Studies on leaf spot disease of <Emphasis Type="Italic">Withania somnifera</Emphasis> and its impact on secondary metabolites

During an investigation of the disease profile of Withania somnifera, it was observed that leaf spot is the most prevalent disease. Repeated isolations from infected leaf tissues and pathogenicity tests showed the association of fungal pathogen identified as Alternaria alternata (Fr.) Keissler. Scanning electron microscopy showed various histological changes in the leaf tissues of infected plants. A decrease in total content of reducing sugars (20%) and chlorophyll (26.5%) was observed in diseased leaves whereas an increase was noticed in proline (25%), free amino acids (3%) and proteins (74.3%). High performance thin layer chromatography (HPTLC) analysis of secondary metabolites viz. withanolides, withaferin-A and total alkaloids of the diseased leaves vis-à-vis control revealed reduction in withaferin-A and withanolides contents by 15.4% and 76.3% respectively, in contrast to an increase in total alkaloids by 49.3%, information hitherto unreported in W. somnifera.     

Molecular genetic diversity and association mapping of nut and kernel traits in Slovenian hazelnut (<Emphasis Type="Italic">Corylus avellana</Emphasis>) germplasm

European hazelnut (Corylus avellana L.), cultivated in several areas of the world including Europe, Anatolia, and the USA, is an economically important nut crop due to its high mineral, oleic acid, amino acid, and phenolic compound content and pleasant flavor. This study examined molecular genetic diversity and population structure of 54 wild accessions and 48 cultivars from the Slovenian national hazelnut collection using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers. Eleven AFLP primer combinations and 49 SSR markers yielded 532 and 504 polymorphic fragments, respectively. As expected for a wind-pollinated, self-incompatible species, levels of genetic diversity were high with cultivars and wild accessions having mean dissimilarity values of 0.50 and 0.60, respectively. In general, cultivars and wild accessions clustered separately in dendrogram, principal coordinate, and population structure analyses with regional clustering of the wild material. The accessions were also characterized for ten nut and seven kernel traits and some wild accessions were shown to have breeding potential. Morphological principal component analysis showed distinct clustering of cultivars and wild accessions. An association mapping panel composed of 64 hazelnut cultivars and wild accessions had considerable variation for the nut and kernel quality traits. Morphological and molecular data were associated to identify markers controlling the traits. In all, 49 SSR markers were significantly associated with nut and kernel traits [P < 0.0001 and LD value (r ²) = 0.15–0.50]. This work is the first use of association mapping in hazelnut and has identified molecular markers associated with important quality parameters in this important nut crop.     

Assessment of molecular diversity and evolutionary relationship of kenaf (Hibiscus cannabinus L.), roselle (H. sabdariffa L.) and their wild relatives

Kenaf (Hibiscus cannabinus L.) and roselle (H. sabdariffa L.) are valuable fibre crop species with diverse end use. Phylogenetic relationship of 73 accessions of kenaf, roselle and their wild relatives from 15 countries was assessed using 44 inter-simple sequence repeat (ISSR) and jute (Corchorus olitorius L.) specific simple sequence repeats (SSR) markers. A total of 113 alleles were identified of which 61.95 % were polymorphic. Jute specific SSR markers exhibited high polymorphism and resolving power in kenaf, although ISSR markers exhibited higher resolving power than SSR markers. Number of polymorphic alleles varied from 1 to 5 for ISSR and 1 to 6 for SSR markers. Cultivated species exhibited higher allele polymorphism (57 %) than the wild species (35 %), but the improved cultivars exhibited lower genetic diversity compared to germplasm accessions. Accessions with common genetic lineage and geographical distribution clustered together. Indian kenaf varieties were distinct from cultivars bred in other countries and shared more genetic homology with African accessions. High genetic diversity was observed in the Indian (J = 0.35–0.74) and exotic kenaf germplasm collections (J = 0.38–0.79), suggesting kenaf might have been introduced in India from Africa through Central Asia during early domestication. Genetic similarity-based cluster analysis was in close accordance with taxonomic classification of Hibiscus.     

