Agrar-, Ernährungs- und Ingenieurwissenschaftliche Fakultät

Host status and damage potential of Meloidogyne species in mint and parsley production

2026-04-21T12:00:35Z

Host status and damage potential of Meloidogyne species in mint and parsley production Noskov, Ilya Peppermint and parsley are widely cultivated medicinal and aromatic plants, and like many other crops, they are vulnerable to infections caused by plant-parasitic nematodes of the genus Meloidogyne. Host status of commonly cultivated varieties and the damage potential of Meloidogyne species from temperate climates in production of these plants remain unknown. Meloidogyne species are also known to interact synergistically with other soil pathogens, contributing to disease complexes. Mint is known to be affected by soil-borne pathogens such as Verticilium dahliae, which causes severe Verticillium wilt disease. It has been reported that certain plant-parasitic nematodes, such as Pratylenchus can interact synergistically with V. dahliae on mint. However, it remains unknown whether Meloidogyne species or species from other plant-parasitic nematode groups are also capable of such interactions. In the present work, peppermint and parsley responses were investigated against Meloidogyne species from temperate climates. In addition, we assessed the potential involvement of M. hapla and Paratylenchus projectus in synergistic interactions with V. dahliae on peppermint. By examining these aspects through three separate studies, we addressed previously underexplored responses of mint and parsley varieties cultivated in Germany to Meloidogyne infection, highlighting the importance of this knowledge for developing effective and sustainable nematode management.
The impact of Meloidogyne species was determined under controlled conditions in the greenhouse. Results showed that the selected mint and parsley varieties are good hosts for Meloidogyne species. However, host status varied depending on the nematode species and plant variety. All studied varieties were susceptible to M. hapla, but showed tolerance to its infection, as no growth reduction was observed. However, at the highest density, M. hapla reduced the essential oil content in peppermint, indicating that tolerance applies only to plant growth but not to plant secondary metabolites. Furthermore, the identification of peppermint 'Multimentha' as a non-host to M. chitwoodi and M. fallax offers valuable control options by crop rotation targeting these nematodes. Additionally, M. hapla and P. projectus exhibited synergistic interactions with V. dahliae in peppermint, increasing Verticillium wilt severity. These findings highlight the critical need for integrated nematode management in peppermint cultivation affected by Verticillium wilt.

Signaling Components Shaping Arabidopsis Defense and Susceptibility in Nematode Interactions

2026-04-15T10:45:38Z

Signaling Components Shaping Arabidopsis Defense and Susceptibility in Nematode Interactions Letia, Sharon Plant-parasitic nematodes (PPNs) are roundworms distinguished by a spear-like stylet at the anterior end of their body, which they use to mechanically damage host cells and facilitate entry. This stylet also serves as a conduit for effectors, proteins that manipulate and modify host biology and it ultimately functions as a siphon to extract nutrients from the host after successful establishment. PPN-associated diseases result in substantial economic losses, estimated at over 150 billion USD annually. Given their economic significance, considerable research has focused on developing management strategies such as chemical treatments, the use of resistant and tolerant varieties, and cultural practices like flooding and crop rotation. However, current PPN management options have significant drawbacks, including the ecological harm caused by chemical controls and the breakdown of resistance in previously resistant crop cultivars. Therefore, there is a pressing need to further investigate the complex interactions between hosts and PPNs to gain mechanistic insights. Such understanding is crucial for developing novel, effective, and sustainable management solutions.

This thesis therefore investigates two major axes of nematode defense, focusing on host susceptibility factors and molecular signaling mechanisms. First, we reveal that Ascaroside#18, a nematode-derived molecular pattern, triggers a unique leucine-rich repeat receptor NILR1-independent defence, distinct from classical pattern-triggered immunity (PTI). Unlike typical PTI, ascr#18-associated resistance acts without causing reactive oxygen species bursts or growth inhibition and operates independently of the peroxisomal β-oxidation pathway. Transcriptomic profiling shows that defense is mediated by downregulation of auxin transport and signaling genes, ultimately suppressing susceptibility to cyst nematodes without activating classical defense pathways. Reduced auxin influx carrier AUX1 and downstream auxin-responsive genes SAUR69 and IAA27 coincide with impaired nematode feeding cell development, highlighting the critical role of auxin signaling as a susceptibility factor.

