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 functio

Rooting depth and water use efficiency of tropical maize inbred lines, differing in drought tolerance

Deep rooting has been identified as strategy for desiccation avoidance in natural vegetation as well as in crops like rice and sorghum. The objectives of this study were to determine root morphology and water uptake of four inbred lines of tropical maize (Zea mays L.) differing in their adaptation to drought. The specific questions were i) if drought tolerance was related to the vertical distribution of the roots, ii) whether root distribution was adaptive or constitutive, and iii) whether it affected water extraction, water status, and water use efficiency (WUE) of the plant. In the main experiment, seedlings were grown to the V5 stage in growth columns (0.80m high) under well-watered (WW) and water-stressed (WS) conditions. The depth above which 95 % of all roots were located (D95) was used to estimate rooting depth. It was generally greater for CML444 and Ac7729/TZSRW (P2) compared to SC-Malawi and Ac7643 (P1). The latter had more lateral roots, mainly in the upper part of the soil column. The increase in D95 was accompanied by increases in transpiration, shoot dry weight, stomatal conductance and relative water content without adverse effects on the WUE. Differences in the morphology were confirmed in the V8 stage in large boxes: CML444 with thicker (0.14mm) and longer (0.32m) crown roots compared to SC-Malawi. Deep rooting, drought sensitive P2 showed markedly reduced WUE, likely due to an inefficient photosynthesis. The data suggest that a combination of high WUE and sufficient water acquisition by a deep root system can increase drought toleranc

Genetic diversity of Swiss maize ( Zea mays L. ssp. mays ) assessed with individuals and bulks on agarose gels

About 65years ago, more than 150 Swiss maize landraces (Zea mays L. ssp. mays) of the flint type were collected and conserved ex situ. Due to the climatically and culturally diverse environment of the Alps, a considerable genetic diversity of this material was assumed. To prove this, an efficient method was required to carry out genetic profiling of all the accessions in the Swiss Gene Bank. Simple sequence repeat marker (SSR) profiling in combination with the visualization of the polymerase chain reaction (PCR) products on agarose gels was chosen. Here a set of 19 different landrace accessions was analyzed to: (i) investigate their genetic diversity, (ii) investigate and display the population structure and (iii) determine whether DNA bulks rather than single plants can be used for such analyses. Four repeated samples of one accession were found to be much closer to one another than to the rest of accessions. Furthermore, specific alleles were identified for several accessions. The PCR products of the bulked DNA samples represented only a small part of the variation revealed by the analysis of individuals. Loci with four base repeat motifs performed better in the analysis of bulks than loci with other repeat motifs. The correlation between genetic distance matrices, based on the analysis of individuals and bulks, respectively, was significant. Thus, the single plant approach allowed for sufficient differentiation of accessions, and DNA bulks visualized on agarose gels led to correlated genetic distances although a limited number of alleles were detected. Although the limited resolution of agarose gels likely causes some bias, profiling of larger sets with the individual plant approach appears feasible and more informative compared to the bulk analysis we conducte

Mapping of QTLs for lateral and axile root growth of tropical maize

Maize genotypes may adapt to dry environments by avoiding desiccation by means of a deeper root system or by maintaining growth and water extraction at low water potentials. The aim of this study was to determine the quantitative genetic control of root growth and root morphology in a population of 236 recombinant inbred lines (RILs) from the cross between CML444 (high-yielding)×SC-Malawi (low-yielding), which segregates for the response to drought stress at flowering. The RILs and the parental lines were grown on blotting paper in growth pouches until the two-leaf stage under non-stressed conditions; the parents were additionally exposed to desiccation stress induced by polyethylene glycol with a molecular weight of 8000 Dalton (PEG-8000). The lengths of axile and lateral roots were measured non-destructively at 2, 5, 7 and 9days after germination, by scanning with an A4 scanner followed by digital image analysis. CML444 had a lower rate constant of lateral root elongation (kLat) than SC-Malawi, but the two genotypes did not differ in their response to desiccation. QTLs affecting root vigor, as depicted by increments in kLat, the elongation rate of axile roots (ERAx) and the number of axile roots (NoAx) were identified in bins 2.04 and 2.05. QTLs for NoAx and ERAx collocated with QTLs for yield parameters in bins 1.03-1.04 and 7.03-04. The correspondence of QTLs for axile root traits in bins 1.02-1.03 and 1.08 and QTLs for lateral roots traits in bins 2.04-2.07 in several mapping populations suggests the presence of genes controlling root growth in a wide range of genetic background

