Importance of appropriate selection environments for breeding maize adapted to organic farming systems

Organic farming systems, characterized by special attention to soil fertility, recycling techniques and low external inputs, gained increased significance in recent years. As a consequence, there is a growing demand for varieties adapted to organic and/or low input farming. The objectives of the present study were to (i) compare the testcross performance of segregating maize (Zea mays) populations under established organic (OF) and conventional farming (CF) systems, (ii) determine quantitative genetic parameters decisive for the selection response under OF vs CF conditions, and (iii) draw conclusions for breeding new varieties optimally adapted to OF. Testcross performance of four different material groups of preselected lines (90 lines per group) derived from early European breeding material was assessed under OF and CF in three different geographic regions in Germany in 2008. Grain yields under OF were 3 to 18% lower than under CF in the individual experiments depending on the test region and, to a lesser extent, on the genetic material. On average, grain dry matter yield under OF was 1077 g m-2 compared to 1186 g m-2 under CF. Phenotypic correlations between OF and CF were small or moderate for grain yield in each of the four material groups (0.22 to 0.45), while strong and highly significant correlations were found for dry matter content (0.89 to 0.94). Genotypes with top grain yields under OF often did not show this superiority under CF and vice versa. Despite considerable heterogeneity of the OF test sites, the heritability for grain yield was in the same order of magnitude under OF and CF. It is concluded that test sites managed by OF are indispensable for making maximum progress in developing maize varieties for these conditions

Methodenvergleich zur Entwicklung von optimalen Maissorten (Populations- und Hybridsorten) für den Ökologischen Landbau

Problemstellung: Der Ökologische Landbau hat in den letzten Jahren in Deutschland zugenommen. Die Versorgung mit Saatgut, das dafür geeignet ist, gewinnt deshalb verstärkt an Bedeutung. Die Ziele waren: Optimierung der Selektionsstrategie zur Entwicklung von Maissorten mit spezieller Anpassung an die Bedingungen des Ökologischen Landbaus; Entwicklung neuer Sorten (Populations- und Hybridsorten) für den Ökologischen Landbau; Erschließung genetischer Ressourcen für den Ökologischen Landbau, insbesondere aus Landsorten, die auf Low-Input-Eignung vorgeprüft wurden. Durchführung: In den Jahren 2004 bis 2006 wurde die Leistung von Testkreuzungen, Experimentalhybriden und neu entwickelten Populationssorten vergleichend unter ökologischen und konventionellen Anbaubedingungen in drei Regionen Deutschlands geprüft. Dabei wurde sowohl Elite- als auch aus Landrassen entwickeltes Zuchtmaterial getestet. Ergebnisse: Anhand zweier Sets spezifisch entwickelter Hybriden konnte gezeigt werden, daß durch gezielte Selektion eine spezifische Anpassung an die ökologische Wirtschaftsweise erreicht werden kann. Wie aufgrund ihrer Struktur erwartet, zeigten die Populationssorten eine überdurchschnittliche Anpassung an die Bedingungen des Ökologischen Landbaus. Die Testkreuzungsergebnisse von Landrassenpopulationen und –linien bestätigten, daß dieses Material eine wertvolle genetische Ressource für die Züchtung von Öko-Sorten ist

Verminderung von Alkaloiden in der Nahrungskette durch die züchterische Verbesserung der Mutterkorn-Resistenz von Winterroggen

Rye as an outcrossing crop is highly susceptible to ergot infection caused by Claviceps purpurea. It is ecologically the best solution to avoid the infection already in the field by growing resistant varieties. Aim of our study is the analysis of inheritance of self-fertile rye material for ergot resistance and alcaloid content. Sixty CMS inbred lines and their 90 CMS crosses were tested in pollen-isolated fields in three environ-ments under the conditions of Ecological Farming by artificial inoculation. The sclerotia weight per head was evaluated as resistance trait. Both, CMS lines and testcrosses showed significant genotypic differences at the individual environments. Correlation between both groups was significant (r=0,6-0,7; P=0,01). The alcaloid contents and the alcaloid spectra of 25 CMS lines revealed no genotypic difference. Breeding of self-fertile rye for a higher resistance to ergot should be successful on the long run

