小偃麦附加系Z1和Z2中外源染色体2Ai-2的结构组成

小偃麦附加系Z1和Z2中外源染色体2Ai-2的结构组成@张增燕$中国农业科学院作物育种栽培研究所!北京100081@辛志勇$中国农业科学院作物育种栽培研究所!北京100081@陈孝$中国农业科学院作物育种栽培研究所!北京100081小偃麦;;附加系;;染色体     

携带抗黄矮病基因的中间偃麦草染色体2Ai—2特异的分子标记

小麦－中间偃麦草二体异附加系Ｚ１、Ｚ２具有一对携带抗黄矮病基因的中间偃麦草染色体２Ａｉ－２。利用中间偃麦草（Ｔｈｉｎｏｐｙｒｕｍ ｉｎｔｅｒｍｅｄｉｕｍ （Ｈｏｓｔ） Ｂａｋｗｏｔｈ ａｎｄ Ｄｅｗｅｙ）和拟鹅冠草（Ｐｓｅｕｄｏｒｏｅｇｎｅｉａ ｓｔｒｉｇｏｓａ）基因组ＤＮＡ作探针,对Ｚ１、Ｚ２进行基因组原位杂交分析。结果表明,Ｚ１、Ｚ２附加的一对中间偃麦草染色体２Ａｉ－２为Ｓｔ－Ｅ染色体,Ｅ组染     

Genomic constitution and variation in five partial amphiploids of wheat–<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> as revealed by GISH,multicolor GISH and seed storage protein analysis

Genomic in situ hybridization (GISH) and multicolor GISH (mcGISH) methodology were used to establish the cytogenetic constitution of five partial amphiploid lines obtained from wheat × Thinopyrum intermedium hybridizations. Line Zhong 1, 2n=52, contained 14 chromosomes from each of the wheat genomes plus ten Th. intermedium chromosomes, with one pair of A-genome chromosomes having a Th. intermedium chromosomal segment translocated to the short arm. Line Zhong 2, 2n=54, had intact ABD wheat genome chromosomes plus 12 Th. intermedium chromosomes. The multicolor GISH results, using different fluorochrome labeled Th. intermedium and the various diploid wheat genomic DNAs as probes, indicated that both Zhong 1 and Zhong 2 contained one pair of Th. intermedium chromosomes with a significant homology to the wheat D genome. High-molecular-weight (HMW) glutenin and gliadin analysis revealed that Zhong 1 and Zhong 2 had identical banding patterns that contained all of the wheat bands and a specific HMW band from Th. intermedium. Zhong 1 and Zhong 2 had good HMW subunits for wheat breeding. Zhong 3 and Zhong 5, both 2n=56, possessed no gross chromosomal aberrations or translocations that were detectable at the GISH level. Zhong 4 also had a chromosome number of 2n=56 and contained the complete wheat ABD-genome chromosomes plus 14 Th. intermedium chromosomes, with one pair of Th. intermedium chromosomes being markedly smaller. Multicolor GISH results indicated that Zhong 4 also contained two pairs of reciprocally translocated chromosomes involving the A and D genomes. Zhong 3, Zhong 4 and Zhong 5 contained a specific gliadin band from Th. intermedium. Based on the above data, it was concluded that inter-genomic transfer of chromosomal segments and/or sequence introgression had occurred in these newly synthesized partial amphiploids despite their diploid-like meiotic behavior and disomic inheritance.     

