RELATIONS BETWEEN GRAPEVINE REPLANT DISEASE AND ROOT COLONIZATION OF GRAPEVINE (VITIS SP) BY FLUORESCENT PSEUDOMONADS AND ENDOMYCORRHIZAL FUNGI

In pot experiments cuttings of grapevine rootstock cultivar '5C' were grown on a soil from a grapevine nursery affected with replant disease (replant soil) and on a similar soil that had not been planted with grapevines before (non-replant soil). Plants were also inoculated with the vesicular-arbuscular (VA) mycorrhizal fungus, Glomus mosseae, or left without mycorrhizal fungus inoculation. Shoot and root growth, mycorrhization of roots and numbers of total aerobic bacteria and fluorescent pseudomonads on the rhizoplane of grapevines were determined at several sampling dates. On replant soil, numbers of fluorescent pseudomonads on the rhizoplane were higher compared to non-replant soil, before differences in shoot and root weight between replant and non-replant soil occurred. Without inoculation with G. mosseae, the mycorrhization of roots was much lower on replant soil (13%) than on non-replant soil (51%). On replant soil, inoculation with G. mosseae increased mycorrhization to 39% and increased shoot length, leaf area and shoot weight. The beneficial effect of VA-fungus inoculation on replant soil was not due to increased nutrient concentrations in leaves. On replant soil, the inoculation with G. mosseae reduced the number of fluorescent pseudomonads on rhizoplane of grapevine, while the numbers of total aerobic bacteria were not influenced by inoculation with G. mosseae. These results suggest a direct or indirect role of fluorescent pseudomonads in replant disease of grapevine.