On the origin of six-rowed barley with brittle rachis, agriocrithon [Hordeum vulgare ssp. vulgare f. agriocrithon (Aberg) Bowd.], based on a DNA marker closely linked to the vrs1 (six-row gene) locus

The origin of six-rowed cultivated barley has been revealed to be more complex since the discovery of agriocrithon, a six-rowed barley with brittle rachis. The present study investigates whether such six-rowed brittle barley is wild or hybrid in nature, by analyzing genetic diversity at the cMWG699 marker locus, which is closely linked to the vrs1 (six-row gene) locus. DNA sequence analysis for 42 accessions showed only three types in six-rowed brittle barleys; in contrast, nine sequence types were found in ten wild barleys, ssp. spontaneum, in our previous study. Nucleotide diversities for the six-rowed brittle barley were 2.8–4.5 times lower than that for the ssp. spontaneum at this marker locus. The three sequence types found in the six-rowed brittle barley also appeared in the six-rowed cultivated barley. A cross-allelism test confirmed that the six-rowed character of the six-rowed brittle barley was controlled by the vrs1 locus. The nucleotide diversity and genealogy demonstrated that f. agriocrithon does not have the same level of diversity as found in wild barley, ssp. spontaneum. Consequently, f. agriocrithon does not appear to represent genuinely wild populations, but more probably originated from hybridization between ssp. spontaneum and six-rowed cultivated barley.     

Resequencing the<Emphasis Type="Italic">Vrs1</Emphasis> gene in Spanish barley landraces revealed reversion of six-rowed to two-rowed spike

Six-rowed spike 1 (Vrs1) is a gene of major importance for barley breeding and germplasm management as it is the main gene determining spike row-type (2-rowed vs. 6-rowed). This is a widely used DUS trait, and has been often associated to phenotypic traits beyond spike type. Comprehensive re-sequencing Vrs1 revealed three two-rowed alleles (Vrs1.b2; Vrs1.b3; Vrs1.t1) and four six-rowed (vrs1.a1; vrs1.a2; vrs1.a3; vrs1.a4) in the natural population. However, the current knowledge about Vrs1 alleles and its distribution among Spanish barley subpopulations is still underexploited. We analyzed the gene in a panel of 215 genotypes, made of Spanish landraces and European cultivars. Among 143 six-rowed accessions, 57 had the vrs1.a1 allele, 83 were vrs1.a2, and three showed the vrs1.a3 allele. Vrs1.b3 was found in most two-rowed accessions, and a new allele was observed in 7 out of 50 two-rowed Spanish landraces. This allele, named Vrs1.b5, contains a ‘T’ insertion in exon 2, originally proposed as the causal mutation giving rise to the six-row vrs1.a2 allele, but has an additional upstream deletion that results in the change of 15 amino acids and a potentially functional protein. We conclude that eight Vrs1 alleles (Vrs1.b2, Vrs1.b3, Vrs1.b5, Vrs1.t1, vrs1.a1, vrs1.a2, vrs1.a3, vrs1.a4) discriminate two and six-rowed barleys. The markers described will be useful for DUS identification, plant breeders, and other crop scientists.     

Genetic variation of <Emphasis Type="Italic">Bmy1</Emphasis> alleles in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) investigated by CAPS analysis

The enzyme beta-amylase is one of the most important hydrolytic enzymes in the grain of malting barley and is encoded by the gene Bmy1. To learn more about its structure and function, a total of 657 barley accessions including 541 Hordeum vulgare ssp. vulgare (HV), and 116 H. vulgare ssp. spontaneum (HS) were selected for the cleaved amplified polymorphic sequence (CAPS) analysis. These materials, covering all the 16 kinds of beta-amylase phenotypes screened from more than 8,500 accessions of the world barley germplasm, were classified into 13 CAPS types in the present study. A combined assay of phenotypes and CAPS types revealed extensive genetic variation at the Bmy1 locus, and in total 23 Bmy1 allele types were identified. The newly identified alleles (A-I-11, A-II-6, A-II-7, A-II-10, B-I-3, B-I-12 and B-I-13) provided us with a novel resource for barley breeding and Bmy1 study. In HV barley, six out of seven major allele types (C-II-1, B-II-2, B-Ia-3, A-II-5, A-II-6, and A-II-7) were shared with HS barley; the B-I-8 allele, which was predominant in north European cultivated barley, was found to be unique. Remarkably, very low Bmy1 genetic variation was detected in Tibetan barleys, which puts the validity of the hypothesis that Tibet is one of the original centers of cultivated barley into question.     

