Andreas Hund - Academia.edu (original) (raw)

Papers by Andreas Hund

Plant Methods, 2015

Plant phenotyping refers to a quantitative description of the plant&a... more Plant phenotyping refers to a quantitative description of the plant's anatomical, ontogenetical, physiological and biochemical properties. Today, rapid developments are taking place in the field of non-destructive, image-analysis -based phenotyping that allow for a characterization of plant traits in high-throughput. During the last decade, 'the field of image-based phenotyping has broadened its focus from the initial characterization of single-plant traits in controlled conditions towards 'real-life' applications of robust field techniques in plant plots and canopies. An important component of successful phenotyping approaches is the holistic characterization of plant performance that can be achieved with several methodologies, ranging from multispectral image analyses via thermographical analyses to growth measurements, also taking root phenotypes into account.

Background: Field-based high throughput phenotyping is a bottleneck for crop breeding research. W... more Background: Field-based high throughput phenotyping is a bottleneck for crop breeding research. We present a novel method for repeated remote phenotyping of maize genotypes using the Zeppelin NT aircraft as an experimental sensor platform. The system has the advantage of a low altitude and cruising speed compared to many drones or airplanes, thus enhancing image resolution while reducing blurring effects. Additionally there was no restriction in sensor weight. Using the platform, red, green and blue colour space (RGB), normalized difference vegetation index (NDVI) and thermal images were acquired throughout the growing season and compared with traits measured on the ground. Ground control points were used to co-register the images and to overlay them with a plot map.

Functional Plant Biology, 2015

Plant and Soil, 2015

Aims Root system architecture traits (RSAT) are crucial for crop productivity, especially under d... more Aims Root system architecture traits (RSAT) are crucial for crop productivity, especially under drought and low soil fertility. The Bshovelomics^method of field excavation of mature root crowns followed by manual phenotyping enables a relatively high throughput as needed for breeding and quantitative genetics. We aimed to develop a new sampling protocol in combination with digital imaging and new software. Methods Sampled rootstocks were split lengthwise, photographed under controlled illumination in an imaging tent and analysed using Root Estimator for Shovelomics Traits (REST). A set of 33 diverse maize hybrids, grown at 46 and 192 kg N ha −1 , was used to evaluate the method and software.

European Journal of Agronomy, 2007

At low temperature, as occurs in the spring, a high photosynthetic performance of maize (Zea mays... more At low temperature, as occurs in the spring, a high photosynthetic performance of maize (Zea mays L.) in combination with a large leaf area is an important measure for early vigor. However, little is known about adaptation of root morphology to low-temperature conditions. The objectives were (i) to characterize a set of 21 modern inbred lines for photosynthesis-related traits and root morphology at 15/13°C (day/night) and (ii) elucidate relationships between shoot and root traits. Plants were grown in sand substrate until the two-leaf (V2) stage; the operating efficiency of photosystem II (ΦPSII), chlorophyll content (SPAD), and leaf area were used to estimate the rate of CO2 assimilation per plant (Aˆp). The genotypes were separated as follows: those that maximize leaf area and those that maximize ΦPSII. The morphological organization of the root systems of the genotypes varied to a great extent. Using a principal component analysis (PCA) of root traits (i.e. length of the primary, seminal, and crown roots), genotypes with homogeneous (similar primary and seminal roots) and heterogeneous (lateral roots of the primary root generally longer than the lateral roots of the seminal roots) root systems were identified. The length of the primary lateral roots was most closely associated with all Aˆp-related traits and with high plant dry weight. Therefore, most of the genotypes with an heterogeneous root system outperformed those with an homogeneous root system with regard to dry matter accumulation and photosynthetic performance. In conclusion, differences in the organization of the embryonic root system are associated with early vigor.

Plant and Soil, 2013

ABSTRACT Background and aims The root surface of a plant usually exceeds the leaf area and is con... more ABSTRACT 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 crops.

