Role of Soil Spatial Organization for Replant Disease

Apple replant disease (ARD) occurs after repeated cultivation of apple trees on the same area. Due to this, tree nurseries and apple orchards are the most affected. ARD symptoms include reduced tree growth and a decline in crop yields. One assumption to explain this phenomenon is that through soil cultivation spatial organization/differentiation created by previous crops is lost and hence new roots cannot grow in favorable sites or avoid unfavorable sites. The aim of our work is to detect the spatial distribution of possible ARD causing factors, both in the bulk soil and in the rhizosphere.

Three different experimental approaches were used to investigate the reaction of root growth to ARD in the soil.
First approach was a split-root experiment in which rhizoboxes with a vertical split in two compartments were used. The results of WinRhizo analysis show that ARD is not systemic (Fig. 1). Roots avoid ARD infected soil and shift their growth into uninfected soil.
Second approach was a column experiment investigating apple root growth in undisturbed soil cores (intact field structure) compared to growth in homogenized, mixed materials. Root growth was accessed by X-ray CT scanning and destructive sampling. Again, roots avoided growth into ARD soil.
The third approach was a patch experiment conducted in rhizoboxes. The ARD soil was placed in a targeted way, either open or enclosed by mesh with 30 µm or 0.45 µm to suspend the migration of certain ARD causing agents (Fig. 2). Root analysis shows a shift towards larger root diameters and specifically that roots avoid the patch with the ARD soil.

A recent experiment combines the approaches of split-root and column experiment, since the use of the column system allows a three-dimensional evaluation of root growth.

The experimental designs and detailed results in the different approaches will be presented.