SUMMARY

The effect of temperature and humidity on the infec-tion of wheat head tissues by four fungal species caus-ing head blight (Fusarium avenaceum, F. graminearum, F. culmorum, Microdochium nivale) was studied by con-trolled-environment experiments. Detached spikes were inoculated at flowering with a spore suspension and incubated at different temperatures (10.0 to 35.0°C), wet and in a saturated atmosphere. Infection frequency of glumes after different incubation times (4 to 72 hours) was determined by re-isolation of the fungi that had been inoculated. Regression models were then elaborated and used to compare species and to de-fine their cardinal temperatures for infection. F. ave-naceum and F. graminearum showed the highest infec-tion frequency, with optimum at 28.0-29.0°C; M. nivale and especially F. culmorum had a lower infection fre-quency, with optimum at 18.0°C and 26.5°C, respec-tively. Spikes were then inoculated at optimum temper-ature for each species, either in the presence or in the absence of a film of water, under different regimes of relative humidity (100 % to 65%). Reduction of relative humidity during incubation increased the frequency of glumes infected by F. culmorum, whereas it created un-favourable conditions for the other species. Key words: wheat scab, Fusarium species, head infec-tion, environmental conditions, regression models. INTRODUCION Fusarium head blight (FHB) is a serious disease of wheat in many areas of the world (Parry et al., 1995). Up to 17 causal organisms have been associated with the disease, but the most common species are Fusariu