Theoretical and Applied Genetics, 2009

Maize genotypes may adapt to dry environments by avoiding desiccation by means of a deeper root s... more 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 (highyielding) 9 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 9 days after germination, by scanning with an A4 scanner followed by digital image analysis. CML444 had a lower rate constant of lateral root elongation (k Lat ) than SC-Malawi, but the two genotypes did not differ in their response to desiccation. QTLs affecting root vigor, as depicted by increments in k Lat , the elongation rate of axile roots (ER Ax ) and the number of axile roots (No Ax ) were identified in bins 2.04 and 2.05. QTLs for No Ax and ER Ax 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 backgrounds.

Crop Science - CROP SCI, 2010

ABSTRACT

The objective of this study was to elucidate the genetic relationship between the specific leaf a... more 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 S 5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (U PSII ) at low temperature, (ii) a population of 226 F 2:3 families from the cross of ETH-DL3 · ETH-DH7, and (iii) a population of 168 F 2:4 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 S 5 inbred lines selected for high or low U PSII 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 U PSII (r = À 0.56, p < 0.05) and SPAD (r = À 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 U PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and U PSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high U PSII at low temperature leads to a constitutively altered SLA.

Traits related to the root length of maize (Zea mays L.), reported by 15 QTL studies of nine mapp... more 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 metaanalysis. 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.

Plant and Soil, 2009

Deep rooting has been identified as strategy for desiccation avoidance in natural vegetation as w... more 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 (0.80 m 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 (0.14 mm) and longer (0.32 m) 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 tolerance.

Plant methods, 2014

Background: A quantitative characterization of root system architecture is currently being attemp... more Background: A quantitative characterization of root system architecture is currently being attempted for various reasons. Non-destructive, rapid analyses of root system architecture are difficult to perform due to the hidden nature of the root. Hence, improved methods to measure root architecture are necessary to support knowledge-based plant breeding and to analyse root growth responses to environmental changes. Here, we report on the development of a novel method to reveal growth and architecture of maize root systems. Results: The method is based on the cultivation of different root types within several layers of two-dimensional, large (50 × 60 cm) plates (rhizoslides). A central plexiglass screen stabilizes the system and is covered on both sides with germination paper providing water and nutrients for the developing root, followed by a transparent cover foil to prevent the roots from falling dry and to stabilize the system. The embryonic roots grow hidden between a Plexiglas surface and paper, whereas crown roots grow visible between paper and the transparent cover. Long cultivation with good image quality up to 20 days (four fully developed leaves) was enhanced by suppressing fungi with a fungicide. Based on hyperspectral microscopy imaging, the quality of different germination papers was tested and three provided sufficient contrast to distinguish between roots and background (segmentation). Illumination, image acquisition and segmentation were optimised to facilitate efficient root image analysis. Several software packages were evaluated with regard to their precision and the time investment needed to measure root system architecture. The software 'Smart Root' allowed precise evaluation of root development but needed substantial user interference. 'GiaRoots' provided the best segmentation method for batch processing in combination with a good analysis of global root characteristics but overestimated root length due to thinning artefacts. 'WhinRhizo' offered the most rapid and precise evaluation of root lengths in diameter classes, but had weaknesses with respect to image segmentation and analysis of root system architecture. Conclusion: A new technique has been established for non-destructive root growth studies and quantification of architectural traits beyond seedlings stages. However, automation of the scanning process and appropriate software remains the bottleneck for high throughput analysis.

