Genetic Variation for Weed Competition and Allelopathy in Rapeseed (Brassica napus L.)

Rapeseed (canola, Brassica napus L.) is the second major oilseed crop of the world and provides a source of healthy oil for human consumption, meal for stock markets and several other by-products. Several weed species afflict the sustainable production and quality of canola. Various agronomic practices such as crop rotation, stubble management (e.g. burning), minimum tillage, application of herbicides and cultivation of herbicide resistant varieties have been deployed to minimise yield losses. There is no doubt that herbicide-tolerant cultivars enable management of weeds which are difficult to control otherwise. However, widespread usage increases the risk of herbicide resistance. This is becoming a major impediment in sustaining high crop productivity. Allelopathic and weed competitive varieties are potential tools to reduce the dependence on herbicides and could be grown to suppress weed growth in commercial canola. Genetic variation and ‘proxy’ traits involved in both crop competition as well as allelopathy have been reported. Further research is required to link genetic variation in weed competition and allelopathy, and genetic/genomic marker technologies to unravel effective alleles to expand breeding activity for weed interference in canola

A DArT platform for quantitative bulked segregant analysis

<p>Abstract</p> <p>Background</p> <p>Bulked segregant analysis (BSA) identifies molecular markers associated with a phenotype by screening two DNA pools of phenotypically distinct plants for markers with skewed allele frequencies. In contrast to gel-based markers, hybridization-based markers such as SFP, DArT or SNP generate quantitative allele-frequency estimates. Only DArT, however, combines this advantage with low development and assay costs and the ability to be deployed for any plant species irrespective of its ploidy level. Here we investigate the suitability of DArT for BSA applications using a barley array as an example.</p> <p>Results</p> <p>In a first test experiment, we compared two bulks of 40 Steptoe/Morex DH plants with contrasting pubescent leaves (mPub) alleles on chromosome 3H. At optimized levels of experimental replication and marker-selection threshold, the BSA scan identified 433 polymorphic markers. The relative hybridization contrast between bulks accurately reflected the between-bulk difference in the frequency of the mPub allele (r = 0.96). The 'platform noise' of DArT assays, estimated by comparing two identical aliquots of a DNA mixture, was significantly lower than the 'pooling noise' reflecting the binomial sampling variance of the bulking process. The allele-frequency difference on chromosome 3H increased in the vicinity of mPub and peaked at the marker with the smallest distance from mPub (4.6 cM). In a validation experiment with only 20 plants per bulk we identified an aluminum (Al) tolerance locus in a Dayton/Zhepi2 DH population on chromosome 4H with < 0.8 cM precision, the same Al-tolerance locus that had been mapped before in other barley populations.</p> <p>Conclusion</p> <p>DArT-BSA identifies genetic loci that influence phenotypic characters in barley with at least 5 cM accuracy and should prove useful as a generic tool for high-throughput, quantitative BSA in plants irrespective of their ploidy level.</p

Cryptanalysis and Performance Evaluation of Enhanced Threshold Proxy Signature Scheme Based on RSA for Known Signers

In these days there are plenty of signature schemes such as the threshold proxy signature scheme (Kumar and Verma 2010). The network is a shared medium so that the weakness security attacks such as eavesdropping, replay attack, and modification attack. Thus, we have to establish a common key for encrypting/decrypting our communications over an insecure network. In this scheme, a threshold proxy signature scheme based on RSA, any or more proxy signers can cooperatively generate a proxy signature while or fewer of them cannot do it. The threshold proxy signature scheme uses the RSA cryptosystem to generate the private and the public key of the signers (Rivest et al., 1978). Comparison is done on the basis of time complexity, space complexity, and communication overhead. We compare the performance of four schemes (Hwang et al. (2003), Kuo and Chen (2005), Yong-Jun et al. (2007), and Li et al. (2007), with the performance of a scheme that has been proposed earlier by the authors of this paper. In the proposed scheme, both the combiner and the secret share holder can verify the correctness of the information that they are receiving from each other. Therefore, the enhanced threshold proxy signature scheme is secure and efficient against notorious conspiracy attacks

Genome-wide Association Study Identifies New Loci for Resistance to Leptosphaeria maculans in Canola

