Abstract
Soil sickness is a widespread problem in replanted apple orchards with a complex symptomatology and etiology influenced by soil and climate conditions. Consequently, a conclusive technical solution is still lacking for intensive apple orchards. The present work aims to analyze the morphological and functional changes occurring in the M9 apple root systems growing in pot filled with soil derived from five different European growing areas. For each growing area, the soil was collected from the apple orchard and used directly in the pot or gamma-ray sterilized before potting. Soil from a neighborhood fallow was also used as control for each growing area. In the non-sterilized replant soils plants developed poor root systems due to a limited biomass allocation. Fibrous roots production was particularly compromised. The roots had a smaller diameter and a lower ramification index. The root cell membrane integrity was also lower. Gamma-ray sterilized replant soils increased root growth, branching and cell integrity, while nearby fallow soil induced an intermediate root behavior. The magnitude of the symptoms showed a significant interaction between soil treatment and sampling site and root growth was correlated with the organic matter content in the soils.