Genetic mapping of some key plant architecture traits in Brassica juncea using a doubled haploid population derived from a cross between two distinct lines: vegetable type Tumida and oleiferous Varuna.

KEY MESSAGE: Genetic mapping of some key plant architectural traits in a vegetable type and an oleiferous B. juncea cross revealed QTL and candidate genes for breeding more productive ideotypes. Brassica juncea (AABB, 2n = 36), commonly called mustard, is an allopolyploid crop of recent origin but contains considerable morphological and genetic variation. An F1-derived doubled haploid population developed from a cross between an Indian oleiferous line, Varuna, and a Chinese stem type vegetable mustard, Tumida showed significant variability for some key plant architectural traits-four stem strength-related traits, stem diameter (Dia), plant height (Plht), branch initiation height (Bih), number of primary branches (Pbr), and days to flowering (Df). Multi-environment QTL analysis identified twenty Stable QTL for the above-mentioned nine plant architectural traits. Though Tumida is ill-adapted to the Indian growing conditions, it was found to contribute favorable alleles in Stable QTL for five architectural traits-press force, Dia, Plht, Bih, and Pbr; these QTL could be used to breed superior ideotypes in the oleiferous mustard lines. A QTL cluster on LG A10 contained Stable QTL for seven architectural traits that included major QTL (phenotypic variance ≥ 10%) for Df and Pbr, with Tumida contributing the trait-enhancing alleles for both. Since early flowering is critical for the cultivation of mustard in the Indian subcontinent, this QTL cannot be used for the improvement of Pbr in the Indian gene pool lines. Conditional QTL analysis for Pbr, however, identified other QTL which could be used for the improvement of Pbr without affecting Df. The Stable QTL intervals were mapped on the genome assemblies of Tumida and Varuna for the identification of candidate genes.

Map-based cloning and promoter variation analysis of the lobed leaf gene BoLMI1a in ornamental kale (Brassica oleracea L. var. acephala).

BACKGROUND: Leaf shape is an important agronomic trait in ornamental kale (Brassica oleracea L. var. acephala). Although some leaf shape-related genes have been reported in ornamental kale, the detailed mechanism underlying leaf shape formation is still unclear. Here, we report a lobed-leaf trait in ornamental kale, aiming to analyze its inheritance and identify the strong candidate gene. RESULTS: Genetic analysis of F2 and BC1 populations demonstrate that the lobed-leaf trait in ornamental kale is controlled by a single dominant gene, termed BoLl-1 (Brassica oleracea lobed-leaf). By performing whole-genome resequencing and linkage analyses, the BoLl-1 gene was finely mapped to a 127-kb interval on chromosome C09 flanked by SNP markers SL4 and SL6, with genetic distances of 0.6 cM and 0.6 cM, respectively. Based on annotations of the genes within this interval, Bo9g181710, an orthologous gene of LATE MERISTEM IDENTITY 1 (LMI1) in Arabidopsis, was predicted as the candidate for BoLl-1, and was renamed BoLMI1a. The expression level of BoLMI1a in lobed-leaf parent 18Q2513 was significantly higher compared with unlobed-leaf parent 18Q2515. Sequence analysis of the parental alleles revealed no sequence variations in the coding sequence of BoLMI1a, whereas a 1737-bp deletion, a 92-bp insertion and an SNP were identified within the BoLMI1a promoter region of parent 18Q2513. Verification analyses with BoLMI1a-specific markers corresponding to the promoter variations revealed that the variations were present only in the lobed-leaf ornamental kale inbred lines. CONCLUSIONS: This study identified a lobed-leaf gene BoLMI1a, which was fine-mapped to a 127-kb fragment. Three variations were identified in the promoter region of BoLMI1a. The transcription level of BoLMI1a between the two parents exhibited great difference, providing new insight into the molecular mechanism underlying leaf shape formation in ornamental kale.

