their tomato seeds are resistant to the US-23 strain of late blight. Resistant seeds can be purchased at most garden centres. Certified disease-free seed potatoes can also be found at garden centres or purchased from a local seed potato grower. Peters says potatoes grown from last year’s garden or those bought from the grocery store are not suitable for planting as these tubers have not been tested and certified as disease-free and could be susceptible to a variety of potato diseases.

AAFC has partnered with industry leaders to identify and track late blight strains in production areas across the country. Scientists are also looking at biological characteristics of the different strains including how they respond to treatments. This knowledge allows for better management and control of the strains in Canadian potato and tomato production areas. While scientists continue to study the disease, they maintain that an ounce of prevention is worth a pound of cure and home gardeners have an important role to play.

If you spot a suspected late blight infection in your garden this season, please contact the Department of Agriculture, Aquaculture and Fisheries at 1-866-778-3762 for information on how to properly dispose of infected plants.

 Syngenta Canada Inc. has announced the launch of Aprovia Top fungicide, offering Canadian potato growers a new tool for foliar early blight control and brown spot suppression.

Early blight, caused by the Alternaria solani fungus, is found in most potato growing regions. Foliar symptoms include small, brown, irregular or circular-shaped lesions that form on the potato plant’s lower leaves later in the season. The disease prefers warm, dry conditions to develop, and can be more severe in plants that are stressed and weakened.

Brown spot, caused by the Alternaria alternata fungus, is closely related to early blight and is found wherever potatoes are grown. Unlike early blight, brown spot can occur at any point during the growing season, producing small, dark brown lesions on the leaf surface.

Aprovia Top fungicide combines two modes of action with preventative and early curative activity on these two key diseases. Difenoconazole (Group 3) is absorbed rapidly by the leaf and moves from one side of the leaf to the other to protect both surfaces against disease. Solatenol (Group 7 SDHI) binds tightly to the leaf’s waxy layer and is gradually absorbed into the leaf tissue to provide long-lasting, residual protection.

Aprovia Top is available now for use in 2017 production. In potatoes, one case will treat up to 40 acres.

 

For potato growers around the world, common scab is a constant vexation. Causing millions of dollars in losses each year, common scab is difficult to control. Recent research, however, has identified options for suppressing the disease, if not getting rid of it all together. Some of the research centres on what soil properties make scab more conducive, while other studies look at natural products that can slow the spread.

“Scab is a troublesome disease,” admits Robert Coffin, a potato agrologist in Prince Edward Island. “There are different genetic strains of scab as well; there are at least five species, so it’s a constant problem. For example, common scab and powdery scab are two different organisms, but both diseases can cause losses in sales because scab infested tubers cannot be sold for table, processing or seed.”

While large strides have been made to control scab, such as using natural bacterial products, seed treatments, soil fumigants, and attempts to find genetic resistance, the disease continues to confound researchers and growers alike. Management options are limited but several help, such as planting varieties with “reasonable resistance” or fumigating the soil, which has proven successful, although is it not permitted for use everywhere.

Some diseases can’t survive in the soil without a host, according to Claudia Goyer, a research scientist with the Agriculture and Agri-Food Canada (AAFC) Fredericton Research and Development Centre. But Goyer says scab can live successfully in the soil without potatoes being present, making it a problem when potatoes are planted.

“The scab bacteria grows on organic matter, like plant residues,” Goyer explains. “What makes it difficult is there are areas of fields that are infested while others are healthy and we do not know why. We now believe there is something different between scab-infested or healthy areas, like soil properties or microbial communities, that could be conducive or suppressive to scab.”

To test this theory, Goyer and her colleagues examined either healthy or scab-infested areas of nine potato fields in Prince Edward Island, New Brunswick and Quebec. The same variety of potato – Red Pontiac – was grown in each field and the team gathered soil samples three times during the year. Several soil properties (including pH, organic carbon, micronutrients and soil texture) were measured to attempt to determine the difference between the soils that contained scab and those that didn’t.

