Aphanomyces

Aphanomyces root rot, a menacing threat to pea and lentil production in Western Canada, demands our immediate attention. Aphanomyces eutieches was identified as a significant issue in Alberta and Saskatchewan in the early 2010s. Since its identification, root rot complex and Aphanomyces eutieches has caused a rapid reduction in pea and lentil acres, and growers have been forced to rethink their production strategies.

The gradient of Aphanomyces infection in peas where the most severe disease can be seen on the left versus healthy plants on the right. Aphanomyces infections are characterized by yellowing and wilting of shoots, pinching of epicotyl, stopping abruptly at the soil line, and lateral roots with watery and honey-brown decay. Source: Dr. Syama Chatterton, Agriculture and Agri-Food Canada (AAFC).
Aphanomyces in Pea. Source: Dr. Chatterton, AAFC.

Aphanomyces root rot is caused by Aphanomyces euteiches, a highly specialized soil and water-borne pathogen, considered a water mould, that infects legumes. While this pathogen has several legume host plants, peas and lentils are the most susceptible to infection.

Aphanomyces can infect the plant at any growth stage, although early-season infections significantly impact yield. Aphanomyces root rot causes severe damage to the roots, causing infected plants to wilt and die prematurely. Later-season infections can delay crop maturity, affecting harvest timing and weakening plant stems, causing severe lodging and harvest challenges.

Alberta Agriculture Root Rot Survey showed a 100% prevalence of root rot (all fields had it), with 67% incidence. There was a 90% prevalence in lentils, with a 14% incidence. In wet years, this can result in more than 70% yield loss in peas and upwards of 60% in lentils under high Aphanomyces root rot infections.

Managing Aphanomyces root rot is a formidable task, primarily due to the long-lived resting spores, known as oospores, the absence of genetic resistance, and the limited control options. These oospores can persist in the soil for many years, surviving as a saprophyte until the next susceptible crop is grown or conditions favour the disease. The lack of genetic resistance and control options further complicate the management of this root rot pathogen.


Causes

Aphanomyces euteiches f.sp pisi causes root rot. Aphanomyces euteiches is classified as an oomycete, or water mould and is not a true fungus. Aphanomyces is particularly adapted to wet, saturated soils and requires moisture to move throughout the soil profile.

Oospores, shown here in host plant root tissue, are round with thick walls that allow them to survive for many years, even in harsh environments. Source: Saskatchewan Ministry of Agriculture.

The resting spores, called oospores, are round and thick-walled, allowing them to survive in the soil during harsh winter conditions.

Once a plant is infected, that single infected plant can spread the disease to the roots of healthy neighbouring plants up to 18 cm or seven inches away.

Risk factors include stress factors that delay germination or slow emergence and plant growth, such as wet conditions, cool temperatures early in the season, shortened rotations, heavy-textured soils that hold moisture longer, soil compaction, nutrient deficiency, and low seed vigour.

Pathogens associated with root rot often appear in a complex, where more than one pathogen is present, making it challenging to identify the primary infection.

The most severe symptoms and crop yellowing are seen when Fusarium and Aphanomyces root rot occur together.

Aphanomyces and Fusarium root rot on lentils. Source: Dr. Chatterton, AAFC.

Learn more about Aphanomyces

Learn about other forms of Root Rot Complex

Review our resources and learn how you can help eliminate the risk of root rot in pulses.