Tolerance to a non-host isolate of Verticillium dahliae in tomato

Tolerance to Verticillium spp. is a condition in which a host plant develops few symptoms despite substantial colonization by the pathogen. In the present paper we have shown that Craigella tomatoes are tolerant to a non-host isolate of V. dahliae, Dvd E6. Symptom expression was used to quantify disease and quantitative PCR to assess the amount of fungus in the stems. The classical incompatible and compatible interactions between Craigella resistant or Craigella susceptible near isolines and V. dahliae, race 1 were used for comparative purposes. Additional experiments using cytological assessment and quantitative PCR showed that in the tolerant interactions one plant defence response, vascular coating, was deployed as effectively as in resistant plants, limiting pathogen distribution. However, a second defence response, which causes the cyclical elimination of fungus from the stem in the classical interactions either does not occur or is substantially delayed in tolerant plants. Thus, the Verticillium population remains stable and substantial throughout the studied time course.