Secondly, work on heterotrimeric G-protein signaling delineates the role of extra-large G-proteins XLG2 and XLG3 as central susceptibility factors induced downstream of cytokinin (CK) signaling. These factors promote nematode parasitism, as demonstrated by Arabidopsis xlg123 mutant lines showing reduced susceptibility to both cyst and root-knot nematode infection, with reduced nematode fitness and impaired feeding structures. XLG2 and XLG3 expression is shown to be CK-dependent, establishing a mechanistic link between hormone signaling and G-protein-mediated susceptibility pathways in host-pathogen interactions.

Collectively, these findings underscore the importance of susceptibility factor modulation via auxin and cytokinin-linked signaling components in nematode defense. The thesis integrates novel insights into how plant immunity can be enhanced by reducing susceptibility, rather than by solely activating classical immune responses. This mechanistic knowledge opens new directions for crop engineering to achieve durable, broad-spectrum nematode resistance.

Root growth and belowground interactions and plasticity of field crops

2026-04-14T08:45:20Z

Root growth and belowground interactions and plasticity of field crops Hadir, Sofia Understanding the growth of roots and belowground interactions of field crops constitutes a pathway to enhancing the performance of field crops. Global challenges related to climate change and a growing population are driving a more rational use of agricultural inputs to reduce soil and water ressources degradation. Roots play a central role in this process, as shown by research that has provided valuable insights into their development, functions, diversity, and adaptations to the environmental conditions.
To contribute to this understanding, the present thesis aims to investigate the root growth and interactions occuring in intercropping systems as well as the effects of nutrient omission on root traits of field crops.
For intercropping, a field experiment was conducted using one faba bean cultivar and two spring wheat cultivars sown at three sowing densities, defining three intercropping designs. Destructive root coring was conducted (0–100 cm) in the intercrops and sole crops at two development stages. FTIR spectroscopy was used to discriminate the species' root masses. In intercrops, sowing density affected more than the cultivar choice the root growth and belowground interactions. The highest sowing density led to a decrease of root biomass and more competitive interaction between faba bean and winter wheat. The lowest sowing densities promoted deeper root growth of wheat. Regarding the cultivar choice, the early root growth in depth and in density of one spring wheat cultivar lowered faba bean root growth. The findings highlight the importance of plant density and root co-occurrence in belowground interactions of intercrops.
To investigate the nutrient availability's effects on root growth and plasticity, root and shoot sampling was conducted in 2019 for sugar beet, 2019/20 and 2020/21 for winter wheat and 2021/2022 for winter rye at the long-term fertilizer experiment (LTFE) Dikopshof. Various fertilizer treatments were chosen in the three studies including: fully fertilized including manure (m) and supplemental mineral fertilizer (s) (NPKCa+m+s), fully fertilized without manure (NPKCa), N omitted (_PKCa), and P omitted (N_KCa) for winter rye and additionally lime omitted (NPK_) and no fertilization for winter wheat and sugar beet. N availability affected root morphology and plasticity: N omission reduced root growth in winter rye and winter wheat, with stage-specific effects on root diameter, root length density and P omission significantly impacts root traits of field crops, demonstrating the plasticity of root systems in adapting to nutrient-limited conditions. Sustained Ca and K omission affected to a less extent root morphological traits. The Results found in this thesis suggest that nutrient availability as well as intercropping system may affect the root growth and plasticity of field crops. However, the responses are species specific, and affected by growth stage. The results provide valuable insights into potential root traits that can be considered in breeding programs and agronomically relevant insights that serve to design sustainable cropping systems.

