|Authors: ||G. Otto, H. Winkler|
Investigation into the sites of infection in rootlets of apple seedlings grown on sick soils by actinomycetes indicated only a low degree of infestation at the end of the vegetation period.
In contrast to that, there was a high infestation rate by endotrophic mycorrhiza.
There were no relationships to the growth of the apple seedlings.
Therefore the temporal course of the infestation process in the same soils was examined.
It was shown that actinomycetes are present in the rootlets even two weeks after planting.
Six weeks after planting the infestation reached a substantial extent.
The actinomycetes infest the the epidermis and the cortex of young uncoloured rootlets, rapidly damaging the root tissue and causing the decay of the roots.
The process of infection is limited to the first period of root growth.
Later on, newly growing rootlets are infected to a pronounced lesser degree.
These results suggest that root pathogenic actinomycetes are the cause of specific apple replant disease.
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