EFFECT OF CONSTANT AND FLUCTUATING TEMPERATURE REGIMES ON SPORULATION OF FOUR FUNGI CAUSING HEAD BLIGHT OF WHEAT
V. Rossi, E. Pattori, A. Ravanetti, S. Giosuè
Macroconidial production of four fungi causing head blight of wheat (Fusarium avenaceum, F. culmorum, F. graminearum, Microdochium nivale) was studied on PDA under constant temperature regimes. Three isolates per species were used, which represented three groups of isolates showing different sporulation capability. Relationships between temperature (5 to 35°C), incubation time (1 to 21 days) and sporulation rate were analysed by a non-linear regression model. Differences between isolates within species did not modify the pattern of sporulation rate in relation to changing temperature. Based on this model, different responses of fungal species to temperature regimes were obtained, in terms of adaptability to different temperatures, speed in beginning production of spores and in reaching maximum sporulation. Considering these features, F. avenaceum was the highest performing fungus, followed by M. nivale, and then by F. graminearum and F. culmorum. The optimum temperature for macroconidial production was 32°C for F. culmorum and F. gramineaum, 28°C for F. avenaceum, and 26°C for M. nivale. In further experiments, a temperature-dependent model elaborated from the regression equations produced accurate estimates of the numbers of macroconidia produced on wheat stems which had been artificially infected with each of the four fungal species and placed onto the soil of a wheat crop. Under such natural conditions, temperature affected sporulation more than the other meteorological factors.