Inoculum density of Cochliobolus sativus in soil and common root rot of wheat cultivars in Queensland.
Both incidence and intensity of disease at tillering, flowering and firm dough stages of wheat development were closely related to density of C. sativus in the soil. Additional inoculum applied with seed increased disease markedly at the low inoculum density site (3 viable propagules/g soil) and slightly at the intermediate site (77/g) but had no effect at the high inoculum density site (132/g), indicating a threshold level for max. disease in the test. Reduction in DW at the low and high sites paralleled the disease at the tillering and flowering stages. Songlen and Timgalen were consistently more diseased than Kite and QT2338/9. This suggests that cultivars may be evaluated for resistance in the field from tillering onward if disease levels are adequate. C. sativus was the dominant fungus isolated from the subcrown internodes of plants from non-inoculated subplots. Fusarium chlamydosporum [F. fusarioides] was also isolated from subcrown internodes with increasing frequency as the season progressed. However, it was considered to be a secondary invader of the plant material.