An intercalary translocation from <Emphasis Type="Italic">Agropyron</Emphasis><Emphasis Type="Italic">cristatum</Emphasis> 6P chromosome into common wheat confers enhanced kernel number per spike

Main conclusion

This study explored 6P chromosomal translocations in wheat, and determined the effects of 6P intercalary chromosome segments on kernel number per wheat spike. Exploiting and utilising gene(s) from wild relative species has become an essential strategy for wheat crop improvement. In the translocation line Pubing2978, the intercalary 6P chromosome segment from Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP) carried valuable multi-kernel gene(s) and was selected from the offspring of the common wheat plant Fukuho and the irradiated wheat-A. cristatum 6P disomic substitution line 4844-8. Genomic in situ hybridisation (GISH), dual-colour fluorescence in situ hybridisation (FISH), and molecular markers were used to detect the small segmental 6P chromosome in the wheat background and its translocation breakpoint. Cytological studies demonstrated that Pubing2978 was a T1AS-6PL-1AS·1AL intercalary translocation with 42 chromosomes. The breakpoint was located near the centromeric region on the wheat chromosome 1AS and was flanked by the markers SSR12 and SSR283 based on an F₂ linkage map. The genotypic data, combined with the phenotypic information, implied that A. cristatum 6P chromosomal segment plays an important role in regulating the kernel number per spike (KPS). By comparison, the mean value of KPS in plants with translocations was approximately 10 higher than that in plants without translocations in three segregated populations. Moreover, the improvement in KPS was likely achieved by increasing both the spikelet number per spike (SNS) and the kernel number per spikelet. These excellent agronomic traits laid the foundation for further investigation of valuable genes and make the Pubing2978 line a promising germplasm for wheat breeding.

     

Efficient Induction of Wheat-Agropyron cristatum 6P Translocation Lines and GISH Detection

The narrow genetic background restricts wheat yield and quality improvement. The wild relatives of wheat are the huge gene pools for wheat improvement and can broaden its genetic basis. Production of wheat-alien translocation lines can transfer alien genes to wheat. So it is important to develop an efficient method to induce wheat-alien chromosome translocation. Agropyron cristatum (P genome) carries many potential genes beneficial to disease resistance, stress tolerance and high yield. Chromosome 6P possesses the desirable genes exhibiting good agronomic traits, such as high grain number per spike, powdery mildew resistance and stress tolerance. In this study, the wheat- A . cristatum disomic addition was used as bridge material to produce wheat- A . cristatum translocation lines induced by ⁶⁰Co-γirradiation. The results of genomic in situ hybridization showed that 216 plants contained alien chromosome translocation among 571 self-pollinated progenies. The frequency of translocation was 37.83%, much higher than previous reports. Moreover, various alien translocation types were identified. The analysis of M₂ showed that 62.5% of intergeneric translocation lines grew normally without losing the translocated chromosomes. The paper reported a high efficient technical method for inducing alien translocation between wheat and Agropyron cristatum . Additionally, these translocation lines will be valuable for not only basic research on genetic balance, interaction and expression of different chromosome segments of wheat and alien species, but also wheat breeding programs to utilize superior agronomic traits and good compensation effect from alien chromosomes.     

Production and identification of wheat-Agropyron cristatum 6P translocation lines

The narrow genetic background of wheat is the primary factor that has restricted the improvement of crop yield in recent years. The kernel number per spike is the most important factor of the many potential characteristics that determine wheat yield. Agropyron cristatum (L.) Gaertn., a wild relative of wheat, has the characteristics of superior numbers of florets and kernels per spike, which are controlled by chromosome 6P. In this study, the wheat-A. cristatum disomic addition and substitution lines were used as bridge materials to produce wheat-A. cristatum 6P translocation lines induced by gametocidal chromosomes and irradiation. The results of genomic in situ hybridization showed that the frequency of translocation induced by gametocidal chromosomes was 5.08%, which was higher than the frequency of irradiated hybrids (2.78%) and irradiated pollen (2.12%). The fluorescence in situ hybridization results of the translocation lines showed that A. cristatum chromosome 6P could be translocated to wheat ABD genome, and the recombination frequency was A genome > B genome > D genome. The alien A. cristatum chromosome 6P was translocated to wheat homoeologous groups 1, 2, 3, 5 and 6. We obtained abundant translocation lines that possessed whole-arm, terminal, segmental and intercalary translocations. Three 6PS-specific and four 6PL-specific markers will be useful to rapidly identify and trace the translocated fragments. The different wheat-A. cristatum 6P translocation lines obtained in this study can provide basic materials for analyzing the alien genes carried by chromosome 6P. The translocation line WAT33-1-3 and introgression lines WAI37-2 and WAI41-1, which had significant characteristics of multikernel (high numbers of kernels per spike), could be utilized as novel germplasms for high-yield wheat breeding.     

