The relationship between volatile organic compounds and apple replant disease

Apple replant disease (ARD) refers to the observed decline in plant growth, fruit yield, and quality after repeated planting of apples at the same site. It is a phenomenon in all apple-producing areas worldwide which leads to an estimated profitability reduction of 50 % over the lifetime of an apple orchard. Up to now, the mechanisms behind ARD are only poorly understood. It has been attributed to the action of a site-specific, multi-kingdom, pathogenic, and parasitic biological complex. Thus, the soil faces (micro-) biome alterations due to previous apple cultures.Upon initial contact, apple roots can detect and avoid soil affected by ARD. So far, it is not known how the roots can sense ARD in soil. Volatile organic compounds (VOCs) are promising candidates as communicators between soil and plant. It is known that VOCs mediate many cases of plant responses to pests or pathogens. Nevertheless, their role in ARD has so far been neglected.A rhizobox experiment was set up to determine the volatile emission of apple plantlets growing in ARD and non-ARD soil. Volatiles are analyzed using untargeted gas chromatography-mass spectrometry with prior concentration on an adsorbents (here: stir bar sorptive extraction, SBSE) and thermodesorption.This first pre-experiment run with the interpretation of the gas chromatogram as the next step. Our aim is to determine whether there are any differences between the volatiles detected in the close proximity of apple roots growing in ARD and in non-ARD soil. Noticeable VOCs will be identified to specify the occurring volatile profiles.We will examine the potential role of VOCs as communicators between plants, the microbiome, and soil. It will be addressed whether the sensing of ARD is related to volatile production.