Beeinflussung von Qualitätsmerkmalen durch Pflanzenzüchtung — Möglichkeiten und Probleme

Zusammenfassung Der steigende Bedarf an Nahrungs- und Futtermitteln, vermehrt durch erhöhte Ansprüche, löste in den letzten Jahrzehnten verstärkte Bemühungen zur züchterischen Qualitätsverbesserung pflanzlicher Grundprodukte aus. Diese Entwicklung ist grundsätzlich keineswegs neu. Bereits aus den Anfängen einer bewußten Pflanzenzüchtung lassen sich dafür zahlreiche Beispiele anführen. Neu aber ist die züchterische Effizienz, mit der heute die Verbesserung von sogenannten inneren Qualitätsmerkmalen betrieben werden kann. Das beruht einerseits auf dem enormen Fortschritt der analytischen Technik, der die Durchmusterung riesiger Anzahlen von Pflanzenmustern in kurzer Zeit mit niedrigen Kosten und sehr kleinen Probenmengen (oft nur Teilen eines Samens) ermöglichte. Andererseits stellen große internationale Sammlungen im Netzwerk der Genbanken solchen Untersuchungen eine bis dahin kaum erreichbare Vielfalt an Genotypen zur Verfügung. Diese kann durch laufende Verbesserungen in der Kunst der experimentellen Mutationsauslösung zunehmend verbreitert werden. Nicht unwichtig sind für den Pflanzenzüchter in vielen Fällen neue Erkenntnisse über beteiligte stoffwechselreaktionen oder Biogeneseschritte der qualitätsbestimmenden Stoffgruppen, wenngleich hier für besser gezielte züchterische Eingriffe noch viel zu tun bleibt. Zuchtmethodisch ist neben anderen Problemen die Frage zu klären, ob der zumeist unzureichende Erfolg der z.Zt. vorwiegend verwendeten drastischen, einfach vererbten Qualitätsmutanten, wie deropaque-Mutante vom Mais oder der Hiproly-Mutante von Gerste, auf eben dieser qualitativen Natur beruht und man sich als Züchter auf lange Sicht nicht mehr auf quantitative, polygen bedingte Merkmalsänderungen stützen sollte. Unentbehrlich schließlich sind für die Qualitätszüchtung langfristig vorausbestimmte Züchtungsprioritäten, die auch noch nach Abschluß der Zuchtarbeiten, d.h. 10–15 Jahren, Gültigkeit haben und die den neuen Sorten dann einen ausreichend breiten Anbau und Markt sicherstellen. Bei den sich laufend erweiternden Erkenntnissen über den Komplex Ernährung sowie den oft rapiden marktwirtschaftlichen Fluktuationen ist diese Grundforderung einer erfolgreichen Qualitätszüchtung heute nicht immer erfüllt. Dementsprechend spielt in der landwirtschaftlichen Erzeugung nach wie vor die Quantität die überragende und die innere Qualität der erzeugten Produkte gewöhnlich nur eine untergeordnete Rolle.

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Manipulations of quality traits by plant breeding — Challenge and problems

Polyploidy, giant growth, and allometric development contributed to the improvement of nutritive quality in cultivated plants since their first origin. But only recently, rapid progress in biochemical analytical techniques, in the evaluation and induction of genetic variability, and in the understanding of underlying physiological processes, gave way to an enormous increase in intensity and efficiency in the field of breeding for quality. The specific methodology of this kind of selection, however, still lacks much essential knowledge and the same holds true for nutritional data, which are basic for the formulation of valid breeding aims.

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Vortrag, gehalten auf der gemeinsamen Tagung der Internationalen Vereinigung zur Erforschung der Qualität von Nahrungspflanzen (CIQ) und der Deutschen Gesellschaft für Qualitätsforschung (Pflanzliche Nahrungsmittel) e.V. (DGQ) in Wädenswil/Schweiz am 7. Oktober 1975.     