Distribution of MWG699 polymorphism in Spanish European barleys.

The STS marker MWG699/TaqI is closely linked to the vrs1 locus and has been proposed as a marker of domestication in barley. This study included 257 cultivated barleys of both two- and six-rowed varieties, mainly from the western Mediterranean region. These included many landraces from the Spanish barley core collection, Moroccan landraces, and a set of accessions from other European countries. Restriction analysis of amplified DNA revealed three alleles, as previously described. Most of the two-rowed entries had the same allele, type K. Six-rowed entries showed both types A and D. Indeed, type D was widespread among Spanish landraces and commercial varieties from central Europe. It was also found in some two-rowed landraces originating from Spain and Morocco. Barleys with the D haplotype were predominantly winter types, whereas the A haplotype was evenly distributed among spring and winter types. These results support the existence of two different genetic sources among six-rowed Spanish landraces.     

Invasion of <Emphasis Type="Italic">Rhynchosporium commune</Emphasis> onto wild barley in the Middle East

Rhynchosporium commune was recently introduced into the Middle East, presumably with the cultivated host barley (Hordeum vulgare). Middle Eastern populations of R. commune on cultivated barley and wild barley (H. spontaneum) were genetically undifferentiated and shared a high proportion of multilocus haplotypes. This suggests that there has been little selection for host specialization on H. spontaneum, a host population often used as a source of resistance genes introduced into its domesticated counterpart, H. vulgare. Low levels of pathogen genetic diversity on H. vulgare as well as on H. spontaneum, indicate that the pathogen was introduced recently into the Middle East, perhaps through immigration on infected cultivated barley seeds, and then invaded the wild barley population. Although it has not been documented, the introduction of the pathogen into the Middle East may have a negative influence on the biodiversity of native Hordeum species.     

Large-scale DNA polymorphism study of <Emphasis Type="Italic">Oryza sativa</Emphasis> and <Emphasis Type="Italic">O. rufipogon</Emphasis> reveals the origin and divergence of Asian rice

Polymorphism over ∼26 kb of DNA sequence spanning 22 loci and one region distributed on chromosomes 1, 2, 3 and 4 was studied in 30 accessions of cultivated rice, Oryza sativa, and its wild relatives. Phylogenetic analysis using all the DNA sequences suggested that O. sativa ssp. indica and ssp. japonica were independently domesticated from a wild species O. rufipogon. O. sativa ssp. indica contained substantial genetic diversity (π = 0.0024), whereas ssp. japonica exhibited extremely low nucleotide diversity (π = 0.0001) suggesting the origin of the latter from a small number of founders. O. sativa ssp. japonica contained a larger number of derived and fixed non-synonymous substitutions as compared to ssp. indica. Nucleotide diversity and genealogical history substantially varied across the 22 loci. A locus, RLD15 on chromosome 2, showed a distinct genealogy with ssp. japonica sequences distantly separated from those of O. rufipogon and O. sativa ssp. indica. Linkage disequilibrium (LD) was analyzed in two different regions. LD in O. rufipogon decays within 5 kb, whereas it extends to ∼50 kb in O. sativa ssp. indica. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Distribution of <Emphasis Type="Italic">Hordoindoline</Emphasis> genes in the genus <Emphasis Type="Italic">Hordeum</Emphasis>