The introgression of chromosome 6P specifying for increased numbers of florets and kernels from Agropyron cristatum into wheat

A wheat (Triticum aestivum L.) line 4844 with superior numbers of florets and grains per spike was derived from the cross between Fukohokomugi wheat and Agropyron cristatum (L.) Gaertn. In order to determine the genetic control of floret and kernel number per spike in this line, chromosome addition and substitution lines that were derived from line 4844 were characterized by means of in situ hybridization, microsatellite (SSR), and gliadin analyses. Genomic in situ hybridization analysis with biotinylated P genomic DNA of A. cristatum as a probe demonstrated that the increased number of florets and grains in a spike was associated with the introgression of an A. cristatum chromosome. Fluorescence in situ hybridization, using a repetitive sequence, pAs1, derived from Aegilops squarrosa L., indicated the replacement of chromosome 6D of wheat in the wheat-A. cristatum chromosome substitution lines. This was confirmed by microsatellite analyses with wheat SSR markers specific for chromosome 6D, suggesting that the A. cristatum chromosome was homoeologous to group 6 and was therefore designated as 6P. This conclvsion was further confirmed by amplification using EST-SSR markers and gliadin analysis. The increased number of florets and kernels within a spike of the wheat-A. cristatum hybrids thus was controlled by gene(s) located on A. cristatum chromosome 6P.     

Marker Assisted Transfer of Two Powdery Mildew Resistance Genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.)

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F₁ of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F₁. The resulting F₁s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC₁F₁. Marker assisted selection was carried both in BC₁F₁ and the BC₂F₁ generations. Introgression of alien chromatin in BC₂F₁ plants varied from 15.4 - 62.9 percent. Out of more than 110 BC₂F₁ plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC₂F₂ plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC₂F₁ plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.     

Mapping of novel powdery mildew resistance gene(s) from <Emphasis Type="Italic">Agropyron cristatum</Emphasis> chromosome 2P

Key message

A physical map of Agropyron cristatum 2P chromosome was constructed for the first time and the novel powdery mildew resistance gene(s) from chromosome 2P was(were) also mapped.

Abstract

Agropyron cristatum (L.) Gaertn. (2n = 28, PPPP), a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies showed that wheat-A. cristatum 2P disomic addition line II-9-3 displayed high resistance to powdery mildew, and the resistance was attributable to A. cristatum chromosome 2P. To utilize and physically map the powdery mildew resistance gene(s), 15 wheat-A. cristatum 2P translocation lines and three A. cristatum 2P deletion lines with different chromosomal segment sizes, obtained from II-9-3 using ⁶⁰Co-γ ray irradiation, were characterized using cytogenetic and molecular marker analysis. A. cristatum 2P chromosomal segments in the translocations were translocated to different wheat chromosomes, including 1A, 4A, 5A, 6A, 7A, 1B, 2B, 3B, 7B, 3D, 4D, and 6D. A physical map of the 2P chromosome was constructed with 82 STS markers, consisting of nine bins with 34 markers on 2PS and eight bins with 48 markers on 2PL. The BC₁F₂ populations of seven wheat-A. cristatum 2P translocation lines (2PT-3, 2PT-4, 2PT-5, 2PT-6, 2PT-8, 2PT-9, and 2PT-10) were developed by self-pollination, tested with powdery mildew and genotyped with 2P-specific STS markers. From these results, the gene(s) conferring powdery mildew resistance was(were) located on 2PL bin FL 0.66–0.86 and 19 2P-specific markers were identified in this bin. Moreover, two new powdery mildew-resistant translocation lines (2PT-4 and 2PT-5) with small 2PL chromosome segments were obtained. The newly developed wheat lines with powdery mildew resistance and the closely linked molecular markers will be valuable for wheat disease breeding in the future.

