Genetic Analysis and Molecular Mapping of a Stripe Rust Resistance Gene YrH9014 in Wheat Line H9014-14-4-6-1

Stripe rust, caused by Puccinia striiformis f. sp. tritici （Pst）, is one of the most widespread and destructive wheat diseases in many wheat-growing regions of the world. The winter wheat translocation line H9014-14-4-6-1 has all stage resistance. To identify stripe rust resistance genes, the segregating populations were developed from the cross between H9014-14-4-6-1 and Mingxian 169 （a wheat cultivar susceptible to all Pst races identified in China）. The seedlings of the parents and F1 plants, Fz, F3 and BC1 generations were tested with Pst races under controlled greenhouse conditions. Two genes for resistance to stripe rust were identified, one dominant gene conferred resistance to SUN11-4, temporarily designated YrH9014 and the other recessive gene conferred resistance to CYR33. The bulked segregant analysis and simple sequence repeat （SSR） markers were used to identify polymorphic markers associated with YrH9014. Seven polymorphic SSR markers were used to genotype the F2 population inoculated with SUN11-4. A linkage map was constructed according to the genotypes of seven SSR markers and resistance gene. The molecular map spanned 24.3 cM, and the genetic distance of the two closest markers Xbarc13 and Xbarc55 to gene locus was 1.4 and 3.6 cM, respectively. Based on the position of SSR marker, the resistance gene YrH9014 was located on chromosome arm 2BS. Amplification of a set of nulli-tetrasomic Chinese Spring lines with SSR marker Xbarc13 indicated that YrH9014 was located on chromosome 2B. Based on chromosomal location, the reaction patterns and pedigree analysis, YrH9014 should be a novel resistance gene to stripe rust. This new gene and flanking markers got from this study should be useful for marker-assisted selection （MAS） in breeding programs for stripe rust.

Genetic Analysis and Molecular Mapping of an All-Stage Stripe Rust Resistance Gene in Triticum aestivum-Haynaldia villosa Translocation Line V3

Triticum aestivum-Hayaldia villosa translocation line V3 has shown effective all-stage resistance to the seven dominant pathotypes of Puccinia striiforms f.sp.tritici prevalent in China.To elucidate the genetic basis of the resistance,the segregating populations were developed from the cross between V3 and susceptible genotype Mingxian 169,seedlings of the parents and F 2 progeny were tested with six prevalent pathotypes,including CYR29,CYR31,CYR32-6,CYR33,Sun11-4,and Sun11-11,F 1 plants and F 3 lines were also inoculated with Sun11-11 to confirm the result further.The genetic studied results showed that the resistance of V3 against CYR29 was conferred by two dominant genes,independently,one dominant gene and one recessive gene conferring independently or a single dominant gene to confer resistance to CYR31,two complementary dominant genes conferring resistance to both CYR32-6 and Sun11-4,two independently dominant genes or three dominant genes（two of the genes show cumulative effect） conferring resistance to CYR33,a single dominant gene for resistance to Sun11-11.Resistance gene analog polymorphism（RGAP） and simple-sequence repeat（SSR） techniques were used to identify molecular markers linked to the single dominant gene（temporarily designated as YrV3） for resistance to Sun11-11.A linkage map of 2 RGAP and 7 SSR markers was constructed for the dominant gene using data from 221 F 2 plants and their derived F 2：3 lines tested with Sun11-11 in the greenhouse.Amplification of the complete set of nulli-tetrasomic lines of Chinese Spring with a RGAP marker RG1 mapped the gene on the chromosome 1B,and then the linked 7 SSR markers located this gene on the long arm of chromosome 1B.The linkage map spanned a genetic distance of 25.0 cM,the SSR markers Xgwm124 and Xcfa2147 closely linked to YrV3 with genetic distances of 3.0 and 3.8 cM,respectively.Based on the linkage map,it concluded that the resistance gene YrV3 was located on chromosome arm 1BL.Given chromosomal location,the reaction patterns and pedigree analysis,YrV3 should be a novel gene for resistance to stripe rust in wheat.These closely linked markers should be useful in stacking genes from different sources for wheat breeding and diversification of resistance genes against stripe rust.