Climate-driven and intrinsic oceanic excitation of low-frequency polar motion variability

2026-04-13T09:45:24Z

Climate-driven and intrinsic oceanic excitation of low-frequency polar motion variability Börger, Lara Earth rotation is fundamental for defining reference systems and applications such as navigation on Earth and in space. In addition to lunisolar torques, internal processes such as mantle deformations or mass redistributions in geophysical fluids affect the rotation of our planet. Along with lunisolar torques, variations in the atmosphere, ocean, terrestrial hydrology, and cryosphere cause small fluctuations, reported as Earth Orientation Parameters and including polar motion and changes in length-of-day (ΔLOD). Since the total angular momentum is conserved, it can only be exchanged between the subsystems of the Earth. The ocean, with its large-scale mass redistributions, induces rotational fluctuations, quantified as excitation functions previously unexplored termed ocean angular momentum (OAM). This thesis aims to shed light on the processes involved in the oceanic excitation of polar motion on interannual time scales. Specifically, the excitation induced by (i) the El Niño–Southern Oscillation (ENSO) and (ii) intrinsic oceanic (i.e., internally generated) variability is quantified. In addition, OAM estimates from three ocean reanalyses are tested for their value in Earth rotation studies, with an eye on potential impacts of the reanalyses' sequential data assimilation (DA) schemes. For periods <120 days and after correction of atmospheric effects, the three reanalyses explain 40–50% of equatorial and 30–40% of ΔLOD excitation variance, comparable to a widely used ocean state estimate. Uncertainties remain at longer time scales, reflecting an increased sensitivity to the chosen DA scheme. With the reliability of the OAM series varying across products and time scales, a statistical combination is a good middle ground by suppressing uncertainties. Quantifying ENSO-induced polar motion excitation is the second contribution of this thesis. Previous studies have shown that ENSO modulates ΔLOD through changes in atmospheric winds. Here, the hypothesis is tested whether ENSO excites polar motion through changes in OAM. The ENSO-induced polar motion is derived from four coupled climate models. The mass term is dominant over the motion term (five orders of magnitude) mainly along 90°E with amplitudes of ±4 mas, particularly via a Pacific-Indian basin-wide mass exchange. During three ENSO cycles (1997/98, 2009/10, 2015/16), OAM changes explain 40–50% of the residual observed polar motion excitation variance, but co-occurrence with other broadband signals complicates a clear attribution to ENSO. The final goal is to investigate the excitation signals associated with intrinsic ocean variability, which emerges from non-linear local processes and can attain large (e.g., basin-wide) scales. Ensemble simulations (1995–2015) indicate that intrinsic OAM fluctuations account for ~46% of interannual oceanic excitation, quantified here for the first time. Mass variability is dominated by a single mode of intrinsic bottom pressure fluctuations, which emerges from Drake Passage and exhibits a see-saw pattern between the Atlantic and Southern/Pacific Oceans. Overall, the results in this thesis provide a valuable contribution to understanding ocean-induced low-frequency polar motion variability. Accurate OAM estimates and consideration of model uncertainties due to, e.g., intrinsic variability, are crucial when the goal is to scrutinise rotation data for more subtle effects from other geophysical fluids. Ocean model limitations could be mitigated by assimilating gravity field data or satellite altimetry in future work. In addition, knowledge of the ENSO-induced oceanic excitation signals—as worked out in this thesis—creates an opportunity to improve the accuracy of both OAM estimates and long-term polar motion predictions.; Klimagetriebene und intrinsische ozeanische Anregung der niederfrequenten Polbewegungsvariabilität
