Markus Liedgens

QTLs for the elongation of axile and lateral roots of maize in response to low water potential.

Changes in root architecture and the maintenance of root growth in drying soil are key traits for the adaptation of maize (Zea mays L.) to drought environments. The goal of this study was to map quantitative trait loci (QTLs) for root growth and its response to dehydration in a population of 208 recombinant inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). The parents, Ac7643 and Ac7729/TZSRW, are known to be drought-tolerant and drought-sensitive, respectively. Roots were grown in pouches under well-watered conditions or at low water potential induced by the osmolyte polyethylene glycol (PEG 8000). Axile root length (LAx) increased linearly, while lateral root length (LLat) increased exponentially over time. Thirteen QTLs were identified for six seedling traits: elongation rates of axile roots (ERAx), the rate constant of lateral root elongation (kLat), the final respective lengths (LAx and LLat), and the ratios kLat/ERAx and LLat/LAx. While QTLs for lateral root traits were constitutively expressed, most QTLs for axile root traits responded to water stress. For axile roots, common QTLs existed for ERAx and LAx. Quantitative trait loci for the elongation rates of axile roots responded more clearly to water stress compared to root length. Two major QTLs were detected: a QTL for general vigor in bin 2.02, affecting most of the traits, and a QTL for the constitutive increase in kLat and kLat/ERAx in bins 6.04–6.05. The latter co-located with a major QTL for the anthesis-silking interval (ASI) reported in published field experiments, suggesting an involvement of root morphology in drought tolerance. Rapid seedling tests are feasible for elucidating the genetic response of root growth to low water potential. Some loci may even have pleiotropic effects on yield-related traits under drought stress.

Leaching and utilization of nitrogen during a spring wheat catch crop succession.

An experiment covering a 2-yr spring wheat (Triticum aestivum L.) catch crop succession was conducted in lysimeters to account for the losses of N due to leaching. We sought to relate these losses to the N uptake of the main crop and to integrate the estimated N loss and uptake into a balance. The non-winter hardy catch crops [yellow mustard (Sinapis alba L.), Phacelia (Phacelia tanacetifolia Benth), and sunflower (Helianthus annuus L.)] as well as bare soil fallow were studied at low and high N input levels of 4 and 29 g N m(-2) yr(-1), respectively. Catch crops allowed for an effective reduction of N leaching of 0.33 to 1.67 g N m(-2) yr(-1) compared to fallow. Reductions in N leaching were achieved mainly by avoiding the fallow period during autumn and winter while the catch crop species grown had little impact. During the spring wheat growing season, N leaching losses were highest after yellow mustard, the most effective catch crop for the entire crop succession. A balance of N indicated that the reductions in N leaching exerted by the catch crops did not result in a higher overall utilization of N by spring wheat. Thus, the efficacy shown by catch crops in reducing N leaching during growth is relatively lower when considering the entire crop succession. In addition, the N saved by growing catch crops does not increase N utilization by succeeding spring wheat.

Root Growth and Nitrate-Nitrogen Leaching of Catch Crops following Spring Wheat

Growing nitrogen (N) catch crops can reduce NO(3)-N leaching after cultivating cereals. The objective of this study was to relate NO(3)-N leaching to variation in the uptake of N and the size and distribution of the root systems of different catch crops species. In a 3-yr lysimeter experiment, phacelia (Phacelia tanacetifolia Benth.), sunflower (Helianthus annuus L.), and a Brassica species (yellow mustard [Brassica alba L.] or a hybrid of turnip rape [B. rapa L. spp. oleifera (DC.) Metzg.] and Chinese cabbage [B. rapa L. ssp. chinensis (L.) Hanelt]) were grown after the harvest of spring wheat under two levels of N supply. Bare soil lysimeters served as the control. Water percolation from the lysimeters and the NO(3)(-) concentration in the leachate were measured weekly from the sowing until the presumed frost-kill of the catch crops. Minirhizotrons were used to assess the spatial and temporal patterns of root growth from 0.10 to 1.00 m. The catch crop species differed in their shoot biomass, N uptake, total NO(3)-N leaching, and root growth. The results suggested that there was no strict relationship between the total NO(3)-N leaching of each catch crop species and the N uptake or parameters that indicate static characteristics of the root system. In contrast, the ranking of each catch crop species by parameters that indicate early root growth was inversely related to the ranking of each catch crop species in NO(3)-N leaching. The rapid establishment of the root system is essential for a catch crop following spring wheat to reduce the amount of NO(3)-N leaching after the harvest of spring wheat.

