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Aphanomyces root rot on pea and lentil in Canada

A ProMED-mail post <https://url.emailprotection.link/?bczGkw5NaxKViInVN3o8WI7SkfPjCplYcnrvkSnR7vDdzBseB4Z4JgOzMtf4NyhKwZ-87t_ekCqY4X1TR9IACFg~~>

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Date: Thu 3 Dec 2020

Source: The Western Producer [abridged, edited] <https://url.emailprotection.link/?bXqdyeT3rWpjklTZmKnovoU80UE6i2ZlNX6qU2ktLaV6V5pjTmiFAFFgZKmh4S0DOwUqaQnconWnKJ3WknatKfaz5-ej5mPenpQZcuYz1tY9CGHSRcNqkYGztejqj0seL>

Root disease is omnipresent in pulses in 2020. There were ideal conditions for aphanomyces in large parts of the prairies in the summer. But exactly how prevalent the disease was is largely unknown because researchers weren't allowed to do in-field surveys due to COVID-19. "So, I don't have hard numbers," said Agriculture Canada's Syama Chatterton.

Her informal survey was largely from pictures. "From what I gathered, it was a really rough year for aphanomyces," she said. Alberta Agriculture shared some data from field surveys, and 100% of pea fields had root rot with about a 67% incidence. Disease incidence was obtained by stopping at 10 spots per field to look for the disease.

Only 14% incidence was recorded for lentils.

How a pea and lentil crop performed in 2020 will affect decisions for that field for years. It's important to keep track of exactly where the crop has problems. When it comes to a forecast for 2021, disease risk for a specific field depends on the prevalence of the disease in the rotational history. Producers should also examine roots of crops.

The reason aphanomyces is so difficult to manage is because oospores sit in the soil until both host roots and water are present.

If there was a lot of disease in a crop, then it likely will need to be rotated out for 6-8 years, maybe longer. Each field is different in terms of how many times pea or lentil can be grown until there are problems. What is happening in Alberta, Saskatchewan, and Manitoba is about a 20-year history with peas or lentils every 4 years.

[Byline: Robin Booker]

Communicated by: ProMED-mail <promed@promedmail.org>

[Aphanomyces (or common) root rot (ARR) of peas is caused by the fungus-like organism (oomycete) _Aphanomyces euteiches_ f.sp. _pisi_ (AEP). It is considered the most devastating disease of peas worldwide, with average yearly losses of 10%, although entire fields may be destroyed when conditions are favourable for the disease. The pathogen can also affect other legumes such as lentils and lucerne, but not beans, which are only susceptible to f.sp. _phaseoli_.

Symptoms may include discoloured, water-soaked areas on lower stems and roots, expanding to extensive rot of the whole root system.

Affected plants develop stunting, wilting, and yellowing of the crown, and they often die prematurely. These symptoms are similar to other root rots caused by, for example, species of _Fusarium_, _Rhizoctonia_, or _Pythium_, and this may lead to ARR being misdiagnosed. ARR can infect crops at any growth stage; disease development is favoured by waterlogged soils.

The pathogen is soil borne; oospores can survive in the soil for 10 years or more. The pathogen is spread with plant material (including plant debris, volunteer crop plants), mechanical means (including contaminated equipment), wind, and water. Disease management is difficult but may include long crop rotations to slow down build-up of soil inoculum, field drainage, choosing fields with low oospore soil load, as well as removal of inoculum sources (such as crop debris).

Fungicide seed treatments may be effective but are subject to strict regulations in many countries. Some ARR resistance has been identified in pea germplasm, but no highly resistant commercial cultivars are available.

In Canada, another pea root rot due to _Fusarium_ species is widely distributed. Coinfection with both pathogens leads to more severe disease and is therefore of special concern.

Other species in the genus cause serious, economically important diseases of sugar beet (_A. cochlioides_) and radish (_A. raphani_).

Maps

Canada (with provinces):

<https://url.emailprotection.link/?bcjOBNIswALIRPt9JpYlUyS3FoDcxZNNjAmJRJIs7ygUmK6PjRuADgJNBYKbXMhe--gkUV1ice_KHO9a0O3miCtpToJQgfdFhIT5QPRLfcHZxo-ixYNrRw_CxS-YdX594>

Pictures

ARR symptoms on pea and lentil:

<https://url.emailprotection.link/?bCzwwV_dqWlfQKV_Vonwvx7gbtrrpjcToWlQOF56Tvv7tp55rOjxsxpbSJ6LQ3ORe96zp3lpf88mXhTxRR-NlrdXdP97bGPNLlH-ao_J7jBtdsmz-8C72X7HggguxSwnDdrpmfFUCWedNx8pcutgW2JL9AU32aW1HnMnIEGN7Tn4RWTgYxD0I3oP87Ri47DFLH6IQVJtTcu_gS8EdzbMTwA~~>,

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and

<https://url.emailprotection.link/?bWhbxtNLVDzlLY9cZ5E9kBh0ls6jr_D-46YXdT5-DtgAicckqKr_sBDK7Iwh_VbJQ5uSengU_h85xpE4h9pyvQMGLan9nk2uAzAdKW7Xx3Q0boyc8nRfi4ha6bAjv-S2BZlGzmoF7C9dCrBWF6MkdETuv4L3Yg1MU7ygpmkM6SXA~>

Affected fields: