Endogenous ABA concentration and cytoplasmic membrane fluidity in microspores of oilseed rape (Brassica napus L.) genotypes differing in responsiveness to androgenesis induction

Key message

A better understanding of androgenesis with a focus on the changes in plasma membrane fluidity and endogenous ABA content affecting embryogenesis induction in microspore suspension of B. napus.

Abstract

Changes in plasma membrane fluidity (MF) and ABA content associated with androgenesis induction were under the study. Both parameters were monitored in microspores of two Brassica napus L. genotypes differing in their response to androgenic induction under heat (1 day at 32 °C). MF was assessed by DPH method. ABA content was evaluated by ELISA. Heat caused microspores’ plasma membrane to become more rigid. Lower MF in microspores of ‘DH 4079’ (of high androgenic potential) seems to maintain proper cell protection and leads to efficient embryogenesis induction. Plasma membrane remodelling coincided with changes of ABA content in microspores and in the culture medium in both genotypes. ABA concentration (μM) and ABA content (fmol per 10⁴ microspores or pmol g^?1 FW) were for the first time measured in microspores. ABA concentration (μM) in microspores and in the culture medium (nM) differed significantly for the genotype and the treatment. The interaction between both variables was also significant. In general, ABA content ranged from <3.5 to 87.1 fmol per 10⁴ microspores. The highest content of ABA was detected in ‘DH 4079’ microspores at 32 °C. Assuming a mean microspores’ radius of 10 μm, it corresponds to ABA concentration of 2.1 μM. Heat shock resulted in quantum of medium pH reduction (0.1–0.2) and increased levels of ABA in microspores and in the medium of both tested genotypes. However, heat induced increase of ABA content in microspores of non-responsive ‘Campino’ had no clear-cut impact, on androgenesis induction efficiency, which suggests a more complex mechanism of process initiation.     

Meiotic chromosome pairing behaviour of natural tetraploids and induced autotetraploids of Actinidia chinensis

Key message

Non-preferential chromosome pairing was identified in tetraploid Actinidia chinensis and a higher mean multivalent frequency in pollen mother cells was found in colchine-induced tetraploids of A. chinensis compared with naturally occurring tetraploids.

Abstract

Diploid and tetraploid Actinidia chinensis are used for the development of kiwifruit cultivars. Diploid germplasm can be exploited in a tetraploid breeding programme via unreduced (2n) gametes and chemical-induced chromosome doubling of diploid cultivars and selections. Meiotic chromosome behaviour in diploid A. chinensis ‘Hort16A’ and colchicine-induced tetraploids from ‘Hort16A’ was analysed and compared with that in a diploid male and tetraploid males of A. chinensis raised from seeds sourced from the wild in China. Both naturally occurring and induced tetraploids formed multivalents, but colchicine-induced tetraploids showed a higher mean multivalent frequency in the pollen mother cells. Lagging chromosomes at anaphase I and II were observed at low frequencies in the colchicine-induced tetraploids. To investigate whether preferential or non-preferential chromosome pairing occurs in tetraploid A. chinensis, the inheritance of microsatellite alleles was analysed in the tetraploid progeny of crosses between A. chinensis (4x) and A. arguta (4x). The frequencies of inherited microsatellite allelic combinations in the hybrids suggested that non-preferential chromosome pairing had occurred in the tetraploid A. chinensis parent.     

Introduction of chromosome segment carrying the seed storage protein genes from chromosome 1V of Dasypyrum villosum showed positive effect on bread-making quality of common wheat

Key message

Development of wheat- D. villosum 1V#4 translocation lines; physically mapping the Glu - V1 and Gli - V1 / Glu - V3 loci; and assess the effects of the introduced Glu - V1 and Gli - V1 / Glu - V3 on wheat bread-making quality.

