This work was carried out in order to quantify the damages in wheat yield due to natural infection by Pyricularia grisea, (causal agent of wheat blast), in different wheat cultivars and breeding lines, during 2004 crop season, at Dourados county, Mato Grosso do Sul State in the absence of other diseases. The experiments were developed under natural conditions and without fungicide spraying, in experimental plots located at Embrapa Agropecuária Oeste and Indápolis. After heading stage, all spikes that showed the characteristic blast symptoms (black point infection in the rachis), had been identified and marked in an area of the 1m². The blast and healthy spikes were harvested, counted and threshed separately. The damages were calculated based on the difference between the actual yield and the estimated yield potential. The results showed that the damages and the blast incidence had been varied according to cultivars/breeding lines and region. The least incidence of blast were observed on cv. BR 18-Terena, with 27% and 42% of infected spikes, from the Embrapa Agropecuária Oeste and Indápolis experiments, respectively. The average damage due to blast, in 20 tested materials, was 387kg/ha or 10.5% of the yield, in the Embrapa Agropecuária Oeste experiment. In Indápolis, the damages were greater, reaching, in average 609kg/ha or 13% of yield. The head weight loss was greater (63.4%) with early infection than with late infection (46.0%). It was observed that grains below the infection point in the rachis were larger than the normal ones, thus compensating to some extent the presence of the empty spikelets. Because the white heads were more visible, the yield losses can be overestimated.
blast; losses; Triticum aestivum; yield