1992 Volume 58 Issue 5 Pages 659-663
Fusarium wilt symptoms were reduced in tomato and cucumber plants when they were inoculated with Fusarium oxysporum f. sp. cucumerinum (non-pathogenic on tomato) and F. oxysporum f. sp. lycopersici (non-pathogenic on cucumber), respectively, prior to inoculation with the pathogenic formae speciales. The respective pathogenic forma specialis was isolated at a significantly high frequency from stem sections of symptomless plants which had been pre-inoculated with the respective non-pathogenic forma specialis or a mixture of the pathogenic and non-pathogenic formae speciales, but it was not isolated from symptomless plants which had been inoculated only with the pathogenic forma specialis. The respective non-pathogenic forma specialis was not isolated from stems of tomato or cucumber, irrespective of symptom development. The number of colony forming units per gram fresh weight of stem was less in pre-inoculated plants without symptoms than in pre-inoculated plants with symptoms. The reduction in symptoms observed in these plants following the induction of resistance by pre-inoculation with a non-pathogenic forma specialis may have been due to repressed proliferation of the pathogenic forma specialis.