“We are trying to learn if it is something physical, chemical or biological, such as soil microbial communities in the soil, that promotes scab,” Goyer explains. “Some microbial communities suppress scab.” Not surprisingly, she also discovered that the greater the presence of the scab bacteria, the greater the disease pressure. “We are still analyzing our data, but we are seeing a correlation between scab and pH levels, with more scab in neutral pH soil. We are also seeing that soil carbon to nitrogen ratio, and nutrients including potassium, magnesium and calcium, were correlated with scab severity, but we aren’t sure why yet.”

Advancements in soil science are making it possible for the researchers to analyze soils more effectively and they are also able to assess new control options more efficiently. Coffin conducted research on Microflora Pro, a natural product that contains two species of Bacillus bacteria. He says the product worked really well in 2015, but the results were inconsistent in 2016.

“Bacterial cultures don’t always stay stable in storage or in soils,” Coffin explains. Therefore, understanding scab and how it infects soil, and continuing work to breed resistant potato varieties, would offer better disease management options.

Goyer’s work on analyzing soil and understanding why certain fields are infested with scab may also help the developers of microbial products create formulations that will work best. The advent of more sophisticated soil science research is paving the way for a better understanding of what bacteria will work best in soil.

“We can truly study soil communities so much more than we could years ago using next-generation sequencing,” Goyer says. “We can see how diverse the soil bacteria and fungal communities that are present in soil are now because of the depth of sequencing. We can capture most of the species present with this approach.” This type of work will help explain the difference in the diversity of soil microbial communities between healthy and scab-infested areas in potato fields.

“Once we understand better what a healthy soil microbial community is,” Goyer continues, “we can see if we can change soil microbial communities so they suppress scab using agricultural practices, inputs like manure and compost, or use of natural bacterial products that suppress scab.

“In the future, we will be able to harness the power of the soil,” Goyer says. “We may be able to manipulate bacteria communities to improve all crops and we could use them to suppress disease.”

Both Goyer and Coffin approve of the idea of using one bacteria to control another. In theory, the best solution would be to combine several bacteria into one product to help with stability, reduce the potential of resistance developing and, possibly, offer balance in the soil. But with so many variables, it takes a great deal of research to get it right.

Goyer says one possibility is that a certain bacteria could be targeted to where it is needed most, similar to the way precision fertilizer application works. Higher amounts of scab-fighting bacteria could be targeted to where soil tests show a high concentration of the disease, and less could be added where scab pressure is low, creating an overall balance across the field.

“Progress is being made,” Coffin says. “With 30,000 to 40,000 genes in a potato plant, it’s like a giant Rubik’s cube when trying to breed a potato with all the desired traits.”

Of course, scab resistance is only one of the desirable traits, which makes finding a solution in the soil another option for controlling scab – and one that Goyer believes shows great promise going forward.

Researchers at the Texas A&M AgriLife Research plant pathology team have intentially infected potato plants with the bacterium that causes zebra chip in order to identify potato varieties with genetic resistance. | READ MORE

Dickeya has been present for several years in Europe and has now been found in Ontario and several American states. The general manager of the PEI Potato Board said there is no sign of the disease in PEI and industry representatives are working hard to keep it that way. | READ MORE

Scientists at the Conneticut Agricultural Experiment Station are using nanoparticle technology to apply copper to the shoots of plants. Based on preliminary findings in the research, these nanoparticles are better at helping deliver the necessary nutrients to the plants and keep them healthy despite the presence of Fusarium in the soil. | READ MORE

Sept. 29, 2016, Ontario – The potato IPM training module, an educational tool with information for the common insect pests, diseases, viruses and disorders of potatoes in Ontario, is now available online. | READ MORE

Sept. 8, 2016 - Although harvest of the late maturing crop has not started yet, it is never too early to start thinking about disease management in 2017. Two fungicides to keep in mind in 2017 are QUASH for early blight and Revus as a seed treatment for late blight.

Sept. 8, 2016 - According to Manitoba Agriculture, aphid counts in weeks 9 increased slightly in most locations. However, one western field had no aphid trapped. While another field in the same region continued to have massive numbers; with significantly higher potato aphids compared to last week. Most of the seed fields are being desiccated, so this will be the last week of aphid report.
 
