identification of a tolerant locus on arabidopsis thaliana to hypervirulent beet curly top virus cfh strain the infection of hosts by the geminivirus depends on the interactions between host and viral factors for viral dna replication viral gene expression and the movement of virus throughout the hosts this work reports that a hypervirulent strain of beet curly top virus bctv is different in its ability to infect several ecotypes of arabidopsis thaliana symptoms appeared on arabidopsis ecotypes around 7 to 10 d after inoculation with bctvcfh symptoms were more severe in ecotype skku including severe leaf curling and development of severely deformed and stunted boting compared to colo as a lab standard ecotype one ecotype ceno was asymptomatic to bctvcfh infection studies of viral dna replication and virus movement in three excised organs of asymptomatic ceno demonstrated that bctvcfh could replicate viral dna and move systemically in this ecotype suggesting that tolerance was due to the blocks of interactions between host and viral factors on symptom development this asymptomatic phenotype is similar to the mutation of leftward orfs especially orf r2 genetic analysis of this ecotype ceno indicated that tolerance is due to a single recessive locus