Inheritance and Molecular Mapping of Stripe Rust Resistance Gene Yr88375 in Chinese Wheat Line Zhongliang 88375

Stripe rust is one of the most important diseases of wheat worldwide. Inheritance of stripe rust resistance and mapping of resistance gene with simple sequence repeat （SSR） markers are studied to formulate efficient strategies for breeding cultivars resistant to stripe rust. Zhongliang 88375, a common wheat line, is highly resistant to all three rusts of wheat in China. The gene conferring rust disease was deduced originating from Elytrigia intermedium. Genetic analysis of Zhongliang 88375 indicated that the resistance to PST race CYR31 was controlled by a single dominant gene, temporarily designated as Yr88375. To molecular map Yr88375, a F2 segregating population consisting of 163 individuals was constructed on the basis of the hybridization between Zhongliang 88375 and a susceptible wheat line Mingxian 169; 320 SSR primer pairs were used for analyzing the genetic linkage relation. Six SSR markers, Xgwm335, Xwmc289, Xwmc810, Xgdmll6, Xbarc59, and Xwmc783, are linked to Yr88375 as they were all located on chromosome 5BL Yr88375 was also located on that chromosome arm, closely linked to Xgdmll6 and Xwmc810 with genetic distances of 3.1 and 3.9 cM, respectively. The furthest marker Xwmc783 was 13.5 cM to Yr88375. Hence, pedigree analysis of Zhongliang 88375 combined with SSR markers supports the conclusion that the highly resistance gene Yr88375 derived from Elytrigia intermedium is a novel gene for resistance to stripe rust in wheat. It could play an important role in wheat breeding programs for stripe rust resistance.

Genetics and Molecular Mapping of a High-Temperature Resistance Gene to Stripe Rust in Seeding-Stage in Winter Wheat Cultivar Lantian 1

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici （Pst）, is a severe foliar disease of common wheat （Triticum aestivum L.） in the world. Resistance is the best approach to control the disease. The winter wheat cultivar Lantian 1 has high-temperature resistance to stripe rust. To determing the gene（s） for the stripe rust resistance, Lantian 1 was crossed with Mingxian 169 （M169）. Seedlings of the parents, and F 1 , F 2 and F 2-3 progenies were tested with races CYR32 of Pst under controlled greenhouse conditions. Lantian 1 has a single partially dominant gene conferred resistance to race CYR32, designated as YrLT1. Simple sequence repeat （SSR） techniques were used to identify molecular markers linked to YrLT1. A linkage group of five SSR markers was constructed for YrLT1 using 166 F 2 plants. Based on the SSR marker consensus map and the position on wheat chromosome, the resistance gene was assigned on chromosome 2DL. Amplification of a set of nulli-tetrasomic Chinese Spring lines with SSR marker Xwmc797 confirmed that the resistance gene was located on the long arm of chromosome 2D. Because of its chromosomal location and the high-temperature resistance, this gene is different from previously described genes. The molecular map spanned 29.9 cM, and the genetic distance of two close markers Xbarc228 and Xcfd16 to resistance gene locus was 4.0 and 5.7 cM, respectively. The polymorphism rates of the flanking markers in 46 wheat lines were 2.1 and 2.1%, respectively; and the two markers in combination could distinguish the alleles at the resistance locus in 97.9% of tested genotypes. This new gene and flanking markers should be useful in developing wheat cultivars with high level and possible durable resistance to stripe rust.