Abstract

Glu-V1 and Gli-V1/Glu-V3 loci, located in the chromosome 1V of Dasypyrum villosum, were proved to have positive effects on grain quality. However, there are very few reports about the transfer of the D. villosum-derived seed storage protein genes into wheat background by chromosome manipulation. In the present study, a total of six CS-1V#4 introgression lines with different alien-fragment sizes were developed through ionizing radiation of the mature female gametes of CS––D. villosum 1V#4 disomic addition line and confirmed by cytogenetic analysis. Genomic in situ hybridization (GISH), chromosome C-banding, twelve 1V#4-specific EST–STS markers and seed storage protein analysis enabled the cytological physical mapping of Glu-V1 and Gli-V1/Glu-V3 loci to the region of FL 0.50–1.00 of 1V#4S of D. villosum. The Glu-V1 allele of D. villosum was Glu-V1a and its coded protein was V71 subunit. Quality analysis indicated that Glu-V1a together with Gli-V1/Glu-V3 loci showed a positive effect on protein content, Zeleny sedimentation value and the rheological characteristics of wheat flour dough. In addition, the positive effect could be maintained when specific Glu-V1 and Gli-V1/Glu-V3 loci were transferred to the wheat genetic background as in the case of T1V#4S-6BS·6BL, T1V#4S·1BL and T1V#4S·1DS translocation lines. These results showed that the chromosome segment carrying the Glu-V1 and Gli-V1/Glu-V3 loci in 1V#4S of D. villosum had positive effect on bread-making quality, and the T1V#4S-6BS·6BL and T1V#4S·1BL translocation lines could be useful germplasms for bread wheat improvement. The developed 1V#4S-specific molecular markers could be used to rapidly identify and trace the alien chromatin of 1V#4S in wheat background.     

A novel T-DNA integration in rice involving two interchromosomal translocations

Key message

A male sterile transgenic rice plant TC-19 harboured a novel T-DNA integration in chromosome 8 with two interchromosomal translocations of 6.55 kb chromosome 3 and 29.8 kb chromosome 9 segments.

Abstract

We report a complex Agrobacterium T-DNA integration in rice (Oryza sativa) associated with two interchromosomal translocations. The T-DNA-tagged rice mutant TC-19, which harboured a single copy of the T-DNA, displayed male sterile phenotype in the homozygous condition. Analysis of the junctions between the T-DNA ends and the rice genome by genome walking showed that the right border is flanked by a chromosome 3 sequence and the left border is flanked by a chromosome 9 sequence. Upon further walking on chromosome 3, a chromosome 3/chromosome 8 fusion was detected. Genome walking from the opposite end of the chromosome 8 break point revealed a chromosome 8/chromosome 9 fusion. Our findings revealed that the T-DNA, together with a 6.55-kb region of chromosome 3 and a 29.8-kb region of chromosome 9, was translocated to chromosome 8. Southern blot analysis of the homozygous TC-19 mutant revealed that the native sequences of chromosome 3 and 9 were restored but the disruption of chromosome 8 in the first intron of the gene Os08g0152500 was not restored. The integration of the complex T-DNA in chromosome 8 caused male sterility.     

Different non-host resistance responses of two rice subspecies,japonica and indica,to Puccinia striiformis f. sp. tritici

Key message

Japonica and indica have different non-host resistance (NHR) abilities to Puccinia striiformis f. sp. tritici ( Pst ), and hydrogen peroxide (H ₂ O ₂ ) has a positive function in NHR to japonica against Pst.

Abstract

Non-host interactions between Puccinia striiformis f. sp. tritici (Pst) and two rice subspecies were characterized using 23 rice varieties, including 11 japonica and 12 indica. Results showed that the infected fungal structures were easily produced in the leaves of indica, whereas only several substomatal vesicles and primary infection hyphae were observed in the leaves of japonica. This result indicated that indica is less resistant or more susceptible to Pst than japonica. Hydrogen peroxide accumulated in the initial phase of japonica–Pst interaction but not in indica–Pst interaction. A set of reactive oxygen species (ROS)-related genes was also induced in response to Pst infection, suggesting that ROS activation is one of the major mechanisms of non-host resistance of rice to Pst.     

Genome-wide QTL and bulked transcriptomic analysis reveals new candidate genes for the control of tuber carotenoid content in potato (Solanum tuberosum L.)

Key message

Genome-wide QTL analysis of potato tuber carotenoid content was investigated in populations of Solanum tuberosum Group Phureja that segregate for flesh colour, revealing a novel major QTL on chromosome 9.