DNA polymorphisms and haplotype patterns of transcription factors involved in barley endosperm development are associated with key agronomic traits

<p>Abstract</p> <p>Background</p> <p>Association mapping is receiving considerable attention in plant genetics for its potential to fine map quantitative trait loci (QTL), validate candidate genes, and identify alleles of interest. In the present study association mapping in barley (<it>Hordeum vulgare </it>L.) is investigated by associating DNA polymorphisms with variation in grain quality traits, plant height, and flowering time to gain further understanding of gene functions involved in the control of these traits. We focused on the four loci <it>BLZ1</it>, <it>BLZ2</it>, <it>BPBF </it>and <it>HvGAMYB </it>that play a role in the regulation of B-hordein expression, the major fraction of the barley storage protein. The association was tested in a collection of 224 spring barley accessions using a two-stage mixed model approach.</p> <p>Results</p> <p>Within the sequenced fragments of four candidate genes we observed different levels of nucleotide diversity. The effect of selection on the candidate genes was tested by Tajima's D which revealed significant values for <it>BLZ1</it>, <it>BLZ2</it>, and <it>BPBF </it>in the subset of two-rowed barleys. Pair-wise LD estimates between the detected SNPs within each candidate gene revealed different intra-genic linkage patterns. On the basis of a more extensive examination of genomic regions surrounding the four candidate genes we found a sharp decrease of LD (<it>r</it>²<0.2 within 1 cM) in all but one flanking regions.</p> <p>Significant marker-trait associations between SNP sites within <it>BLZ1 </it>and flowering time, <it>BPBF </it>and crude protein content and <it>BPBF </it>and starch content were detected. Most haplotypes occurred at frequencies <0.05 and therefore were rejected from the association analysis. Based on haplotype information, <it>BPBF </it>was associated to crude protein content and starch content, <it>BLZ2 </it>showed association to thousand-grain weight and <it>BLZ1 </it>was found to be associated with flowering time and plant height.</p> <p>Conclusions</p> <p>Differences in nucleotide diversity and LD pattern within the candidate genes <it>BLZ1</it>, <it>BLZ2</it>, <it>BPBF</it>, and <it>HvGAMYB </it>reflect the impact of selection on the nucleotide sequence of the four candidate loci.</p> <p>Despite significant associations, the analysed candidate genes only explained a minor part of the total genetic variation although they are known to be important factors influencing the expression of seed quality traits. Therefore, we assume that grain quality as well as plant height and flowering time are influenced by many factors each contributing a small part to the expression of the phenotype. A genome-wide association analysis could provide a more comprehensive picture of loci involved in the regulation of grain quality, thousand grain weight and the other agronomic traits that were analyzed in this study. However, despite available high-throughput genotyping arrays the marker density along the barely genome is still insufficient to cover all associations in a whole genome scan. Therefore, the candidate gene-based approach will further play an important role in barley association studies.</p

High level of conservation between genes coding for the GAMYB transcription factor in barley (Hordeum vulgare L.) and bread wheat (Triticum aestivum L.) collections