Die Erdrotation ist grundlegend für die Definition von Referenzsystemen und Anwendungen wie die Navigation auf der Erde und im Weltraum. Neben lunisolarer Drehmomente verursachen Massenverlagerungen in Atmosphäre, Hydrosphäre und Kryosphäre Schwankungen in der Polbewegung und der Rotationsrate (ΔLOD). Der Gesamtdrehimpuls bleibt erhalten, Teile davon können jedoch zwischen den Subsystemen ausgetauscht werden. Besonders der Ozean regt durch großskalige Massenumverteilungen Rotationsschwankungen an, welche sich über den ozeanischen Drehimpuls (ocean angular momentum, OAM) quantifizieren lassen. Ziel dieser Arbeit ist die Untersuchung bislang unberücksichtigter Prozesse in der ozeanischen Anregung der niederfrequenten Polbewegung. Konkret werden Anregungssignale im Zusammenhang mit (i) El Niño–Southern Oscillation (ENSO) und (ii) der intrinsischen (d.h., intern generierten) Variabilität des Ozeans betrachtet. Darüber hinaus werden erstmals OAM-Schätzungen aus Ozean-Reanalysen auf ihren Nutzen für Erdrotationsstudien geprüft, insbesondere hinsichtlich möglicher Einflüsse der verwendeten Datenassimilationsschemata. Für <120 Tage und nach Reduktion atmosphärischer Beiträge erklären die drei Reanalysen 40–50% der Varianz der äquatorialen und 30–40% der Varianz der ΔLOD-Anregung, vergleichbar mit den Statistiken einer oftmals verwendeten ozeanischen Zustandsschätzung. Auf längeren Zeitskalen lassen sich teils fadenscheinige Fluktuationen in den OAM-Reihen erkennen, wobei eine statistische Kombination der drei Produkte Unsicherheiten reduziert. Im zweiten Kernbeitrag wird anhand des Outputs gekoppelter Klimamodelle untersucht, ob ENSO die Polbewegung durch OAM-Schwankungen anregt. Der Massenterm dominiert das ENSO-Signal in OAM gegenüber dem Bewegungsterm um fünf Größenordnungen mit Amplituden von ±4 mas, insbesondere über einen beckenweiten Massenaustausch zwischen Indik und Pazifik. Für die ENSO-Zyklen in 1997/98, 2009/10 und 2015/16 erklären OAM-Änderungen 40–50% der Varianz der nicht-ozeanischen Polbewegungsanregung, doch überlagernde breitbandige Anregungssignale erschweren eine eindeutige Zuordnung zu ENSO. Schließlich wird die Rolle der intrinsischen Ozeanvariabilität untersucht, welche aus kleinräumigen Instabilitäten hervorgeht, durch Ausgleichsmechanismen im Ozean aber beckenweite Ausdehnung erreichen kann. Ensemble-Simulationen (1995–2015) zeigen, dass die intrinsischen OAM-Schwankungen ~46% der äquatorialen ozeanischen Anregung mit Perioden >1 Jahr ausmachen. Die Variabilität des Massenterms ist auf eine einzige Mode an Bodendruckschwankungen zurückzuführen, die vermutlich durch nicht-lineare Dynamik in der Drake-Passage erzeugt wird und ein Dipol-Muster zwischen dem Atlantik und dem Südlichen/Pazifischen Ozean annimmt. Insgesamt tragen diese Ergebnisse wesentlich zum Verständnis der ozeanischen Anregung der niederfrequenten Polbewegung bei. Genaue OAM-Schätzungen und die Berücksichtigung von Modellunsicherheiten, beispielsweise in Zusammenhang mit intrinsischer Variabilität, sind entscheidend, wenn es darum geht, beobachtete Erdrotationsschwankungen auf kleinere Effekte anderer Fluide hin zu untersuchen. Einschränkungen der Modelle lassen sich in zukünftigen Studien durch die Assimilation von Schwerefeld- oder Satellitenaltimetriedaten verringern. Darüber hinaus bietet das neu gewonnene Wissen um die zu erwartenden OAM-Signale während verschiedener ENSO-Phasen die Möglichkeit, sowohl die Genauigkeit von OAM-Schätzungen als auch Langzeitvorhersagen der Polbewegung zu verbessern.