Benjamin Wittkop

Status and perspectives of breeding for enhanced yield and quality of oilseed crops for Europe

Vegetable oils are a high-value agricultural commodity for use in refined edible oil products and as renewable industrial or fuel oils, and as the world population increases demand for high-quality seed oils continues to grow. Worldwide the oilseed market is dominated by soybean (Glycinemax), followed by oilseed rape/canola (Brassicanapus). In Europe the major oilseed crop is oilseed rape (B. napus), followed some way behind by sunflower (Helianthusannuus) and other minor crops like linseed (Linumusitatissimum) or camelina (Camelinasativa). The seed oil of these crops is characterized by a specific quality, i.e. fatty acid composition and other fat-soluble compounds: Camelina and linseed oils are characterised by high contents of linolenic acid (C18:3); in sunflower very high-oleic (up to 90% C18:1) types exist in addition to classical high-linoleic (C18:2) oilseeds; in B. napus a broad diversity of oil-types is available in addition to the modern 00 (canola) type, e.g. high-erucic acid rapeseed or high-oleic and low-linolenic cultivars. Moreover, vegetable oils contain valuable minor compounds such as tocopherols (vitamin E). Increases of such contents by breeding have lead to value-added edible oils. After oil extraction, oilseed meals—such as rapeseed extraction meal—contain a high-quality protein that can be used as a valuable animal feed. However, in comparison to soybean the meal from oilseed rape also contains relatively high amounts of anti-nutritive fibre compounds, phenolic acids, phytate and glucosinolates. Breeding efforts with respect to meal quality are therefore aimed at reduction of anti-nutritive components, while increasing the oil content, quality and yield also remains a major aim in oilseed rape breeding. This review article provides a general overview of the status of oilseed production in Europe and uses examples from winter oilseed rape to illustrate key breeding aims for sustainable and high-yielding production of high-quality vegetable oil. Emphasis is placed on analytical tools for high-throughput selection of overall seed quality.

A High-Density SNP Map for Accurate Mapping of Seed Fibre QTL in Brassica napus L

A high density genetic linkage map for the complex allotetraploid crop species Brassica napus (oilseed rape) was constructed in a late-generation recombinant inbred line (RIL) population, using genome-wide single nucleotide polymorphism (SNP) markers assayed by the Brassica 60 K Infinium BeadChip Array. The linkage map contains 9164 SNP markers covering 1832.9 cM. 1232 bins account for 7648 of the markers. A subset of 2795 SNP markers, with an average distance of 0.66 cM between adjacent markers, was applied for QTL mapping of seed colour and the cell wall fiber components acid detergent lignin (ADL), cellulose and hemicellulose. After phenotypic analyses across four different environments a total of 11 QTL were detected for seed colour and fiber traits. The high-density map considerably improved QTL resolution compared to the previous low-density maps. A previously identified major QTL with very high effects on seed colour and ADL was pinpointed to a narrow genome interval on chromosome A09, while a minor QTL explaining 8.1% to 14.1% of variation for ADL was detected on chromosome C05. Five and three QTL accounting for 4.7% to 21.9% and 7.3% to 16.9% of the phenotypic variation for cellulose and hemicellulose, respectively, were also detected. To our knowledge this is the first description of QTL for seed cellulose and hemicellulose in B. napus, representing interesting new targets for improving oil content. The high density SNP genetic map enables navigation from interesting B. napus QTL to Brassica genome sequences, giving useful new information for understanding the genetics of key seed quality traits in rapeseed.

Identification of QTLs for phenolic compounds in oilseed rape (Brassica napus L.) by association mapping using SSR markers

Association mapping identifies quantitative trait loci (QTLs) by examining the marker-trait associations that can be attributed to the strength of linkage disequilibrium between markers and functional polymorphisms across a set of diverse germplasm. In this study, association mapping was performed to detect QTL-linked and genome wide SSR markers linked to phenolic compounds of extraction meal in a population of 49 genetically diverse oilseed rape cultivars of dark-seeded, winter-type oilseed rape accessions. Correction for population structure was performed using 559 genome wide SSR markers. Results showed that seed colour is an important contributor to seed meal quality. Totally, 52 SSR markers linked to phenolic compounds were detected, five of them being QTL linked markers. Some of these markers were already mapped on Brassica napus chromosomes that contain known QTL controlling oilseed rape meal quality traits. Our results demonstrate that association mapping is a useful approach to complement and enhance previous QTL information for marker-assisted selection.

Regional association analysis delineates a sequenced chromosome region influencing antinutritive seed meal compounds in oilseed rape.