… of the Royal …, 2012

Tolerance to high and low temperature is an important breeding aim for Central and Northern Europ... more Tolerance to high and low temperature is an important breeding aim for Central and Northern Europe, where temperature fluctuations are predicted to increase. However, the extent to which genotypes differ in their response to the whole range of possible temperatures is not well understood. We tested the hypothesis that the combination of maize (Zea mays L.) inbred lines with differing temperature optima for root growth would lead to superior hybrids. This hypothesis is based on the concept of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;marginal overdominance&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; in which the hybrid expresses higher relative fitness than its parents, summed over all situations. The elongation rates of axile and lateral roots of the reciprocal cross between two flint and two dent inbred lines were assessed at temperatures between 15°C and 40°C. Indeed, the cross between UH005 and UH250 with lateral root growth temperature optima at 34°C and 28°C, respectively, resulted in intermediate hybrids. At temperatures below and above 31°C, the hybrids&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; root growth was comparable to the better parent, respectively, thereby increasing temperature tolerance of the hybrid compared with its parents. The implications of and reasons for this heterosis effect are discussed in the context of breeding for abiotic stress tolerance and of putatively underlying molecular mechanisms. This finding paves the way for more detailed investigations of this phenomenon in future studies.

European Journal of Agronomy, 2008

Mild chilling stress and slow soil warming are common causes for a retarded early development of ... more Mild chilling stress and slow soil warming are common causes for a retarded early development of maize (Zea mays L.). The objective of this study was to evaluate cold tolerance of a divers set of 14 inbred lines with respect to root morphology as well as the function of the photosynthetic apparatus. Plants were grown until the 2-leaf stage under

The objective of this study was to elucidate the genetic relationship between the specific leaf a... more 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 S 5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (U PSII ) at low temperature, (ii) a population of 226 F 2:3 families from the cross of ETH-DL3 · ETH-DH7, and (iii) a population of 168 F 2:4 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 S 5 inbred lines selected for high or low U PSII 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 U PSII (r = À 0.56, p < 0.05) and SPAD (r = À 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 U PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and U PSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high U PSII at low temperature leads to a constitutively altered SLA.

Genetic Resources and Crop …, 2008

Abstract About 65 years ago, more than 150 Swiss maize landraces (Zea mays L. ssp. mays) of the f... more Abstract About 65 years 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. ...

Plant and Soil, 2011

Traits related to the root length of maize (Zea mays L.), reported by 15 QTL studies of nine mapp... more 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 metaanalysis. 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.

Plant Methods, 2015

Plant phenotyping refers to a quantitative description of the plant&amp;amp;amp;amp;amp;amp;a... more Plant phenotyping refers to a quantitative description of the plant&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s anatomical, ontogenetical, physiological and biochemical properties. Today, rapid developments are taking place in the field of non-destructive, image-analysis -based phenotyping that allow for a characterization of plant traits in high-throughput. During the last decade, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;the field of image-based phenotyping has broadened its focus from the initial characterization of single-plant traits in controlled conditions towards &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;real-life&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; applications of robust field techniques in plant plots and canopies. An important component of successful phenotyping approaches is the holistic characterization of plant performance that can be achieved with several methodologies, ranging from multispectral image analyses via thermographical analyses to growth measurements, also taking root phenotypes into account.

Background: Field-based high throughput phenotyping is a bottleneck for crop breeding research. W... more Background: Field-based high throughput phenotyping is a bottleneck for crop breeding research. We present a novel method for repeated remote phenotyping of maize genotypes using the Zeppelin NT aircraft as an experimental sensor platform. The system has the advantage of a low altitude and cruising speed compared to many drones or airplanes, thus enhancing image resolution while reducing blurring effects. Additionally there was no restriction in sensor weight. Using the platform, red, green and blue colour space (RGB), normalized difference vegetation index (NDVI) and thermal images were acquired throughout the growing season and compared with traits measured on the ground. Ground control points were used to co-register the images and to overlay them with a plot map.

Functional Plant Biology, 2015

Plant and Soil, 2015

Aims Root system architecture traits (RSAT) are crucial for crop productivity, especially under d... more Aims Root system architecture traits (RSAT) are crucial for crop productivity, especially under drought and low soil fertility. The Bshovelomics^method of field excavation of mature root crowns followed by manual phenotyping enables a relatively high throughput as needed for breeding and quantitative genetics. We aimed to develop a new sampling protocol in combination with digital imaging and new software. Methods Sampled rootstocks were split lengthwise, photographed under controlled illumination in an imaging tent and analysed using Root Estimator for Shovelomics Traits (REST). A set of 33 diverse maize hybrids, grown at 46 and 192 kg N ha −1 , was used to evaluate the method and software.