Discovery of QTLs for water mining and water use efficiency traits in rice under water-limited condition through association mapping

Developing trait introgressed rice cultivars is essential to sustain yield under aerobic conditions. Here, we report DNA markers governing variability in root traits, water use efficiency (WUE) and other biometric traits like total leaf area by association mapping. A set of 173 diverse rice germplasm accessions were phenotyped for root traits in specially designed root structures and WUE using carbon isotope discrimination (Δ¹³C) during the monsoon season (July to October) of two consecutive years (2007 and 2008). The panel was genotyped using 291 SSR markers spanning the entire genome of rice. Root biomass varied between 1.8 and 16.3 g plant^?1 while root length between 22 and 78 cm representing significant genetic variability. Similarly, Δ¹³C varied from 18 to 23 ‰. The SSR markers showed extensive polymorphism with around 73 % of all the markers revealing polymorphism information content values more than 0.5. Model-based structure analysis using the squared-allele frequency correlations revealed six subgroups among the panel with an average LD decay of about 10–20 cM. The Benjamini–Hochberg analysis was carried out to compute the false discovery rate combined with the analysis of effective LD. A total of 82 markers were involved in 175 significant (corrected P values and Q values <0.05) marker–trait associations (MTAs) across experiment 1 and experiment 2 and for the pooled data. Out of these, 22 markers were found to be associated with more than one trait. Common markers with significant associations were discovered for root biomass, total leaf area and total biomass suggesting the interdependency of these traits. Finally, 12 markers showed significant and stable MTAs across the experiments for different traits. An in silico analysis indicated that 45 % of the MTAs overlapped with previously reported QTLs and can be used for QTL introgression through breeding.     

Utility of a multidisciplinary approach for genome diagnostics of cultivated and wild germplasm resources of medicinal Withania somnifera, and the status of new species, W. ashwagandha, in the cultivated taxon

Realizing the inconsistencies that exist in the extent and nature of differentiation in the Withania somnifera genetic resources in India, the 21 cultivated and wild accessions, and the two hybrids (cultivated?×?wild accessions and vice versa) were investigated for morphological, cytogenetical, chemical profiling, and crossability features. Their nuclear and chloroplast genomes were also assayed at the nucleotide sequence level, and by use of DNA markers. Chloroplast DNA diversity and somatic chromosome number (2n?=?48) were not helpful in identifying the differences. Other approaches, on the other hand, especially restriction endonuclease digests, types and sequence length composition of ITS 1 and ITS 2 of nuclear ribosomal DNA, AFLP fingerprinting, and crossability barriers unambiguously provided startling discrete differences between the cultivated and wild accessions, indicating a clear division of W. somnifera into two distinct lineages. These data, therefore, are indicative of the fact that because of the unique characteristics of its nuclear genome, and strong crossability barriers vis-à-vis wild accessions of W. somnifera, the cultivated accessions should be relegated to the rank of the separate species, W. ashwagandha.     

Enhanced production of withaferin-A in shoot cultures of Withania somnifera (L) Dunal

Withania somnifera (L) Dunal, commonly known as ashwagandha or Indian ginseng, is the source of large number of pharmacologically active withanolides. Withaferin-A (WS-3), a major withanolide of W. somnifera, has been proven to be an effective anti-cancer molecule. In this study, a liquid culture system for shoot proliferation, biomass accumulation and withaferin-A production of an elite accession (AGB002) of W. somnifera was investigated. The nodal explants cultured on Murashige and Skoog (MS) semi-solid medium supplemented with various concentrations of 6-benzyl adenine (BA) and Kinetin (Kn) elicited varied responses. The highest number of regenerated shoots per ex-plant (35?±?3.25) and the maximum average shoot length (5.0?±?0.25 cm) were recorded on MS medium supplemented with BA (5.0 μM). The shoots were further proliferated in half and full strength MS liquid medium supplemented with the same concentration BA. It was interesting to note that shoots cultured on MS half strength liquid medium fortified with 4 gL-1 FW (fresh weight) shoot inoculum mass derived from 5 week old nodal explants of W. somnifera showed highest accumulation of biomass and withaferin A content in 5 weeks. Withaferin A was produced in relatively high amounts (1.30 % and 1.10 % DW) in shoots cultured in half and full strength MS liquid media respectively as compared to natural field grown plants (0.85 % DW). A considerable amount of the withaferin A was also excreted in the culture medium. Successful proliferation of shoots in liquid medium and the synthesis of withaferin A in vitro opens new avenues for bioreactor scale-up and the large-scale production of the compound.     