Soil heterogeneity at the field scale: a challenge for precision crop protection

Crop protection seldom takes into account soil heterogeneity at the field scale. Yet, variable site characteristics affect the incidence of pests as well as the efficacy and fate of pesticides in soil. This article reviews crucial starting points for incorporating soil information into precision crop protection (PCP). At present, the lack of adequate field maps is a major drawback. Conventional soil analyses are too expensive to capture soil heterogeneity at the field scale with the required spatial resolution. Therefore, we discuss alternative procedures exemplified by our own results concerning (i) minimally and non-invasive sensor techniques for the estimation of soil properties, (ii) the evidence of soil heterogeneity with respect to PCP, and (iii) current possibilities for incorporation of high resolution soil information into crop protection decisions. Soil organic carbon (SOC) and soil texture are extremely interesting for PCP. Their determination with minimally invasive techniques requires the sampling of soils, because the sensors must be used in the laboratory. However, this technique delivers precise information at low cost. We accurately determined SOC in the near-infrared. In the mid-infrared, texture and lime content were also exactly quantified. Non-invasive sensors require less effort. The airborne HyMap sensor was suitable for the detection of variability in SOC at high resolution, thus promising further progress regarding SOC data acquisition from bare soil. The apparent electrical conductivity as measured by an EM38 sensor was shown to be a suitable proxy for soil texture and layering. A survey of arable fields near Bonn (Germany) revealed widespread within-field heterogeneity of texture-related ECa, SOC and other characteristics. Maps of herbicide sorption and application rate were derived from sensor data, showing that optimal herbicide dosage is strongly governed by soil variability. A phytoassay with isoproturon confirmed the reliability of spatially varied herbicide application rates. Mapping areas with an enhanced leaching risk within fields allows them to be kept free of pesticides with related regulatory restrictions. We conclude that the use of information on soil heterogeneity within the concept of PCP is beneficial, both economically and ecologically.     

Early pathogen detection under different water status and the assessment of spray application in vineyards through the use of thermal imagery

Remote detection using thermal imagery has potential for use in the pre-symptomatic diagnosis of abiotic stress or of early disease detection. The latter is an issue of great importance since late detection of fungus attacks or poor spray coverage are major factors contributing to weak disease control affecting fruit quality or reducing yield in grapes. In greenhouse experiments the effects on spatial and temporal variability of leaf temperature of grapevine (Vitis vinifera L. cv. Riesling) leaves inoculated with a fungal pathogen (Plasmopara viticola (Berk. & Curt. Ex de Bary) were studied in either well-irrigated or non-irrigated potted plants. Due to the high sensitivity of leaf temperature to the amount of water transpired, infra-red thermography can be used to monitor irregularities in temperature at an early stage of pathogen development. Evidence for characteristic thermal responses in grapevines was apparent well before visible symptoms appeared. Contrasting thermal effects due to the pathogen attack were found between measurements on well-irrigated and water-stressed plants. Furthermore, from a technical point of view, thermal imagery has the potential to assess the evenness of spray coverage within a canopy, hence optimizing pesticide application efficiency.     

Breeding for organic agriculture: the example of winter wheat in Austria

Breeding for organic agriculture (BFOA) is a strategy for a commercial breeding company based on the exploitation of the frequently observed high correlation for many traits between conventional, low input (LI) and organic agriculture (ORG). Indirect selection under LI can be useful to roughly divide the germplasm into the genotypes better adapted to high input and those better adapted to LI or ORG conditions. BFOA is an evolving process, in which two methods are currently applied: early generations are either selected following the pedigree system under LI, or grown as bulk populations on ORG fields. In the latter case the system switches to LI after individual ear selection under ORG conditions. In both methods, the first replicated yield trial is grown parallel under ORG and LI. Subsequently, the genotypes are grouped into conventional or ORG advanced trial series. The BFOA strategy allows that the larger genetic variability of both the organic and conventional gene pool can be exploited in the selection for ORG. Hitherto, seven winter wheat varieties were released in Austria after exclusive organic VCU testing.     

Development and application of functional markers in maize

Summary Functional markers (FMs) are derived from polymorphic sites within genes causally involved in phenotypic trait variation (Andersen, J.R. & T. Lübberstedt, 2003. Trends Plant Sci 8: 554–560). FM development requires allele sequences of functionally characterized genes from which polymorphic, functional motifs affecting plant phenotype can be identified. In maize and other species with low levels of linkage disequilibrium, association studies have the potential to identify sequence motifs, such as a few nucleotides or insertions/deletions, affecting trait expression. In one of the pioneering studies, nine sequence motifs in the dwarf8 gene of maize were shown to be associated with variation for flowering time (Thornsberry, J.M., M.M. Goodman, J. Doebley, S. Kresovich, D. Nielsen & E.S. Buckler, 2001. Nat Genet 28: 286–289). Proof of sequence motif function can be obtained by comparing isogenic genotypes differing in single sequence motifs. At current, the most appropriate approach for this purpose in crops is targeting induced local lesions in genomes (TILLING) (McCallum, C.M., L. Comai, E.A. Greene & S. Henikoff, 2000. Nat Biotechnol 18: 455–457). In central Europe, maize is mainly grown as forage crop, with forage quality as major trait, which can be determined as proportion of digestible neutral detergent fiber (DNDF). Brown midrib gene knock out mutations have been shown to be beneficial for forage quality but disadvantageous for overall agronomic performance. Two brown midrib genes (bm1 and bm3) have been shown to be involved in monolignol biosynthesis. These two and additional lignin biosynthesis genes have been isolated based on sequence homology. Additional candidate genes putatively affecting forage quality have been identified by expression profiling using, e.g., isogenic bm lines. Furthermore, we identified an association between a polymorphism at the COMT locus and DNDF in a collection of European elite inbred lines.     

