Mareike Kavka

Introduction: Phosphorus (P) is essential for legume growth and symbiotic nitrogen fixation, yet its low availability in many soils frequently constrains plant productivity. Methods: To evaluate phenotypic and genotypic variation in P efficiency, 200 genetically diverse accessions of the Medicago sativa complex were assessed under high and low P conditions in a greenhouse experiment, followed by detailed root system architecture (RSA) analysis in a subset of 20 accessions using a rhizotron system. Results: Significant intraspecific variation was observed for shoot and root dry matter, root-to-shoot ratio, shoot P content, and P utilisation efficiency (PUE). Across the full panel of 200 accessions, shoot and root dry matter decreased by 24% and 23% respectively under low P, and in the subset of 20 accessions PUE increased by 38% under low P. Genome-wide association studies identified candidate genes associated with plant height and biomass related traits under high and low P conditions including genes involved in cell-wall modification, hormonal regulation, and growth-related stress responses. Rhizotron analyses revealed RSA plasticity, with increased specific root length and specific convex hull area under low P, reflecting morphological adjustments that enhance soil exploration. Discussion: Accessions that combined stable biomass production, high PUE, and adaptive RSA features under low P represent valuable genetic resources for breeding nutrient-efficient alfalfa cultivars suitable for low-input agricultural systems.

The genus Medicago , which includes the widely cultivated forage crop alfalfa, is of significant agricultural and ecological importance. Understanding genetic diversity in Medicago is essential for the conservation of its germplasm and its utilisation in plant breeding. This study aimed to assess the genetic diversity and population structure of the Medicago germplasm collection at the German Federal Ex situ Gene Bank. Genotyping‐by‐sequencing was used to analyse 1234 accessions of the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), representing 40 Medicago species. After filtering, a high‐quality dataset of 23,315 single nucleotide polymorphisms (SNPs) was generated. Our analyses revealed distinct genetic clusters corresponding to Medicago species and sections, with cultivated M. sativa L. and M. × varia Martyn clustering together with less genetic diversity compared to their wild counterparts. This reflects the shared genetic composition and extensive gene flow between M. sativa and M. × varia , commonly considered a hybrid between M. sativa and M. falcata L. Wild species displayed a more complex genetic structure, with polyphyletic patterns indicating higher genetic differentiation that reflects their diverse evolutionary histories and ecological adaptations. In conclusion, the comprehensive diversity analysis of the IPK Medicago collection provides valuable insights for gene bank management, targeted conservation efforts and strategic breeding initiatives.

Treatment of seeds with cold atmospheric pressure plasma (CAPP) is in its proof-of-concept phase with regard to its effect on germination and plant growth. To increase the germination of hardseeded red clover (Trifolium pratense L.), seeds are usually scarified, which is time-consuming and labour-intensive. The aim of this study was to compare the effect of different CAPP devices (indirect treatment: plasma processed air, direct treatment: corona discharge, argon and air dielectric barrier discharge) on germination and early growth of different long-term stored red clover accessions and to determine whether germination can be increased to meet seed management requirements. Sixty different red clover seed lots (diverse accessions and harvest years) with different initial germination percentages were divided into three batches of 20 lots each and the effect of the different plasma treatments on germination and development were examined in laboratory and greenhouse. The overall results indicate a plasma discharge- and accession-depended enhancement of germination speed which was detected in all batches but most pronounced in Batch 1. While direct treatments, especially with corona discharge-plasma, increased germination speed (up to 58% germination seven days after sowing vs. 44% in control in laboratory conditions), treatment with plasma processed air resulted partially in reduced germination speed (42%). Despite a small but significant increase in total germination of maximum five percentage points, no treatment led to an increase from 62% or 70% in control (depending on experiment) to at least 80% germination percentage to meet storage requirements for seed banks. Stimulating effects on biomass of young plants under greenhouse cultivation conditions were observed in Batch 1, but were absent in Batch 2 and 3 and therefore inconclusive. Future research is needed to elucidate influencing factors on plasma effects in red clover seed lots which include but are not limited to the effect of seed coat compounds and seed coat thickness.

Background: Potatoes require phosphorus (P) for growth, tuber production and starch quality, but their small and shallow root system limits the nutrient acquisition. This results in excessive use of mineral P fertilisers, leading to environmental and economic concerns due to resource depletion. Identifying potato genotypes with high P efficiency and understanding the underlying genes responsible are crucial for molecular breeding and crop improvement. The present study aims at exploring the phenotypic and genotypic variation among potato genotypes from Gross Luesewitz Potato Collections (GLKS) and identifying markers significantly associated with P efficiency. Results: Phenotypic characterisation of a diversity set of 200 potato accessions for their response to P deprivation in a pot experiment showed a significant variance regarding biomass production, root length, plants height and P efficiency between the genotypes, with moderate to high heritability for these traits. Shoot biomass decreased by 66% on average under low P, while the root biomass decreased by 36% on average. The extent of the reduction was genotype specific, with some genotypes exhibiting higher root biomass and longer root length under low P than in control conditions. Outstanding genotypes were identified such as GLKS 11,578 (Kristall) with a dense and shallow root system or GLKS 10,591 (Tiger) with a long and extensive root system. Genome-wide association analysis identified 27 unique significant marker-trait associations including 13 associated with biomass, 3 with plant height and 11 with P efficiency, with a majority of them related to P utilization efficiency (7) and shoot biomass (11). Conclusion: Our research is one the firsts to present a genome-wide association study in potatoes for P efficiency. Our study highlighted significant phenotypic variation among the genotypes, while promising targets for improving P efficiency traits in potato through genomic selection and marker-assisted breeding.