Gas exchange,carbon balance and stomatal traits in wild and cultivated rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genotypes

Carbon balancing within the plant species is an important feature for climatic adaptability. Photosynthesis and respiration traits are directly linked with carbon balance. These features were studied in 20 wild rice accessions Oryza spp., and cultivars. Wide variation was observed within the wild rice accessions for photosynthetic oxygen evolution or photosynthetic rate (A), dark (R _d), and light induced respiration (LIR) rates, as well as stomatal density and number. The mean rate of A varied from 10.49 μmol O₂ m^?2 s^?1 in cultivated species and 13.09 μmol O₂ m^?2 s^?1 in wild spp., The mean R _d is 2.09 μmol O₂ m^?2 s^?1 and 2.31 μmol O₂ m^?2 s^?1 in cultivated and wild spp., respectively. Light induced Respiration (LIR) was found to be almost twice in wild rice spp., (16.75 μmol O₂ m^?2 s^?1) compared to cultivated Oryza spp., Among the various parameters, this study reveals LIR and A as the key factors for positive carbon balance. Stomatal contribution towards carbon balance appears to be more dependent on abaxial surface where several number of stomata are situated. Correlation analysis indicates that R _d and LIR increase with the increase in A. In this study, O. nivara (CR 100100, CR 100097), O. rufipogon (IR 103404) and O. glumaepatula (IR104387) were identified as potential donors which could be used in rice breeding program. Co-ordination between gas exchange and patchiness in stomatal behaviour appears to be important for carbon balance and environmental adaptation of wild rice accessions, therefore, survival under harsh environment.     

Assessment of genetic diversity and morpho-physiological traits related to drought tolerance in Stylosanthes scabra

Among the many Stylosanthes species, Stylosanthes scabra, a range fodder legume, performs better under limited water condition. In the present investigation, thirty-four accessions of S. scabra were assessed under limited water condition, for various morpho-physiological characters associated with drought. In general, S. scabra exhibited better tolerance to drought, as evidenced by high leaf thickness and greater accumulation of proline, and malondialdehyde (MDA) in water stress condition. Transpiration efficiency (TE) was high, in both control and water stress conditions and positively correlated with root, shoot, and total dry matters, in both control and stress conditions (r ² = ranged from 0.589 to 0.961 in control and from 0.351 to 0.985 in stress). Of these, 25 accessions were assessed for estimation of genetic diversity, employing random amplified polymorphic DNA (RAPD) markers. A total of 210 RAPD bands, obtained with 32 primers, revealed high polymorphic information content (0.49) and marker index (4.41). Dendrogram analysis indicated close proximity among the accessions of S. scabra. These accessions were clustered in high similarity range (84.01–98.36 %). Accession IG-366A separated from other clusters at 85.62 % similarity level. RAPD marker system revealed 13 accessions exhibiting >90 % genetic similarity while the other accessions exhibited similarity ranging from 68 to 90 %. A higher level of genetic similarity which was also evident from the similar levels of TE, biomass production, root/shoot ratio, MDA, proline contents and drought tolerance index, indicated a cause–effect relationship among them. Results also indicated that among the accessions, S. scabra rate-reducing resistance allo-tetraploid lines were better suited for hard and cracking soils, under complete rain-fed condition.     