Pigment variation and transcriptional response of the pigment synthesis pathway in the S2309 triple-color ornamental kale (Brassica oleracea L. var. acephala) line.

Ornamental kale is popular because of its colorful leaves and few studies have investigated the mechanism of color changes. In this study, an ornamental kale line (S2309) with three leaf colors was developed. Analysis of the anthocyanin, chlorophyll, and carotenoid contents and RNA-seq were performed on the three leaf color types. There was less chlorophyll in the white leaves and purple leaves than in the green leaves, and the anthocyanin content was greatest in the purple leaves. All the downregulated DEGs related to chlorophyll metabolism were detected only in the S2309_G vs. S2309_W comparison, which indicated that the decrease in chlorophyll content was caused mainly by the inhibition of chlorophyll biosynthesis during the leaf color change from green to white. Moreover, the expression of 19 DEGs involved in the anthocyanin biosynthesis pathway was upregulated. These results provide new insight into the mechanisms underlying the three-color formation.

Quantitative Analysis of UV-B Radiation Interception in 3D Plant Structures and Intraindividual Distribution of Phenolic Contents.

Ultraviolet-B (UV-B) acts as a regulatory stimulus, inducing the dose-dependent biosynthesis of phenolic compounds such as flavonoids at the leaf level. However, the heterogeneity of biosynthesis activation generated within a whole plant is not fully understood until now and cannot be interpreted without quantification of UV-B radiation interception. In this study, we analyzed the spatial UV-B radiation interception of kales (Brassica oleracea L. var. Acephala) grown under supplemental UV-B LED using ray-tracing simulation with 3-dimension-scanned models and leaf optical properties. The UV-B-induced phenolic compounds and flavonoids accumulated more, with higher UV-B interception and younger leaves. To distinguish the effects of UV-B energy and leaf developmental age, the contents were regressed separately and simultaneously. The effect of intercepted UV-B on flavonoid content was 4.9-fold that of leaf age, but the effects on phenolic compound biosynthesis were similar. This study confirmed the feasibility and relevance of UV-B radiation interception analysis and paves the way to explore the physical and physiological base determining the intraindividual distribution of phenolic compound in controlled environments.

Map-based cloning and characterization of BoCCD4, a gene responsible for white/yellow petal color in B. oleracea.

BACKGROUND: Brassica oleracea exhibits extensive phenotypic diversity. As an important trait, petal color varies among different B. oleracea cultivars, enabling the study of the genetic basis of this trait. In a previous study, the gene responsible for petal color in B. oleracea was mapped to a 503-kb region on chromosome 3, but the candidate gene has not yet been identified. RESULTS: In the present study, we report that the candidate gene was further delineated to a 207-kb fragment. BoCCD4, a homolog of the Arabidopsis carotenoid cleavage dioxygenase 4 (CCD4) gene, was selected for evaluation as the candidate gene. Sequence analysis of the YL-1 inbred line revealed three insertions/deletions and 34 single-nucleotide polymorphisms in the coding region of BoCCD4. Functional complementation showed that BoCCD4 from the white-petal inbred line 11-192 can rescue the yellow-petal trait of YL-1. Expression analysis revealed that BoCCD4 is exclusively expressed in petal tissue of white-petal plants, and phylogenetic analysis indicated that CCD4 homologs may share evolutionarily conserved roles in carotenoid metabolism. These findings demonstrate that BoCCD4 is responsible for white/yellow petal color variation in B. oleracea. CONCLUSIONS: This study demonstrated that function loss of BoCCD4, a homolog of Arabidopsis CCD4, is responsible for yellow petal color in B. oleracea.

Molecular analysis of anthocyanin biosynthesis-related genes reveal BoTT8 associated with purple hypocotyl of broccoli (Brassica oleracea var. italica L.).

