Yield loss of winter oilseed rape in relation to severity of stem canker (Leptosphaeria maculans ) in the UK
Fitt, Bruce D.L.
West, Jon S.
The relationships between yield loss and incidence or severity of stem canker in winter oilseed rape were analysed using data from experiments at Rothamsted in 1991/92, Withington in 1992/93, Boxworth in 1993/94 and Rothamsted in 1997/98. Critical point models and area under disease progress curve (AUDPC) models were better than multiple point models for describing relationships between yield (t ha-1) and incidence or severity of stem canker. Since yield in t ha-1 is influenced by many factors other than disease, % yield loss was calculated. Critical point models and AUDPC models relating % yield loss to stem canker were constructed and models for different experiments were compared. A critical point model relating % yield loss to stem canker incidence (GS 6.3-6.4), and AUDPC models for incidence or severity from growth stages 4.8 to 6.4 were derived from the combined data sets for the three experiments. The relationships between % yield loss and % plants with different stem canker severity scores at different growth stages, and between % yield loss and incidence or severity of both basal stem cankers and upper stem lesions were also analysed