Effects of Different Cropping Systems on the Occurrence of Fluorescent Pseudomonads

AbstractIn field experiments, winter wheat was grown under different crop rotation regimes (monoculture; rotation with field beans) and differentiated intensity (cv.‘Jubilar’ with 120 kg N/ha and 1l CCC/ha; cv.‘Okapi’ with 180 kg N/ha and l CCC/ha). Plant, protection measures were carried out at three levels (no treatment; specific treatments under consideration of damage thresholds; routine spraying program). The occurrence of aerobic bacteria, fluorescent pseudomonads and strong siderophore‐producers as well as the effect of the different cropping systems on the two groups of bacteria mentioned last were determined during the vegetation period at the beginning of shooting, at full bloom and after harvesting on the surface of the roots of wheat plants. In comparison to the total population of aerobic bacteria, the populations of fluorescent pseudomonads and of the strong siderophore‐producing bacteria changed in a characteristic way: whereas at the beginning of shooting the highest and at full bloom the, lowest numbers were determined, a slight increase could be observed after harvest.On roots of wheat plants in monoculture, higher numbers of fluorescent pseudomonads and strong siderophore‐producers were detected at the begining of shooting and at full bloom, than on those grown in rotation with field beans. The roots of cv. ‘Okapi’ (higher cropping intensity) were colonized to a higher degree by both groups of bacteria as compared to those of cv. ‘Jubilar’. After application of herbicides, a stimulation of these micro‐organisms was observed at the beginning of shooting.The influences of different crop rotation schemes, intensities of cropping and plant protection measures on the occurrence of fluorescent pseudomonads were altogether less pronounced than the natural fluctuations of the population during the growth of the wheat.On the basis of morphological, physiological and biochemical properties, it could be shown that different biovars of the species Pseudomonas fluorescens dominated in the experimental field.