Characterization of Potato spindle tuber viroid (PSTVd) incidence and new variants from ornamentals

We analyzed the spreading and persistence of PSTVd variants in several ornamentals in the territory of the Czech Republic. The pool of PSTVd variants detected in Solanum jasminoides, S. muricatum, Datura sp. and Brugmansia sp. was biolistically transferred to Matricaria chamomilla, Argyranthemum frutescens and Diascia sp., species which we found as sensitive hosts for PSTVd from ornamentals. The PSTVd pool showed sequence changes and increased variation after its transfer to potato, suggesting a wide adaptation potential of PSTVd in this crop. Potato exhibited genotype-dependent leaf and spindle tuber symptoms, when inoculated with the sap from S. jasminoides infected with the predominant and sequence-stable PSTVd-S1.     

Activation of apoptosis in vivo by a hydrocarbon-stapled BH3 helix

BCL-2 family proteins constitute a critical control point for the regulation of apoptosis. Protein interaction between BCL-2 members is a prominent mechanism of control and is mediated through the amphipathic alpha-helical BH3 segment, an essential death domain. We used a chemical strategy, termed hydrocarbon stapling, to generate BH3 peptides with improved pharmacologic properties. The stapled peptides, called "stabilized alpha-helix of BCL-2 domains" (SAHBs), proved to be helical, protease-resistant, and cell-permeable molecules that bound with increased affinity to multidomain BCL-2 member pockets. A SAHB of the BH3 domain from the BID protein specifically activated the apoptotic pathway to kill leukemia cells. In addition, SAHB effectively inhibited the growth of human leukemia xenografts in vivo. Hydrocarbon stapling of native peptides may provide a useful strategy for experimental and therapeutic modulation of protein-protein interactions in many signaling pathways.     

Nuclear magnetic resonance spectroscopy and chemometrics to identify pine nuts that cause taste disturbance

Nontargeted 400 MHz (13)C and (1)H nuclear magnetic resonance (NMR) spectroscopy was used in the context of food surveillance to reveal Pinus species whose nuts cause taste disturbance following their consumption, the so-called pine nut syndrome (PNS). Using principal component analysis, three groups of pine nuts were distinguished. PNS-causing products were found in only one of the groups, which however also included some normal products. Sensory analysis was still required to confirm PNS, but NMR allowed the sorting of 53% of 57 samples, which belong to the two groups not containing PNS species. Furthermore, soft independent modeling of class analogy was able to classify the samples between the three groups. NMR spectroscopy was judged as suitable for the screening of pine nuts for PNS. This process may be advantageous as a means of importation control that will allow the identification of samples suitable for direct clearance and those that require further sensory analysis.     

Validation of a real-time PCR for the quantitative estimation of a G143A mutation in the cytochrome bc1 gene of Pyrenophora teres

A single nucleotide polymorphism (SNP) in the cytochrome b gene confers resistance to strobilurin fungicides for several fungal pathogens. Therefore, on the basis of a change at amino acid position 143 from glycine to alanine, a real-time PCR assay was established for the quantitative detection of the analogous SNP in the cytochrome b sequence of Pyrenophora teres Drechsler, which causes barley net blotch. Allelic discrimination was achieved by using allele specific primers with artificially mismatched nucleic acid bases and minor groove binding probes. Validation parameters for the lower limits of the working range, namely limits of detection (LOD) and limits of quantification (LOQ), were statistically determined by the variance of calibration data, as well as by the variance of the 100% non-strobilurin-resistant allele DNA sample (blank values). It was found that the detection was limited by the variance of blank values (five in 801 458 copies; 0.0006%), whereas the quantification was limited by the variance of calibration data (37 in 801 458 copies; 0.0046%). The real-time PCR assay was finally used to monitor strobilurin-resistant cytochrome b alleles in barley net blotch field samples, which were already classified in in vivo biotests to be fully sensitive to strobilurins. All signals for strobilurin-resistant cytochrome b alleles were below the LOD, and therefore the results are in total agreement with the phenotypes revealed by biotests.