Silvia Bachmann

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.

Potato wild relatives provide a considerable source of variation for important traits in cultivated potato (Solanum tuberosum L.) breeding. This study evaluates the variation of tuber starch content and nitrogen utilization efficiency (NutE) in wild potato germplasm. For the experiments regarding starch content, 28 accessions of ten different tuber-bearing wild Solanum-species were chosen, and in vitro plantlets were raised from seeds. Twenty plantlets (= genotypes) per accession were then cultivated in the greenhouse until natural senescence and tuber starch content was determined. The average tuber starch content across all genotypes tested was 21.7% of fresh mass. Contents above 28% of fresh mass were found in 50 genotypes, belonging to the species S. chacoense, S. commersonii, S. jamesii, and S. pinnatisectum. Subsequently, 22 wild genotypes revealing high tuber starch contents and four modern varieties of cultivated potato were studied as in vitro plantlets under optimal and low N supply (30 and 7.5 mmol L⁻¹ N). Low N supply lead to a genotype-dependent reduction of shoot dry mass between 13 and 46%. The majority of the wild types also reduced root dry mass by 26 to 62%, while others maintained root growth and even exceeded the NutE of the varieties under low N supply. Thus, wild potato germplasm appears superior to cultivars in terms of tuber starch contents and N utilization efficiency, which should be investigated in further studies.

Potato is considered having a low phosphorus (P) efficiency compared to other crops. Therefore, P fertilization requirements are high. New cultivars with improved P efficiency may contribute to save limited mineral P sources and to reduce eutrophication of surface water bodies. The present study aims to characterize the P efficiency of different potato genotypes and to identify mechanisms, which improve P efficiency in cultivated potato. A diversity set of 32 potato accessions was used to assess their P efficiency. From this set, five cultivars were selected and two pot experiments with different P-fertilization strategies including a non-fertilized control were conducted to estimate effects of P deficiency on general agronomic and P related traits, root development, phosphatase activity and micro RNA 399 (miR399) expression. Significant differences between the 32 genotypes were found for P use efficiency (PUE). P acquisition efficiency (PAE) as P content in low P in relation to P content in high P was positively correlated to relative biomass production while PUE was not. Selected genotypes displayed a strong relation between total root length and P content. Root phosphatase activity and miR399 expression increased under P deficiency. However, tuber yields of four cultivars, grown on a soil with suboptimal content of plant available P, were not significantly affected in comparison to yields of well-fertilized plots. We conclude from the present study that PUE and PAE are important traits when selecting for plants requiring less fertilizer inputs but PAE might be more important for cropping on deficient soils. A large root system might be the most important trait for P acquisition on such soils and therefore in breeding for P efficient crops. Lowering P fertilizer inputs might not necessarily reduce tuber yields.

Biogas digestates contain valuable nutrients but also have high water contents. Di-gestates were sampled from two different biogas facilities before and after solid-liquid separation and were analyzed with regard to their composition and phosphorus (P) fractions. Additionally, to investigate the P fertilizer effects of these digestates in comparison with undigested slurry or TripleSuper-P (TSP), they were applied in a pot experiment (6 kg soil per pot) in an amount corresponding to 200 mg P per pot in combination with various crops (amaranth, maize, maize + beans mixed cropping, sorghum). A separation of digestates resulted in higher P concentrations of the solid fraction in comparison with the liquid fraction. The proportion of the readily soluble P fractions (H₂O-P, NaHCO₃-P) to the total P was higher than 70 % in all digestates. The digestates increased P uptake of the tested crops and concentrations of bioavailable P in the soil to the same extent as highly soluble TSP. Activities of soil enzymes were lower after application of the digestates in comparison to unfermented slurry. The fertilizer management of digestates can be improved by a solid-liquid separation since the solid fraction showed a relatively high concentration of P resulting in a reduction in application doses required to meet the P demands of crops.