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Vernalization, the requirement of a period of low temperature to induce transition from the vegetative to reproductive state, is an evolutionarily and economically important trait in the Triticeae. The genetic basis of vernalization in cultivated barley (Hordeum vulgare subsp. vulgare) can be defined using the two-locus VRN-H1/VRN-H2 model. We analyzed the allelic characteristics of HvBM5A, the candidate gene for VRN-H1, from ten cultivated barley accessions and one wild progenitor accession (subsp. spontaneum), representing the three barley growth habits - winter, facultative, and spring. We present multiple lines of evidence, including sequence, linkage map location, and expression, that support HvBM5A being VRN-H1. While the predicted polypeptides from different growth habits are identical, spring accessions contain a deletion in the first intron of HvBM5A that may be important for regulation. While spring HvBM5A alleles are typified by the intron-localized deletion, in some cases, the promoter may also determine the allele type. The presence/absence of the tightly linked ZCCT-H gene family members on chromosome 4H perfectly correlates with growth habit and we conclude that one of the three ZCCT-H genes is VRN-H2. The VRN-H2 locus is present in winter genotypes and deleted from the facultative and spring genotypes analyzed in this study, suggesting the facultative growth habit (cold tolerant, vernalization unresponsive) is a result of deletion of the VRN-H2 locus and presence of a winter HvBM5A allele. All reported barley vernalization QTLs can be explained by the two-locus VRN-H1/VRN-H2 model based on the presence/absence of VRN-H2 and a winter vs. spring HvBM5A allele.

Introduction Rusts caused by Basidiomycetes of the order Uredinales are among the most serious plant fungal diseases, present worldwide on cereals, vegetables, field crops such as cotton and soybeans, and [...], The potential of the model grass Brachypodium distachyon L. (Brachypodium) for studying grass-pathogen interactions is still underexploited. We aimed to identify genomic regions in Brachypodium associated with quantitative resistance to the false brome rust fungus Puccinia brachypodii. The inbred lines Bd3-1 and Bd1-1, differing in their level of resistance to P. brachypodii, were crossed to develop an [F.sub.2] population. This was evaluated for reaction to a virulent isolate of P brachypodii at both the seedling and advanced growth stages. To validate the results obtained on the [F.sub.2], resistance was quantified in [F.sub.2]-derived [F.sub.3] families in two experiments. Disease evaluations showed quantitative and transgressive segregation for resistance. A new AFLP-based Brachypodium linkage map consisting of 203 loci and spanning 812 cM was developed and anchored to the genome sequence with SSR and SNP markers. Three false brome rust resistance QTLs were identified on chromosomes 2, 3, and 4, and they were detected across experiments. This study is the first quantitative trait analysis in Brachypodium. Resistance to P. brachypodii was governed by a few QTLs: two acting at the seedling stage and one acting at both seedling and advanced growth stages. The results obtained offer perspectives to elucidate the molecular basis of quantitative resistance to rust fungi. Key words: Brachypodium distachyon, AFLP, linkage map, false brome rust, quantitative resistance, QTL. Le potentiel d'utilisation de la graminee modele Brachypodium distachyon L. (Brachypodium) pour l'etude des interactions plante-pathogene est encore sous-utilise. Les auteurs ont voulu identifier des regions genomiques du Brachypodium qui sont associees a la resistance quantitative a l'agent fongique de la rouille brachypode, Puccinia brachypodii. Les lignees fixees Bd3-1 et Bd1-1, lesquelles different en ce qui a trait a leur resistance au P. brachypodii, ont ete croisees pour produire une population [F.sub.2]. Celle-ci a ete evaluee pour sa reaction a un isolat virulent du P. brachypodii a la fois au stade plantule et aux stades plus avances. Pour valider les resultats obtenus chez la [F.sub.2], la resistance a ete quantifiee chez des familles [F.sub.3] derivees d'individus [F.sub.2] au cours de deux essais. Les evaluations de la maladie ont montre une segregation quantitative et transgressive. Une nouvelle carte genetique de marqueurs AFLP comprenant 203 locus et s'etendant sur 812 cM a ete developpee et ancree a la sequence genomique grace a des marqueurs SSR et SNP. Trois QTL de resistance a la rouille brachypode ont ete identifies sur les chromosomes 2, 3 et 4, et ils ont ete detectes dans tous les essais. Ce travail constitue la premiere analyse d'un caractere quantitatif chez Brachypodium. La resistance au P. brachypodii est gouvernee par quelques QTL, deux agissant au stade plantule et un agissant a la fois au stade plantule et aux stades plus avances. Les resultats obtenus offrent des perspectives pour elucider les bases moleculaires de la resistance quantitative aux agents fongiques des rouilles. Mots-cles : Brachypodium distachyon, AFLP, carte genetique, rouille brachypode, resistance quantitative, QTL. [Traduit par la Redaction]