Soil-borne wheat mosaic virus (SBWMV) is transmitted by the soil borne fungus Polymyxa graminis and is responsible for an important virus disease on wheat (Triticum aestivum). In order to evaluate the yield reduction in wheat due to SBWMV and in triticale, an experiment was carried out in naturally infested soil using wheat cultivars BR 32, BR 23, Embrapa 120, OR1, IAC 5-Maringá, Embrapa 27, Embrapa 16 and triticale cultivars (Triticum secale) Embrapa 53 and Iapar 23. Seeds were sown at an experimental farm of the "Embrapa Trigo". The plant height, the number of tillers, the number of grains per spike, number of grains per plant, grain weight and thousand grain weight were evaluated. The data were submitted to analysis of variance, comparing the average/medium with the Scott & Knott at 5% of probability. A reduction height of plants up to 27.5% was observed on the 'IAC 5-Maringá'. The number of tillers, in 'BR 32' showed a reduction of 25% in the symptomatic plants, while 'OR 1' increased the number of tillers in 32.4% under the same conditions. The weight reduction of grain per plant varied from seven to 56% in wheat and from 51 to 59% in triticale. The thousand-grain weight varied from four to 26% in wheat and from 23 to 30% in triticale.