European Journal of Agronomy, 2007

At low temperature, as occurs in the spring, a high photosynthetic performance of maize (Zea mays... more At low temperature, as occurs in the spring, a high photosynthetic performance of maize (Zea mays L.) in combination with a large leaf area is an important measure for early vigor. However, little is known about adaptation of root morphology to low-temperature conditions. The objectives were (i) to characterize a set of 21 modern inbred lines for photosynthesis-related traits and root morphology at 15/13°C (day/night) and (ii) elucidate relationships between shoot and root traits. Plants were grown in sand substrate until the two-leaf (V2) stage; the operating efficiency of photosystem II (ΦPSII), chlorophyll content (SPAD), and leaf area were used to estimate the rate of CO2 assimilation per plant (Aˆp). The genotypes were separated as follows: those that maximize leaf area and those that maximize ΦPSII. The morphological organization of the root systems of the genotypes varied to a great extent. Using a principal component analysis (PCA) of root traits (i.e. length of the primary, seminal, and crown roots), genotypes with homogeneous (similar primary and seminal roots) and heterogeneous (lateral roots of the primary root generally longer than the lateral roots of the seminal roots) root systems were identified. The length of the primary lateral roots was most closely associated with all Aˆp-related traits and with high plant dry weight. Therefore, most of the genotypes with an heterogeneous root system outperformed those with an homogeneous root system with regard to dry matter accumulation and photosynthetic performance. In conclusion, differences in the organization of the embryonic root system are associated with early vigor.

Plant and Soil, 2013

ABSTRACT Background and aims The root surface of a plant usually exceeds the leaf area and is con... more ABSTRACT 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&#39; 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 crops.

Theoretical and Applied Genetics, 2009

Maize genotypes may adapt to dry environments by avoiding desiccation by means of a deeper root s... more 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 (highyielding) 9 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 9 days after germination, by scanning with an A4 scanner followed by digital image analysis. CML444 had a lower rate constant of lateral root elongation (k Lat ) than SC-Malawi, but the two genotypes did not differ in their response to desiccation. QTLs affecting root vigor, as depicted by increments in k Lat , the elongation rate of axile roots (ER Ax ) and the number of axile roots (No Ax ) were identified in bins 2.04 and 2.05. QTLs for No Ax and ER Ax 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 backgrounds.

Crop Science - CROP SCI, 2010

ABSTRACT

The objective of this study was to elucidate the genetic relationship between the specific leaf a... more 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 S 5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (U PSII ) at low temperature, (ii) a population of 226 F 2:3 families from the cross of ETH-DL3 · ETH-DH7, and (iii) a population of 168 F 2:4 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 S 5 inbred lines selected for high or low U PSII 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 U PSII (r = À 0.56, p < 0.05) and SPAD (r = À 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 U PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and U PSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high U PSII at low temperature leads to a constitutively altered SLA.

Traits related to the root length of maize (Zea mays L.), reported by 15 QTL studies of nine mapp... more 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 metaanalysis. 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.

Plant and Soil, 2009

Deep rooting has been identified as strategy for desiccation avoidance in natural vegetation as w... more 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 (0.80 m 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 (0.14 mm) and longer (0.32 m) 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 tolerance.

