T. Beneddra et al., CORRELATION BETWEEN SUSCEPTIBILITY TO CROWN GALL AND SENSITIVITY TO CYTOKININ IN ASPEN CULTIVARS, Phytopathology, 86(2), 1996, pp. 225-231
Closely related aspen cultivars (Populus tremula x P. alba) were ranke
d as resistant, intermediate, or susceptible to crown gall according t
o their tumor response to the selected strains C58, B6, and 354 of Agr
obacterium tumefaciens, respectively. As shown with mutant agrobacteri
a that harbored derivatives of pTiB6S3, a strain retained its ability
to define differences in susceptibility among aspen cultivars as long
as it had a functional ipt gene and, therefore, could induce the biosy
nthesis of a cytokinin in transformed plants. This suggested that diff
erences in susceptibility to crown gall were related to differences in
sensitivity to cytokinin. Cultivar sensitivity to cytokinin was deter
mined in vitro by a leaf disk assay. Aspen cultivars resistant to the
highest cytokinin concentrations (32 mu M benzyladenine) were also fou
nd to be resistant to A. tumefaciens strain B6 and the most resistant
to natural crown gall infections. This result showed that sensitivity
to cytokinin was a plant factor controlling tumorigenesis.