Hordoindoline (Hin) genes, which are known to comprise Hina, Hinb-1, and Hinb-2, are associated with grain hardness in barley. However, the interspecific variation in the Hin genes in the genus Hordeum has not been studied in detail. We examined the variation in Hin genes and used it to infer the phylogenetic relationships between the genes found in two H. vulgare subspecies (cultivated barley and H. vulgare subsp. spontaneum) and 10 wild relatives (H. bogdanii, H. brachyantherum, H. bulbosum, H. chilense, H. comosum, H. marinum, H. murinum, H. patagonicum, H. pusillum, and H. roshevitzii). The Hina and Hinb genes of these species were amplified by PCR. We found two Hinb genes in three wild species (H. bogdanii, H. brachyantherum, and H. roshevitzii) and preliminarily named them Hinb-A and Hinb-B. Cluster analysis showed that the 17 Hinb genes present in Hordeum formed two distinct clusters (named A and B). Seven Hinb genes were included in Cluster-A, and 10 Hinb genes were included in Cluster-B. All Hinb-A genes were included in Cluster-A, while all of the Hinb-B genes were included in Cluster-B. In contrast, the Hinb-1 and Hinb-2 genes in H. vulgare were included in Cluster-B. These results suggest that the Hinb genes duplicated during the early stages of diversification in the genus Hordeum. On the other hand, the Hinb-1 and Hinb-2 genes in H. vulgare seem to have been generated by a duplication of the Hinb gene after the split of the lineages leading to H. vulgare and H. bulbosum.     

Genetic Diversity Analysis of Tibetan Wild Barley Using SSR Markers

One hundred and six accessions of wild barley collected from Tibet, China, including 50 entries of the two-rowed wild barley Hordeum vulgare ssp. spontaneum (HS), 29 entries of the six-rowed wild barley Hordeum vulgare ssp. agriocrithon (HA), and 27 entries of the six-rowed wild barley Hordeum vulgare ssp. agriocrithon var. lagunculiforme (HL), were analyzed using 30 SSR markers selected from the seven barley linkage groups for studying genetic diversity and evolutionary relationship of the three subspecies of Tibetan wild barley to cultivated barley in China. Over the 30 genetic loci that were studied, 229 alleles were identified among the 106 accessions, of which 70 were common alleles. H. vulgare ssp. spontaneum possesses about thrice more private alleles (2.83 alleles/locus) than HS (0.93 alleles/locus), whereas almost no private alleles were detected in HL. The genetic diversity among-subspecies is much higher than that within-subspecies. Generally, the genetic diversity among the three subspecies is of the order HS > HL > HA. Phylogenetic analysis of the 106 accessions showed that all the accessions of HS and HA was clustered in their own groups, whereas the 27 accessions of HL were separated into two groups (14 entries with group HS and the rest with group HA). This indicated that HL was an intermediate form between HS and HA. Based on this study and previous works, we suggested that Chinese cultivated barley might evolve from HS via HL to HA.     

AB-QTL analysis in spring barley: III. Identification of exotic alleles for the improvement of malting quality in spring barley (<Emphasis Type="Italic">H. vulgare</Emphasis> ssp. <Emphasis Type="Italic">spontaneum</Emphasis>)

