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Simultaneous inoculation with races 1 and 2 of the vascular wilt pathogen Fusarium oxysporum f.sp. lycopersici provided a high level of protection against race 2 in three tomato cultivars carrying resistance gene I , which confers resistance to race 1 but not race 2. However, simultaneous inoculation did not provide any protection in cultivars lacking this gene. Protection resulted in reduction and delay of wilt symptoms. Similarly, avirulent races of F. oxysporum f.sp. melonis protected muskmelon plants against virulent races of the same forma specialis. A ratio 10:1 between spore concentrations of inducer and challenger organism gave the highest cross protection, but ratio 0.1:1 still provided significant disease reduction. Cross protection was also obtained when inoculation with the inducer organism was performed 6 or 12 h before inoculation with the challenger organism. Autoclaved spores of the inducer did not have any protective effect, indicating that living propagules were required to initiate protection. The results suggest the presence of a gene-for-gene interaction between F. oxysporum f.sp. lycopersici -tomato and F. oxysporum f.sp. melonis -muskmelon, in which cross protection against a virulent race is mediated by recognition of a specific elicitor from the avirulent race by the plant resistance gene product and by subsequent induction of the plant defense reaction. |
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