On the action and mechanism of withaferin-A from Withania somnifera,a novel and potent melanin dispersing agent in frog melanophores

The present work was carried out to determine the effects of lyophilized root extracts of Withania somnifera along with pure withaferin-A, on the isolated skin melanophores of frog, Rana tigerina which are disguised type of smooth muscle cells and offer excellent in vitro opportunities for studying the effects of pharmacological and pharmaceutical agents. The lyophilized extract of W. somnifera and its active ingredient withaferin-A induced powerful dose-dependent physiologically significant melanin dispersal effects in the isolated skin melanophores of R. tigerina, which were completely blocked by atropine as well as hyoscine. The per se melanin dispersal effects of lyophilized extracts of W. somnifera and its active ingredient withaferin-A got highly potentiated by neostigmine. It appears that the melanin dispersal effects of the extracts of W. somnifera and withaferin-A is mediated by cholino-muscarinic like receptors having similar properties.     

Arbuscular mycorrhizal fungal diversity in high-altitude hypersaline Andean wetlands studied by 454-sequencing and morphological approaches

Withania somnifera, also known as Indian ginseng is known to contain valuable bioactive compounds, called withanolides that structurally resemble ginsenosides of Panax ginseng. These compounds provide the basis of pharmacological relevance in traditional systems of medicine. In the present study, 150 hairy root lines of W. somnifera were induced of which nine fast growing lines were analysed for their growth and withanolide content. Hairy root line W9 was selected due to its high specific growth rate (0.196 ± 0.005 d^?1) and high withanolide content. The response to different concentrations of elicitors (methyl jasmonate and P. indica cell homogenate) and various exposure durations was assessed in the W9 hairy root line. The withanolide content as well as the pattern of gene expression from MVA, MEP and sterol pathway, was evaluated using qPCR. Though gene expression and withanolide content were found to be elevated in almost all MeJ and CHP treatments, the exposure of hairy roots to 15 μM MeJ for 4 h gave the maximum withanolide yield. The results suggest that the elicitation potential of methyl jasmonate was higher than that of P. indica cell homogenate for increasing withanolide levels in hairy roots of W. somnifera.     

Population structure and association mapping of yield contributing agronomic traits in foxtail millet

Key message

Association analyses accounting for population structure and relative kinship identified eight SSR markers ( p < 0.01) showing significant association ( R ²  = 18 %) with nine agronomic traits in foxtail millet.

Abstract

Association mapping is an efficient tool for identifying genes regulating complex traits. Although association mapping using genomic simple sequence repeat (SSR) markers has been successfully demonstrated in many agronomically important crops, very few reports are available on marker-trait association analysis in foxtail millet. In the present study, 184 foxtail millet accessions from diverse geographical locations were genotyped using 50 SSR markers representing the nine chromosomes of foxtail millet. The genetic diversity within these accessions was examined using a genetic distance-based and a general model-based clustering method. The model-based analysis using 50 SSR markers identified an underlying population structure comprising five sub-populations which corresponded well with distance-based groupings. The phenotyping of plants was carried out in the field for three consecutive years for 20 yield contributing agronomic traits. The linkage disequilibrium analysis considering population structure and relative kinship identified eight SSR markers (p < 0.01) on different chromosomes showing significant association (R ² = 18 %) with nine agronomic traits. Four of these markers were associated with multiple traits. The integration of genetic and physical map information of eight SSR markers with their functional annotation revealed strong association of two markers encoding for phospholipid acyltransferase and ubiquitin carboxyl-terminal hydrolase located on the same chromosome (5) with flag leaf width and grain yield, respectively. Our findings on association mapping is the first report on Indian foxtail millet germplasm and this could be effectively applied in foxtail millet breeding to further uncover marker-trait associations with a large number of markers.     