Blackleg, caused by Leptosphaeria maculans, is a significant disease which affects the sustainable production of canola. This study reports a genome-wide association study based on 18,804 polymorphic SNPs to identify loci associated with qualitative and quantitative resistance to L. maculans. Genomic regions delimited with 503 significant SNP markers, that are associated with resistance evaluated using 12 single spore isolates and pathotypes from four canola stubble were identified. Several significant associations were detected at known disease resistance loci including in the vicinity of recently cloned Rlm2/LepR3 genes, and at new loci on chromosomes A01/C01, A02/C02, A03/C03, A05/C05, A06, A08, and A09. In addition, we validated statistically significant associations on A01, A07 and A10 in four genetic mapping populations, demonstrating that GWAS marker loci are indeed associated with resistance to L. maculans. One of the novel loci identified for the first time, Rlm12, conveys adult plant resistance and mapped within 13.2 kb from Arabidopsis R gene of TIR-NBS class. We showed that resistance loci are located in the vicinity of R genes of A. thaliana and B. napus on the sequenced genome of B. napus cv. Darmor-bzh. Significantly associated SNP markers provide a valuable tool to enrich germplasm for favorable alleles in order to improve the level of resistance to L. maculans in canola

Novel quantitative trait loci from an interspecific Brassica rapa derivative improve pod shatter resistance in Brassica napus

Pod shatter is a trait of agricultural relevance that ensures plants dehisce seeds in their native environment and has been subjected to domestication and selection for non-shattering types in several broadacre crops. However, pod shattering causes a significant yield reduction in canola (Brassica napus L.) crops. An interspecific breeding line BC95042 derived from a B. rapa/B. napus cross showed improved pod shatter resistance (up to 12-fold than a shatter-prone B. napus variety). To uncover the genetic basis and improve pod shatter resistance in new varieties, we analysed F2 and F2:3 derived populations from the cross between BC95042 and an advanced breeding line, BC95041, and genotyped with 15,498 DArTseq markers. Through genome scan, interval and inclusive composite interval mapping analyses, we identified seven quantitative trait loci (QTLs) associated with pod rupture energy, a measure for pod shatter resistance or pod strength, and they locate on A02, A03, A05, A09 and C01 chromosomes. Both parental lines contributed alleles for pod shatter resistance. We identified five pairs of significant epistatic QTLs for additive x additive, additive dominance and dominance x dominance interactions between A01/C01, A03/A07, A07/C03, A03/C03, and C01/C02 chromosomes for rupture energy. QTL effects on A03/A07 and A01/C01 were in the repulsion phase. Comparative mapping identified several candidate genes (AG, ABI3, ARF3, BP1, CEL6, FIL, FUL, GA2OX2, IND, LATE, LEUNIG, MAGL15, RPL, QRT2, RGA, SPT and TCP10) underlying main QTL and epistatic QTL interactions for pod shatter resistance. Three QTLs detected on A02, A03, and A09 were near the FUL (FRUITFULL) homologues BnaA03g39820D and BnaA09g05500D. Focusing on the FUL, we investigated putative motifs, sequence variants and the evolutionary rate of its homologues in 373 resequenced B. napus accessions of interest. BnaA09g05500D is subjected to purifying selection as it had a low Ka/Ks ratio compared to other FUL homologues in B. napus. This study provides a valuable resource for genetic improvement for yield through an understanding of the genetic mechanism controlling pod shatter resistance in Brassica species

Stable Quantitative Resistance Loci to Blackleg Disease in Canola (Brassica napus L.) Over Continents

