An Investigation of the Susceptibility of Arabidopsis thaliana to Isolates of Two Species of Verticillium

Eight isolates of Verticillium longisporum and seven of Verticillium dahliae were examined for their pathogen- icity to Arabidopsis thaliana. Two-week-old seedlings of two A. thaliana ecotypes were inoculated with conidial suspensions (1.6 ´ 104 conidia/ml) and maintained in sterile conditions on microtitre plates for 25 days. The seedlings were assessed daily for ¯owering time, height at ¯owering and mortality. From this data the propor- tion of plants ¯owering was calculated and the suscep- tibility of each ecotype to individual isolate was quanti®ed. The A. thaliana ecotypes were inoculated by several isolates of V. dahliae and V. longisporum with the disease symptoms observed being similar to those characteristic of Verticillium-infected Brassica napus. Responses to Verticillium isolates varied and for both ecotypes signi®cant di€erences (P £ 0.05) were recorded in days to ¯owering between the V. longisporum isolates VD6 and VD12 and the V. dahliae isolate INRA617 and all other isolates. There were no other signi®cant e€ects correlated with isolate origin or Verticillium species.