Disease incidence in sugar beet fields is correlated with microbial diversity and distinct biological markers

Sugar beets (Beta vulgaris L.), which are one of the major sources for sugar, alternative energy and fuel, are affected by several fungal pathogens at harvest time. In order to identify correlations between the microbiome of field-grown sugar beets and their health status before harvest, we studied 2,200 antifungal antagonists together with 73 amplicon datasets obtained with 16S rRNA gene fragments as well as the fungal ITS region in samples from 13 different field sites in Austria and Germany. Overall a substantial loss of microbial diversity (bacteriome H’: 8 vs. 6.5; mycobiome H’: 4.5 vs. 3.5) as well as a substantially different taxonomic composition was observed in root rot-affected sugar beets when compared to healthy beets. The Gram-positive Lactobacillales as well as distinct fungal taxa such as Candida, Penicillium and Fusarium were identified as indicators of root rot on microbiome level. In contrast, higher microbial diversity as well as distinct fungal genera assigned to Vishniacozyma and Plectosphaerella were associated with the microbiome of healthy plants. The taxonomic shifts in the fungal microbiome were accompanied by trophic specialization; pathotrophic and symbiotrophic fungi were replaced by saprotrophic fungi in diseased sugar beets. Moreover, samples with high proportions of antagonistic bacteria were not vulnerable to shifts in the fungal microbiome. The overall findings show implications between microbial antagonists and plant health as well as key taxa that are indicative for the health status in beets. They provide the basis for the development of improved disease management systems, and preventive counteractions.