The hemibiotrophic fungus, Leptosphaeria maculans is the most devastating pathogen, causing blackleg disease in canola (Brassica napus L). To study the genomic regions involved in quantitative resistance (QR), 259–276 DH lines from Darmor-bzh/Yudal (DYDH) population were assessed for resistance to blackleg under shade house and field conditions across 3 years. In different experiments, the broad sense heritability varied from 43 to 95%. A total of 27 significant quantitative trait loci (QTL) for QR were detected on 12 chromosomes and explained between 2.14 and 10.13% of the genotypic variance. Of the significant QTL, at least seven were repeatedly detected across different experiments on chromosomes A02, A07, A09, A10, C01, and C09. Resistance alleles were mainly contributed by ‘Darmor-bzh’ but ‘Yudal’ also contributed few of them. Our results suggest that plant maturity and plant height may have a pleiotropic effect on QR in our conditions. We confirmed that Rlm9 which is present in ‘Darmor-bzh’ is not effective to confer resistance in our Australian field conditions. Comparative mapping showed that several R genes coding for nucleotide-binding leucine-rich repeat (LRR) receptors map in close proximity (within 200 Kb) of the significant trait-marker associations on the reference ‘Darmor-bzh’ genome assembly. More importantly, eight significant QTL regions were detected across diverse growing environments: Australia, France, and United Kingdom. These stable QTL identified herein can be utilized for enhancing QR in elite canola germplasm via marker- assisted or genomic selection strategies

Stolen citizenship, stolen freedoms

With the rise of capitalism in post-colonial India, initially as a subsidiary part of a mixed economy with the state occupying its ‘commanding heights’, and later, especially after 1991, in the context of a new hegemony of globalised neoliberal capital, it was widely assumed that unfree labour, especially feudal forms of slavery in debt bondage, would vanish into history. This, however, has not happened. Inter-generational bondage to a single household has indeed become rarer. But the spread of capitalism has not created conditions of ‘free’ labour in India; instead pre-capitalist relations of labour unfreedoms continue to persist in abundance in the modified form of neo-bondage. This paper looks closely at one category of Indian workers – namely circular labour migrants – who are particularly susceptible to these forms of neo-slavery.Avec le développement du capitalisme dans l’Inde post-coloniale, considéré à l’origine comme une partie subsidiaire d’une économie mixte dont l’État était censé occuper les « hauts commandements », et plus tard – spécialement après 1991–, dans le contexte de l’hégémonie nouvelle d’un capital néo-libéral globalisé, il était largement admis que le travail non-libre, en particulier les formes féodales de l’esclavage pour dettes appartiendraient à l’histoire. Ce n’est cependant pas arrivé. La dépendance intergénérationelle à une seule famille s’est sensiblement raréfiée. Mais la diffusion du capitalisme n’a pas créé les conditions du travail « libre » en Inde ; au contraire, les relations précapitalistes du travail non-libre ont changé et persistent aujourd’hui sous forme de néo-esclavage ou de néo-dépendance. Cet article examine avec précision une catégorie de travailleurs que l’on nomme les migrants circulaires en Inde, et qui sont particulièrement exposés à ces formes de néo-esclavage.Con el desarrollo del capitalismo en India post-colonial, considerado inicialmente como parte subsidiaria de una economía mixta de la que el Estado tomaría las riendas, y luego –especialmente desde 1991–, en el contexto de la nueva hegemonía de un capital neoliberal globalizado, se consideraba que el trabajo no-libre, en especial las formas feudales de la esclavitud por deudas pasarían a la historia. No fue así. Si bien la dependencia intergeneracional dentro de una misma familia es cada vez menos frecuente, la difusión del capitalismo no ha creado las condiciones del trabajo “libre” en India. Por el contrario, las relaciones pre-capitalistas del trabajo no-libre han dado paso a nuevas formas, sumamente persistentes, de neo-esclavitud y de neo-dependencia. Este artículo examina con precisión una categoría de trabajadores designados, en India, como migrantes circulares, particularmente expuestos a estas formas de neo-esclavitud.Com o desenvolvimento do capitalismo na Índia pós-colonial, primeiro como parte subsidiária de uma economia mista onde o Estado segurava as rédeas da economia e a seguir, sobretudo depois de 1991, com a nova hegemonia do capital neo-liberal globalizado, era geralmente suposto que o trabalho não-livre, e nomeadamente as formas feudais de escravidão por dívidas, sumiriam no passado. Porém, isso não aconteceu. Se bem que a servidão intergeracional numa mesma família tornou-se mais rara, a expansão do capitalismo não criou condições de trabalho « livre » na Índia. Em vez disso, as relações de trabalho não-livre pre-capitalistas persistem largamente como formas modificadas de neo-escravidão e neo-dependência. Este artigo examina mais detidamente uma categoria de trabalhadores, designados como migrantes circulares, particularmente sujeitos a estas formas de neo-escravidão