Field trials were undertaken in Suffolk in commercial crops of autumn-sown oilseed rape cv.
Capricorn during 1993/94, cv. Apex in 1994/95. Plots were artificially infected with beet western
yellows virus (BWYV) using viruliferous Myzus persicae, giving 73 to 94% infection. Control plots
had natural infection ranging from 0 to 17·8%. Destructive plant samples were taken from each of
the infected and control plots throughout the seasons for growth analyses, and final yields were
measured on 44 m2 areas combine harvested from each plot. The seed yields of infected plots were
26 and 11% lower than control plots in 1994 and 1995 respectively (P<0·001).
Harvested seed yields were shown to be inversely proportional to the area of the plot that was
inoculated with BWYV. Infection significantly lowered the oil content in 1995 from 47·9 to 46·8%
(P<0·001), and increased glucosinolate levels from 16·12 to 18·37 μmol/g (P<0·01). BWYV caused
a significant reduction in plant height and in numbers of primary branches in the 1993/94 trial and
had an effect on the dry weight of the leaves, stalks, racemes and pods at some sample dates in both
seasons. Virus-testing of infected plants showed that BWYV was present in the pod wall, the septum
and seed coat; two of 78 embryo samples also contained virus. It was concluded that BWYV can
cause significant yield losses in those years in which there is a high incidence of virus in the
overwintered crops.