Joint Colloquium of Physics and Chemistry on Tuesday, July 5, 2022, at 5:15 p.m. in the Faraday Lecture Hall, the following will speak,

Prof. Dr. Traud Winkelmann Institute for Horticultural Production Systems, Leibnitz University Hannover

on the topic:


Abstract: Tree nurseries and apple orchards are facing the worldwide problem of apple replant disease (ARD) which results in growth depression and fruit yield and quality reduction. The etiology of this complex soil-borne disease which persists at the affected sites for decades is still not fully understood. It can best be described as a dysbiotic state and a negative plant-soil feedback. Sustainable and effective management options still need to be developed or optimized. We gained important insights into plant reactions to ARD from transcriptomic comparisons of apple roots growing in ARD-affected and disinfected soils: genes involved in phytoalexin biosynthesis were strongly upregulated in roots in ARD soils as were the contents of the phytoalexins. Their role in the disease awaits clarification: on the one hand they can support the plant by acting against the ARD-causing organisms, but on the other hand these toxic metabolites could be harmful to the root cells in which they accumulate. Therefore, studies on their exudation are in progress. Regarding ARD-associated organisms, results by us and partners indicate the following: (i) Members of the Nectriaceae were found enriched in the rhizosphere and isolated from symptomatic root segments and were proven pathogenic. (ii) The relative abundance of Streptomyces was significantly increased in rhizospheres and roots from ARD soils. (iii) A contribution of plant parasitic nematodes to ARD could not be confirmed, but instead, populations of free-living nematodes and their associated microbiome differed between ARD and control soils. (iv) An increase in microbial genes related to stress sensing in the rhizosphere of ARD-affected soils as well as a lower abundance of genes coding for enzymes involved in the degradation of aromatic compounds was observed in the first metagenomic study.