Abstract

The carotenoid content of edible plant storage organs is a key nutritional and quality trait. Although the structural genes that encode the biosynthetic enzymes are well characterised, much less is known about the factors that determine overall storage organ content. In this study, genome-wide QTL mapping, in concert with an efficient ‘genetical genomics’ analysis using bulked samples, has been employed to investigate the genetic architecture of potato tuber carotenoid content. Two diploid populations of Solanum tuberosum Group Phureja were genotyped (AFLP, SSR and DArT markers) and analysed for their tuber carotenoid content over two growing seasons. Common to both populations were QTL that explained relatively small proportions of the variation in constituent carotenoids and a major QTL on chromosome 3 explaining up to 71 % of the variation in carotenoid content. In one of the populations (01H15), a second major carotenoid QTL was identified on chromosome 9, explaining up to 20 % of the phenotypic variation. Whereas the major chromosome 3 QTL was likely to be due to an allele of a gene encoding β-carotene hydroxylase, no known carotenoid biosynthetic genes are located in the vicinity of the chromosome 9 QTL. A unique expression profiling strategy using phenotypically distinct bulks comprised individuals with similar carotenoid content provided further support for the QTL mapping to chromosome 9. This study shows the potential of using the potato genome sequence to link genetic maps to data arising from eQTL approaches to enhance the discovery of candidate genes underlying QTLs.     

Identification of a robust molecular marker for the detection of the stem rust resistance gene Sr45 in common wheat

Key message

Fine mapping of the Ug99 effective stem rust resistance gene Sr45 introgressed into common wheat from the D -genome goatgrass Aegilops tauschii.

Abstract

Stem rust resistance gene Sr45, discovered in Aegilops tauschii, the progenitor of the D -genome of wheat, is effective against commercially important Puccinia graminis f. sp. tritici races prevalent in Australia, South Africa and the Ug99 race group. A synthetic hexaploid wheat (RL5406) generated by crossing Ae. tauschii accession RL5289 (carrying Sr45 and the leaf rust resistance gene Lr21) with a tetraploid experimental line ‘TetraCanthatch’ was previously used as the source in the transfer of these rust resistance genes to other hexaploid cultivars. Previous genetic studies on hexaploid wheats mapped Sr45 on the short arm of chromosome 1D with the following gene order: centromere–Sr45–Sr33–Lr21–telomere. To identify closely linked markers, we fine mapped the Sr45 region in a large mapping population generated by crossing CS1D5406 (disomic substitution line with chromosome 1D of RL5406 substituted for Chinese Spring 1D) with Chinese Spring. Closely linked markers based on 1DS-specific microsatellites, expressed sequence tags and AFLP were useful in the delineation of the Sr45 region. Sequences from an AFLP marker amplified a fragment that was linked with Sr45 at a distance of 0.39 cM. The fragment was located in a bacterial artificial chromosome clone of contig (ctg)2981 of the Ae. tauschii accession AL8/78 physical map. A PCR marker derived from clone MI221O11 of ctg2981 amplified 1DS-specific sequence that harboured an 18-bp indel polymorphism that specifically tagged the Sr45 carrying haplotype. This new Sr45 marker can be combined with a previously reported marker for Lr21, which will facilitate selecting Sr45 and Lr21 in breeding populations.     

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.     

New names,combinations, and lectotypifications in Heterotheca (Compositae: Astereae)

The following new names and combinations are proposed:Heterotheca barbata (Rydb.) Semple,H. horrida subsp.cinerascens (S. F. Blake) Semple,H. fulcrata vararizonica Semple,H. fulcrata var.senilis (Wooton & Standley) Semple,H. oregona var.compacta (Keck) Semple,H. oregona var.rudis (Greene) Semple,H. oregona var.scaberrima (A. Gray) Semple,H. pumila (Greene) Semple,H. villosa var.pedunculata (Greene) V. Harms ex Semple, andH. zionensis Semple. The following chromosome numbers are reported for the first time:H. fulcrata var.arizonica, 2n=9 _II ;H. horrida subsp.cinerascens, 2n=18 _II ;H. pumila, 2n=9 _II ,2n=18 _II ;H. zionensis, 2n=9 _II .     

A major QTL associated with Fusarium oxysporum race 1 resistance identified in genetic populations derived from closely related watermelon lines using selective genotyping and genotyping-by-sequencing for SNP discovery

Key message

A major quantitative trait locus (QTL) for Fusarium oxysporum Fr. f. sp. niveum race 1 resistance was identified by employing a “selective genotyping” approach together with genotyping-by-sequencing technology to identify QTLs and single nucleotide polymorphisms associated with the resistance among closely related watermelon genotypes.

