EFFECTS OF TEMPERATURE ON VIABILITY OF PATHOGENIC FUSARIUM SPECIES

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.