RT Dissertation/Thesis
T1 Assessing the genetic variation of phosphate efficiency in European maize (Zea mays L.)
A1 Weiß,Thea Mi
WP 2022/08/30
AB Why should plant breeders in Central Europe care about phosphate efficiency? Soil phosphorus levels have mostly reached high to very high levels over the last decades in intensively farmed, livestock-rich regions. However, the European Union demands a restructuring of the agricultural production systems through setting ambitious goals envisaged in the Farm to Fork Strategy. By 2030, fertilizer use should be reduced by 20 %, nutrient losses by at least 50 %. As a consequence, farmers have to be even more efficient with crop inputs, among them the globally limited resource of phosphorus fertilizers, while maintaining high yields. Plant breeding means thinking ahead. Therefore, phosphate-efficient varieties should be developed to help farmers meet this challenge and reduce the need for additional fertilizers. One prerequisite to reach this target is that genotypic variation for the relevant traits is available. Moreover, approaches that assist selection by accurate but also time- and resource-efficient prediction of genotypes are highly valuable in breeding. Finally, the choice of the selection environment and suitable trait assessment for the improvement of phosphate efficiency under well-supplied conditions, need to be elaborated.
In this dissertation, a diverse set of maize genotypes from ancient landraces to modern hybrids was investigated for phosphate efficiency-related traits under well-supplied P soil conditions. Multi-environmental field trials were conducted in 2019 and 2020. 
The reaction to different starter fertilizer treatments of the 20 commercially most important maize hybrids grown in Germany was studied. In the hybrid trial, the factor environment had a significant effect on the impact of starter fertilizers. Especially in early developmental stages genotypes showed a different response to the application of starter fertilizers. On the overall very well-supplied soils, we observed no significant genotype-by-starter fertilizer interaction. Nonetheless, we identified hybrids, which maintained high yields also if no starter fertilizer was provided. Thus, it seems that sufficient variation is available to select and breed for phosphate efficiency under reduced fertilizer conditions. 
Furthermore, the concept of phenomic prediction, based on near-infrared spectra instead of marker data to predict the performance of genotypes, was applied to 400 diverse lines of maize and compared to genomic prediction. For this, we used seed-based near-infrared spectroscopy data to perform phenomic selection in our line material, which comprised doubled haploid lines from landraces and elite lines. We observed that phenomic prediction generally performed comparable to genomic prediction or even better. In particular, the phenomic selection approach holds great potential for predictions among different groups of breeding material as it is less prone to artifacts resulting from population structure. Phenomic selection is therefore deemed a useful and cost-efficient tool to predict complex traits, including phosphorus concentration and grain yield, which together form the basis to determine phosphate efficiency.
Lastly, 20 different indicators for phosphate efficiency were calculated, the genetic variation of the different measures present in this unique set of lines was quantified, and recommendations for breeding were derived. Of the different measures for phosphate efficiency reported in literature, Flint landraces demonstrated valuable allelic diversity with regard to phosphate efficiency during the seedling stage. Due to the highly complex genetic architecture of phosphate efficiency-related traits, a combination of genomic and phenotypic selection appears best suited for their improvement in breeding. Taken together, phosphate efficiency, including its definition and meaning, is largely dependent on the available phosphorus in the target environment as well as the farm type, which specifies the harvested produce and thereby the entire phosphorus removal from the field.
In conclusion, future maize breeding should work in environments that are similar to the future target environments, meaning reduced fertilizer inputs and eventually lower soil P levels. Our results demonstrate that breeding of varieties, which perform well without starter fertilizers is feasible and meaningful under the well-supplied conditions prevalent in Central Europe. For the improvement of the highly complex trait phosphate efficiency through breeding we recommend to apply genomic and phenomic prediction along with classical phenotypic screening of genotypes and by this making our food systems more resilient towards upcoming challenges in agriculture.
K1 Pflanzenzüchtung
K1 Mais
K1 Phosphor
K1 Phosphatdünger
K1 phänomische und genomische Selektion
K1 Phosphateffizienz
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2022/2063