Malting quality is genetically determined by the complex interaction of numerous traits which are expressed prior to and, in particular, during the malting process. Here, we applied the advanced backcross quantitative trait locus (AB-QTL) strategy (Tanksley and Nelson, Theor Appl Genet 92:191–203, 1996), to detect QTLs for malting quality traits and, in addition, to identify favourable exotic alleles for the improvement of malting quality. For this, the BC₂DH population S42 was generated from a cross between the spring barley cultivar Scarlett and the wild barley accession ISR42-8 (Hordeum vulgare ssp. spontaneum). A QTL analysis in S42 for seven malting parameters measured in two different environments yielded 48 QTLs. The exotic genotype improved the trait performance at 18 (37.5%) of 48 QTLs. These favourable exotic alleles were detected, in particular, on the chromosome arms 3HL, 4HS, 4HL and 6HL. The exotic allele on 4HL, for example, improved α-amylase activity by 16.3%, fermentability by 0.8% and reduced raw protein by 2.4%. On chromosome 6HL, the exotic allele increased α-amylase by 16.0%, fermentability by 1.3%, friability by 7.3% and reduced viscosity by 2.9%. Favourable transgressive segregation, i.e. S42 lines exhibiting significantly better performance than the recurrent parent Scarlett, was recorded for four traits. For α-amylase, fermentability, fine-grind extract and VZ45 20, 16, 2 and 26 S42 lines, respectively, surpassed the recurrent parent Scarlett. The present study hence demonstrates that wild barley does harbour valuable alleles, which can enrich the genetic basis of cultivated barley and improve malting quality traits.     

High-resolution Mapping and Analysis of the Resistance Locus <Emphasis Type="Italic">Rpi-abpt</Emphasis> Against <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Potato

Introduction of more durable resistance against Phytophthora infestans causing late blight into the cultivated potato is of importance for sustainable agriculture. We identified a new monogenically inherited resistance locus that is localized on chromosome 4. The resistance is derived from an ABPT clone, which is originally a complex quadruple hybrid in which Solanum acaule, S. bulbocastanum, S. phureja and S. tuberosum were involved. Resistance data of the original resistant accessions of the wild species and analysis of mobility of AFLP markers linked to the resistance locus suggest that the resistance locus is originating from S. bulbocastanum. A population of 1383 genotypes was screened with two AFLP markers flanking the Rpi-abpt locus and 98 recombinants were identified. An accurate high-resolution map was constructed and the Rpi-abpt locus was localized in a 0.5 cM interval. One AFLP marker was found to co-segregate with the Rpi-abpt locus. Its DNA sequence was highly similar with sequences found on a tomato BAC containing several resistance gene analogues on chromosome 4 and its translated protein sequence appeared to be homologous to several disease resistance related proteins. The results indicated that the Rpi-abpt gene is a member of an R gene cluster.     

Development of candidate introgression lines using an exotic barley accession (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> ssp.<Emphasis Type="Italic"> spontaneum</Emphasis>) as donor

In the present paper, we report on the selection of two sets of candidate introgression lines (pre-ILs) in spring barley. Two BC₂DH populations, S42 and T42, were generated by introgressing an accession of Hordeum vulgare ssp. spontaneum (ISR42-8, from Israel) into two different spring barley cultivars, Scarlett (S) and Thuringia (T). From these BC₂DH populations two sets with 49 (S42) and 43 (T42) pre-ILs were selected, and their genomic architecture as revealed by SSR marker analysis was characterised. The selected pre-ILs cover at least 98.1% (S42) and 93.0% (T42) of the exotic genome in overlapping introgressions and contain on average 2 (S42) and 1.5 (T42) additional non-target introgressions. In order to illustrate a potential application and validation of these pre-ILs, the phenotypic effect of the exotic introgression at the locus of the major photoperiod response gene Ppd-H1 was analysed. Pre-ILs carrying the introgression at the Ppd-H1 locus flowered significantly earlier than the elite parents, and the introgression maintained its effect across the two genetic backgrounds and across four tested environments. The selected pre-ILs represent a first promising step towards the assessment and utilization of genetic variation present in exotic barley. They may promote the breeding progress, serve for the verification of QTL effects and provide a valuable resource for the unravelling of gene function, e.g. by expression profiling or map-based cloning.     

Molecular mapping of <Emphasis Type="Italic">Rym17</Emphasis>, a dominant and <Emphasis Type="Italic">rym18</Emphasis> a recessive barley yellow mosaic virus (BaYMV) resistance genes derived from <Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.