One more potato psyllid adult was confirmed on Aug. 24 in a card from Northfolk-Treherne Rural Municipality.For more information and detailed report please visit: www.mbpotatoes.ca

August 26, 2016 -  According to Dr. Vikram Bisht, of Manitoba Agriculture, aphid counts in weeks 8 in all but one sample were low. There was one Green Peach Aphid (GPA) trapped in southern seed growing area, but not anywhere else. Potato aphids were trapped in southern and central areas. One field showed a sudden influx of aphids, probably from nearby crops being harvested or desiccated. There were low counts of Aster leafhoppers were trapped in all seed areas.

Some of the seed fields are being desiccated, so Bisht reports there will be one more week of aphid monitoring. The results from suction and pan traps in seed fields for the 6th and 7th week of sampling can be seen in a chart (please click here):

In 2016 season, as in 2015, as part of the Canadian Hort Council, Growing Forward 2, Canadian Potato Psyllid and Zebra Chip Monitoring Network project, yellow sticky cards are being sent to Dan Johnson, Univ of Lethbridge. One potato psyllid adult was confirmed today (August 22) in a card (in field July 12-18) from Northfolk-Treherne Rural Municipality. This is the first find for 2016 in a province outside Alberta.

North Dakota has also reported occurrence of potato psyllids in their fields. "We have confirmed that psyllids are present potato fields in western ND. Psyllids are the vector of zebra chip disease and can do damage without the Lso bacterium (Gary Secor, NDSU)".

August 15, 2016 - New late blight finds were reported on potato from Carman, Winkler areas and on tomato crops east of East of Portage and east of Highway #75, according to Vikram Bisht. Frequent fungicide applications are being applied to control the disease; and in one case the tomato plants have been pulled out and destroyed.

Samples have been collected for strain identification. All of the previous samples, tested by Lethbridge Research and Development Center were determined to be US-23 strain.

"There is increasing metalaxyl insensitivity in the Pi from these samples and the use of Ridomil would probably have only marginal benefit," says Bisht.

It is important, he continues, to scout for late blight, especially in low lying, irrigation pivot center, wheel tracks of irrigation systems (guns/pivots), tree-line protected areas and under hydro-power lines (areas where applicators may have difficulty covering).

It is also critical at this time to monitor potato and tomato plants in home gardens. The DSVs (late blight risk values) accumulated over 7-days at various weather stations suggest mostly moderate risk in most of the province. There is forecast for rain and risk of thunderstorms today afternoon in many potato growing areas. Full fungicide coverage of foliage in high risk areas should be maintained.

Due to continued high moisture levels in many fields, it may be helpful to harvest the low lying areas last, so it will be easier to manage the storages.

Also, a post-harvest treatment with phosphorus acid / phosphite fungicide could be considered for such fields, adds Bisht.

Disease update
The number of new finds of late blight seems to have slowed down, even though the disease continues to be a concern. All of the isolates tested so far, were determined to be US23. Late blight was found in market-garden plots of potato and tomato in Oakville area, in Central Manitoba. 

There were scattered rains and strong winds on Aug. 4 and 7, which may have spread the disease. 

It is extremely important to continue to scout for late blight, especially in low lying, irrigation pivot center, wheel tracks of irrigation systems (guns/pivots), tree-line protected areas and under hydro-power lines (areas where applicators may have difficulty covering). Full fungicide coverage of foliage in high risk areas should be maintained. It is also critical at this time to monitor potato and tomato plants in home gardens. 

The DSVs (late blight risk values) accumulated over seven days at various weather stations suggest mostly moderate risk in most of the province. There is forecast for a few rain days in many potato growing areas, in the coming week. 

Due to wet and warm conditions there are reports of stem rot/blackleg. Hail damage and European Corn Borer (ECB) injury appears to have contributed to some of the stem rotting. Early blight in general appears to be very minor.