Molecular mapping of leaf rust resistance genes in the wheat line Yu 356-9

The Chinese wheat line Yu 356-9 exhibits a high level of resistance to leaf rust. In order to decipher the genetic base of resistance in Yu 356-9, gene postulation, inheritance analyses, and chromosome linkage mapping were carried out. Gene postulation completed using 15 leaf rust pathotypes and 36 isogenic lines indicated that Yu 356-9 was resistant to all pathotypes tested. F1 and F2 plants from the cross Yu 356-9 （resistant）/Zhengzhou 5389 （susceptible） were tested with leaf rust pathotype ＂FHNQ＂ in the greenhouse. Results indicated a 3：1 segregation ratio, indicative of the presence of a single dominant leaf rust resistance gene in Yu 356-9 which was temporarily designated as LrYu. Bulk segregant analysis and molecular marker assays were used to map LrYu. Five simple sequence repeat （SSR） markers on chromosome 2BS were found closely linked to LrYu. Among these markers, Xwmc770 is the most closely linked, with a genetic distance of 5.7 cM.

Identification and Molecular Mapping of the Rs Dm R Locus Conferring Resistance to Downy Mildew at Seedling Stage in Radish(Raphanus sativus L.)

Downy mildew （DM）, caused by the fungus Peronospora parasitica, is a destructive disease of radish （Raphanus sativus L.） worldwide. Host resistance has been considered as an attractive and environmentally friendly approach to control the disease. However, the genetic mechanisms of resistance in radish to the pathogen remain unknown. To determine the inheritance of resistance to DM, F1, F2 and BC1F1 populations derived from reciprocal crosses between a resistant line NAU-dhp08 and a susceptible line NAU-qtbjq-06 were evaluated for their responses to DM at seedling stage. All F1 hybrid plants showed high resistance to DM and maternal effect was not detected. The segregation for resistant to susceptible individuals statistically iftted a 3：1 ratio in two F2 populations （F2（SR） and F2（RS））, and 1：1 ratio in two BC1F1 populations, indicating that resistance to DM at seedling stage in radish was controlled by a single dominant locus designated as RsDmR. A total of 1 972 primer pairs （1 036 SRAP, 628 RAPD, 126 RGA, 110 EST-SSR and 72 ISSR） were screened, and 36 were polymorphic between the resistant and susceptible bulks, and consequently used for genotyping individuals in the F2 population. Three markers （Em9/ga24370, NAUISSR826700 and Me7/em10400） linked to the RsDmR locus within a 10.0 cM distance were identiifed using bulked segregant analysis （BSA）. The SRAP marker Em9/ga24370 was the most tightly linked one with a distance of 2.3 cM to RsDmR. These markers tightly linked to the RsDmR locus would facilitate marker-assisted selection and resistance gene pyramiding in radish breeding programs.

Genetics and Molecular Mapping of Stripe Rust Resistance Gene YrShan515 in Chinese Wheat Cultivar Shan 515

Stripe rust is one of the most important wheat diseases worldwide. To identify new resistance genes is significant in wheat breeding. In this study, stripe rust resistance of a Chinese cultivar Shan 515 was tested with Chinese predominant races of P. striiformis f. sp. tritici in the seedling stage, and genetic analysis and simple sequence repeats （SSR） technique were used to identify the inheritance model of seedling stripe rust resistance in cultivar Shan 515 and to mark the sites of resistance gene（s） on chromosome. The genetic analysis indicated that the resistance of Shan 515 against Su11-4 was conferred by a single dominant gene, which was temporarily designated as YrShan515. Using bulked segregant analysis （BSA） and SSR markers, 12 SSR markers （Xwmc335, Xwmc696, Xwmc476, Xbarc267, Xgwm333, Xwmc653, Xwmc396, Xgwm213, Xgwm112, Xgwm274, Xcfd22, Xgwm131, and Xwmc517） located on wheat chromosome 7BL were linked to YrShan515 with genetic distance ranging from 3 to 24 cM. Based on the previously published genetic map and Chinese Spring nulli-tetrasomic analysis, YrShan515 was located on wheat chromosome 7BL. Polymorphism of wheat cultivars collected from Huanghuai wheat grown regions were screened with two markers, Xwmc653 and Xbarc267, and all of these wheat cultivars tested did not present the polymorphic bands as Shan 515 did. Therefore, it suggested that YrShan515 might be a allele of the available yellow rust resistance gene. The mapping of the new resistance gene in Shan 515 is useful for wheat breeding and diversification of resistance genes against stripe rust in commercial wheat cultivars in China.

