THE EFFECT OF CEREAL BREAK CROPS ON BARLEY MILD MOSAIC-VIRUS

The effects of growing one, two or three years of resistant barley or winter wheat on barley mild mosaic virus were studied in experiments o n two naturally-infested sites in Gloucestershire and Cambridgeshire. Disease incidence and yield of the susceptible cultivars Igri and Mari s Otter following a three year break were not significantly different from those of control plots that had grown continuous susceptible barl ey. The effects of cropping sequence treatment on soil populations of the fungus vector, Polymyxa graminis, were assessed by estimating most probable numbers of propagules following bioassays. Variability was l arge and neither total numbers of propagules, nor those carrying virus , was significantly affected by the cropping treatments.