This study describes the use of regional association analyses to delineate a sequenced region of a Brassica napus chromosome with a significant effect on antinutritive seed meal compounds in oilseed rape. A major quantitative trait locus (QTL) influencing seed colour, fibre content, and phenolic compounds was mapped to the same position on B. napus chromosome A9 in biparental mapping populations from two different yellow-seeded × black-seeded B. napus crosses. Sequences of markers spanning the QTL region identified synteny to a sequence contig from the corresponding chromosome A9 in Brassica rapa. Remapping of sequence-derived markers originating from the B. rapa sequence contig confirmed their position within the QTL. One of these markers also mapped to a seed colour and fibre QTL on the same chromosome in a black-seeded × black-seeded B. napus cross. Consequently, regional association analysis was performed in a genetically diverse panel of dark-seeded, winter-type oilseed rape accessions. For this we used closely spaced simple sequence repeat (SSR) markers spanning the sequence contig covering the QTL region. Correction for population structure was performed using a set of genome-wide SSR markers. The identification of QTL-derived markers with significant associations to seed colour, fibre content, and phenolic compounds in the association panel enabled the identification of positional and functional candidate genes for B. napus seed meal quality within a small segment of the B. rapa genome sequence.

Seedling development in a Brassica napus diversity set and its relationship to agronomic performance

Brassica napus L. is the leading European oilseed crop and has therefore a high economical importance. The objectives of our study were to examine (1) the patterns of phenotypic diversity in a species-wide B. napus germplasm set of 518 inbreds with respect to various seedling development, agronomic, and seed quality traits as well as (2) the interrelationship of the examined traits and their use in selection on correlated traits. The B. napus germplasm set was evaluated in greenhouse and field trials for several seedling development, agronomic, and seed quality traits. The traits were highly correlated within the individual trait categories and moderately correlated between the different trait categories. We observed differences in phenotypic diversity among the examined eight germplasm types. The reduction of phenotypic diversity was on average more pronounced for the seedling development traits than for the agronomic and seed quality traits, suggesting that plant breeders need to introgress new genetic variation with respect to the former.

New NIRS Calibrations for Fiber Fractions Reveal Broad Genetic Variation in Brassica napus Seed Quality

Near-infrared reflectance spectroscopy (NIRS) calibrations were developed for the estimation of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) in intact seeds of oilseed rape ( Brassica napus ). A set of 338 diverse winter oilseed rape genotypes showing broad variation for seed color was used as a basis for the new calibrations. Different calibrations were generated for 10 or 1 mL seed volumes, respectively. In both seed volumes good coefficients of determination for external validation (R(2)) of the calibrations were obtained for ADL, the major antinutritional fiber fraction in oilseed rape meal, and adequate calibrations for NDF and ADF. Evaluation of diverse B. napus germplasm with the new calibrations revealed a surprisingly broad variation in contents of ADL in dark-seeded oilseed rape. The ability to use NIRS for efficient selection of low-fiber genotypes, irrespective of seed color, represents an important breakthrough in breeding for improved nutritional quality of seed extraction meals from oilseed rape.

Agronomic and Seed Quality Traits Dissected by Genome-Wide Association Mapping in Brassica napus.

In Brassica napus breeding, traits related to commercial success are of highest importance for plant breeders. However, such traits can only be assessed in an advanced developmental stage. Molecular markers genetically linked to such traits have the potential to accelerate the breeding process of B. napus by marker-assisted selection. Therefore, the objectives of this study were to identify (i) genome regions associated with the examined agronomic and seed quality traits, (ii) the interrelationship of population structure and the detected associations, and (iii) candidate genes for the revealed associations. The diversity set used in this study consisted of 405 B. napus inbred lines which were genotyped using a 6K single nucleotide polymorphism (SNP) array and phenotyped for agronomic and seed quality traits in field trials. In a genome-wide association study, we detected a total of 112 associations between SNPs and the seed quality traits as well as 46 SNP-trait associations for the agronomic traits with a P < 1.28e-05 (Bonferroni correction of α = 0.05) for the inbreds of the spring and winter trial. For the seed quality traits, a single SNP-sulfur concentration in seeds (SUL) association explained up to 67.3% of the phenotypic variance, whereas for the agronomic traits, a single SNP-blossom color (BLC) association explained up to 30.2% of the phenotypic variance. In a basic local alignment search tool (BLAST) search within a distance of 2.5 Mbp around these SNP-trait associations, 62 hits of potential candidate genes with a BLAST-score of ≥100 and a sequence identity of ≥70% to A. thaliana or B. rapa could be found for the agronomic SNP-trait associations and 187 hits of potential candidate genes for the seed quality SNP-trait associations.