PK23-2, a line of six-rowed barley (Hordeum vulgare L.) originating from Pakistan, has resistance to Japanese strains I and III of the barley yellow mosaic virus (BaYMV). To identify the source of resistance in this line, reciprocal crosses were made between the susceptible cultivar Daisen-gold and PK23-2. Genetic analyses in the F₁ generation, F₂ generation, and a doubled haploid population (DH45) derived from the F₁ revealed that PK23-2 harbors one dominant and one recessive resistance genes. A linkage map was constructed using 61 lines of DH45 and 127 DNA markers; this map covered 1268.8 cM in 10 linkage groups. One QTL having a LOD score of 4.07 and explaining 26.8% of the phenotypic variance explained (PVE) for resistance to BaYMV was detected at DNA marker ABG070 on chromosome 3H. Another QTL having a LOD score of 3.53 and PVE of 27.2% was located at marker Bmag0490 on chromosome 4H. The resistance gene on chromosome 3H, here named Rym17, showed dominant inheritance, whereas the gene on chromosome 4H, here named rym18, showed recessive inheritance in F₁ populations derived from crosses between several resistant lines of DH45 and Daisen-gold. The BaYMV recessive resistance genes rym1, rym3, and rym5, found in Japanese barley germplasm, were not allelic to rym18. These results revealed that PK23-2 harbors two previously unidentified resistance genes, Rym17 on 3H and rym18 on 4H; Rym17 is the first dominant BaYMV resistance gene to be identified in primary gene pool. These new genes, particularly dominant Rym17, represent a potentially valuable genetic resource against BaYMV disease.     

<Emphasis Type="Italic">S</Emphasis> locus-linked F-box genes expressed in anthers of <Emphasis Type="Italic">Hordeum bulbosum</Emphasis>

Diploid Hordeum bulbosum (a wild relative of cultivated barley) exhibits a two-locus self-incompatibility (SI) system gametophytically controlled by the unlinked multiallelic loci S and Z. This unique SI system is observed in the grasses (Poaceae) including the tribe Triticeae. This paper describes the identification and characterization of two F-box genes cosegregating with the S locus in H. bulbosum, named Hordeum S locus-linked F-box 1 (HSLF1) and HSLF2, which were derived from an S ₃ haplotype-specific clone (HAS175) obtained by previous AMF (AFLP-based mRNA fingerprinting) analysis. Sequence analysis showed that both genes encode similar F-box proteins with a C-terminal leucine-rich repeat (LRR) domain, which are distinct from S locus (or S haplotype-specific) F-box protein (SLF/SFB), a class of F-box proteins identified as the pollen S determinant in S-RNase-based gametophytic SI systems. A number of homologous F-box genes with an LRR domain were found in the rice genome, although the functions of the gene family are unknown. One allele of the HSLF1 gene (HSLF1-S ₃) was expressed specifically in mature anthers, whereas no expression was detected from the other two alleles examined. Although the degree of sequence polymorphism among the three HSLF1 alleles was low, a frameshift mutation was found in one of the unexpressed alleles. The HSLF2 gene showed a low level of expression with no tissue specificity as well as little sequence polymorphism among the three alleles. The multiplicity of S locus-linked F-box genes is discussed in comparison with those found in the S-RNase-based SI system. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB511822–AB511825 and AB511859–AB511862.     

Polymorphism of hordein-coding loci in cultivated barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) in Afghanistan

Polymorphism of hordeins encoded by the Hrd A, Hrd B, and Hrd F loci was analyzed in 84 accessions of local barley (Hordeum vulgare L.) varieties from major agricultural regions of Afghanistan using starch gel electrophoresis. Forty alleles of the Hrd A locus with the frequencies from 0.12 to 32.73%, 62 alleles of the Hrd B locus with the frequencies from 0.12 to 14.29%, and five alleles of the Hrd F locus with the frequencies from 0.59 to 32.15% have been identified. The conclusion about genetic similarity of barley populations from different regions of Afghanistan is made on the basis of cluster analysis of the matrix of allele frequencies in barley populations from 31 localities. The local barley populations form four unequal clusters. The largest cluster I includes populations from 14 localities of Afghanistan. The second largest cluster IV consists of populations from ten localities, and clusters II and III comprise populations from four and three localities, respectively. Each of the four clusters includes populations from different regions of northern and southern Afghanistan. Based on our results, we conclude that the diversity of hordein-coding loci and the distribution of their alleles among different regions of Afghanistan are the consequences of introduction of barley landraces and their distribution over trade routes.     