Broccoli (Brassica oleracea var. italica L.) is a highly nutritious vegetable that typically forms pure green or purple florets. However, green broccoli florets sometimes accumulate slight purplish pigmentation in response environmental factors, decreasing their market value. In the present study, we aimed to develop molecular markers to distinguish broccoli genotypes as pure green or purplish floret color at the early seedling stage. Anthocyanins are known to be involved in the purple pigmentation in plants. The purplish broccoli lines were shown to accumulate purple pigmentation in the hypocotyls of very young seedlings; therefore, the expression profiles of the structural and regulatory genes of anthocyanin biosynthesis were analyzed in the hypocotyls using qRT-PCR. BoPAL, BoDFR, BoMYB114, BoTT8, BoMYC1.1, BoMYC1.2, and BoTTG1 were identified as putative candidate genes responsible for the purple hypocotyl color. BoTT8 was much more highly expressed in the purple than green hypocotyls; therefore, it was cloned and sequenced from various broccoli lines, revealing SNP and InDel variations between these genotypes. We tested four SNPs (G > A; A > T; G > C; T > G) in the first three exons and a 14-bp InDel (ATATTTATATATAT) in the BoTT8 promoter in 51 broccoli genotypes, and we found these genetic variations could distinguish the green lines, purple lines, and F1 hybrids. These novel molecular markers could be useful in broccoli breeding programs to develop a true green or purple broccoli cultivar.

Selenium alleviated chromium stress in Chinese cabbage (Brassica campestris L. ssp. Pekinensis) by regulating root morphology and metal element uptake.

Excessive chromium (Cr) causes toxicity to plants, while the beneficial effects of selenium (Se) have been verified in plants under various adverse conditions. Under Cr stress, the impacts of exogenous Se on root morphology and metal element uptake were investigated in root of Chinese cabbage by cellular and biochemical approaches. Exogenous Se alleviated Cr-induced irreversible damage to root morphology, plasma membrane integrity and ultrastructure of root tip cells. Compared with Cr treatment alone, exogenous Se reduced root Cr content by 17%. Se supply changed the subcellular distribution of Cr in root, and the concentration of Cr was reduced in the fractions of plastids and mitochondria, while increased in soluble fraction. Besides, exogenous Se counteracted the nutrient elements (Na, Ca, Fe, Mn, Cu and Zn) loss induced by Cr. For plant with Se pretreatment, the increase rate of Cr influx was lower than that of plant without Se pretreatment, particularly in solution containing high concentration (100-400 µmol L-1) of Cr. In addition, higher Km value was observed in plant with Se pretreatment, which indicated a lower Cr affinity than that of plant without Se pretreatment. The results suggest that Se modified root morphology and regulated nutrient elements uptake by root, which might play a combined role in reducing Cr uptake by root, consequently alleviating Cr stress and maintaining plant growth.

Interspecific Differences in the Larval Performance of Pieris Butterflies (Lepidoptera: Pieridae) Are Associated with Differences in the Glucosinolate Profiles of Host Plants.

The tremendous diversity of plants and herbivores has arisen from a coevolutionary relationship characterized by plant defense and herbivore counter adaptation. Pierid butterfly species feed on Brassicales plants that produce glucosinolates as a chemical deterrent against herbivory. In turn, the larvae of pierids have nitrile specifier proteins (NSPs) that are expressed in their gut and disarm glucosinolates. Pierid butterflies are known to have diversified in response to glucosinolate diversification in Brassicales. Therefore, each pierid species is expected to have a spectrum of host plants characterized by specific glucosinolate profiles. In this study, we tested whether the larval performance of different Pieris species, a genus in Pieridae (Lepidoptera: Pieridae), was associated with plant defense traits of putative host plants. We conducted feeding assays using larvae of three Pieris species and 10 species of the Brassicaceae family possessing different leaf physical traits and glucosinolate profile measurements. The larvae of Pieris rapae responded differently in the feeding assays compared with the other two Pieris species. This difference was associated with differences in glucosinolate profiles but not with variations in physical traits of the host plants. This result suggests that individual Pieris species are adapted to a subset of glucosinolate profiles within the Brassicaceae. Our results support the idea that the host ranges of Pieris species depend on larval responses to glucosinolate diversification in the host species, supporting the hypothesis of coevolution between butterflies and host plants mediated by the chemical arms race.