Complementary diversity for nitrogen uptake and utilisation efficiency reveals broad potential for increased sustainability of oilseed rape production

AimsNitrogen use efficiency (NUE) has become a major global megatrend for sustainable agricultural production, particularly in association with the reduced release of nitrogen-derived greenhouse gases from soils and nitrate contamination of waterways. Oilseed rape (Brassica napus L.), the second most important oilseed crop worldwide, requires relatively high N fertilisation but releases an N balance surplus after harvest. The use of genetic variation to breed more efficient varieties is a promising option to improve agricultural sustainability.MethodsWe assessed 30 diverse winter oilseed rape accessions at contrasting nitrogen fertilisation levels for 33 physiological traits associated with N uptake and utilisation efficiency. Relationships among traits across the diversity panel were used to identify key complementary factors contributing to overall NUE.ResultsTrait correlations revealed considerable variation for NUE parameters, including positive effects of early flowering and high leaf N concentration on enhanced N utilisation under low N input. Furthermore, seed yield per se was found to be more important than the seed N concentration for simultaneously achieving both high N utilisation and reduced N balance surplus.ConclusionIndependent inheritance of N uptake and N utilisation traits suggests potential for further improvement of NUE in oilseed rape by targeted combination of contributing factors in new, high-yielding varieties.

The MADS Box Genes ABS, SHP1, and SHP2 Are Essential for the Coordination of Cell Divisions in Ovule and Seed Coat Development and for Endosperm Formation in Arabidopsis thaliana.

Seed formation is a pivotal process in plant reproduction and dispersal. It begins with megagametophyte development in the ovule, followed by fertilization and subsequently coordinated development of embryo, endosperm, and maternal seed coat. Two closely related MADS-box genes, SHATTERPROOF 1 and 2 (SHP1 and SHP2) are involved in specifying ovule integument identity in Arabidopsis thaliana. The MADS box gene ARABIDOPSIS BSISTER (ABS or TT16) is required, together with SEEDSTICK (STK) for the formation of endothelium, part of the seed coat and innermost tissue layer formed by the maternal plant. Little is known about the genetic interaction of SHP1 and SHP2 with ABS and the coordination of endosperm and seed coat development. In this work, mutant and expression analysis shed light on this aspect of concerted development. Triple tt16 shp1 shp2 mutants produce malformed seedlings, seed coat formation defects, fewer seeds, and mucilage reduction. While shp1 shp2 mutants fail to coordinate the timely development of ovules, tt16 mutants show less peripheral endosperm after fertilization. Failure in coordinated division of the innermost integument layer in early ovule stages leads to inner seed coat defects in tt16 and tt16 shp1 shp2 triple mutant seeds. An antagonistic action of ABS and SHP1/SHP2 is observed in inner seed coat layer formation. Expression analysis also indicates that ABS represses SHP1, SHP2, and FRUITFUL expression. Our work shows that the evolutionary conserved Bsister genes are required not only for endothelium but also for endosperm development and genetically interact with SHP1 and SHP2 in a partially antagonistic manner.

Recent Genetic Gains in Nitrogen Use Efficiency in Oilseed Rape

Nitrogen is essential for plant growth, and N fertilization allows farmers to obtain high yields and produce sufficient agricultural commodities. On the other hand, nitrogen losses potentially cause adverse effects to ecosystems and to human health. Increasing nitrogen use efficiency (NUE) is vital to solve the conflict between productivity, to secure the demand of a growing world population, and the protection of the environment. To ensure this, genetic improvement is considered to be a paramount aspect toward ecofriendly crop production. Winter oilseed rape (Brassica napus L.) is the second most important oilseed crop in the world and is cultivated in many regions across the temperate zones. To our knowledge, this study reports the most comprehensive field-based data generated to date for an empirical evaluation of genetic improvement in winter oilseed rape varieties under two divergent nitrogen fertilization levels (NFLs). A collection of 30 elite varieties registered between 1989 and 2014, including hybrids and open pollinated varieties, was tested in a 2-year experiment in 10 environments across Germany for changes in seed yield and seed quality traits. Furthermore, NUE was calculated. We observed a highly significant genetics-driven increase in seed yield per-se and, thus, increased NUE at both NFLs. On average, seed yield from modern open-pollinated varieties and modern hybrids was higher than from old open-pollinated varieties and old hybrids. The annual yield progress across all tested varieties was ~35 kg ha−1 year−1 at low nitrogen and 45 kg ha−1 year−1 under high nitrogen fertilization. Furthermore, in modern varieties an increased oil concentration and decreased protein concentration was observed. Despite, the significant effects of nitrogen fertilization, a surprisingly low average seed yield gap of 180 kg N ha−1 was noted between high and low nitrogen fertilization. Due to contrary effects of N fertilization on seed yield per-se and seed oil concentration an oil yield of 2.04 t ha−1 was measured at both N levels. Collectively, the data reveal that genetic improvement through modern breeding techniques in conjunction with reduced N fertilizer inputs has a tremendous potential to increase NUE of oilseed rape.