STUDIES ON THE IMPORTANCE OF WILD BEET AS A SOURCE OF PATHOGENS FOR THE SUGAR-BEET CROP

Beet yellows virus, beet mosaic virus, rust (Uromyces betae (Pers) Lev.), and downy mildew (Peronospora schachtii Fuckel.) were found to be common in wild beet (Beta vulgaris s.-sp. maritima L.) growing on the foreshores of south Wales and southern England. The virus diseases were more prevalent in southeast England than in the west, rust more in the west than in the east, and downy mildew is equally prevalent in all regions. Beet yellows is the most commercially important disease and is more common in sugar-beet crops in East Anglia than elsewhere in Great Britain. There was no evidence that beet yellows spread in East Anglia from wild beet to nearby sugar-beet crops during the springs of 1958 or 1959, and Myzus persicae Sulz., the principal vector of yellows, was rarely found on wild beet growing on the foreshore. In glasshouse experiments aphids colonized sugar-beet plants watered with tap water in preference to those watered with sea water. Daily watering with sea water made plants unpalatable to aphids within 14 days. Aphids also preferred leaves sprayed with distilled water to those that had been sprayed with sea water. Salt solutions gave results similar to those obtained with sea water.