Pest update
The aphid counts remained low in the third week (July 5-11) and the fourth week (July 12-18) especially in the southern seed production area. Potato aphids, but not Green Peach aphids (GPAs), were found in these weeks. There were no aster leafhoppers (ALH) and potato leafhoppers (PLH) noted in the traps. 

In the fifth week (July 19-25), the aphid counts have increased significantly over the previous week. Green peach aphids were trapped from the Portage area only. The potato aphids were trapped in all the three seed production areas. Potato aphids are fairly efficient PVY transmitters, but not as efficient as GPAs. The “other aphids” in the traps are poor transmitters, but make up with higher numbers. 

With other crops in the region maturing and near harvest, the aphids will find the green potato crop very attractive. It may be helpful to the seed growers to consider tank mixing insecticide with the aphid-oils application, especially if the crop planted had some level of PVY in the seed itself. 

The results from suction and pan traps in seed fields for the third, fourth and fifth week can be found here.

Currently, there is no report of any serious Colorado potato beetle (CPB) feeding in commercial potatoes. 

European Corn Borer:
Delta trap monitoring for the ECB moths using pheromone lures continue to show some adult moth activity – in Carberry, Brookdale in Rural Municipality of North Cypress-Langford, Treherne (RM of Victoria), Shilo (RM Cornwallis), Glenboro (RM of Glenboro-South Cypress) and Carman (RM of Dufferin) area. 

After a peak activity in mid-July, the number of trapping has reduced. After the appearance of very young larvae (Figure 1) was the trigger for insecticide application in fields close to last year’s serious infestations. Some ECB injury and larvae were noticed in the Carberry area. 

Insecticide application could be considered when significant larval counts appear, and especially in areas where the stem infestation was high in 2015. Please consult the 2016 Manitoba Guide to Field Crop Protection for the choice of insecticides.

 

Heat edema has been observed in Ontario, and should disappear when humidex values drop below 30 C. Photo courtesy of Eugenia Banks.

 

July 27, 2016, Ontario – Two potato problems have developed due to high temperatures, writes Eugenia Banks in her latest Ontario potato update.

Fusarium wilt
The long and relentless heat wave that is affecting Ontario has provided favorable conditions for diseases and physiological problems that we do not often see. One of them is Fusarium wilt caused by Fusarium oxysporum, a relatively common soil fungus that thrives when soil temperatures are around 29 C. 

A grower found patches of Fusarium wilt this year in a field of Andovers. Also wilted plants here and there were noticeable in the field. The base of the stems emerging from the seed was woody. At ground level the stems were dark brown, rotten or hollowed but did not have a strong fishy smell. The upper part of the stems was still green but wilted. Most of the plants pulled had rotten seed, but with no fishy smell.

Gary Secor from North Dakota State University helped with the identification of this problem. He isolated Fusarium oxysporum from the diseased stems. There was no sign of blackleg, dickeya or verticillium. 

How to control this disease? 
Fusarium oxysporum is more prevalent in very hot summers, just like our 2016 growing season. There is nothing that can be done about the weather, but: 

● Avoid ammonium nitrogen as a source of N 

● Keep potassium levels adequate 

● Acid soils favour Fusarium wilt. Liming soils help, but may increase the risk of common scab. 

Heat edema
This problem has been observed in two fields of the variety Canela Russet, growing in two different production areas. Small bumps form on the leaves that, with time, rupture leaving round, brown necrotic spots. The centres of the spots often drop out leaving holes in the leaves. Holes in leaves usually means insect feeding, but there were no insects in the fields. Ian MacRae, an entomologist at the University of Minnesota, did not think that the holes looked like insect feeding. Jeff Miller from Miller Research in Idaho suggested heat edema, a physiological disorder. Edema is related to water retention (see page 122 in the Potato Field Guide), but heat edema is different. The cells expand trying to diffuse the heat and eventually rupture. Because it is a physiological problem, heat edema should disappear when humidex values (temperature plus humidity) drop below 30 C. Yesterday, I checked one of the fields and noticed that, because of the hot weather, necrotic spots were developing on new leaves. 

Prolonged heat waves bring all sorts of different problems to potato plants. Working with potatoes is a never-ending learning experience! 

 

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