FUSARIUM HEAD BLIGHT AND DON CONTAMINATION MANAGEMENT IN SOFT AND DURUM WHEAT CULTIVATION - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 135

Ramirez et al., 2005). This could explain the apparent contradiction with the interpretation
given by Paulitz (1996) concerning the results of his experiments in which higher
atmospheric concentrations of G. zeae were reported during the night hours: the higher
concentration of G. zeae at night might be the effect of spore deposition and not of spore
release as explained by the author. On the contrary, the low number of spores detected during
the daytime might be due to the presence of mixed or turbulent layers. Thus, spore deposition
may be separated from spore release in both time and space (Schmale et al., 2006).

3.3. Germination, Head Infection, Growth

Warm, humid weather, frequent rainfall and heavy dew favour spore germination.
Pinkish-red mycelium and conidia develop abundantly in infected spikelets and the infection
can spread to adjacent spikelets or through the entire head. Infected kernels become shrivelled
and discoloured with a white, pink, or light-brown scaly appearance, as a result of mycelial
outgrowths from the pericarp (Logrieco et al., 2003).
Temperature, relative humidity and water activity of the host are the fundamental factors
that affect fungal germination and growth. In general, F. graminearum mycelium grows well
over a wide range of temperatures, up to 30°C, and is associated with the warmer regions of
the world, whereas F. poae is found more frequently in temperate climates. Most of the
species can be found in much of the geographical area affected by FHB, but individual
species usually dominate a specific region and F. graminearum dominates in a majority of
regions (Osborne and Stein, 2007).

Table 2. Minimum (Tmin), optimum (Topt), and maximum (Tmax)
temperatures for the germination of four different fungal species that cause
Fusarium head blight in wheat

Species Tmin Topt Tmax

F. avenaceum

14 20 - 28 35

F. culmorum

16 20 - 26 33

F. graminearum

5 - 10 24 - 29 35

F. poae

20 - 25

M. nivale

10 15 - 20 28

(Rossi et al. , 2001; Brennan et al. , 2003; Hope et al. , 2005; Ramirez et al. , 2006).

Rossi et al. (2001), carrying out in vitro experiments, studied the effect of relative
humidity (RH) and temperature on the infection by F. graminearum , F. culmorum , F.
avenaceum and M. nivale . They reported that when spikes were incubated at different RH the
frequency of the infected glumes was very high when wetted at 100% RH and very low at all
the other RH tested (95%, 85%, 75% and 65%) for all the species except for F. culmorum
whose frequency only started to significantly increase at 75% RH. As far as temperature is
concerned, they found a minimum temperature between 10.0 and 16.5°C, an optimum one
between 18 and 29°C and a maximum one between 28.5 and 35.5°C (Table 4). Brennan et al.
(2003) reported lower optimum temperatures for the same fungal species (differences from 2
to 8°C in the case of F. nivale ). Ramirez et al. (2006) reported similar results concerning the