SUBSOIL ROOT GROWTH OF FIELD GROWN SPRING WHEAT GENOTYPES (TRITICUM AESTIVUM L.) DIFFERING IN NITROGEN USE EFFICIENCY PARAMETERS

In a two-year (1999–2000) field experiment four Swiss spring wheat (Triticum aestivum L.) genotypes (cvs. ‘Albis’, ‘Toronit’ and ‘Pizol’ and an experimental line ‘L94491’) were compared for genotypic differences in the root parameters that determine uptake potential and nitrogen use efficiency (NUE):root surface area (RSA) and its components, root length density (RLD) and the diameter of the roots. The genotypes were grown under no (N0) and under ample fertilizer nitrogen (N) [ammonium nitrate (NH4NO3); N1; 250 kg N ha−1] supply. Root samples were taken from all the genotypes at anthesis from the subsoil (30–60 cm). Genotypic effects on RLD and RSA were evident only in 2000 and large amounts of N fertilizer usually diminished root growth. Adequate soil moisture in 1999 may have favored the establishment of the root system of all the genotypes before anthesis. Parameters of NUE for each genotype were also determined at anthesis and at physiological maturity. ‘Albis’ the least efficient cv. in recovering fertilizer N (ranged from 36.5 to 61.1%) with the lowest N uptake efficiency (0.47 to 0.79 kg kg−1) had the lowest RLD and RSA in both seasons. Among genotypes ‘Toronit’, a high-yielding cv., efficient in recovering fertilizer N, exhibited the higher NUE (22.4 to 29.3 kg kg−1) and tended to have the highest values of RLD and RSA. Nitrogen fertilization also led to an increase in the proportion of roots with diameters less than 300 μm and decreased the proportion of roots with diameters of 300 to 700 μm. These trends were more pronounced for cv. ‘Pizol’ in 1999 and for cv. ‘Toronit’ in 1999 and 2000. By anthesis in a humid temperate climate, there are no marked differences in the subsoil root growth of the examined genotypes. Some peculiarities on the root growth characteristics of the cultivars ‘Albis’ and ‘Toronit’ may partially explain their different NUE performance.

Performance of Winter Wheat Varieties in White Clover Living Mulch

ABSTRACT The choice of variety for agricultural systems with multiple crops may differ from the one used in sole crop because of the changes in environmental conditions brought about by interspecific plant competition. Information about varietal performance under living mulch conditions as well as the suitability of the results of the official variety testing, conducted under conventional cropping conditions, for such systems is lacking for small grain cereals such as winter wheat (Triticum aestivum L.). In the current study, nine different winter wheat varieties were established in an existing living mulch of white clover (Trifolium repens L.) in three trials in the Swiss Midlands in the years 2003 and 2004. The winter wheat was directly sown in widely spaced rows (0.375 m) at a density of 450 viable grains m−2. Grain yield varied between 1.83 and 4.11 Mg ha−1. Plant height was correlated (r = 0.92, p < 0.001) with the grain yield, suggesting that varieties with long shoots may have an advantage because of the more intense shading of the white clover plants. However, the best yielding varieties were also those with the most intense tillering. Recorded values of grain quality traits (grain weight, test weight and protein content) for the tested varieties were analogous under the living mulch conditions of the current trials to those obtained in the official variety testing. This analogy was not observed for the grain yield, except for one trial, where the competitive strength of the white clover was reduced by mechanical interference prior to the seeding of the wheat, which positively affected tillering and hence grain yield. Thus, the use of better yielding varieties of winter wheat in living mulches is at the cost of decreased grain quality. The combination of yield and quality goals in living mulch systems will rather depend on the minimization of the competition of the cover crop on the wheat plants than on the variety choice following recommendations based on trials conducted under conventional cropping conditions.

Dynamics of Root Development of Spring Wheat Genotypes Varying in Nitrogen Use Efficiency

Three spring wheat genotypes (cv. Albis and Toronit and the experimental line L94491) identified to vary in nitrogen use efficiency characteristics, were studied in lysimeters under two levels of N supply (0 and 250 Kg N ha-1) in 1999 and 2000. No. of roots cm-2 were obtained from regular minirhizotron observations at soil depths of 0.10, 0.25, 0.45, 0.80 and 1.00 m and fitted to a logistic equation. The parameters of the logistic model were influenced by all study factors, indicating a high plasticity of the root system of spring wheat to respond to different soil conditions. A single main genotype effect was observed among all tested factors: the asymptotic no. of roots cm-2 was significantly higher for Toronit than Albis and especially L94491 in the topsoil (0.10 and 0.30 m). Contrastingly, the N supply modified the asymptotic growth in 1999 at 0.10 m and in both years at 0.25 m as well as the root growth pattern at 0.80 in 1999 and at 0.10 m and 0.25 m soil depth in both years