A soil-free root observation system for the study of root-microorganism interactions in maize

Background and aims: The root surface of a plant usually exceeds the leaf area and is constantly exposed to a variety of soil-borne microorganisms. Root pathogens and pests, as well as belowground interactions with beneficial microbes, can significantly influence a plants' performance. Unfortunately, the analysis of these interactions is often limited because of the arduous task of accessing roots growing in soil. Here, we present a soil-free root observation system (SF-ROBS) designed to grow maize (Zea mays) plants and to study root interactions with either beneficial or pathogenic microbes. Methods: The SF-ROBS consists of pouches lined with wet filter paper supplying nutrient solution. Results: The aspect of maize grown in the SF-ROBS was similar to soil-grown maize; the plant growth was similar for the shoot but different for the roots (biomass and length increased in the SF-ROBS). SF-ROBS-grown roots were successfully inoculated with the hemi-biotrophic maize fungal pathogen Colletotrichum graminicola and the beneficial rhizobacteria Pseudomonas putida KT2440. Thus, the SF-ROBS is a system suitable to study two major belowground phenomena, namely root fungal defense reactions and interactions of roots with beneficial soil-borne bacteria. Conclusions: This system contributes to a better understanding of belowground plant microbe interactions in maize and most likely also in other crop

Cold Tolerance of the Photosynthetic Apparatus: Pleiotropic Relationship between Photosynthetic Performance and Specific Leaf Area of Maize Seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (ΦPSII) at low temperature, (ii) a population of 226 F2:3 families from the cross of ETH-DL3 × ETH-DH7, and (iii) a population of 168 F2:4 families from the cross of Lo964 × Lo1016 were tested at low (15/13°C day/night) or at optimal (25/22°C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13°C the groups of S5 inbred lines selected for high or low ΦPSII differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with ΦPSII (r= − 0.56, p < 0.05) and SPAD (r = − 0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13°C, while co-location was not detected at 25/22°C. The co-selection of SLA and ΦPSII in the inbred lines and the co-location of QTL for SLA, SPAD, and ΦPSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high ΦPSII at low temperature leads to a constitutively altered SL

Swiss maize (Zea mays L) landraces. Their genetic diversity and distinctiveness in a global comparison

Swiss maize landraces are expected to be genetically diverse, as they have been cultivated in different climatic regions of Switzerland for almost 500 years. A core collection of 35 Swiss maize landraces was recently defined. This core collection was analyzed in the present study, with the objectives (i) to resolve genetic diversity and phylogeny of the core collection, (ii) to relate these results to those obtained in a worldwide collection of maize landraces, thereby (iii) analyzing separation and admixture and (iv) to identify unique alleles that were detected only in Swiss maize landraces (Swiss alleles). A high diversity (HT = 0.61) in an international comparison and many Swiss alleles pointed at the value of this core collection as a plant genetic resource. The genetic differentiation within the core collection was in very good accordance with the geographic separation caused by the Swiss Alps. The accessions grouped into three major clusters, two northern and a southern one. Additionally, landraces from Valais built an intermediate cluster, which is probably the result of hybridization between different European germplasm. Continuous maize cultivation in remote areas may have favored genetic drift and intentional selection by farmers and may have led to this particular cluster. In the international comparison, northern Swiss accessions were related to European and American Northern Flints, whereas southern Swiss accessions were closely related to southern European Flints (e.g. Italian Orange Flints). Some northern Swiss accession combined high diversity with many Swiss alleles, which may be valuable for broadening the European Flint pool

High-resolution quantification of root dynamics in split-nutrient rhizoslides reveals rapid and strong proliferation of maize roots in response to local high nitrogen

Patches rich in nitrogen are rapidly colonized by selective root growth in maize, which was quantified at high time resolution with state-of-the-art non-invasive imaging techniques in a paper-based growth syste

Development of a matrix-based technology platform for the high throughput analysis of 3D cell cultures

The screening of large cell libraries is an important process in pharmaceutical discovery and R&D, e.g. to define drug targets or develop effective medicines. The goal of this project is the implementation of a screening platform based on 3D cultivation of primary human mesothelioma cells encapsulated in alginate hydrogels. To this end, new hydrogel compositions will be designed, tested and finally utilized in the Nanoliter Reactor (NLR) cultivation system that enables high throughput analysis of 3D cell cultures