Abstract

Fusarium wilt is a major disease of watermelon caused by the soil-borne fungus Fusarium oxysporum Schlechtend.:Fr. f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hans (Fon). In this study, a genetic population of 168 F₃ families (24 plants in each family) exhibited continuous distribution for Fon race 1 response. Using a “selective genotyping” approach, DNA was isolated from 91 F₂ plants whose F₃ progeny exhibited the highest resistance (30 F₂ plants) versus highest susceptibility (32 F₂ plants), or moderate resistance to Fon race 1 (29 F₂ plants). Genotyping-by-sequencing (GBS) technology was used on these 91 selected F₂ samples to produce 266 single nucleotide polymorphism (SNP) markers, representing the 11 chromosomes of watermelon. A major quantitative trait locus (QTL) associated with resistance to Fon race 1 was identified with a peak logarithm of odds (LOD) of 33.31 and 1-LOD confidence interval from 2.3 to 8.4 cM on chromosome 1 of the watermelon genetic map. This QTL was designated “Fo-1.1” and is positioned in a genomic region where several putative pathogenesis-related or putative disease-resistant gene sequences were identified. Additional independent, but minor QTLs were identified on chromosome 1 (LOD 4.16), chromosome 3 (LOD 4.36), chromosome 4 (LOD 4.52), chromosome 9 (LOD 6.8), and chromosome 10 (LOD 5.03 and 4.26). Following the identification of a major QTL for resistance using the “selective genotyping” approach, all 168 plants of the F ₂ population were genotyped using the SNP nearest the peak LOD, confirming the association of this SNP marker with Fon race 1 resistance. The results in this study should be useful for further elucidating the mechanism of resistance to Fusarium wilt and in the development of molecular markers for use in breeding programs of watermelon.     

Comparative QTL analysis of root lesion nematode resistance in barley

Key message

This study demonstrates for the first time that resistance to different root lesion nematodes ( P. neglectus and P. penetrans ) is controlled by a common QTL. A major resistance QTL ( Rlnnp6H ) has been mapped to chromosome 6H using two independent barley populations.

Abstract

Root lesion nematodes (Pratylenchus spp.) are important pests in cereal production worldwide. We selected two doubled haploid populations of barley (Igri × Franka and Uschi × HHOR 3073) and infected them with Pratylenchus penetrans and Pratylenchus neglectus. Nematode multiplication rates were measured 7 or 10 weeks after infection. In both populations, continuous phenotypic variations for nematode multiplication rates were detected indicating a quantitative inheritance of resistance. In the Igri × Franka population, four P. penetrans resistance QTLs were mapped with 857 molecular markers on four linkage groups (2H, 5H, 6H and 7H). In the Uschi × HHOR 3073 population, eleven resistance QTLs (P. penetrans and P. neglectus) were mapped with 646 molecular markers on linkage groups 1H, 3H, 4H, 5H, 6H and 7H. A major resistance QTL named Rlnnp6H (LOD score 6.42–11.19) with a large phenotypic effect (27.5–36.6 %) for both pests was mapped in both populations to chromosome 6H. Another resistance QTL for both pests was mapped on linkage group 5H (Igri × Franka population). These data provide first evidence for common resistance mechanisms against different root lesion nematode species. The molecular markers are a powerful tool for the selection of resistant barley lines among segregating populations because resistance tests are time consuming and laborious.     

Fine mapping of Co-x,an anthracnose resistance gene to a highly virulent strain of Colletotrichum lindemuthianum in common bean

Key message

The Co - x anthracnose R gene of common bean was fine-mapped into a 58 kb region at one end of chromosome 1, where no canonical NB-LRR-encoding genes are present in G19833 genome sequence.

