Population dynamics of <i>Agrobacterium vitis</i> in two grapevine varieties during the vegetation period

Abstract

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 Müller-Thurgau and Riesling grapevines which were freed from A. vitis by thermotherapy and inoculated with A. vitis NW90.
Every week, 5 plants of the two varieties were examined for A. vitis in new shoots, around the inoculation site, in one- and two-year-old parts of the stem, in the rootstock and in the roots. Beyond the inoculation site the A. vitis population density was too low for statistical evaluation of population dynamics. At the inoculation site a seasonal course of the A. vitis population was found in both grapevine varieties. The A. vitis population density 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 density 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 the population dynamics of A. vitis followed parallel courses in both grapevine varieties, differences in the population density and in the onset of the autumn increase were determined. This could be attributed to physiological differences of the two varieties. The migration of pathogenic bacteria from the inoculation site to the roots took at least 15 weeks.