Phenotypic diversity and association mapping for fruit quality traits in cultivated tomato and related species

Association mapping has been proposed as an efficient approach to assist in the identification of the molecular basis of agronomical traits in plants. For this purpose, we analyzed the phenotypic and genetic diversity of a large collection of tomato accessions including 44 heirloom and vintage cultivars (Solanum lycopersicum), 127 S. lycopersicum var. cerasiforme (cherry tomato) and 17 Solanum pimpinellifolium accessions. The accessions were genotyped using a SNPlex? assay of 192 SNPs, among which 121 were informative for subsequent analysis. Linkage disequilibrium (LD) of pairwise loci and population structure were analyzed, and the association analysis between SNP genotypes and ten fruit quality traits was performed using a mixed linear model. High level of LD was found in the collection at the whole genome level. It was lower when considering only the 127 S. lycopersicum var. cerasiforme accessions. Genetic structure analysis showed that the population was structured into two main groups, corresponding to cultivated and wild types and many intermediates. The number of associations detected per trait varied, according to the way the structure was taken into account, with 0–41 associations detected per trait in the whole collection and a maximum of four associations in the S. lycopersicum var. cerasiforme accessions. A total of 40 associations (30 %) were co-localized with previously identified quantitative trait loci. This study thus showed the potential and limits of using association mapping in tomato populations.     

Grain zinc, iron and protein concentrations and zinc-efficiency in wild emmer wheat under contrasting irrigation regimes

Micronutrient malnutrition, and particularly deficiency in zinc (Zn) and iron (Fe), afflicts over three billion people worldwide, and nearly half of the world’s cereal-growing area is affected by soil Zn deficiency. Wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the progenitor of domesticated durum wheat and bread wheat, offers a valuable source of economically important genetic diversity including grain mineral concentrations. Twenty two wild emmer wheat accessions, representing a wide range of drought resistance capacity, as well as two durum wheat cultivars were examined under two contrasting irrigation regimes (well-watered control and water-limited), for grain yield, total biomass production and grain Zn, Fe and protein concentrations. The wild emmer accessions exhibited high genetic diversity for yield and grain Zn, Fe and protein concentrations under both irrigation regimes, with a considerable potential for improvement of the cultivated wheat. Grain Zn, Fe and protein concentrations were positively correlated with one another. Although irrigation regime significantly affected ranking of genotypes, a few wild emmer accessions were identified for their advantage over durum wheat, having consistently higher grain Zn (e.g., 125 mg kg^?1), Fe (85 mg kg^?1) and protein (250 g kg^?1) concentrations and high yield capacity. Plants grown from seeds originated from both irrigation regimes were also examined for Zn efficiency (Zn deficiency tolerance) on a Zn-deficient calcareous soil. Zinc efficiency, expressed as the ratio of shoot dry matter production under Zn deficiency to Zn fertilization, showed large genetic variation among the genotypes tested. The source of seeds from maternal plants grown under both irrigation regimes had very little effect on Zn efficiency. Several wild emmer accessions revealed combination of high Zn efficiency and drought stress resistance. The results indicate high genetic potential of wild emmer wheat to improve grain Zn, Fe and protein concentrations, Zn deficiency tolerance and drought resistance in cultivated wheat.     

Susceptibility and physiological responses of Jatropha curcas accessions to broad mite infestation

The broad mite Polyphagotarsonemus latus is a key pest of physic nut (Jatropha curcas L.). The purpose of this study was to identify physic nut accessions that are less susceptible to P. latus, in support of the breeding program of J. curcas. We first evaluated population growth rate and injury symptoms of P. latus on different J. curcas accessions and then carried out physiological analyses on P. latus-infested and uninfested accessions. From the germplasm bank of the Federal University of Viçosa, 15 physic nut accessions with high seed oil content, with different genetic background, were tested. The following traits were evaluated: instantaneous population growth rate of P. latus (r _i ), injury symptoms, relative leaf water content, specific leaf area, gas exchange, photosynthetic pigments, nitrogen and biomass of the aerial part. Significant differences were observed for P. latus population growth rate and injury symptoms among accessions. A positive correlation between P. latus growth rate and injury was found. The UFVJC72 accession stood out as the more resistant, considering P. latus growth rate and injury symptoms, compared with most accessions. Physiological responses did not vary among accessions, but did between infested and uninfested plants. In P. latus-infested plants, net photosynthesis was on average 50.5 % lower than in uninfested plants, whereas stomatal conductance and transpiration decreased by 46.2 and 51.6 %, respectively.     

