Abstract
Tubers of yam (Dioscorea alata cv. 'White Lisbon '), affected by internal brown spot, produced foliage with mosaic symptoms whereas normal-looking tubers produced leaves that were more uniformly green. Almost all the normal-looking and mosaic-affected plants that were tested contained slightly flexuous virus-like particle of about 750 x 13 nm. Mosaic-affected plants, in addition, contained bacilliform virus-like particles of 130 x 29 nm. Infection with this bacilliform virus thus seems to be a prerequisite for the development of internal brown spot.
