Identification and characterization of Fusarium spp. associated with root rots of field pea in North Dakota

Root rots are a major concern in field pea production in North Dakota. However, it is unclear which pathogens are involved in causing these diseases. This report brings together findings from surveys conducted over four years (2004, 2005, 2008, and 2009). The 2004 and 2005 surveys were mainly aimed at establishing the importance of pea root rot in North Dakota and providing an indication of the most prevalent root rot pathogens. The 2008 and 2009 surveys involved thorough evaluation of root rot incidence and severity, and included isolations and characterization of Fusarium species associated with the root rots. Greater mean root rot incidence and severity were observed in 2009 compared to three previous years. Fusarium species were the most frequently isolated fungal species from infected pea roots, of which F. oxysporum (66.7 and 94.7 % of the fields) and F. avenaceum (71.8 and 89.5 % of the fields) were most commonly isolated in 2008 and 2009, respectively. Pathogenicity tests showed that all nine Fusarium species isolated from symptomatic roots were capable of causing root rot of pea, and isolates of F. avenaceum were the most virulent at causing root rot. Significant differences in virulence were observed among F. avenaceum isolates. The prevalence of F. avenaceum on roots of field peas, and the ability of isolates of this species to cause severe root rot, emphasizes the possibility of this pathogen to emerge as a potential risk under the current cropping practices for pulse crops in North Dakota, and potentially in other regions with similar growing conditions.