High-density AFLP map of nonbrittle rachis 1 (<Emphasis Type="Italic">btr1</Emphasis>) and 2 (<Emphasis Type="Italic">btr2</Emphasis>) genes in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

Wild relatives of barley disperse their seeds at maturity by means of their brittle rachis. In cultivated barley, brittleness of the rachis was lost during domestication. Nonbrittle rachis of occidental barley lines is controlled by a single gene (btr1) on chromosome 3H. However, nonbrittle rachis of oriental barley lines is controlled by a major gene (btr2) on chromosome 3H and two quantitative trait loci on chromosomes 5HL and 7H. This result suggests multiple mutations of the genes involved in the formation of brittle rachis in oriental lines. The btr1 and btr2 loci did not recombine in the mapping population analyzed. This result agrees with the theory of tight linkage between the two loci. A high-density amplified fragment-length polymorphism (AFLP) map of the btr1/btr2 region was constructed, providing an average density of 0.08 cM/locus. A phylogenetic tree based on the AFLPs showed clear separation of occidental and oriental barley lines. Thus, barley consists of at least two lineages as far as revealed by molecular markers linked to nonbrittle rachis genes.Electronic Supplementary Material Supplementary material is available for this article at An erratum to this article can be found at     

Analysis of the barley chromosome 2 region containing the six-rowed spike gene <Emphasis Type="Italic">vrs1</Emphasis> reveals a breakdown of rice–barley micro collinearity by a transposition

In cultivated barley (Hordeum vulgare ssp. vulgare), six-rowed spikes produce three times as many seeds per spike as do two-rowed spikes. The determinant of this trait is the Mendelian gene vrs1, located on chromosome 2H, which is syntenous with rice (Oryza sativa) chromosomes 4 and 7. We exploited barley–rice micro-synteny to increase marker density in the vrs1 region as a prelude to its map-based cloning. The rice genomic sequence, covering a 980 kb contig, identified barley ESTs linked to vrs1. A high level of conservation of gene sequence was obtained between barley chromosome 2H and rice chromosome 4. A total of 22 EST-based STS markers were placed within the target region, and the linear order of these markers in barley and rice was identical. The genetic window containing vrs1 was narrowed from 0.5 to 0.06 cM, which facilitated covering the vrs1 region by a 518 kb barley BAC contig. An analysis of the contig sequence revealed that a rice Vrs1 orthologue is present on chromosome 7, suggesting a transposition of the chromosomal segment containing Vrs1 within barley chromosome 2H. The breakdown of micro-collinearity illustrates the limitations of synteny cloning, and stresses the importance of implementing genomic studies directly in the target species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A <Emphasis Type="Italic">Pseudo-Response Regulator</Emphasis> is misexpressed in the photoperiod insensitive <Emphasis Type="Italic">Ppd-D1a</Emphasis> mutant of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Ppd-D1 on chromosome 2D is the major photoperiod response locus in hexaploid wheat (Triticum aestivum). A semi-dominant mutation widely used in the “green revolution” converts wheat from a long day (LD) to a photoperiod insensitive (day neutral) plant, providing adaptation to a broad range of environments. Comparative mapping shows Ppd-D1 to be colinear with the Ppd-H1 gene of barley (Hordeum vulgare) which is a member of the pseudo-response regulator (PRR) gene family. To investigate the relationship between wheat and barley photoperiod genes we isolated homologues of Ppd-H1 from a ‘Chinese Spring’ wheat BAC library and compared them to sequences from other wheat varieties with known Ppd alleles. Varieties with the photoperiod insensitive Ppd-D1a allele which causes early flowering in short (SD) or LDs had a 2 kb deletion upstream of the coding region. This was associated with misexpression of the 2D PRR gene and expression of the key floral regulator FT in SDs, showing that photoperiod insensitivity is due to activation of a known photoperiod pathway irrespective of day length. Five Ppd-D1 alleles were found but only the 2 kb deletion was associated with photoperiod insensitivity. Photoperiod insensitivity can also be conferred by mutation at a homoeologous locus on chromosome 2B (Ppd-B1). No candidate mutation was found in the 2B PRR gene but polymorphism within the 2B PRR gene cosegregated with the Ppd-B1 locus in a doubled haploid population, suggesting that insensitivity on 2B is due to a mutation outside the sequenced region or to a closely linked gene. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. J. Beales and A. Turner contributed equally to the work.     