Abstract

Anthracnose, caused by the phytopathogenic fungus Colletotrichum lindemuthianum, is one of the most damaging diseases of common bean, Phaseolus vulgaris. Various resistance (R) genes, named Co-, conferring race-specific resistance to different strains of C. lindemuthianum have been identified. The Andean cultivar JaloEEP558 was reported to carry Co-x on chromosome 1, conferring resistance to the highly virulent strain 100. To fine map Co-x, 181 recombinant inbred lines derived from the cross between JaloEEP558 and BAT93 were genotyped with polymerase chain reaction (PCR)-based markers developed using the genome sequence of the Andean genotype G19833. Analysis of RILs carrying key recombination events positioned Co-x at one end of chromosome 1 to a 58 kb region of the G19833 genome sequence. Annotation of this target region revealed eight genes: three phosphoinositide-specific phospholipases C (PI-PLC), one zinc finger protein and four kinases, suggesting that Co-x is not a classical nucleotide-binding leucine-rich encoding gene. In addition, we identified and characterized the seven members of common bean PI-PLC gene family distributed into two clusters located at the ends of chromosomes 1 and 8. Co-x is not a member of Co-1 allelic series since these two genes are separated by at least 190 kb. Comparative analysis between soybean and common bean revealed that the Co-x syntenic region, located at one end of Glycine max chromosome 18, carries Rhg1, a major QTL contributing to soybean cyst nematode resistance. The PCR-based markers generated in this study should be useful in marker-assisted selection for pyramiding Co-x with other R genes.     

Zinc and iron concentration QTL mapped in a Triticum spelta × T. aestivum cross

Key message

Ten QTL underlying the accumulation of Zn and Fe in the grain were mapped in a set of RILs bred from the cross Triticum spelta × T. aestivum . Five of these loci (two for Zn and three for Fe) were consistently detected across seven environments.

Abstract

The genetic basis of accumulation in the grain of Zn and Fe was investigated via QTL mapping in a recombinant inbred line (RIL) population bred from a cross between Triticum spelta and T. aestivum. The concentration of the two elements was measured from grain produced in three locations over two consecutive cropping seasons and from a greenhouse trial. The range in Zn and Fe concentration across the RILs was, respectively, 18.8–73.5 and 25.3–59.5 ppm, and the concentrations of the two elements were positively correlated with one another (rp =+0.79). Ten QTL (five each for Zn and Fe accumulation) were detected, mapping to seven different chromosomes. The chromosome 2B and 6A grain Zn QTL were consistently expressed across environments. The proportion of the phenotype explained (PVE) by QZn.bhu-2B was >16 %, and the locus was closely linked to the SNP marker 1101425|F|0, while QZn.bhu-6A (7.0 % PVE) was closely linked to DArT marker 3026160|F|0. Of the five Fe QTL detected, three, all mapping to chromosome 1A were detected in all seven environments. The PVE for QFe.bhu-3B was 26.0 %.     

QTL mapping for salt tolerance and domestication-related traits in Vigna marina subsp. oblonga,a halophytic species

Key message

QTL mapping in F ₂ population [ V. luteola × V. marina subsp. oblonga ] revealed that the salt tolerance in V. marina subsp. oblonga is controlled by a single major QTL.

Abstract

The habitats of beach cowpea (Vigna marina) are sandy beaches in tropical and subtropical regions. As a species that grows closest to the sea, it has potential to be a gene source for breeding salt-tolerant crops. We reported here for the first time, quantitative trait loci (QTLs) mapping for salt tolerance in V. marina. A genetic linkage map was constructed from an F₂ population of 120 plants derived from an interspecific cross between V. luteola and V. marina subsp. oblonga. The map comprised 150 SSR markers. The markers were clustered into 11 linkage groups spanning 777.6 cM in length with a mean distance between the adjacent markers of 5.59 cM. The F_2:3 population was evaluated for salt tolerance under hydroponic conditions at the seedling and developmental stages. Segregation analysis indicated that salt tolerance in V. marina is controlled by a few genes. Multiple interval mapping consistently identified one major QTL which can explain about 50 % of phenotypic variance. The flanking markers may facilitate transfer of the salt tolerance allele from V. marina subsp. oblonga into related Vigna crops. The QTL for domestication-related traits from V. marina are also discussed.     

Combined use of bulked segregant analysis and microarrays reveals SNP markers pinpointing a major QTL for resistance to Phytophthora capsici in pepper

Key message

Bulked segregant analysis (BSA) using Affymetrix GeneChips revealed candidate genes underlying the major QTL for Phytophthora capsici resistance in Capsicum . Using the candidate genes, reliable markers for Phytophthora resistance were developed and validated.

