In this work populations of Agrobacterium vitis were monitored within
one year. Starting in the middle of May, the population density of A.
vitis was screened every week in all parts of two-year-old Muller-Thur
gau and Riesling grapevines which were freed from A. vitis by thermoth
erapy and inoculated with A. vitis NW90. Every week, 5 plants of the t
wo varieties were examined for A. vitis in new shoots, around the inoc
ulation site, in one- and two-year-old parts of the stem, in the roots
tock and in the roots. Beyond the inoculation site the A. vitis popula
tion density was too low for statistical evaluation of population dyna
mics. At the inoculation site a seasonal course of the A. vitis popula
tion was found in both grapevine varieties. The A. vitis population de
nsity was highest at the end of May, but little later it dropped to a
low level during the sommer months. A second maximum of population den
sity was determined in October which reached nearly the same value as
in spring. Population density of A. vitis correlated to physiological
changes of the grapevine plant during the vegetation period. Though th
e population dynamics of A. vitis followed parallel courses in both gr
apevine varieties, differences in the population density and in the on
set of the autumn increase were determined. This could be attributed t
o physiological differences of the two varieties. The migration of pat
hogenic bacteria from the inoculation site to the roots took at least
15 weeks. The importance of A. vitis population dynamics in the epidem
iological context is discussed.