Perennial ryegrass (Lolium perenne L.) is one of the most important forage grass species in temperate climates. However, natural perennial ryegrass populations have been exploited to only a limited extent by breeders. Therefore, 41 ecotypic Lolium perenne populations collected across Europe were studied for their agronomic performance in a 3-year common garden experiment located in north-eastern Germany (Poel Island, Mecklenburg Western Pomerania). Agronomic performances were evaluated on 30 plants per population for 11 traits related to forage value and environmental adaptation. Population means for studied traits were correlated to the values of climate variables at their collection sites. Populations clearly differed in their phenotypic performance, and eight populations originating from Belgium, France and Germany outperformed the other populations by showing the lowest winter damage, strongest spring growth and regrowth capacity after cuts and low disease susceptibility. Specifically, in the first experimental year, trait performances, in particular winter damage, spring growth and heading date, were related to the local climate at the site of origin of populations. Acclimation to the climate conditions at the experimental site might explain why these correlations were less pronounced in the second and third experimental years. The characterized populations might now be considered to improve specific traits in breeding.

Background: Seed retention is the basic prerequisite for seed harvest. However, only little breeding progress has been achieved for this trait in the major forage grasses. The aim of this study was to evaluate the potential of plant genetic resources of the important fodder grasses Festuca pratensis Huds. and Lolium perenne L. as source for seed retention in the breeding process. Furthermore, the morphology of the abscission zone, where shattering occurs, was studied on the cell tissue level in different developmental stages of contrasting accessions. Results: 150 and 286 accessions of Festuca pratensis and Lolium perenne were screened for seed retention, respectively. Contrasting accessions were selected to be tested in a second year. We found a great variation in seed retention in Festuca pratensis and Lolium perenne, ranging from 13 to 71% (average: 35%) and 12 to 94% (average: 49%), respectively, in the first year. Seed retention was generally lower in the second year. Cultivars were within the accessions with highest seed retention in Festuca pratensis, but had lower seed retention than ecotypes in Lolium perenne. Field-shattered seeds had a lower thousand grain weight than retained seeds. Cell layers of the abscission zone appeared already in early seed stages and were nested within each other in accessions with high seed retention, while there were two to three superimposed layers in accessions with low seed retention. Conclusions: Plant genetic resources of Lolium perenne might be a valuable source for breeding varieties with high seed retention. However, simultaneous selection for high seed weight is necessary for developing successful commercial cultivars.

Background: Plants are not able to take up organically bound phosphorus (P) before it is hydrolyzed by extracellular phosphatases while intracellular phosphatases play a role in P remobilization.Aims: The aim of this study was to evaluate intra‐ and extracellular acid phosphatase activity as well as root and shoot growth of two modern starch potato cultivars at different levels of P deprivation.Methods: In vitro propagated potato plantlets (cultivars Kuba and Cardoso) were grown in sand and fertigated with five different P concentrations, ranging from 1 to 0.05 mM P. Growth parameters, plant P concentrations, and acid phosphatase activities were determined after 40 days.Results: Shoot and root biomass decreased gradually with decreasing P supply, while the root‐to‐shoot ratio increased. Shoot P concentration decreased steadily, but root P concentration remained constant at P levels below 0.5 mM. Root‐associated and root intracellular acid phosphatase activity increased in both cultivars with rising levels of P deprivation. The activity of acid phosphatases in old but not in young leaves was increased with P deprivation. Intracellular acid phosphatase activity was genotype dependent, with higher activity in the cultivar Kuba than in Cardoso.Conclusions: Our results point to a tissue specific regulation of acid phosphatase activity depending on plant P status and potato genotype. Increasing root‐associated acid phosphatase activities may help P starved potato plants to ensure a sufficient P nutrition. Further research is needed to unravel the roles of leaf intracellular acid phosphatases in potato.

Soil salinity is a critical problem for rice production and is also often associated with phosphors (P) deficiency. Plant hormones, like brassinosteroids, were shown to play a role in plant responses to different stresses and are also expected to mitigate salt stress. The aim of this study was to compare shoot growth and root architecture traits of two rice cultivars (INCA LP-5 and Perla de Cuba) during early plant development in response to salt, P limitation and a brassinosteroid. Seeds were placed in (I) paper rolls for 7 days and (II) mini-rhizotrons for 21 days without or with salt (50 mM NaCl), without or with 24-epibrassinolide (10⁻⁶ M) pre-treatment, and with two levels of P (10 or 1 ppm). The root system of LP-5 was larger in size and extent, while the roots of Perla were growing denser. Salt affected mainly the size- and extent-related root characteristics and explained about 70% of the variance. The effect of P was more pronounced without salt treatment. In Perla, P supply reduced the salt effect on root growth. The brassinosteroid had hardly any effect on the development of the plants in both experiments. Due to the high dependence on experimental factors, root length and related traits can be recommended for selecting young rice cultivars regarding salt stress and P deprivation.