Fusarium Diseases of Canadian Grain Crops: Impact and Disease Management Strategies

Abstract

The genus Fusarium, first described in the early nineteenth century, is composed of a wide range of soil-borne saprophytic and pathogenic fungi. More than a few hundred different phylogenetic species of Fusarium have been identified to date. Plant species are the main target of Fusarium pathogenicity, although some species, including F. chlamydosporum, F. oxysporum and F. verticillioides, have been shown to infect immune-compromised humans. It is said that most plant species are susceptible to at least one disease caused by Fusarium fungi. Fusarium species can cause vascular wilt diseases, for which a broad range of host plants are susceptible, involving fungal colonization of the xylem via the roots and the growing mycelium eventually causes vessel obstruction, blocking transport of water to the aerial parts of the plant. In dicots, over 100 formae speciales of F. oxysporum have been identified as causative agents in vascular wilt, including F. oxysporum ff. spp. lycopersici, phaseoli and pisi, which infect tomato, beans and pea crops, respectively. Fusarium species also cause root rots and stem rots of various field crops worldwide, including peas and related pulse crops. In cereals and corn (maize) Fusarium crown rot (FCR) and Fusarium stalk (stem) rot, respectively, are caused by a different group of Fusarium pathogens from those responsible for diseases in dicots, and include F. graminearum, F. culmorum, F. avenaceum, F. verticillioides and F. pseudograminearum. In addition to root and stem rot diseases, Fusarium species also infect the inflorescence structures, causing Fusarium head blight (FHB; also known as scab) in cereals and Fusarium ear blight (sometimes referred to as FEB) in maize, and leads to damage and yield loss in developing kernels. There is an overlap of species responsible for Fusarium crown and stalk rots with those responsible for Fusarium head and ear blights. Many of these species produce harmful mycotoxins, including trichothecenes and fumonisins, which accumulate in the kernels of infected heads. In this chapter, we will start with an introduction to Fusarium species, their classification and genetics, provide a review of the Fusarium diseases of three groups of Canadian field crops (cereals, maize and pulses), followed by sections on disease management strategies, and Fusarium toxin quantification methods.