The viability of three species of Fusarium pathogenic to winter cereal
s was differently affected by temperature. F. culmorum survived in vit
ro in soil for 4 months at 8, 20 and 30-degrees-C, the number of colon
y forming units (CFU) recorded at these temperatures after incubation
being 125, 185 and 624 % respectively when compared with the number pr
esent at the beginning of the experiment. F. avenaceum and F. heterosp
orum barely survived at 8-degrees-C after incubation for 4 months but
at 20-degrees-C the numbers of CFU were 314 and 380 % respectively, wh
ile at 30-degrees-C the corresponding number for each of these species
was 200 %. At natural soil temperatures in winter, the number of CFU
of F. culmorum after 4.5 months decreased to 60, 70 and 87 % of the nu
mber present at the beginning of this experiment when infested soil wa
s buried at depths of 7-10, 15-20 and 30 cm respectively. In the upper
soil layer where winter temperatures were lowest, survival of F. aven
aceum and F. heterosporum did not occur. Survival rates for these two
species at a depth of 15-20 cm were 20 and 5 % respectively. In the de
epest layer of soil (30 cm) survival of these two species was 30 % for
F. avenaceum and 10 % for F. heterosporum of the number present at th
e beginning of this experiment. These results demonstrate that during
the early spring stages of growth of winter wheat, inoculum of F. culm
orum, unlike that of F. avenaceum and F. heterosporum, is also a sourc
e of infection in the top soil layer in our climatic conditions.