Lipidomic study reveals the effect of morphological variation and other metabolite interactions on the lipid composition in various cultivars of Bok choy.

Bok choy is an important Brassica vegetable which is also known for its wide range of cultivars that differ in their appearance, leaf color, size and shape. For the purpose to investigate the effect of these phenotypic differences on their lipid composition, seven morphotypes of NHCC (Suzhouqing, Aijaohuang, Wutacai, Yellowrose, Ziluolan, Xiangqingcai and Zicaitai) were selected for this study. For this reason, extensive metabolic approach was adopted which was mainly focused on lipidomics. The overall metabolic position of lipids was determined and the isolated lipid compounds were characterized on the basis of their lipid classes. Moreover, discriminative analysis was applied to monitor the distribution pattern of lipid in different cultivars. Aijiaohuang was the leading cultivar which contained highest lipid levels, whereas least proportion was found in Zicaitai. We proposed that leaf color might have an effect on the lipid composition such as purple cultivars were dominated in glycerophopholipids, light green in fatty acids and dark green were rich in glycerolipids. The level of metabolites differed greatly among different genotypes. Lipid-metabolite interactions revealed the positive correlation of lipids with flavonoid and hydroxycinnamoyl derivatives, whereas negative correlation was noticed in case of phenylamines. This is the first comprehensive study based on lipidomics in order to evaluate the substantial impact of various phenotypes on the metabolic composition of NHCC.

Immunity at Cauliflower Hydathodes Controls Systemic Infection by Xanthomonas campestris pv campestris.

Hydathodes are water pores found on leaves of a wide range of vascular plants and are the sites of guttation. We report here on the detailed anatomy of cauliflower (Brassicaoleracea) and Arabidopsis (Arabidopsis thaliana) hydathodes. Hydathode surface presents pores resembling stomata giving access to large cavities. Beneath, the epithem is composed of a lacunar and highly vascularized parenchyma offering a direct connection between leaf surface and xylem vessels. Arabidopsis hydathode pores were responsive to ABA and light similar to stomata. The flg22 flagellin peptide, a well-characterized elicitor of plant basal immunity, did not induce closure of hydathode pores in contrast to stomata. Because hydathodes are natural infection routes for several pathogens, we investigated hydathode infection by the adapted vascular phytopathogenic bacterium Xanthomonas campestris pv campestris (Xcc), the causal agent of black rot disease of Brassicaceae. Microscopic observations of hydathodes six days postinoculation indicated a digestion of the epithem cells and a high bacterial multiplication. Postinvasive immunity was shown to limit pathogen growth in the epithem and is actively suppressed by the type III secretion system and its effector proteins. Altogether, these results give a detailed anatomic description of Brassicaceae hydathodes and highlight the efficient use of this tissue as an initial niche for subsequent vascular systemic dissemination of Xcc in distant plant tissues.

Polyploidy and the relationship between leaf structure and function: implications for correlated evolution of anatomy, morphology, and physiology in Brassica.

