Rainer Messmer

A consensus map of QTLs controlling the root length of maize

Traits related to the root length of maize (Zea mays L.), reported by 15 QTL studies of nine mapping populations, were subjected to a QTL meta-analysis. Traits were grouped according to ontology, and we propose a system of abbreviations to unambiguously identify the different root types and branching orders. The nine maps were merged into a consensus map, and the number and positions of putative QTL clusters (MQTLs) were determined. A total of 161 QTLs was grouped into 24 MQTLs and 16 individual QTLs. Seven MQTLs harbored root traits, which had been reported to be collocated with QTLs for grain yield or other drought-responsive traits in the field. The most consistent collocations were observed for the number and weight of the seminal roots (five loci). Based on our analysis at least six loci are good candidates for further evaluation (bins 1.07, 2.04, 2.08, 3.06, 6.05 and 7.04). For example, the MQTL in bin 2.04 harbored ten different single QTLs; the MQTLs in bins 1.07 and 3.06 combined 11 and 7 QTLs, respectively, that were detected in more than three populations. The presented database is a first step for a comprehensive overview of the genetic architecture of root system architecture and its ecophysiological function.

Association mapping for chilling tolerance in elite flint and dent maize inbred lines evaluated in growth chamber and field experiments

Chilling sensitivity of maize is a strong limitation for its cultivation in the cooler areas of the northern and southern hemisphere because reduced growth in early stages impairs on later biomass accumulation. Efficient breeding for chilling tolerance is hampered by both the complex physiological response of maize to chilling temperatures and the difficulty to accurately measure chilling tolerance in the field under fluctuating climatic conditions. For this research, we used genome-wide association (GWA) mapping to identify genes underlying chilling tolerance under both controlled and field conditions in a broad germplasm collection of 375 maize inbred lines genotyped with 56 110 single nucleotide polymorphism (SNP). We identified 19 highly significant association signals explaining between 5.7 and 52.5% of the phenotypic variance observed for early growth and chlorophyll fluorescence parameters. The allelic effect of several SNPs identified for early growth was associated with temperature and incident radiation. Candidate genes involved in ethylene signalling, brassinolide, and lignin biosynthesis were found in their vicinity. The frequent involvement of candidate genes into signalling or gene expression regulation underlines the complex response of photosynthetic performance and early growth to climatic conditions, and supports pleiotropism as a major cause of co-locations of quantitative trait loci for these highly polygenic traits.

QTLs for early vigor of tropical maize

A strong photosynthetic performance and rapid leaf development, are important indicators of vigorous early growth. The aim of this study was to (1) evaluate the tropical maize (Zea mays L.) inbred lines CML444 and SC-Malawi for their photosynthetic performance at different growth stages and (2) assess quantitative trait loci (QTL) of photosynthesis-related traits in their 236 recombinant inbred lines at the heterotrophic growth stage. CML444 had a higher leaf chlorophyll (SPAD) content than SC-Malawi. Ten QTLs were found for the quantum efficiency of photosystem II (ΦPSII; four), SPAD (three) and the specific leaf area (SLA; three). The relevance of seedling QTLs for ΦPSII, SPAD and SLA for yield formation is emphasized by seven collocations (bins 5.01, 7.03, 8.05) with QTLs for kernel number and grain yield under field conditions. QTLs for SPAD at the V2 and at the reproductive stage did not collocate, indicating differences in the genetic control of SPAD at different growth stages. Knowing which loci affect SLA, SPAD and ΦPSII simultaneously and which do not will help to optimize light harvest by the canopy.