The effects of rootstock and scion on tobacco mosaic virus infection in susceptible, tolerant and immune cultivars of tomato

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SUMMARYReciprocal grafts were made between tomato cultivars Potentate, susceptible, and Virocross, tolerant (heterozygous for resistance gene Tm‐i) to tobacco mosaic virus (TMV) isolates of Pelham type o and between isogenic lines of cv. Craigella, susceptible and homozygous for gene Tm‐i. The grafted plants were inoculated with a type o isolate; both scion and stock inoculation were studied in the former, scion inoculation only, in the latter. With scion inoculation the virus content of a tolerant scion was greater on a susceptible stock than on a tolerant one, but that of a susceptible scion was unaffected by the type of stock: in contrast, the virus content of a tolerant stock was unaffected by the type of scion but that of a susceptible stock was less with a tolerant than with a susceptible scion. With root inoculation the virus contents of both tolerant and susceptible scions were greater on a susceptible than on a tolerant stock.With cv. Craigella the genotype Tm‐1/Tm‐1 was found to be immune to the type o isolate used, but in grafts the leaves of Tm‐1/Tm‐1 scions became tolerant to leaf inoculation when on susceptible stocks and the virus entered the stock. Tm‐1/Tm‐1 stocks became infected when attached to infected, susceptible scions and did not affect the virus content of those scions.The results indicate that a susceptible healthy stock may change the reaction of a tolerant or immune scion to infection by a strain of TMV.