Plant methods, 2014

Background: A quantitative characterization of root system architecture is currently being attemp... more Background: A quantitative characterization of root system architecture is currently being attempted for various reasons. Non-destructive, rapid analyses of root system architecture are difficult to perform due to the hidden nature of the root. Hence, improved methods to measure root architecture are necessary to support knowledge-based plant breeding and to analyse root growth responses to environmental changes. Here, we report on the development of a novel method to reveal growth and architecture of maize root systems. Results: The method is based on the cultivation of different root types within several layers of two-dimensional, large (50 × 60 cm) plates (rhizoslides). A central plexiglass screen stabilizes the system and is covered on both sides with germination paper providing water and nutrients for the developing root, followed by a transparent cover foil to prevent the roots from falling dry and to stabilize the system. The embryonic roots grow hidden between a Plexiglas surface and paper, whereas crown roots grow visible between paper and the transparent cover. Long cultivation with good image quality up to 20 days (four fully developed leaves) was enhanced by suppressing fungi with a fungicide. Based on hyperspectral microscopy imaging, the quality of different germination papers was tested and three provided sufficient contrast to distinguish between roots and background (segmentation). Illumination, image acquisition and segmentation were optimised to facilitate efficient root image analysis. Several software packages were evaluated with regard to their precision and the time investment needed to measure root system architecture. The software 'Smart Root' allowed precise evaluation of root development but needed substantial user interference. 'GiaRoots' provided the best segmentation method for batch processing in combination with a good analysis of global root characteristics but overestimated root length due to thinning artefacts. 'WhinRhizo' offered the most rapid and precise evaluation of root lengths in diameter classes, but had weaknesses with respect to image segmentation and analysis of root system architecture. Conclusion: A new technique has been established for non-destructive root growth studies and quantification of architectural traits beyond seedlings stages. However, automation of the scanning process and appropriate software remains the bottleneck for high throughput analysis.

… of the Royal …, 2012

Tolerance to high and low temperature is an important breeding aim for Central and Northern Europ... more Tolerance to high and low temperature is an important breeding aim for Central and Northern Europe, where temperature fluctuations are predicted to increase. However, the extent to which genotypes differ in their response to the whole range of possible temperatures is not well understood. We tested the hypothesis that the combination of maize (Zea mays L.) inbred lines with differing temperature optima for root growth would lead to superior hybrids. This hypothesis is based on the concept of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;marginal overdominance&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; in which the hybrid expresses higher relative fitness than its parents, summed over all situations. The elongation rates of axile and lateral roots of the reciprocal cross between two flint and two dent inbred lines were assessed at temperatures between 15°C and 40°C. Indeed, the cross between UH005 and UH250 with lateral root growth temperature optima at 34°C and 28°C, respectively, resulted in intermediate hybrids. At temperatures below and above 31°C, the hybrids&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; root growth was comparable to the better parent, respectively, thereby increasing temperature tolerance of the hybrid compared with its parents. The implications of and reasons for this heterosis effect are discussed in the context of breeding for abiotic stress tolerance and of putatively underlying molecular mechanisms. This finding paves the way for more detailed investigations of this phenomenon in future studies.

European Journal of Agronomy, 2008

Mild chilling stress and slow soil warming are common causes for a retarded early development of ... more Mild chilling stress and slow soil warming are common causes for a retarded early development of maize (Zea mays L.). The objective of this study was to evaluate cold tolerance of a divers set of 14 inbred lines with respect to root morphology as well as the function of the photosynthetic apparatus. Plants were grown until the 2-leaf stage under

The objective of this study was to elucidate the genetic relationship between the specific leaf a... more 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 S 5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (U PSII ) at low temperature, (ii) a population of 226 F 2:3 families from the cross of ETH-DL3 · ETH-DH7, and (iii) a population of 168 F 2:4 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 S 5 inbred lines selected for high or low U PSII 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 U PSII (r = À 0.56, p < 0.05) and SPAD (r = À 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 U PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and U PSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high U PSII at low temperature leads to a constitutively altered SLA.

Genetic Resources and Crop …, 2008

Abstract About 65 years ago, more than 150 Swiss maize landraces (Zea mays L. ssp. mays) of the f... more Abstract About 65 years 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. ...

Plant and Soil, 2011

Traits related to the root length of maize (Zea mays L.), reported by 15 QTL studies of nine mapp... more 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 metaanalysis. 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.