Abstract

Phytophthora capsici L. is one of the most destructive pathogens of pepper (Capsicum spp.). Resistance of pepper against P. capsici is controlled by quantitative trait loci (QTL), including a major QTL on chromosome 5 that is the predominant contributor to resistance. Here, to maximize the effect of this QTL and study its underlying genes, an F₂ population and recombinant inbred lines were inoculated with P. capsici strain JHAI1-7 zoospores at a low concentration (3 × 10³/mL). Resistance phenotype segregation ratios for the populations fit a 3:1 and 1:1 (resistant:susceptible) segregation model, respectively, consistent with a single dominant gene model. Bulked segregant analysis (BSA) using Affymetrix GeneChips revealed a single position polymorphism (SPP) marker mapping to the major QTL. When this SPP marker (Phyto5SAR) together with other SNP markers located on chromosome 5 was used to confirm the position of the major QTL, Phyto5SAR showed the highest LOD value at the QTL. A scaffold sequence (scaffold194) containing Phyto5SAR was identified from the C. annuum genome database. The scaffold contained two putative NBS-LRR genes and one SAR 8.2A gene as candidates for contributing to P. capsici resistance. Markers linked to these genes were developed and validated by testing 100 F₁ commercial cultivars. Among the markers, Phyto5NBS1 showed about 90 % accuracy in predicting resistance phenotypes to a low-virulence P. capsici isolate. These results suggest that Phyto5NBS1 is a reliable marker for P. capsici resistance and can be used for identification of a gene(s) underlying the major QTL on chromosome 5.     

Fertile introgression products generated via somatic hybridization between wheat and Thinopyrum intermedium

Key message

Fertile hybrids were produced with genetic material transferred from Th. intermedium into a wheat background and supply a source of genetic variation to wheat improvement.

Abstract

Both symmetric and asymmetric somatic hybrids have been obtained from the combination of wheatgrass (Thinopyrum intermedium) and bread wheat (Triticum aestivum). Two wheat protoplast populations, one derived from embryogenic calli and the other from a non-regenerable, rapidly dividing cell line, were fused with Th. intermedium protoplasts which had been (or not been) pre-irradiated with UV. Among the 124 regenerated calli, 64 could be categorized as being of hybrid origin on the basis of plant morphology, peroxidase isozyme, RAPD DNA profiling and karyological analysis. Numerous green plantlets were regenerated from 13 calli recovered from either the symmetric hybrid (no UV pre-treatment) or the asymmetric one (30 s UV irradiation). One of these hybrid plants proved to be vigorous and self-fertile. The regenerants were all closer in phenotype to wheat than to Th. intermedium. Genomic in situ hybridization analysis showed that the chromosomes in the hybrids were largely intact wheat ones, although a few Th. intermedium chromosome fragments had been incorporated within them.     

Genetic analysis and molecular mapping of crown rust resistance in common wheat

Key Message

This is the first report on genetic analysis and genome mapping of major dominant genes for near non-host resistance to barley crown rust ( Puccinia coronata var. hordei ) in common wheat.

Abstract

Barley crown rust, caused by Puccinia coronata var. hordei, primarily occurs on barley (Hordeum vulgare L.) in the Great Plain regions of the United States. However, a few genotypes of common wheat (Triticum aestivum L.) were susceptible to this pathogen among 750 wheat accessions evaluated. To investigate the genetics of crown rust resistance in wheat, a susceptible winter wheat accession PI 350005 was used in crosses with two resistant wheat varieties, Chinese Spring and Chris. Analysis of F₁ plants and F₂ populations from these two crosses indicated that crown rust resistance is controlled by one and two dominant genes in Chris and Chinese Spring, respectively. To determine the chromosome location of the resistance gene Cr1 in Chris, a set of 21 monosomic lines derived from Chris was used as female parents to cross with a susceptible spring type selection (SSTS35) derived from the PI 350005/Chris cross. Monosomic analysis indicated that Cr1 is located on chromosome 5D in Chris and one of the crown rust resistance genes is located on chromosome 2D in Chinese Spring. The other gene in Chinese Spring is not on 5D and thus is different from Cr1. Molecular linkage analysis and QTL mapping using a population of 136 doubled haploid lines derived from Chris/PI 350005 further positioned Cr1 between SSR markers Xwmc41-2 and Xgdm63 located on the long arm of chromosome 5D. Our study suggests that near non-host resistance to crown rust in these different common wheat genotypes is simply inherited.