Relations génétiques entre caractéristiques de la phase juvénile et productivité chez le maïs ensilage I. - Vigueur au stade jeune et productivité

La vigueur au stade jeune, facteur de productivité et de stabilité du maïs ensilage, est mesurée au stade plantule (2 à 3 feuilles visibles) et au moment de la différenciation florale à partir de critères pondéraux. Trente familles de demi-frères denté x corné sont comparées pour ces critères, qui sont par ailleurs mis en relation avec des caractéristiques du stade adulte : productivité et teneur en matière sèche à la récolte, caractères morphologiques. Les productivités en matière sèche des organes en croissance au stade plantule sont fortement liées au prélèvement de matière sèche dans la semence. Il subsiste toutefois, au niveau des parties aériennes, des différences de vigueur qui, dans les conditions de l'essai, sont positivement liées aux différences de rendement en matière sèche à la récolte. Le poids de la partie ( 1er entrenoeud + coléoptile) semble intéressant comme covariable pour estimer correctement au champ un critère de rapidité de levée. On n'observe pas de liaison entre caractéristiques du stade adulte et vigueur au moment de la différenciation florale. La corrélation (rendement en matière sèche, teneur en matière sèche) observée dans cet essai est proche de zéro. On interprète ce fait par l'intervention d'un stress hydrique au cours de la période floraison-maturité, qui aura

Etude de la competition interparcellaire chez le tournesol.

10 illus.National audienc

Transcriptomic analysis of the interaction between <it>Helianthus annuus </it>and its obligate parasite <it>Plasmopara halstedii </it>shows single nucleotide polymorphisms in CRN sequences

<p>Abstract</p> <p>Background</p> <p>Downy mildew in sunflowers (<it>Helianthus annuus </it>L.) is caused by the oomycete <it>Plasmopara halstedii </it>(Farl.) Berlese et de Toni. Despite efforts by the international community to breed mildew-resistant varieties, downy mildew remains a major threat to the sunflower crop. Very few genomic, genetic and molecular resources are currently available to study this pathogen. Using a 454 sequencing method, expressed sequence tags (EST) during the interaction between <it>H. annuus </it>and <it>P. halstedii </it>have been generated and a search was performed for sites in putative effectors to show polymorphisms between the different races of <it>P. halstedii</it>.</p> <p>Results</p> <p>A 454 pyrosequencing run of two infected sunflower samples (inbred lines XRQ and PSC8 infected with race 710 of <it>P. halstedii</it>, which exhibit incompatible and compatible interactions, respectively) generated 113,720 and 172,107 useable reads. From these reads, 44,948 contigs and singletons have been produced. A bioinformatic portal, HP, was specifically created for in-depth analysis of these clusters. Using <it>in silico </it>filtering, 405 clusters were defined as being specific to oomycetes, and 172 were defined as non-specific oomycete clusters. A subset of these two categories was checked using PCR amplification, and 86% of the tested clusters were validated. Twenty putative RXLR and CRN effectors were detected using PSI-BLAST. Using corresponding sequences from four races (100, 304, 703 and 710), 22 SNPs were detected, providing new information on pathogen polymorphisms.</p> <p>Conclusions</p> <p>This study identified a large number of genes that are expressed during <it>H. annuus/P. halstedii </it>compatible or incompatible interactions. It also reveals, for the first time, that an infection mechanism exists in <it>P. halstedii </it>similar to that in other oomycetes associated with the presence of putative RXLR and CRN effectors. SNPs discovered in CRN effector sequences were used to determine the genetic distances between the four races of <it>P. halstedii</it>. This work therefore provides valuable tools for further discoveries regarding the <it>H. annuus/P. halstedii </it>pathosystem.</p

The sunflower genome provides insights into oil metabolism, flowering and Asterid evolution

The domesticated sunflower, Helianthus annuus L., is a global oil crop that has promise for climate change adaptation, because it can maintain stable yields across a wide variety of environmental conditions, including drought. Even greater resilience is achievable through the mining of resistance alleles from compatible wild sunflower relatives, including numerous extremophile species. Here we report a high-quality reference for the sunflower genome (3.6 gigabases), together with extensive transcriptomic data from vegetative and floral organs. The genome mostly consists of highly similar, related sequences and required single-molecule real-time sequencing technologies for successful assembly. Genome analyses enabled the reconstruction of the evolutionary history of the Asterids, further establishing the existence of a whole-genome triplication at the base of the Asterids II clade and a sunflower-specific whole-genome duplication around 29 million years ago. An integrative approach combining quantitative genetics, expression and diversity data permitted development of comprehensive gene networks for two major breeding traits, flowering time and oil metabolism, and revealed new candidate genes in these networks. We found that the genomic architecture of flowering time has been shaped by the most recent whole-genome duplication, which suggests that ancient paralogues can remain in the same regulatory networks for dozens of millions of years. This genome represents a cornerstone for future research programs aiming to exploit genetic diversity to improve biotic and abiotic stress resistance and oil production, while also considering agricultural constraints and human nutritional needs