Background Sugar loss due to storage rot has a substantial economic impact on the sugar industry. The gradual spread of saprophytic fungi such as Fusarium and Penicillium spp. during storage in beet clamps is an ongoing challenge for postharvest processing. Early detection of shifts in microbial communities in beet clamps is a promising approach for the initiation of targeted countermeasures during developing storage rot. In a combined approach, high-throughput sequencing of bacterial and fungal genetic markers was complemented with cultivation-dependent methods and provided detailed insights into microbial communities colonizing stored roots. These data were used to develop a multi-target qPCR technique for early detection of postharvest diseases. Results The comparison of beet microbiomes from six clamps in Austria and Germany highlighted regional differences; nevertheless, universal indicators of the health status were identified. Apart from a significant decrease in microbial diversity in decaying sugar beets ( p ≤ 0.01), a distinctive shift in the taxonomic composition of the overall microbiome was found. Fungal taxa such as Candida and Penicillium together with the gram-positive Lactobacillus were the main disease indicators in the microbiome of decaying sugar beets. In contrast, the genera Plectosphaerella and Vishniacozyma as well as a higher microbial diversity in general were found to reflect the microbiome of healthy beets. Based on these findings, a qPCR-based early detection technique was developed and confirmed a twofold decrease of health indicators and an up to 10,000-fold increase of disease indicators in beet clamps. This was further verified with analyses of the sugar content in storage samples. Conclusion By conducting a detailed assessment of temporal microbiome changes during the storage of sugar beets, distinct indicator species were identified that reflect progressing rot and losses in sugar content. The insights generated in this study provide a novel basis to improve current or develop next-generation postharvest management techniques by tracking disease indicators during storage. Electronic supplementary material The online version of this article (10.1186/s40168-019-0728-0) contains supplementary material, which is available to authorized users.

Sugar beets (Beta vulgaris), 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 internal transcribed spacer region in samples from 13 different field sites in Austria and Germany. Overall, a substantial loss of microbial diversity (bacteriome H’: 8 versus 6.5; mycobiome H’: 4.5 versus 3.5) as well as a substantially different taxonomic composition was observed in root rot-affected sugar beets when compared with 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 the 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.

Field experiments employing yellow water-traps with vials releasing methyl salicylate, butyl isothiocyanate, 4-pentenyl isothiocyanate and diethyltoluamide were conducted during the spring migration of Phorodon humuli (Schrank), with the aim of identifying substances which might be used in the field to deter landing on hop plants. Methyl salicylate and the two isothiocyanates reduced trap catches of P. humuli. During the spring of 1994 a slowrelease formulation of methyl salicylate and a /?-acid-rich hop resin sprayed on to hop plants did not reduce aphid infestations significantly. In autumn cis,cis-nepetalactol, the main component of P. humuli's sex pheromone, prepared by various synthetic routes, increased trap catches of males and gynoparae equally. Catches of males in pheromone traps situated in a hop garden decreased with increasing trap height. Catches of males in traps charged with increasing doses of the cis,cisnepetalactol peaked at 1 mg and then plateaued, whereas catches of gynoparae peaked similarly at 1 mg and then decreased. The effects of kairomones from an extract of the primary host, sex pheromone and a visual cue from yellow compared with clear water-traps were additive. The prospects for developing a semiochemicals-based control strategy against P. hurnuli, using some or all of the above elements, are discussed.

Die Untersuchungen waren auf die Frage ausgerichtet, inwieweit die mittels Elektroultrafiltration (EUF)) gewonnenen N‐Fraktionen des Bodens die N‐Verfügbarkeit für Getreide widerspiegeln. Alle Bodenproben wurden aus dem Oberboden von Ackerschlägen praktischer Landwirte gezogen, wobei unterschiedliche Bodentypen und Bodenarten einbegriffen waren. Die noch im Herbst nach der Zuckerrübenernte gezogenen Bodenproben sowie die Proben, die im Januar unter Getreide gezogen wurden, wiesen in ihren EUF‐Extrakten hauptsächlich organischen N und nur zu einem geringeren Anteil NO3‐N auf. Die Abnahme im Gehalt an EUF‐extrahierbarem N im Verlauf des Frühjahres (März bis Ende Mai) korrelierte hochsignifikant mit der Stickstoffaufnahme von Weizen und mit dessen Kornertrag. Hierbei zeigte sich in den nicht mit N gedüngten Parzellen, daß dem organischen N des EUF‐Extraktes als mineralisierbare N‐Quelle eine größere Bedeutung zukommt als dem extrahierten NO3. Die an 20 verschiedenen Schlägen ermittelte Beziehung zwischen den EUF‐N‐Gehalten von im Frühjahr gezogenen Bodenproben und dem Kornertrag von Weizen war hochsignifikant (r = 0,79***). Auch zwischen der N‐Aufnahme des Weizens und den EUF‐N‐Gehalten des Bodens wurden hochsignifikante Korrelationen gefunden.

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