The infection of hosts by the geminivirus depends on the interactions between host and viral factors for vi-ral 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 inocu-lation with BCTV-CFH. Symptoms were more severe in ecotype SKKU including severe leaf curling and development of severely deformed and stunted bolting compared to Col-O as a lab standard ecotype. One ecotype Cen-O was asymptomatic to BCTV-CFH in-fection. Studies of viral DNA replication and virus movement in three excised organs of asymptomatic Cen-O demonstrated that BCTV-CFH could replicate viral DNA and move systemically in this ecotype, sug-gesting that tolerance was due to the blocks of interac-tions between host and viral factors on symptom de-velopment. This asymptomatic phenotype is similar to the mutation of leftward ORFs, especially ORF R2. Genetic analysis of this ecotype Cen-O indicated that tolerance is due to a single recessive locus.

Keywords: BCTV, Arabidopsis, Geminivirus, Tolerance.