TY - THES T1 - Utilization of landraces of European flint maize for breeding and genetic research A1 - Renner,Juliane Y1 - 2023/07/05 N2 - Maize is one of the most important crops species for agriculture worldwide. Since its domestication, landraces formed the traditional type of variety. Selection and genetic factors formed a broad diversity of open-pollinated populations well adapted to local conditions. This changed with the introduction of hybrid breeding when nearly all existing landraces disappeared from their use in agriculture and as source material for breeding. Molecular analyses showed a narrow genetic base of the flint heterotic pool compared to the dent pool. Since genetic resources in maize are one of the richest of all major crops, the exploitation of this untapped reservoir of genetic variation in landraces could be an option to reverse the ongoing narrowing of the genetic basis to meet the demands of a growing world population as well as new challenges under a changing global climate and reduced inputs. The main goal of this study was the evaluation of European flint maize landraces to unlock their genetic diversity. In detail our objectives were to (i) determine the variation for testcross performance of European maize landraces; (ii) evaluate the phenotypic and genotypic variation of immortalized lines within and among landraces; (iii) compare the per se performance of those line libraries with elite lines as well as founder lines from the European flint germplasm pool; (iv) analyze the breeding potential of immortalized lines from landraces in comparison with elite material to improve the narrow genetic base of the flint heterotic pool; (v) demonstrate the high mapping resolution of DH libraries from landraces in association mapping down to causal variants and underlying genes; and (vi) provide conclusions and guidelines for breeding and research using libraries of immortalized lines from landraces. In a first experiment, we evaluated in multi-environment trials a broad collection of 70 European flint landraces for their testcross performance in combination with two elite dent testers. In comparison with the yield of modern hybrids, grain yield of the testcrosses of landraces was on average 26% lower, but a high genotypic variance among the landrace was observed for all traits and correlations were moderate to high for most trait combinations similar to those found in elite materials. Genetic correlations between the two testcross series exceeded 0.74 for all traits, suggesting that evaluation of testcross performance in combination with one or two single-cross tester(s) from the opposite pool is sufficient to assess the breeding potential of landraces. In a second experiment, we produced libraries of DH lines from the most promising landraces identified in the first experiment. In total 389 DH lines from six European flint landraces were evaluated together with four flint founder lines and 53 elite flint lines for 16 agronomic traits in four locations. In general, the genotypic variance (σ^2G) was larger within than among the DH libraries and exceeded also σ^2G of the elite flint lines. Furthermore, the means and σ^2G varied among the DH libraries resulting in large differences of the usefulness criterion. Mean grain yield of the elite flint lines exceeded that of the flint founder lines by 25% and DH libraries by 62%, indicating the impressive breeding progress achieved in the elite material and the substantial genetic load still present in the DH libraries. Nevertheless, the usefulness of the best DH lines was comparable to that of the elite flint lines for many traits including grain yield, underpinning the tremendous potential of landraces for broadening the genetic base of the elite germplasm. In a third experiment the materials from the 2nd experiment were genotyped with the MaizeSNP50 BeadChip from Illumina® and seeds of all genotypes were used for extracting and analyzing 288 metabolites with GC-MS. Data for agronomic traits and metabolites were used for a novel association mapping study. The much faster decay of linkage disequilibrium for adjacent markers in the DH libraries compared with the elite flint lines resulted in unprecedented map resolution. This was strikingly demonstrated by fine-mapping a QTL for oil content down to the phenylalanine insertion F469 in DGAT1-2 as the causal variant. Further, for the metabolite allantoin, which is related to abiotic stress response, promoter polymorphisms as well as differential expression of an allantoinase were identified as putative causes of variation despite a moderate size of the mapping population. These results are very encouraging to use DH libraries from landraces for association mapping and dissect QTL potentially down to the causal variants. However, larger population sizes of each DH library are recommended, similar to those commonly used with other approaches such as the NAM design, for detection of QTL explaining only a small portion of the genetic variance. This opens a new avenue for utilization of natural and/or engineered alleles in breeding. In conclusion, the genetic variation present in European flint maize landraces represents a unique source to reverse the ongoing narrowing of the genetic basis of the elite germplasm of this heterotic pool. For identifying the most promising landraces, we propose a multi-stage approach, where based on an assessment of the molecular diversity about one hundred landraces are evaluated in observation trials for agro-ecological adaptation and testcrosses with one single-cross tester are used for evaluating their general combining ability with the opposite heterotic pool. For a small number (< 6) of landraces a large number of DH lines are developed, which are phenotyped and genotyped for further use in association mapping and genomic selection with the ultimate goal to make these “gold reserves” accessible for maize breeding with modern approaches. KW - Mais, genetische Ressourcen KW - Landrassen KW - genetische Ressourcen KW - Doppelhaploide KW - Assoziationskartierung CY - Hohenheim PB - Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim AD - Garbenstr. 15, 70593 Stuttgart UR - http://opus.uni-hohenheim.de/volltexte/2023/2158 ER -