Genetic analysis and molecular mapping of a novel gene for zebra mutation in rice (Oryza sativa L.)

A novel zebra mutant, zebra-15, derived from the restorer line JinhuilO （Oryza sativa L. ssp. indica） treated by EMS, displayed a distinctive zebra leaf from seedling stage to jointing stage. Its chlorophyll content decreased （55.4%） and the ratio of Chla/Chlb increased （90.2%） significantly in the yellow part of the zebra-15, compared with the wild type. Net photosynthetic rate and fluorescence kinetic parameters showed that the decrease of chlorophyll content significantly influenced the photosynthetic efficiency of the mutant. Genetic analysis of F2 segregation populations derived from the cross of XinonglA and zebra-15 indicated that the zebra leaf trait is controlled by a single recessive nuclear gene. Ninety-eight out of four hundred and eighty pairs of SSR markers showed the diversity between the XinonglA and the zebra-15, their F2 population was then used for gene mapping. Zebra-15 （Z-15） gene was primarily restricted on the short arm of chromosome 5 by 150 F2 recessive individuals, 19.6 cM from marker RM3322 and 6.0 cM from marker RM6082. Thirty-six SSR markers were newly designed in the restricted location, and the Z-15 was finally located between markers nSSR516 and nSSR502 with the physical region 258 kb by using 1,054 F2 recessive individuals.

Molecular and Physical Mapping of Powdery Mildew Resistance Genes and QTLs in Wheat: A Review

Wheat powdery mildew （Pro） is a major disease of wheat worldwide. During the past years, numerous studies have been published on molecular mapping of Pm resistance gene（s） in wheat. We summarized the relevant findings of 89 major re- sistance gene mapping studies and 25 quantitative trait loci （QTL） mapping studies. Major Pm resistance genes and QTLs were found on all wheat chromosomes, but the Pm resistance genes/QTLs were not randomly distributed on each chromosome of wheat. The summarized data showed that the A or B genome has more major Pm resistance genes than the D genome and chromosomes 1A, 2A, 2B, 5B, 5D, 6B, 7A and 7B harbor more major Pm resistance genes than the other chromosomes. For adult plant resistance （APR） genes/QTLs, B genome of wheat harbors more APR genes than A and D genomes, and chromo- somes 2A, 4A, 5A, 1B, 2B, 3B, 5B, 6B, 7B, 2D, 5D and 7D harbor more Pm resistance QTLs than the other chromosomes, suggesting that A genome except 1A, 3A and 6A, B genome except 4B, D genome except 1D, 3D, 4D, and 6D play an impor- tant role in wheat combating against powdery mildew. Furthermore, Pm resistance genes are derived from wheat and its rela- tives, which suggested that the resistance sources are diverse and Pm resistance genes are diverse and useful in combating against the powdery mildew isolates. In this review, four APR genes, Pm38/Lr34/Yr18/Sr57, Pm46/Lr67/Yr46/Sr55, Pm？/Lr27/Yr30/ SY2 and Pm39/Lr46/Yr29, are not only resistant to powdery mildew but also effective for rust diseases in the field, indicating that such genes are stable and useful in wheat breeding programmes. The summarized data also provide chromosome locations or linked markers for Pm resistance genes/QTLs. Markers linked to these genes can also be utilized to pyramid diverse Pm resis- tance genes/QTLs more efficiently by marker-assisted selection.