     

Anatomy and Cytogenetic Identification of a Wheat-Psathyrostachys huashanica Keng Line with Early Maturation

In previous studies, our research team successfully transferred the Ns genome from Psathyrostachys huashanica Keng into Triticum aestivum (common wheat cv. 7182) using embryo culture. In the present study, one of these lines, i.e., hybrid progeny 25-10-3, which matured about 10–14 days earlier than its wheat parent, was assessed using sequenced characterized amplified region (SCAR) analysis, EST-SSR and EST-STS molecular markers, and genomic in situ hybridization (GISH). We found that this was a stable wheat-P. huashanica disomic addition line (2n = 44 = 22 II) and the results demonstrated that it was a 6Ns disomic chromosome addition line, but it exhibited many different features compared with previously characterized lines, i.e., a longer awn, early maturation, and no twin spikelets. It was considered to be an early-maturing variety based on the early stage of inflorescence initiation in field experiments and binocular microscope observations over three consecutive years. This characteristic was distinct, especially from the single ridge stage and double ridge stage until the glume stage. In addition, it had a higher photosynthesis rate and economic values than common wheat cv. 7182, i.e., more spikelets per spike, more florets per spikelet, more kernels per spike, and a higher thousand-grain weight. These results suggest that this material may comprise a genetic pool of beneficial genes or chromosome segments, which are suitable for introgression to improve the quality of common wheat.     

QTLs of cold tolerance-related traits at the booting stage for NIL-RILs in rice revealed by SSR

QTLs for cold tolerance-related traits at the booting stage using balanced population for 1525 recombinant inbred lines of near-isogenic lines (viz.NIL-RILs for BC5F3 and BC₅F₄ and BC₅F₅) over 3 years and two locations by backcrossing the strongly cold-tolerant landrace (Kunmingxiaobaigu) and a cold-sensitive cultivar (Towada) was analyzed. In this study, 676 microsatellite markers were employed to identify QTLs conferring cold tolerance at booting stage. Single marker analysis revealed that 12 markers associated with cold tolerance on chromosome 1, 4 and 5. Using a LOD significance threshold of 3.0,compositive interval mapping based on a mixed linear model revealed eight QTLs for 10 cold tolerance-related traits on chromosomes 1, 4, and 5. They were tentatively designatedqCTB-1-1, qCTB-4-1, qCTB-4-2, qCTB-4-3, qCTB-4-4, qCTB-4-5, qCTB-4-6, andqCTB-5-1. The marker intervals of them were narrowed to 0.3-6.8 cM. Genetic distances between the peaks of the QTL and nearest markers varied from 0 to 0.04 cM. We were noticed in some traits associated cold tolerance, such asqCTB-1-1 for 5 traits (plant height, panicle exsertion, spike length, blighted grains per spike and spikelet fertility),qCTB-4-1 for 8 traits (plant height, node length under spike, leaf length, leaf width, spike length, full grains per spike, total grains per spike and spikelet fertility),qCTB-4-2 for 3 traits (spike length, full grains per spike and spikelet fertility),qCTB-5-1 for 5 traits (plant height, panicle exsertion, blighted grains per spike, full grains per spike and spikelet fertility). The variance explained by a single QTL ranged from 0.80 to 16.80%. Three QTLs (qCTB-1-1, qCTB-4-1, qCTB-4-2) were detected in two or more trials. Our study sets a foundation for cloning cold-tolerance genes and provides opportunities to understand the mechanism of cold tolerance at the booting stage.     

Production and cytogenetic analysis of BC1, BC2, and BC3 progenies of an intergeneric hybrid between Triticum aestivum (L.) Thell. and tetraploid Agropyron cristatum (L.) Gaertn.

Summary Intergeneric hybrids between Triticum aestivum cv Chinese Spring and Agropyron cristatum 4x (2n= 5x=35, ABDPP genomes) with a high level of homoeologous meiotic pairing between the wheat chromosomes were backcrossed 3 times to wheat. Pollination of the F₁ hybrid with Chinese Spring resulted in 22 BC₁ seeds with an average seed set of 1.52%. Five BC₁ plants with 39–41 chromosomes were raised using embryo rescue techniques. Chromosome pairing in the BC₁ was characterized by a high frequency of multivalent associations, but in spite of this there was no evidence of homoeologous pairing between chromosomes of wheat and those of Agropyron. All of the plants were self sterile. The embryo rescue technique was again essential to produce 39 BC₂ plants with chromosome numbers ranging from 37 to 67. The phenomenon of meiotic non-reduction was also observed in the BC₃ progenies. In this generation male and female fertility greatly increased, and meiotic pairing was fairly regular. Some monosomic (2n=43) and double monosomic (2n=44) lines were produced. Analysis of these progenies should permit the extraction of the seven possible wheat-Agropyron disomic addition lines including those with the added chromosomes carrying the genes involved in meiotic non-reduction and in suppression of Ph activity.     