BACKGROUND: Polyploidy is well studied from a genetic and genomic perspective, but the morphological, anatomical, and physiological consequences of polyploidy remain relatively uncharacterized. Whether these potential changes bear on functional integration or are idiosyncratic remains an open question. Repeated allotetraploid events and multiple genomic combinations as well as overlapping targets of artificial selection make the Brassica triangle an excellent system for exploring variation in the connection between plant structure (anatomy and morphology) and function (physiology). We examine phenotypic integration among structural aspects of leaves including external morphology and internal anatomy with leaf-level physiology among several species of Brassica. We compare diploid and allotetraploid species to ascertain patterns of phenotypic correlations among structural and functional traits and test the hypothesis that allotetraploidy results in trait disintegration allowing for transgressive phenotypes and additional evolutionary and crop improvement potential. RESULTS: Among six Brassica species, we found significant effects of species and ploidy level for morphological, anatomical and physiological traits. We identified three suites of intercorrelated traits in both diploid parents and allotetraploids: Morphological traits (such as leaf area and perimeter) anatomic traits (including ab- and ad- axial epidermis) and aspects of physiology. In general, there were more correlations between structural and functional traits for allotetraploid hybrids than diploid parents. Parents and hybrids did not have any significant structure-function correlations in common. Of particular note, there were no significant correlations between morphological structure and physiological function in the diploid parents. Increased phenotypic integration in the allotetraploid hybrids may be due, in part, to increased trait ranges or simply different structure-function relationships. CONCLUSIONS: Genomic and chromosomal instability in early generation allotetraploids may allow Brassica species to explore new trait space and potentially reach higher adaptive peaks than their progenitor species could, despite temporary fitness costs associated with unstable genomes. The trait correlations that disappear after hybridization as well as the novel trait correlations observed in allotetraploid hybrids may represent relatively evolutionarily labile associations and therefore could be ideal targets for artificial selection and crop improvement.

MicroRNA319a-targeted Brassica rapa ssp. pekinensis TCP genes modulate head shape in chinese cabbage by differential cell division arrest in leaf regions.

Leafy heads of cabbage (Brassica oleracea), Chinese cabbage (Brassica rapa), and lettuce (Lactuca sativa) are composed of extremely incurved leaves. The shape of these heads often dictates the quality, and thus the commercial value, of these crops. Using quantitative trait locus mapping of head traits within a population of 150 recombinant inbred lines of Chinese cabbage, we investigated the relationship between expression levels of microRNA-targeted Brassica rapa ssp. pekinensis TEOSINTE BRANCHED1, cycloidea, and PCF transcription factor4 (BrpTCP4) genes and head shape. Here, we demonstrate that a cylindrical head shape is associated with relatively low BrpTCP4-1 expression, whereas a round head shape is associated with high BrpTCP4-1 expression. In the round-type Chinese cabbage, microRNA319 (miR319) accumulation and BrpTCP4-1 expression decrease from the apical to central regions of leaves. Overexpression of BrpMIR319a2 reduced the expression levels of BrpTCP4 and resulted in an even distribution of BrpTCP4 transcripts within all leaf regions. Changes in temporal and spatial patterns of BrpTCP4 expression appear to be associated with excess growth of both apical and interveinal regions, straightened leaf tips, and a transition from the round to the cylindrical head shape. These results suggest that the miR319a-targeted BrpTCP gene regulates the round shape of leafy heads via differential cell division arrest in leaf regions. Therefore, the manipulation of miR319a and BrpTCP4 genes is a potentially important tool for use in the genetic improvement of head shape in these crops.

Structured Light-Based 3D Reconstruction System for Plants.

Camera-based 3D reconstruction of physical objects is one of the most popular computer vision trends in recent years. Many systems have been built to model different real-world subjects, but there is lack of a completely robust system for plants. This paper presents a full 3D reconstruction system that incorporates both hardware structures (including the proposed structured light system to enhance textures on object surfaces) and software algorithms (including the proposed 3D point cloud registration and plant feature measurement). This paper demonstrates the ability to produce 3D models of whole plants created from multiple pairs of stereo images taken at different viewing angles, without the need to destructively cut away any parts of a plant. The ability to accurately predict phenotyping features, such as the number of leaves, plant height, leaf size and internode distances, is also demonstrated. Experimental results show that, for plants having a range of leaf sizes and a distance between leaves appropriate for the hardware design, the algorithms successfully predict phenotyping features in the target crops, with a recall of 0.97 and a precision of 0.89 for leaf detection and less than a 13-mm error for plant size, leaf size and internode distance.

Brassica villosa, a system for studying non-glandular trichomes and genes in the Brassicas.