Characterization and Molecular Mapping of a New Virescent Mutant in Rice

Plant leaves play a significant role in photosynthesis. Normal chloroplast development is critical for plant growth and yield performance. Defect of the chlorophyll in chloroplasts may cause abnormal leaf colors, such as yellow, white, or stripe. Chloroplasts have their own genomes encoding for about 100 genes that are essential for plastid protein synthesis and photosynthesis （Kanno and Hirai, 1993; Sato et al., 1999）. Moreover, over 3000 proteins encoded by plant nuclear genomes target to the chloroplasts and participate in the chloroplast development and/or photosynthesis. Hitherto, a number of plant genes, which encode for enzymes involved in chlorophyll biosynthetic pathways,

Molecular mapping of two semidwarf genes in an indica rice variety Aitaiyin3(Oryza sativa L.)

Genetic analysis established that Aitaiyin3,a dwarf rice variety derived from a semidwarf cultivar Taiyin1,carries two recessive semidwarf genes.By using simple sequence repeat(SSR)markers,we mapped the two semidwarf genes,sd-1 and sd-t2 on chromosomes 1 and 4,respectively.Sd-t2 was thus named because the semidrawf gene sd-t has already been identified from Aitaiyin 2 whose origin could be traced back to Taiyin1.The result of the molecular mapping of sd-1 gene revealed it is linked to four SSR markers found on chromosome 1.These markers are:RM297,RM302,RM212,and OSR3 spaced at 4.7 cM,0 cM,0.8cM and 0 cM,respectively.Sd-t2 was found to be located on chromosome 4 using five SSR markers:two markers,SSR332 and RM1305 located proximal to sd-t2 are spaced 11.6 cM,3.8 cM,respectively,while the three distally located primers,RM5633,RM307,and RM401 are separated by distances of 0.4 cM,0.0 cM,and 0.4 cM,respectively.

Rice molecular markers and genetic mapping:Current status and prospects

Dramatic changes in climatic conditions that supplement the biotic and abiotic stresses pose severe threat to the sustainable rice production and have made it a difficult task for rice molecular breeders to enhance production and productivity under these stress factors. The main focus of rice molecular breeders is to understand the fundamentals of molecular pathways involved in complex agronomic traits to increase the yield. The availability of complete rice genome sequence and recent improvements in rice genomics research has made it possible to detect and map accurately a large number of genes by using linkage to DNA markers. Linkage mapping is an effective approach to identify the genetic markers which are co-segregating with target traits within the family. The ideas of genetic diversity, quantitative trait locus（QTL） mapping, and marker-assisted selection（MAS） are evolving into more efficient concepts of linkage disequilibrium（LD） also called association mapping and genomic selection（GS）, respectively. The use of cost-effective DNA markers derived from the fine mapped position of the genes for important agronomic traits will provide opportunities for breeders to develop high-yielding, stress-resistant, and better quality rice cultivars. Here we focus on the progress of molecular marker technologies, their application in genetic mapping and evolution of association mapping techniques in rice.

Constructing Molecular Marker Linkage Maps of Chromosome 14Sh and 22Sh and QTL Mapping for Major Traits by Use of Substitution Lines of Gossypium hirsutum L.

CSB14Sh,which is isogenic for its recurrent parent TM-1 except for chromosome 14 short arm,was crossed with TM-1,and the F2 population was produced.A total of 3800 SSR primer pairs covering the whole genome were used to screen polymorphism among two parents,TM-1 and CSB14Sh,

Research Advances in Molecular Mechanism of Thermo-sensitive Genic Male Sterility in Plants

Thermo-sensitive genic male sterile （TGMS） lines have specific superiority in heterosis utilization of crops. So far, thermo-sensitive genic male sterile lines have been found in many plants and are widely used in two-line hybrid breeding. With the rapid development of molecular biology, the molecular nature of thermo-sensitive genic male sterility has been revealed, which lays the foundation for further devel- opment and utilization of thermo-sensitive genic male sterile lines. In this study, the molecular mechanisms of fertility conversion of plant thermo-sensitive genic male sterile lines were reviewed from gene molecular mapping and gene differential ex- pression, and the mechanisms of gene differential expression in thermo-sensitive genic male sterile lines were further discussed.