Genetic diversity of cucumber estimated by morpho-physiological and EST-SSR markers

In the present study, genetic variation among 40 cucumber genotypes was analyzed by means of morpho-physiological traits and 21 EST-SSR markers. Diversity was observed for morpho-physiological characters like days to 50% female flowering (37–46.9, number of fruits/plant (1.33–5.80), average fruit weight (41–333), vine length (36–364), relative water content (58.5–92.7), electrolyte leakage (15.9–37.1), photosynthetic efficiency (0.40–0.75) and chlorophyll concentration index (11.1–28.6). The pair wise Jaccard similarity coefficient ranged from 0.00 to 0.27 for quantitative traits and 0.24 to 0.96 for EST-SSR markers indicating that the accessions represent genetically diverse populations. With twenty-one EST-SSR markers, polymorphism revealed among 40 cucumber genotypes, number of alleles varied 2–6 with an average 3.05. Polymorphism information content varied from 0.002 to 0.989 (mean = 0.308). The number of effective allele (Ne), expected heterozygosity (He) and unbiased expected heterozygosity (uHe) of these EST-SSRs were 1.079–1.753, 0.074–0.428 and 0.074–0.434, respectively. Same 21 EST-SSR markers transferability checked in four other Cucumis species: snapmelon (Cucumis melo var. momordica), muskmelon (Cucumis melo L.), pickling melon (Cucumis melo var. conomon) and wild muskmelon (Cucumis melo var. agrestis) with frequency of 61.9, 95.2, 76.2, and 76.2%, respectively. Present study provides useful information on variability, which can assist geneticists with desirable traits for cucumber germplasm utilization. Observed physiological parameters may assists in selection of genotype for abiotic stress tolerance also, EST-SSR markers may be useful for genetic studies in related species.     

SSR and morphological trait based population structure analysis of 130 diverse flax (Linum usitatissimum L.) accessions

A total of 130 flax accessions of diverse morphotypes and worldwide origin were assessed for genetic diversity and population structure using 11 morphological traits and microsatellite markers (15 gSSRs and 7 EST–SSRs). Analysis performed after classifying these accessions on the basis of plant height, branching pattern, seed size, Indian/foreign origin into six categories called sub-populations viz. fibre type exotic, fibre type indigenous, intermediate type exotic, intermediate type indigenous, linseed type exotic and linseed type indigenous. The study assessed different diversity indices, AMOVA, population structure and included a principal coordinate analysis based on different marker systems. The highest diversity was exhibited by gSSR markers (SI = 0.46; He = 0.31; P = 85.11). AMOVA based on all markers explained significant difference among fibre type, intermediate type and linseed type populations of flax. In terms of variation explained by different markers, EST-SSR markers (12%) better differentiated flax populations compared to morphological (9%) and gSSR (6%) markers at P = 0.01. The maximum Nei's unbiased genetic distance (D = 0.11) was observed between fibre type and linseed type exotic sub-populations based on EST-SSR markers. The combined structure analysis by using all markers grouped Indian fibre type accessions (63.4%) in a separate cluster along with the Indian intermediate type (48.7%), whereas Indian accessions (82.16%) of linseed type constituted an independent cluster. These findings were supported by the results of the principal coordinate analysis. Morphological markers employed in the study found complementary with microsatellite based markers in deciphering genetic diversity and population structure of the flax germplasm.     

Ploidy Level and DNA Content of Erianthus arundinaceus as Determined by Flow Cytometry and the Association with Biological Characteristics

Erianthus arundinaceus is not only an important germplasm resource for sugarcane breeding but also a potential bioenergy plant. Making clear the distribution of the chromosome ploidy of wild E. arundinaceus in china is the premise of the research and utilization of this species. Therefore, the objectives of this study were to determine the ploidy level and DNA content of the 55 E. arundinaceus accessions using flow cytometry and to identify the correlation between ploidy and phenotypic traits. Among the 55 accessions, four tetraploids and 51 hexaploids were identified. The four tetraploids originated from Mengma Yunnan, Shuangjiang Yunnan, Gaozhou Guangdong and Chengle Sichuan. The mean DNA content was 4.82 pg/2C for the tetraploid and 7.30 pg/2C for the hexaploid plants. The ploidy was negatively correlated with cellulose content and positively correlated (P<0.05) with plant height, stem diameter, leaf width, dry weight per plant, fresh weight per plant and hemicellulose content. However, ploidy was not correlated with leaf length, tiller number and the ratio of dry weight and fresh weight. This study will be useful for revealing the distribution of the ploidy of wild E. arundinaceus in Chin, traits markers analysis, and utilization of this species, such as cultivar improvement and sugarcane breeding in the future.     