Brassica villosa is a wild Brassica C genome species with very dense trichome coverage and strong resistance to many insect pests of Brassica oilseeds and vegetables. Transcriptome analysis of hairy B. villosa leaves indicated higher expression of several important trichome initiation genes compared with glabrous B. napus leaves and consistent with the Arabidopsis model of trichome development. However, transcripts of the TRY inhibitory gene in hairy B. villosa were surprisingly high relative to B. napus and relative transcript levels of SAD2, EGL3, and several XIX genes were low, suggesting potential ancillary or less important trichome-related roles for these genes in Brassica species compared with Arabidopsis. Several antioxidant, calcium, non-calcium metal and secondary metabolite genes also showed differential expression between these two species. These coincided with accumulation of two alkaloid-like compounds, high levels of calcium, and other metals in B. villosa trichomes that are correlated with the known tolerance of B. villosa to high salt and the calcium-rich natural habitat of this wild species. This first time report on the isolation of large amounts of pure B. villosa trichomes, on trichome content, and on relative gene expression differences in an exceptionally hairy Brassica species compared with a glabrous species opens doors for the scientific community to understand trichome gene function in the Brassicas and highlights the potential of B. villosa as a trichome research platform.

Genotype-environment interactions affecting preflowering physiological and morphological traits of Brassica rapa grown in two watering regimes.

Plant growth and productivity are greatly affected by drought, which is likely to become more threatening with the predicted global temperature increase. Understanding the genetic architecture of complex quantitative traits and their interaction with water availability may lead to improved crop adaptation to a wide range of environments. Here, the genetic basis of 20 physiological and morphological traits is explored by describing plant performance and growth in a Brassica rapa recombinant inbred line (RIL) population grown on a sandy substrate supplemented with nutrient solution, under control and drought conditions. Altogether, 54 quantitative trait loci (QTL) were identified, of which many colocated in 11 QTL clusters. Seventeen QTL showed significant QTL-environment interaction (Q×E), indicating genetic variation for phenotypic plasticity. Of the measured traits, only hypocotyl length did not show significant genotype-environment interaction (G×E) in both environments in all experiments. Correlation analysis showed that, in the control environment, stomatal conductance was positively correlated with total leaf dry weight (DW) and aboveground DW, whereas in the drought environment, stomatal conductance showed a significant negative correlation with total leaf DW and aboveground DW. This correlation was explained by antagonistic fitness effects in the drought environment, controlled by a QTL cluster on chromosome A7. These results demonstrate that Q×E is an important component of the genetic variance and can play a great role in improving drought tolerance in future breeding programmes.

Induced polyploidization in Brassica campestris L. (Brassicaceae).

Present experimental design has been made up to obtain crop with higher ploidy level via synthetic polyploidization. Since ploidy manipulation is generally associated with the obtainment of some increased enviable traits of the crop and also provides them greater adaptability to unfavorable or harsh circumstances as compared to its diploids counterparts. Thus, herein present research autotetraploids of Brassica campestris L. have been lucratively achieved by the application of colchicine. Two methods of treatment were utilized i.e. seed treatment and seedling treatment. No polyploidy could be obtained through seed treatment while seedling treatment responded well towards polyploidy. However, the status of autotetraploidy has been confirmed by cytomorphological investigations of treated plants as against its diploids counterparts. For the purpose, morphological parameters such as increased stomata size, pollen diameter, flower size, reproductive organs whereas reduction in plant height, leaf length, leaf breadth, stomata frequency, number of flowers/inflorescence etc. were appraised. Further, cytological observations were made that had clearly revealed the doubling of genome in the autotetraploids as compared to diploids. Meanwhile, pollen fertility and size of pollen grains were evaluated as well.

Morphological and molecular diversity in mid-late and late maturity genotypes of cauliflower.