Construction of Molecular Genetic Linkage Map Based on an RIL Population of Rice and Detection of QTLs for Tiller Angle

In this study, an RIL （recombinant inbred line） population containing 240 lines was developed by single seed descent method （SSD） based on a parent com- bination of small-grain indica cultivar Kasalath and large-grain japanica cultivar TD70 with significant differences in plant type traits, to construct the molecular genetic linkage map. Totally 838 SSR （Simple Sequence Repeat） markers were used for polymorphism screening between parents, 302 SSR markers with polymorphism were detected, with a frequency of 36.04%; 141 SSR markers with clear amplified bands and uniform distribution in the genome were finally used for genotype analysis of the RIL population. According to the experimental results, the frequency of male and female genotype in this RIL population was respectively 53% and 47%, suggesting good balance in population structure. A molecular genetic linkage map of rice was constructed by 141 markers based on a RIL population of 240 lines, with a total genetic distance of about 1 832.47 cM covering all 12 chromosomes, an average genetic distance between markers of 12.70 cM and a range of genetic distance be- tween markers of 0.43-36.11 cM, which is consistent with basic requirements of quantitative trait locus （QTL） mapping. Except for few markers on chromosomes 1 and 8, the order and location of markers is similar to the published sequences of Nipponbare. QTL analysis for the tiller angle was conducted with this RIL population of 240 lines, and results showed that three QTLs controlling tiller angle were detected on chromosome 8, 9 and 11, which were named qTA8, qTA9 and qTA11, with a contribution rate of 4.10%, 26.08% and 4.35%, respectively. To be specific, qTA9 contained Tiller Angle Controlling （TAC1） gene. The construction of this molecular genetic linkage map laid the foundation for genetic analysis and QTL mapping of various traits in the progeny of indica and japonica.

Segmental Duplications Are Common in Rice Genome

Segmental duplications on rice (Oryza sativa L.) chromosomes 8, 9, 11, and 12 were studied by examining the distributions of sequences resolved by 13 probes detecting multiple copies of DNA sequences. Four of the hybridization bands detected by a repetitive sequence probe, rTRS, were mapped to the ends of all the four chromosomes. Two or three of the bands detected by each of the other 12 probes were also mapped to different chromosomes. The bands detected by the same probe usually occurred in similar locations of different chromosomes. Loci detected by different DNA probes were often similarly arranged on different chromosomes. Chromosomes 8 and 9 showed colinearity of marker loci arrangement indicating a possible common origin. A segment on chromosome 9 was also very similar to the previously reported duplicated fragments on the ends of chromosomes 11 and 12 which were also detected in this study, indicating a likely common origin. Moreover, the various degrees of distributional similarity of the segments suggest a complex relationship among the chromosomes in the evolution of the rice genome. These results support the proposition that chromosome duplication and diversification may be a mechanism for the origin and evolution of the chromosomes in the rice genome.

Clustering of Major Genes Conferring Blast Resistance in a Durable Resistance Rice Cultivar Gumei 2

By using 304 recombinant inbred lines derived from indica rice cross Zhong 156/Gumei 2, a linkage map consisting of 177 marker loci and covering 12 rice chromosomes was constructed and employed for mapping genes conferring blast resistance in rice. Genomic location of gene Pi25(t) conferring neck blast resistance to the Chinese isolate 92-183 (race ZC15) was verified to be located between markers A7 and RG456 on chromosome 6, with genetic distances of 1.7 cM and 1.5 cM to A7 and RG456, respectively. Leaf blast resistance of Gumei 2 to the Philippine isolate Ca89 (lineage 4) was found to be controlled by a single gene. The gene tentatively designated as Pi26(\) was located between makers B10 and R674 on chromosome 6, with genetic distances of 5.7 cM and 25.8 cM to B10 and R674 respectively. Resistant alleles at both gene loci were derived from Gumei 2, indicating an existence of resistance gene cluster in Gumei 2.

