Root Rot Epidemic in Canadian Pulses

REGINA - Mar 4/18 - SNS -- Agriculture Canada's root rot survey in pulses in western Canada discovered that Aphanomyces pathogens were present in 100% of the fields, though infection rates were lower.

On a one to seven scale of severity, Agriculture Canada said the average for all fields with peas in western Canada was between three and 3.3, com´pared to 2.0 severity for lentils. Active infections were discovered in 10% of lentil fields and 40% of field peas.

ProMed, the international society for infectious diseases, says Aphanomyces (or common) root rot (ARR) is considered the most devastating disease of peas worldwide, with average yearly losses of 10% although entire fields may be destroyed when conditions are favorable 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 discolored, 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 often die prematurely.

These symptoms are similar to other root rots caused, for example, by species of _Fusarium_, _Rhizoctonia_ or _Pythium_ and this may lead to ARR being misdiagnosed. ARR can infect crops at any stage and disease development is favored by waterlogged soils.

ARR is soil borne and oospores can survive in the soil for 10 years or more. The pathogen is spread with plant material (including plant debris and 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 and 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. Co-infection with both pathogen leads to more severe disease and is therefore of special concern.