Chromosomal location of genes for stem rust resistance derived from ‘Waldron’ wheat

The chromosomal locations of genes for resistance to stem rust (Puccinia graminis Pers.: Pers. f. sp. tritici Eriks. & E. Henn.) in the wheat (Triticum aestivum L.) cultivar ‘Waldron’ (WDR) were determined by monosomic analyses. Wheat lines WDR-B1, -C2, -E4, and -F1,which have single genes for resistance to stem rust derived previously from WDR sel. ‘Little Club’, were crossed onto a complete set of 21 ‘Chinese Spring’ monosomics. The F₂ and backcross-F₁ (BC₁F₁) seedlings from each of the 84 crosses were tested for reaction to culture 111-SS2 (CRL-LCBB) of stem rust, and a few selected segregants were analyzed cytologically for chromosome number. The F₂ from 2 crosses of WDR-C2, -E4 and -F1 and the BC₁F₁ from 2 crosses of WDR-F1 were tested also with culture Or11c (CRL-QBCN). Significant deviations from disomic ratios towards monosomic ratios in the F₂ and BC₁F₁ were used to determine which chromosomes carried the genes for resistance. Cytological analyses of certain BC₁F₁ and susceptible F₂ plants were used to help identify the location of the genes for rust resistance. WDR-B1 has a gene, herein designated Sr41, for resistance on chromosome 4D. WDR-C2 has a gene on chromosome 7 A that may be the same as one previously designated SrWld2. WDR-E4 has a gene on chromosome 2A, possibly SrWld1, which is effective against most or all North American stem rust cultures. WDR-F1 has a gene on chromosome 6B that is the same as or similar to Sr11.     

Molecular cytogenetic characterization of Roegneria ciliaris chromosome additions in common wheat

The development of alien addition lines is important both for transferring useful genes from related species into common wheat and for studying the relationship between alien chromosomes and those of wheat. Roegneria ciliaris (2n=4x=28, S^cS^cY^cY^c) is reported to be a potential source of resistance to wheat scab, which may be useful in wheat improvement. The amphiploid common wheat-R. ciliaris and BC₁F₇ or BC₂F₆ derivatives were screened by C-banding, genomic in situ hybridization (GISH), fluorescent in situ hybridization (FISH) and restriction fragment length polymorphism (RFLP) for the presence of R. ciliaris chromatin introgressed into wheat. Six lines were identified as disomic chromosome additions (DA), one as a ditelosomic addition (Dt), two as double disomic additions (dDA) and one as a monosomic chromosome addition (MA). RFLP analysis using wheat homoeologous group-specific clones indicated that the R. ciliaris chromosomes involved in these lines belong to groups 1, 2, 3, 5 and 7. The genomic affinities of the added R. ciliaris chromosomes were determined by FISH analysis using the repetitive sequence pCbTaq4.14 as a probe. These data suggest that the R. ciliaris chromosomes in five lines belong to the S^c genome. Based on the molecular cytogenetic data, the lines are designated as DA2S^c#1, Dt2S^c#1L, DA3S^c#1, dDA1S^c#2+5Y^c#1, DA5Y^c#1, DA7S^c#1, DA7Y^c#1 and MA?Y^c#1. Based on the present and previous work, 8 of the 14 chromosomes of R. ciliaris have been transferred into wheat.     