携带抗黄矮病基因的中间偃麦草染色体2Ai_2特异的分子标记

The wheat-Thinopyrum intermedium addition lines Z1,Z2 contain a pair of Th. intermedium chromosomes 2Ai-2 carrying the gene with resistance to barley yellow dwarf virus (BYDV). Genomic in situ hybridization (GISH) was used to analyze the chromosome constitution of Z1,Z2 by using genomic DNA probes from Th. intermedium and Pseudoroegneria strigosa. The results showed that the chromosome constitution of either Z1 or Z2 composes of 42 wheat chromosomes and two Th. intermedium chromosomes (2Ai-2). The 2Ai-2 chromosome is St-E intercalary translocation, in which the E genomic chromosome segment translocated into the middle region of the long arm of chromosome belonging to St genome. With the genomic DNA probe of Ps. strigosa, the GISH pattern specific to the 2Ai-2 chromosome may be used as a molecular cytogenetic marker. A detailed RFLP analysis on Z1, Z2 and their parents was carried out by using 12 probes on the wheat group 2 chromosomes. Twenty RFLP markers specific to the 2Ai-2 chromosome were identified. Two RAPD markers of OPR16 –350 and OPH09 -1580, specific to the 2Ai-2 chromosome, were identified from 280 RAPD primers. These molecular markers could be used to assisted-select translocation lines with small segment of the 2Ai-2 chromosome and provide tools to localize the BYDV resistance.     

Characterization of a partial wheat-Thinopyrum intermedium amphiploid and its reaction to fungal diseases of wheat

Partial amphiploids between wheat (Triticum aestivum L.) and Thinopyrum species play an important role in the transfer and use of traits from alien species. A wheat-Thinopyrum intermedium partial amphiploid, TAI8335, and its alien parent were characterized by a combination of genomic in situ hybridization (GISH) and cytological observations. Evidence from GISH indicated that the donor parent Th. intermedium possessed seven pairs of S, seven J(s) and 21 J chromosomes. Mitotic observation showed that the majority of TAI8335 plants had 56 chromosomes, but a few had 54 to 55, in some cases with two to three additional telochromosomes. The chromosomes in most pollen mother cells of plants with 2n = 56 formed 28 bivalents, averaging 27.12 in 223 cells, suggesting a basic cytological stability. Sequential GISH patterns using genomic Pseudoroegneria spicata and genomic Th. intermedium DNA as probes revealed that TAI8335 had fourteen chromosomes derived from Th. intermedium and its alien genome consisted of one pair of S-, three pairs of J(s) - and one pair of J-genome chromosomes as well as two translocated chromosome pairs, one being a Robertsonian translocation and another an intercalary translocation, both of which involved J and S genome. Two of the telochromosomes in the aneuploid plants originated from the J genome and one from wheat. Disease screening demonstrated this line was highly resistant to leaf rust, stem rust, stripe rust and powdery mildew. This study showed that the partial amphiploid TAI8335 appears to serve as a novel source for the transfer of resistance genes for multiple fungal pathogens to wheat.     

Molecular cytogenetic characterization of wheat--Thinopyrum elongatum addition, substitution and translocation lines with a novel source of resistance to wheat Fusarium Head Blight

Thinopyrum elongatum(2n = 2x = 14,EE),a wild relative of wheat,has been suggested as a potentially novel source of resistance to several major wheat diseases including Fusarium Head Blight(FHB).In this study,a series of wheat(cv.Chinese Spring,CS) substitution and ditelosomic lines,including Th.elongatum additions,were assessed for TypeⅡresistance to FHB.Results indicated that the lines containing chromosome 7E of Th.elongatum gave a high level of resistance to FHB,wherein the infection did not spread beyond the inoculated floret.Furthermore,it was determined that the novel resistance gene(s) of 7E was located on the short-arm(7ES) based on sharp difference in FHB resistance between the two 7E ditelosomic lines for each arm.On the other hand,Th.elongatum chromosomes 5E and 6E likely contain gene(s) for susceptibility to FHB because the disease spreads rapidly within the inoculated spikes of these lines. Genomic in situ hybridization(GISH) analysis revealed that the alien chromosomes in the addition and substitution lines were intact,and the lines did not contain discernible genomic aberrations.GISH and multicolor-GISH analyses were further performed on three translocation lines that also showed high levels of resistance to FHB.Lines TA3499 and TA3695 were shown to contain one pair of wheat-Th. elongatum translocated chromosomes involving fragments of 7D plus a segment of the 7E,while line TA3493 was found to contain one pair of wheat-Th.elongatum translocated chromosomes involving the D- and A-genome chromosomes of wheat.Thus,this study has established that the short-arm of chromosome 7E of Th.elongatum harbors gene(s) highly resistant to the spreading of FHB,and chromatin of 7E introgressed into wheat chromosomes largely retained the resistance,implicating the feasibility of using these lines as novel material for breeding FHB-resistant wheat cultivars.     