The transcription factor GAMYB is involved in gibberellin signalling in cereal aleurone cells and in plant developmental processes. Nucleotide diversity of HvGAMYB and TaGAMYB was investigated in 155 barley (Hordeum vulgare) and 42 wheat (Triticum aestivum) accessions, respectively. Polymorphisms defined 18 haplotypes in the barley collection and 1, 7 and 3 haplotypes for the A, B, and D genomes of wheat, respectively. We found that (1) Hv- and TaGAMYB genes have identical structures. (2) Both genes show a high level of nucleotide identity (>95%) in the coding sequences and the distribution of polymorphisms is similar in both collections. At the protein level the functional domain is identical in both species. (3) GAMYB genes map to a syntenic position on chromosome 3. GAMYB genes are different in both collections with respect to the Tajima D statistic and linkage disequilibrium (LD). A moderate level of LD was observed in the barley collection. In wheat, LD is absolute between polymorphic sites, mostly located in the first intron, while it decays within the gene. Differences in Tajima D values might be due to a lower selection pressure on HvGAMYB, compared to its wheat orthologue. Altogether our results provide evidence that there have been only few evolutionary changes in Hv- and TaGAMYB. This confirms the close relationship between these species and also highlights the functional importance of this transcription factor

Biology, Genetics, and Management of Ergot (Claviceps spp.) in Rye, Sorghum, and Pearl Millet

Ergot is a disease of cereals and grasses caused by fungi in the genus Claviceps. Of particular concern are Claviceps purpurea in temperate regions, C. africana in sorghum (worldwide), and C. fusiformis in pearl millet (Africa, Asia). The fungi infect young, usually unfertilized ovaries, replacing the seeds by dark mycelial masses known as sclerotia. The percentage of sclerotia in marketable grain is strictly regulated in many countries. In winter rye, ergot has been known in Europe since the early Middle Ages. The alkaloids produced by the fungus severely affect the health of humans and warm-blooded animals. In sorghum and pearl millet, ergot became a problem when growers adopted hybrid technology, which increased host susceptibility. Plant traits reducing ergot infection include immediate pollination of receptive stigmas, closed flowering (cleistogamy), and physiological resistance. Genetic, nonpollen-mediated variation in ergot susceptibility could be demonstrated in all three affected cereals. Fungicides have limited efficacy and application is weather dependent. Sorting out the sclerotia from the harvest by photocells is expensive and time consuming. In conclusion, molecular-based hybrid rye breeding could improve pollen fertility by introgressing effective restorer genes thus bringing down the ergot infection level to that of conventional population cultivars. A further reduction might be feasible in the future by selecting more resistant germplasm

Experimental data confirm the importance of appropriate selection environments for breeding maize adapted to organic farming systems

Organic farming systems, characterized by special attention to soil fertility, recycling techniques and low external inputs, gained increased significance in recent years. As a consequence, there is a growing demand for varieties adapted to organic and/or low input farming. In several studies modern varieties as well as landraces have been tested for their suitability for organic farming (OF), whereas special breeding programs aiming at genotypes optimized for this farming system are scarce. Comparing the testcross performance of unselected recombinant inbred lines derived from the widely used US hybrid B73 x Mo17 under conventional (CF) and organic farming systems, Lorenzana and Bernardo (2008) concluded that high yielding maize hybrids for OF can be developed by screening under CF. In contrast, Burger et al. (2008) found moderate phenotypic between OF and CF in unselected breeding material indicating strong genotype x farming system interactions. Apparently, specific yield associated characteristics are necessary to reach maximum performance under OF and CF, respectively. Such traits include early vigour, competitiveness to weeds, and high nitrogen use efficiency under OF on the one hand, and resistance to green snapping and early root lodging under CF on the other. Thus, selection under OF conditions might be needed to fully exploit the genetic potential of maize for this management system. This is in line with previous studies demonstrating that breeding maize for improved nitrogen use efficiency was more efficient under low nitrogen levels compared to indirect selection under high nitrogen conditions (Presterl et al. 2003). But organic farming conditions are very difficult to characterize since they strongly depend on factors like crop rotation, soil fertility, organic fertilizer input, weed, pest and disease pressure, making it challenging to choose a representative selection environment. The objectives of the present study were to (i) compare the testcross performance of segregating maize populations under established organic and conventional farming (CF) systems, (ii) determine quantitative genetic parameters decisive for the selection response under OF versus CF conditions, and (iii) draw conclusions for breeding new varieties optimally adapted to OF systems