Cross Protection Between Strains of Fusarium oxysporum f. sp. vasinfectum and its Effect on Vascular Resistance Mechanisms

The severity of symptoms induced in cotton plants by stem inoculation with Fusarium oxysporum f. sp. vasinfectum was reduced by inoculation with a non-pathogenic strain (NPS) of the fungus 3 days previously. Symptom reduction was associated with reduced populations of the pathogen in the stele tissue of the stem. This cross-protective response became effective within 24 h of inoculation with the NPS. Although both vascular occlusion and terpenoid aldehyde synthesis were induced by theNPS, the short time required for cross protection to become effective and the duration of the effect, indicated that vascular occlusion rather than fungitoxicity of the terpenoid aldehyde compounds was the mechanism of protection.