Characterization of a glutamine synthetase gene DvGS1 from Dunaliella viridis and investigation of the impact on expression of DvGS1 in transgenic Arabidopsis thaliana

A novel glutamine synthetase (GS) gene DvGS1 showing highest amino acid sequence identity of 78 % with the other homologous GS proteins from green algae, was isolated and characterized from Dunaliella viridis. Phylogenetic analysis revealed that DvGS1 occupied an independent phylogenetic position which was different with the GSs from higher plants, animals and microbes. Functional complement in E. coli mutant confirmed that the DvGS1 encoded functional GS enzyme. Real-time PCR analysis of DvGS1 in D. viridis cells under nitrogen starvation revealed that the mRNA level of DvGS1 was positively up-regulated in 12 h. The DvGS1 levels at the points of 12 and 24 h were separately twofold and fourfold of the level before nitrogen starvation. In order to investigate the potential application of DvGS1 in higher plants, the transgenic study of DvGS1 in Arabidopsis thaliana was carried out. Phenotype identification demonstrated that all three transgenic lines of T3 generation showed obviously enhanced root length (26 %), fresh weight (22–46 % at two concentrations of nitrate supplies), stem length (26 %), leaf size (29 %) and silique number (30 %) compared with the wild-type Arabidopsis. Biochemical analysis confirmed that all three transgenic lines had higher total nitrogen content, soluble protein concentration, total amino acid content and the leaf GS activity than the wild type plants. The free NH₄ ⁺ and NO₃ ^? concentration in fresh leaves of three transgenic lines were reduced by 17–26 % and 14–15 % separately (at two concentrations of nitrate supplies) compared with those of the wild types. All the results indicated that over-expression of DvGS1 in Arabidopsis significantly results in the improvement of growth phenotype and the host’s nitrogen use efficiency.     

Identification of genomic regions involved in resistance against Sclerotinia sclerotiorum from wild Brassica oleracea

The lack of resistant source has greatly restrained resistance breeding of rapeseed (Brassica napus, AACC) against Sclerotinia sclerotiorum which causes severe yield losses in rapeseed production all over the world. Recently, several wild Brassica oleracea accessions (CC) with high level of resistance have been identified (Mei et al. in Euphytica 177:393–400, 2011), bringing a new hope to improve Sclerotinia resistance of rapeseed. To map quantitative trait loci (QTL) for Sclerotinia resistance from wild B. oleracea, an F2 population consisting of 149 genotypes, with several clones of each genotypes, was developed from one F1 individual derived from the cross between a resistant accession of wild B. oleracea (B. incana) and a susceptible accession of cultivated B. oleracea var. alboglabra. The F2 population was evaluated for Sclerotinia reaction in 2009 and 2010 under controlled condition. Significant differences among genotypes and high heritability for leaf and stem reaction indicated that genetic components accounted for a large portion of the phenotypic variance. A total of 12 QTL for leaf resistance and six QTL for stem resistance were identified in 2 years, each explaining 2.2–28.4 % of the phenotypic variation. The combined effect of alleles from wild B. oleracea reduced the relative susceptibility by 22.5 % in leaves and 15 % in stems on average over 2 years. A 12.8-cM genetic region on chromosome C09 of B. oleracea consisting of two major QTL intervals for both leaf and stem resistance was assigned into a 2.7-Mb genomic region on chromosome A09 of B. rapa, harboring about 30 putative resistance-related genes. Significant negative corrections were found between flowering time and relative susceptibility of leaf and stem. The association of flowering time with Sclerotinia resistance is discussed.