Root Rot Research and Management Options - PulsePoint

April 16, 2019

Researchers are making progress on methods to manage and prevent root rot, but it is a slow process

by Delaney Seiferling

Dry weather caused problems for many Saskatchewan farmers last growing season, but it also brought benefits, including a drop in the amount of root rot that had been observed in fields for the last five years. “We see some improvement in dry years,” says Dr. Syama Chatterton, who has been studying root rot for several years. “The dry cycles are helping.”

Chatterton, a Research Scientist for Agriculture and Agri-Food Canada (AAFC), conducted field surveys across Western Canada between 2014 and 2017 and found that Fusarium root rot had been present in about 50 per cent of pea fields and 60 per cent of lentil fields, on average. Another 50 per cent of pea fields and 40 per cent of lentil fields tested positive for the presence of Aphanomyces (the most destructive form of root rot), on average, over the same amount of time. These percentages were closer to 60 to 80 per cent in wetter years.

Chatterton cautions however that dry weather alone does not completely alleviate the many concerns over this potentially devastating soil-borne disease. For one thing, dry weather seems to affect peas more than lentils.

“Lentils in particular do a lot better in dry years than peas — we see a lot less Aphanomyces on lentils in a dry year than on peas,” Chatterton says. She also suspects that the heavy snow pack leftover from the 2018/19 winter season could foster more development of the disease. “If we get a lot of wet, saturated soils in the spring it can still contribute to the problem, even if we end up in another dry year.”

Chatterton’s research over the last several years has shifted focus away from quantifying the presence and distribution of root rot in Western Canada, to instead look at the best ways farmers can control and prevent it, and understanding its development. Now, after having done three to four years of research looking at the distribution of Aphanomyces and Fusarium root rot, the research team feels they can move on to the next area of research. “We are still getting out and looking at fields, but more so now to build and validate a decision support system,” Chatterton says.

Management Optionsfor Root Rot

One of the worst elements about root rot is the lack of in-crop management options. Unfortunately, research has not made much progress in this area in recent years, Chatterton says. Her previous work tested some potential options, including using Phostrol^® fungicide and Edge^® herbicide, but neither yielded positive results in terms of reducing disease severity. Another option her research looked at was seed treatment, which she determined had some impact during the early season but no long-term effects.

“There is not a lot of residual or systemic activity with seed treatments, so it was not surprising that we did not see an effect carried forward past the three-to-four week mark.” The lack of effective management options is not surprising, Chatterton says, as Aphanomyces has been one of the more difficult pathogens to manage in peas. “We have tried a lot of things but we are not shocked that we have not found a silver bullet yet. We might never find a silver bullet.” Because of this, the best option for farmers will the development of varieties with genetic resistance.

Plant pathologists such as Dr. Sabine Banniza are working with breeders at the University of Saskatchewan’s Crop Development Centre (CDC) on developing resistant varieties, and they have made progress in terms of moving partial resistance into adapted pea cultivars in recent years. They expect to be able to move these cultivars into field trials in the next three to four years.

With another two to three years of co-op testing required after field trials, we are still at least six years away from having resistant pea varieties, which means that for now, the best option for farmers is to focus on prevention of the disease.

Prevention Options

The best way to prevent this disease? Deliberately manage your crop history and rotation history, Chatterton says. Generally, problems occur in fields that have had an intense rotation of peas or lentils for a number of years.

“If you are approaching that stage where you have had five to six pea or lentil crops in a tight rotation, we do recommend getting that field tested for the presence of Aphanomyces,” she says. Seed testing labs are currently the best source to get testing done. If your fields test positive, the current recommendation is to move away from peas and lentils in those fields for six to eight years.

“We are still doing research on what that exact number is and unfortunately the research itself will take six to eight years,” Chatterton says. “There is no way to speed up field trials.”

In the meantime, Chatterton is working on a tool that will help farmers better assess their risk levels a lot more efficiently, by quantifying the amount of Aphanomyces and two Fusarium species within the soil. The tool has already been developed but currently only works to detect fields that are highly infested, so Chatterton is honing it to offer more precise readings.

“The issue is that fields just below the threshold level still give lots of false negative results, and those are the fields that are most important to test,” she says. “We are currently trying to improve the accuracy of detection so that instead of getting a positive or negative result you might get a low, medium, or high level of infestation. Then you can make decisions based on where you are sitting on the spectrum.” She expects the tool will be available to farmers within two years.

The next phase of Chatterton’s research will be focused on addressing breeding, physiology, and agronomy to help mitigate effects of root rot. This research is part of the Pulse Science Cluster, funded by Agriculture and Agri-Food Canada (AAFC), Saskatchewan Pulse Growers, Alberta Pulse Growers, and Manitoba Pulse and Soybean Growers under the Canadian Agricultural Partnership program.

Root Rot Symptoms

• Poor emergence, stunting, yellowing of leaf tissue, a less well-developed root system, decay, and brown discolouration of roots.
• Nodules are often reduced in size and number, are pale in colour, or have not developed.
• Typically occur in patches and may expand if conditions are favourable for the pathogens over several growing seasons. Symptoms are often associated with areas of flooding or waterlogging.
• Difficult to identify root pathogens once plants are heavily damaged or dead, due to the presence of other organisms that feed on decaying tissue.
• Pathogens associated with root rot often appear as a complex, where more than one pathogen is present, making identification of the primary causal agent difficult.

Root Rot Stress Factors

• Wet conditions: Wet feet stresses plants and reduces rhizobial activity. Some root rot pathogens need water to germinate and infect roots.
• Cool temperatures early in the season: Slow plant growth and slow nitrogen availability from organic matter.
• Shortened rotations: Increase level of pathogens in soil.
• Heavy textured soils: More prone to waterlogging and compaction.
• Soil compaction: Root growth impeded and less aeration.
• Nutrient deficiency: Slows seedling growth.

Seed Testing Labs that offer analysis for root rot disease:

20/20 Seed Labs
2020seedlabs.ca
507–11 Avenue
Nisku, AB T9E 7N5
Toll Free: 1.877.420.2099
Fax Toll Free: 1.888.900.1810
3489 Pembina Hwy
Winnipeg, MB R3V 1A4
1.204.261.3755

BDS Laboratories
bdslabs.com
Northern Bank Building
#13 Qu’Appelle Street
P.O. Box 363
Qu’Appelle, SK S0G 4A0

SGS BioVision
biovision.ca
Unit 310, 280 Portage Close
Sherwood Park, AB T8H 2R6
1.800.952.5407

Discovery Seed Labs
seedtesting.com
450 Melville Street
Saskatoon, SK S7J 4M2
1.306.249.4484

Quantum Genetix
quantumgenetix.com
HWY 16 & Floral Rd
Site 501 Comp 11
RR 5 Station Main
Saskatoon, SK S7K 3J8
1.306.956.2071