Genetic diversity is the prerequisite for the success of crop improvement programmes. Keeping in view, the current investigation was undertaken to assess the agro-morphological and molecular diversity involving 36 diverse mid-late and late cauliflower genotypes following α-RBD design during winter season 2021-22. Six morphological descriptors predicted as polymorphic using Shannon diversity index with maximum for leaf margin (0.94). The genotypes grouped into nine clusters based on D2 analysis with four as monogenotypic and gross plant weight (32.38%) revealed maximum contribution towards the genetic diversity. Molecular diversity analysis revealed 2-7 alleles among 36 polymorphic simple sequence repeats (SSR) with average of 4.22. Primer BoESSR492 (0.77) showed maximum polymorphic information content (PIC) with mean of 0.58. SSR analysis revealed two clusters each with two subclusters with a composite pattern of genotype distribution. STRUCTURE analysis showed homogenous mixture with least amount of gene pool introgression within the genotypes. Thus, based on morphological and molecular studies, the diverse genotypes namely, DPCaCMS-1, DPCaf-W4, DPCaf-US, DPCaf-W131W, DPCaf-S121, DPCaf-18, DPCaf-13, DPCaf-29 and DPCaf-CMS5 can be utilized in hybridization to isolate potential transgressive segregants to broaden the genetic base of cauliflower or involve them to exploit heterosis.

A new broccoli × broccoli immortal mapping population and framework genetic map: tools for breeders and complex trait analysis.

A unique broccoli × broccoli doubled haploid (DH) population has been created from the F(1) of a cross between two DH broccoli lines derived from cultivars Green Duke and Marathon. We genotyped 154 individuals from this population with simple sequence repeat and amplified fragment length polymorphism markers to create a B. oleracea L. var. italica 'intra-crop' specific framework linkage map. The map is composed of nine linkage groups with a total length of 946.7 cM. Previous published B. oleracea maps have been constructed using diverse crosses between morphotypes of B. oleracea; this map therefore represents a useful breeding resource for the dissection of broccoli specific traits. Phenotype data have been collected from the population over five growing seasons; the framework linkage map has been used to locate quantitative trait loci for agronomically important broccoli traits including head weight (saleable yield), head diameter, stalk diameter, weight loss and relative weight loss during storage, as well as traits for broccoli leaf architecture. This population and associated linkage map will aid breeders to directly map agronomically important traits for the improvement of elite broccoli cultivars.

Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions.

BACKGROUND AND AIMS: Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen. methods: Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed. KEY RESULTS: The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH. CONCLUSIONS: Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice.

Different fertility and meiotic regularity in allohexaploids derived from trigenomic hybrids between three cultivated Brassica allotetraploids and B. maurorum.

The wild species Brassica maurorum Durieu (MM, 2n = 16) is useful for the improvement of Brassica crops. Herein, interspecific reciprocal crosses between B. maurorum and three cultivated Brassica allotetraploids were carried out with the aid of embryo rescue. Trigenomic hybrids with Brassica napus (AACC, 2n = 38) and Brassica carinata (BBCC, 2n = 34) were produced from reciprocal crosses, but the hybrids with Brassica juncea (AABB, 2n = 36) were obtained only when B. maurorum was used as female. All the hybrids were morphologically intermediate between their parents, and were male and female sterile. By in vitro chromosome doubling of the trigenomic hybrids, the allohexaploids (AACC.MM/MM.AACC, 2n = 54; BBCC.MM, 2n = 50; MM.AABB, 2n = 52) were established and characterized for their phenotype and cytology. The fertilities of three allohexaploids were different, for AACC.MM and MM.AACC failed to produce seeds by selfing, but BBCC.MM showed low seed-set and MM.AABB had good seed-set. They also expressed variable extents of male meiotic regularity as to chromosome pairing and segregation, with MM.AABB > BBCC.MM > AACC.MM/MM.AACC, the same order as their fertility. So their meiotic behavior contributed to the fertility. Finally, the potential of these allohexaploids as a bridge for genetic improvement of Brassica crops was discussed.