An investigation of the susceptibility of Arabidopsis thaliana to isolatesof two species of Verticillium

Eight isolates of Verticillium longisporum and seven of Verticillium dahlia e were examined for their pathogenicity to Arabidopsis thaliana. Two-week-o ld seedlings of two A. thaliana ecotypes were inoculated with conidial susp ensions (1.6 x 10(4) conidia/ml) and maintained in sterile conditions on mi crotitre plates for 25 days. The seedlings were assessed daily for flowerin g time, height at flowering and mortality. From this data the proportion of plants flowering was calculated and the susceptibility of each ecotype to individual isolate was quantified. The A. thaliana ecotypes were inoculated by several isolates of V. dahliae and V. longisporum with the disease symp toms observed being similar to those characteristic of Verticillium-infecte d Brassica napus. Responses to Verticillium isolates varied and for both ec otypes significant differences (P less than or equal to 0.05) were recorded in days to flowering between the V. longisporum isolates VD6 and VD12 and the V. dahliae isolate INRA617 and all other isolates. There were no other significant effects correlated with isolate origin or Verticillium species.