Development of Triticum aestivum-Leymus racemosus translocation lines using gametocidal chromosomes

Specific chromosomes of certain Aegilops species introduced into wheat genome background may often facilitate chromosome breakage and refusion, and finally result in a variety of chromosome restructuring. Such a phenomenon is commonly called gametocidal effect of the chromosomes. The chromosome 2C of Ae. cylindrica is one of such chromosomes. In the present study, scab resistant wheat-L. racemosus addition lines involving chromosomes Lr.2 and Lr.7 were crossed to wheat-Ae. cylindrica disomic addition line Add2C. Then F₁ hybrids were subsequently backcrossed with wheat cv “Chinese Spring”. BC₁ plants with chromosome structural aberration were identified by C-banding. In the self-pollinated progenies of these plants, three translocation lines were developed and characterized by mitotic and meiotic analysis combined with C-banding and fluorescent in situ hybridization (FISH) using biotin-labeled genomic DNA of L. racemosus as probe. Some other putative translocation lines to be further characterized were also found. The practicability and efficiency of the translocation between wheat and alien chromosomes induced by gametocidal chromosomes, as well as the potential use of the developed alien translocation lines were also discussed.     

Development of <Emphasis Type="Italic">Triticum aestivum-Leymus racemosus</Emphasis> translocation lines using gametocidal chromosomes

Specific chromosomes of certain Aegilops species introduced into wheat genome background may often facilitate chromosome breakage and refusion, and finally result in a variety of chromosome restructuring. Such a phenomenon is commonly called gametocidal effect of the chromosomes. The chromosome 2C of Ae. cylindrica is one of such chromosomes. In the present study, scab resistant wheat-L. racemosus addition lines involving chromosomes Lr.2 and Lr.7 were crossed to wheat-Ae. cylindrica disomic addition line Add2C. Then F₁ hybrids were subsequently backcrossed with wheat cv “Chinese Spring”. BC₁ plants with chromosome structural aberration were identified by C-banding. In the self-pollinated progenies of these plants, three translocation lines were developed and characterized by mitotic and meiotic analysis combined with C-banding and fluorescent in situ hybridization (FISH) using biotin-labeled genomic DNA of L. racemosus as probe. Some other putative translocation lines to be further characterized were also found. The practicability and efficiency of the translocation between wheat and alien chromosomes induced by gametocidal chromosomes, as well as the potential use of the developed alien translocation lines were also discussed.     

Marker-assisted development and evaluation of near-isogenic lines for scab resistance QTLs of wheat

Fusarium head blight or scab resistance in wheat is a complex quantitative trait affected greatly by environments. Therefore, the quantitative trait loci (QTL) for scab resistance found in mapping projects require validation to be effectively utilized in breeding programs. In this study, by employing both forward and background selections with the help of molecular markers, near-isogenic lines (NILs) for scab resistance QTLs Qfh.nau-2B, Qfhs.nau-3B, Qfhi.nau-4B and Qfhi.nau-5A, three of which originating in scab resistance germplasm Wangshuibai, were developed with the elite line Miangyang 99-323 as the recurrent parent. During the process of backcross, selection was based solely on marker genotypes of the target regions, and on recipient genome recovery rate in BC₂F₁ and BC₃F₁. All the identified BC₃F₁ plants with the target QTL regions have more than 94% recipient genome composition (RGC), and out of four to five of them a plant with over 97% RGC were obtained in each backcross combination. Compared with Mianyang 99-323, the Qfhs.nau-3B NIL showed much better resistance to disease spread within spikes, the Qfhi.nau-4B and Qfhi.nau-5A NILs showed much better resistance to initial infection, and the Qfh.nau-2B NIL showed improvement in both types of resistance. These results were consistent with findings in the previous QTL mapping studies. Morphologically and agronomically these NILs were similar to Mianyang 99-323 except that Qfhi.nau-4B NIL was taller and had a longer spike, and Qfhi.nau-5A NIL had narrower leaves. These results demonstrated the feasibility of marker-assisted utilization of scab resistance QTLs.     

<Emphasis Type="Italic">Pm62</Emphasis>, an adult-plant powdery mildew resistance gene introgressed from <Emphasis Type="Italic">Dasypyrum villosum</Emphasis> chromosome arm 2VL into wheat

Key message

Pm62, a novel adult-plant resistance (APR) gene against powdery mildew, was transferred from D. villosum into common wheat in the form of Robertsonian translocation T2BS.2VL#5.

