We show that among ecotypes of Arabidopsis, there is considerable variation in 
their susceptibility to crown gall disease. Differences in susceptibility are 
heritable and, in one ecotype, segregate as a single major contributing locus. 
In several ecotypes, recalcitrance to tumorigenesis results from decreased 
binding of Agrobacterium to inoculated root explants. The recalcitrance of 
another ecotype occurs at a late step in T-DNA transfer. Transient expression of 
a T-DNA-encoded beta-glucuronidase gusA gene is efficient, but the ecotype is 
deficient in crown gall tumorigenesis, transformation to kanamycin resistance, 
and stable GUS expression. This ecotype is also more sensitive to gamma 
radiation than is a susceptible ecotype. DNA gel blot analysis showed that after 
infection by Agrobacterium, less T-DNA was integrated into the genome of the 
recalcitrant ecotype than was integrated into the genome of a highly susceptible 
ecotype.