Introgression of an intermediate <Emphasis Type="Italic">VRNH1</Emphasis> allele in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) leads to reduced vernalization requirement without affecting freezing tolerance

The process of vernalization is mainly controlled by two genes in winter barley (Hordeum vulgare L.), VRNH1 and VRNH2. A recessive allele at VRNH1 and a dominant allele at VRNH2 must be present to induce a vernalization requirement. In addition, this process is usually associated with greater low-temperature tolerance. Spanish barleys originated in areas with mild winters and display a reduced vernalization requirement compared with standard winter cultivars. The objective of this study was to investigate the genetic origin of this reduced vernalization requirement and its effect on frost tolerance. We introgressed the regions of a typical Spanish barley line that carry VRNH1 and VRNH2 into a winter cultivar, Plaisant, using marker-assisted backcrossing. We present the results of a set of 12 lines introgressed with all four possible combinations of VRNH1 and VRNH2, which were evaluated for vernalization requirement and frost tolerance. The reduced vernalization requirement of the Spanish parent was confirmed, and was found to be due completely to the effect of the VRNH1 region. The backcross lines showed no decline in frost tolerance compared with that of the recurrent parent unless they carried an extra segment of chromosome 5H. This extra segment, a carryover of the backcross process, apparently contained the well-known frost tolerance quantitative trait locus Fr-H2. We demonstrate that it is possible to manipulate the vernalization requirement with only minor effects on frost tolerance. This finding opens the path to creating new types of barley cultivars that are better suited to specific environments, especially in a climate-change scenario.     

Evolution of nematode-resistant <Emphasis Type="Italic">Mi</Emphasis>-<Emphasis Type="Italic">1</Emphasis> gene homologs in three species of <Emphasis Type="Italic">Solanum</Emphasis>

Plants have evolved several defense mechanisms, including resistance genes. Resistance to the root-knot nematode Meloidogyne incognita has been found in wild plant species. The molecular basis for this resistance has been best studied in the wild tomato Solanum peruvianum and it is based on a single dominant gene, Mi-1.2, which is found in a cluster of seven genes. This nematode attacks fiercely several crops, including potatoes. The genomic arrangement, number of copies, function and evolution of Mi-1 homologs in potatoes remain unknown. In this study, we analyzed partial genome sequences of the cultivated potato species S. tuberosum and S. phureja and identified 59 Mi-1 homologs. Mi-1 homologs in S. tuberosum seem to be arranged in clusters and located on chromosome 6 of the potato genome. Previous studies have suggested that Mi-1 genes in tomato evolved rapidly by frequent sequence exchanges among gene copies within the same cluster, losing orthologous relationships. In contrast, Mi-1 homologs from cultivated potato species (S. tuberosum and S. phureja) seem to have evolved by a birth-and-death process, in which genes evolve mostly by mutations and interallelic recombinations in addition to sequence exchanges.