Quantitative Trait Loci for Resistance Against Fusarium Wilt Based on Three Cotton F_2 Populations

Fusarium wilt （FW） is one of the most common cotton diseases in the world. Identification of QTLs conferring resistance to FW is key for the incorporation of resistance genes into elite cultivars. Two intraspecific （cross between Gossypium hirsuturn L.） and one interspecific （cross between Gossypium hirsutum L. and Gossypium bardence L.） F2 populations were constructed by using a highly resistant cultivar and crossing it to a susceptible cultivar with 154, 79, and 148 offsprings, respectively. Simple sequence repeats （SSR） were used to screen genomic regions closely linked to FW resistance. The results showed that five QTLs associated with FW resistance were detected in two intraspecific populations using a composite interval mapping method under four different conditions. Four of these loci located on Chr. 2/Chr. 17 neighboring markers JESPR304 or CIR305 which explained 13.1 to 45.9% of the phenotypic effect. Furthermore, JESPR304 and CIR305 were previously testified and found to be tightly linked. It is possible that these four QTLs detected under different conditions were the same resistance QTL/gene. We consider that there is the possibility of a major FW resistant gene in intraspecific populations. In the interspecific mapping populations two QTLs were detected on Chr. 9 and Chr. 12/26 which explained great phenotypic variance of 49.4 and 45.7%. As the location of QTLs for FW resistance among the intraspecific and the interspecfic populations were totally different, it is suggested that there may be different resistance mechanisms between G. bardence L. and G. hursutum L. Thus, the present research provides an opportunity to understand the genetic control of resistance to FW in Gossypium hirsutum and Gossypium bardence and to conduct MAS in breeding programs to develop FW resistant cultivars.

A SSR Linkage Map of Maizex Teosinte F_2 Population and Analysis of Segregation Distortion

In this study,a linkage genetic map was constructed using a F2 population derived from a cross between a elite maize inbred,B73,and its progenitor,Teosinte（Z.mays ssp.mexicana）,through 205 simple sequence repeat（SSR） markers and one morphological marker.By Mapmaker 3.0,polymorphic markers were clustered into 10 groups,covering 10 chromosomes of maizexteosinte,with a total length of 2 002.4 cM and an average interval of 9.7 cM.Genotyping errors were detected using R/QTL（LOD=2.0） in 109 markers referring to 176 individuals,distributed across all 10 chromosomes with a ratio 1.2%.Projected error loci were re-run and 304 out of the 460 were confirmed as errors and replaced.A new linkage map was constructed,in which markers maintained the same order but the total map length decreased to 1 947.8 cM,with an average interval of 9.4 cM between markers.In total,25.2%（P0.05） markers were identified to have segregation distortion,in which 34.6% deviated towards the pollination parent（B73）,30.8% deviated towards Teosinte,32.7% deviated towards heterozygote and 1.9% deviated towards both parents.This map was also compared with published maizexteosinte and maize IBM map.

Mapping of Defense Response Gene Homologs and Their Association with Resistance Loci in Maize

Defense response genes in higher plant species are involved in a variety of signal transduction pathways and biochemical reactions to counterattack invading pathogens. In this study, a total of 366 non-redundant defense response gene homologs （DRHs）, including 124 unigenes/expressed sequence tags, 226 tentative consensuses, and 16 DRH contigs have been identified by mining the Maize Genetics and Genomics and The Institute for Genomic Research maize databases using 35 essential defense response genes. Of 366 DRHs, 202 are mapped to 152 loci across ten maize chromosomes via both the genetic and in silico mapping approaches. The mapped DRHs seem to cluster together rather than be evenly distributed along the maize genome. Approximately half of these DHRs are located in regions harboring either major resistance genes or quantitative trait loci （QTL）. Therefore, this comprehensive DRH linkage map will provide reference sequences to identify either positional candidate genes for resistance genes and/or QTLs or to develop makers for fine-mapping and marker-assisted selection of resistance genes and/or QTLs.