Abstract

Powdery mildew, which is caused by the fungus Blumeria graminis f. sp. tritici, is a major disease of wheat resulting in substantial yield and quality losses in many wheat production regions of the world. Introgression of resistance from wild species into common wheat has application for controlling this disease. A Triticum durum-Dasypyrum villosum chromosome 2V#5 disomic addition line, N59B-1 (2n?=?30), improved resistance to powdery mildew at the adult-plant stage, which was attributable to chromosome 2V#5. To transfer this resistance into bread wheat, a total of 298 BC₁F₁ plants derived from the crossing between N59B-1 and Chinese Spring were screened by combined genomic in situ hybridization and fluorescent in situ hybridization, 2V-specific marker analysis, and reaction to powdery mildew to confirm that a dominant adult-plant resistance gene, designated as Pm62, was located on chromosome 2VL#5. Subsequently, the 2VL#5 (2D) disomic substitution line (NAU1825) and the homozygous T2BS.2VL#5 Robertsonian translocation line (NAU1823), with normal plant vigor and full fertility, were identified by molecular and cytogenetic analyses of the BC₁F₂ generation. The effects of the T2BS.2VL#5 recombinant chromosome on agronomic traits were also evaluated in the F₂ segregation population. The results suggest that the translocated chromosome may have no distinct effect on plant height, 1000-kernel weight or flowering period, but a slight effect on spike length and seeds per spike. The translocation line NAU1823 has being utilized as a novel germplasm in breeding for powdery mildew resistance, and the effects of the T2BS.2VL#5 recombinant chromosome on yield-related and flour quality characters will be further assessed.

     

Identification of QTLs for hybrid fertility in inter-subspecific crosses of rice (Oryza sativa L.)

Two subspecies in rice, japonica and indica, have their own ecotypic traits. However, reproductive barriers such as spikelet sterility in hybrid progenies between subspecies have been an obstacle in breeding programs for combining desirable traits from both subspecies through inter-subspecific hybridization. The 166 F₉ RILs and two BC₁F₁s’ were analyzed for spikelet and pollen fertility with the parents and F₁ between Dasanbyeo (DS, indica) / TR22183 (TR, japonica). A frame map was constructed using a total of 218 polymorphic STS and SSR markers. In both BC₁F₁s’ of DS//DS/TR and TR//DS/TR, clusters of significant QTLs for spikelet and pollen fertility were identified on the short arm of chromosome 5 and chromosome 8. Nine and ten digenic epistatic interactions for DS//DS/TR and TR//DS//TR were identified, respectively. HF-QTLs were detected at the similar position with subspecies-specific markers and segregation distortion loci, implying that HF-QTLs might be associated with the differentiation of indica and japonica. Hybrid fertility/sterility and its relationship with other traits are discussed in relation to the reproductive barriers between subspecies of rice.     

Development of intron targeted amplified polymorphic markers of metal homeostasis genes for monitoring their introgression from <Emphasis Type="Italic">Aegilops</Emphasis> species to wheat

The identification of transfers of useful alien genes for metal homeostasis from non-progenitor Aegilops species using the widely available anchored wheat SSR markers is difficult due to their lower polymorphism with the distant related wild species and the lack of locus specificity further restricts their application. The present study deals with the development of intron targeted amplified polymorphic (ITAP) markers for the metal homeostasis genes present on chromosomes of groups 2 and 7 of Triticeae. The mRNA sequences of 27 metal homeostasis genes were retrieved from different plant species using NCBI database and their BLASTn was performed against the wheat draft genome sequences in Ensemblplants to get exonic and intronic sequences of the corresponding metal homeostasis genes in wheat. The ITAP primers were developed in such a way that they would anneal to the conserved flanking exonic regions of the genes and amplify across highly variable introns within the PCR limits. The primers led to the amplification of variable intronic sequences of genes with polymorphism between non-progenitor Aegilops species and the recipient wheat cultivars. Further, the polymorphic ITAP markers were used to characterize the transfers of metal homeostasis genes from the non-progenitor Aegilops species to the BC₂F₅ wheat-Aegilops derivatives, developed through induced homoeologous pairing. The derivatives with significant percent increase in grain Fe and Zn content over the elite cultivar PBW343 LrP showed the introgression of some of the useful Aegilops alleles of the metal homeostasis genes. The use of different metal homeostasis genes using this approach is the first report of the direct contribution of the genes for increasing the grain micronutrient content for developing biofortified wheat lines with reduced linkage drag.     

