Pathogenicity of Fusarium oxysporum on different Vitis rootstocks

The susceptibility of eight Vitis rootstocks to an isolate of Fusarium oxys porum, originally obtained from vineyard-rotted grape roots, was tested wit h excised roots in the laboratory and with roots attached to living vines i n the field. Excised root assays indicated that the Vitis vinifera rootstoc k Carignane was most susceptible followed by the V. vinifera-hybrid rootsto ck AXR#1, and the non-V. vinifera rootstocks 110R and St. George, which wer e the least susceptible of those infected. Inoculations with this isolate o f F. oxysporum failed to cause rot on excised roots of the non-V. vinifera rootstocks 3309C, 420A, 5C, and Freedom. Only rootstocks Carignane and AXR# 1 became infected when non-excised roots were inoculated. Rootstocks that a re most susceptible to grape phylloxera appeared to be highly susceptible t o this isolate of F. oxysporum. Additional assays on the infectivity, growt h, and sporulation of this isolate at different temperatures indicated that fungal activity increased with temperature within the range of 18-26 degre es C.