Survey of foliar diseases in faba bean ( Vicia faba L.), and pathogenicity of fungi associated with diseases, on the Canadian Prairies

A survey of 103 commercial faba bean (Vicia faba L.) fields was conducted in Alberta and Saskatchewan from 2017 to 2019 to determine the incidence and severity of foliar diseases and to identify associated fungi. Foliar disease incidence was high (>75%) in both Alberta and Saskatchewan in all three years and reached 100% in Alberta in 2019. However, disease severity was low (<2.0 on a 1–5 scale) in both provinces, except in Alberta in 2019 when average disease severity was 3.2. A total of 4,057 fungal isolates were recovered from leaf samples exhibiting foliar leaf spot and blight symptoms. Based on culture morphology and internal transcribed spacer (ITS) sequence similarity, fungal genera were identified as Botrytis (11.1%), Alternaria (43.3%), Fusarium (6.5%), and Stemphylium (24.4%). Sclerotinia and Colletotrichum constituted 4.7%. Polymerase chain reaction using species-specific primers was employed to amplify DNA to distinguish between B. fabae and B. cinerea. The abundance of B. fabae (88.2%) dominated over B. cinerea (11.8%) causing faba bean chocolate spot. Pathogenicity tests on whole plants revealed both Botrytis species induced chocolate spot symptoms, while other associated fungal isolates caused disease symptoms different from chocolate spot upon inoculation. However, it was very difficult to distinguish between symptoms caused by Stemphylium and Botrytis on field samples. Information from this survey is important for understanding the diversity and abundance of pathogens and for developing management practices of foliar diseases of faba bean in the prairies.