Genetic analysis of a novel broad-spectrum powdery mildew resistance gene from the wheat-<Emphasis Type="Italic">Agropyron cristatum</Emphasis> introgression line Pubing 74

Main conclusion

A novel broad-spectrum powdery mildew resistance gene PmPB74 was identified in wheat- Agropyron cristatum introgression line Pubing 74. Development of wheat cultivars with broad-spectrum, durable resistance to powdery mildew has been restricted by lack of superior genetic resources. In this study, a wheat-A. cristatum introgression line Pubing 74, originally selected from a wide cross between the common wheat cultivar Fukuhokomugi (Fukuho) and Agropyron cristatum (L.) Gaertn (2n = 4x = 28; genome PPPP), displayed resistance to powdery mildew at both the seedling and adult stages. The putative alien chromosomal fragment in Pubing 74 was below the detection limit of genomic in situ hybridization (GISH), but evidence for other non-GISH-detectable introgressions was provided by the presence of three STS markers specific to A. cristatum. Genetic analysis indicated that Pubing 74 carried a single dominant gene for powdery mildew resistance, temporarily designated PmPB74. Molecular mapping showed that PmPB74 was located on wheat chromosome arm 5DS, and flanked by markers Xcfd81 and HRM02 at genetic distances of 2.5 and 1.7 cM, respectively. Compared with other lines with powdery mildew resistance gene(s) on wheat chromosome arm 5DS, Pubing 74 was resistant to all 28 Blumeria graminis f. sp tritici (Bgt) isolates from different wheat-producing regions of northern China. Allelism tests indicated that PmPB74 was not allelic to PmPB3558 or Pm2. Our work showed that PmPB74 is a novel gene with broad resistance to powdery mildew, and hence will be helpful in broadening the genetic basis of powdery mildew resistance in wheat.

     

Premature progression of anther early developmental programs accompanied by comprehensive alterations in transcription during high-temperature injury in barley plants

Kernel number per spike is one of the most important yield components of wheat. To map QTLs related to kernel number including spike length (SPL), spikelet number per spike (SPN), fertile spikelet number (FSPN), sterile spikelet number (SSPN) and compactness, and to characterize the inheritance modes of the QTLs and two-locus interactions, 136 recombinant inbred lines (RILs) derived from ‘Nanda2419’ x ‘Wangshuibai’ and an immortalized F₂ population (IF₂) generated by randomly permutated intermating of these RILs were investigated. QTL mapping made use of the previously constructed over 3300 cM linkage map of the RIL population. Three, five, two, two and six chromosome regions were identified, respectively, for their association with SPL, SPN, FSPN, SSPN, and compactness in at least two of the three environments examined. All compactness QTLs but one shared the respective intervals of QSpn.nau-5A and the SPL QTLs. Xcfd46–Xwmc702 interval on chromosome 7D was related to all traits but SSPN and had consistently the largest effects. The fact that not all the compactness QTL intervals were related to both SPL and SPN indicates that compactness is regulated by different mechanisms. Interval coincidence between QTLs of SPL and SPN and between QTLs of FSPN and SSPN was minimal. For all the traits, favorable alleles exist in both parents. Inheritance modes from additiveness to overdominance of the QTLs were revealed and two-locus interactions were detected, implying that the traits studied are under complex genetic control. The results could contribute to wheat yield improvement and better use of Wangshuibai and Nanda2419 the two special germplasms in wheat breeding program.     

Variation in Anther Culture Response and Fertility of Backcrossed Hybrids between Indica and Japonica Rice (Oryza sativa)

This study was conducted to investigate the variations of fertility, callus induction and plant regeneration in backcrossed hybrids between a responsive japonica variety (Mankeumbyeo, recurrent parent) and a recalcitrant indica variety (Ranta Emas, donor parent) to anther culture. The mean spikelet fertility of inter-subspecific F₁ and BC₁F₁ hybrids was 33.5% and 67.2%, and the spikelet fertility of BC₁F₁ among backcrossed hybrids showed the most extensive variation (a low of 4.5% to a high of 90.6%). The mean fertility and distribution range in BC₅F₁ hybrids were almost the same as that of the japonica recurrent parent (94.6%). The mean callus induction of F₁ and BC₁F₁ hybrids was higher than that of donor parent, and the distribution range in BC₁F₁ hybrids varied from a low 0% to a high 18.7%. The mean callus induction and plant regeneration of BC₄F₁ hybrids was almost that of japonica recurrent parent, and there were no statistical differences between BC₄F₁ and BC₅F₁ hybrids. These results may help to accelerate the introgression of desirable traits from indica into japonica rice using anther culture of backcross hybrids as a breeding strategy.