用顺序GISH-FISH 技术鉴定小麦-中间偃麦草小片段易位系

利用顺序基因组-重复序列原位杂交技术对1个来自中3不育系和普通小麦恢75杂种后代稳定株系H96276-2的染色体组成进行了分析。以中间偃麦草（Agropyronintermedium）基因组DNA为探针的荧光原位杂交结果表明,H96276-2的体细胞中有42条染色体,包括20对小麦染色体和1对小麦-中间偃麦草易位染色体,中间偃麦草染色体的易位片段位于1对小麦染色体的端部。进而用重复序列探针pSc119进行第2次荧光原位杂交,证明H96276-2中的中间偃麦草染色体易位片段位于小麦2B染色体的短臂上。     

中间偃麦草的GISH分析

以染色体组为E^eE^e的二倍体长穗偃麦草（Thinopyrum elongatum,2n=2x=14)、染色体组为E^bE^b的二倍体比萨偃麦草（Th.bessarabicum,2n=2x=14）、染色体组为StStStSt的四倍体拟鹅冠草（Pseudoroegneiria strigosa,2n=4x=28)的总基因组DNA为探针,对中间偃麦草（Th.intermedium)进行GISH分析。结果表明,中间偃麦草是由2个亲缘关系较近的染色体组、1个亲缘关系较远的染色体组构成;中间偃麦草所含的亲缘关系较近的染色体组分别与二倍长穗偃麦草染色体组E^e、比萨偃麦草染色体组E^b、以及1个亲缘关系较远的染色体组与拟鹅冠草染色体组St基本相似,但不完全一样,因此,中间偃麦草的染色体组用E^etE^etE^btStSt表示。     

Molecular cytogenetic discrimination and reaction to wheat streak mosaic virus and the wheat curl mite in Zhong series of wheat--Thinopyrum intermedium partial amphiploids.

Thinopyrum intermedium (2n = 6x = 42, JJJsJsSS) is potentially a useful source of resistance to wheat streak mosaic virus (WSMV) and its vector, the wheat curl mite (WCM). Five partial amphiploids, namely Zhong 1, Zhong 2, Zhong 3, Zhong 4, and Zhong 5, derived from Triticum aestivum x Thinopyrum intermedium crosses produced in China, were screened for WSMV and WCM resistance. Zhong 1 and Zhong 2 had high levels of resistance to WSMV and WCM. The other three partial amphiploids, Zhong 3, 4, and 5, were resistant to WSMV, but were susceptible to WCM. Genomic in situ hybridization (GISH) using a genomic DNA probe from Pseudoroegneria strigosa (SS, 2n = 14) demonstrated that two partial amphiploids, Zhong 1 and Zhong 2, have almost the identical 10 Th. intermedium chromosomes, including four Js, four J, and two S genome chromosomes. Both of them carry two pairs of J and a pair of Js genome chromosomes and two different translocations that were not observed in the other three Zhong lines. The partial amphiploids Zhong 3, 4, and 5 have another type of basic genomic composition, which is similar to a reconstituted alien genome consisting of four S and four Js genome chromosomes of Th. intermedium (Zhong 5 has two Js chromosomes plus two Js-W translocations) with six translocated chromosomes between S and Js or J genomes. All three lines carry a specific S-S-Js translocated chromosome, which might confer resistance to barley yellow dwarf virus (BYDV-PAV). The present study identified a specific Js2 chromosome present in all five of the Zhong lines, confirming that a Js chromosome carries WSMV resistance. Resistance to WCM may be linked with J or Js chromosomes. The discovery of high levels of resistance to both WSMV and WCM in Zhong 1 and Zhong 2 offers a useful source of resistance to both the virus and its vector for wheat breeding programs.     

Genomic in situ hybridization (GISH) analyses of Thinopyrum intermedium, its partial amphiploid Zhong 5, and disease-resistant derivatives in wheat

Genomic in situhybridization (GISH) to root-tip cells at mitotic metaphase, using genomic DNA probes from Thinopyrum intermedium and Pseudoroegneria strigosa, was used to examine the genomic constitution of Th. intermedium, the 56-chromosome partial amphiploid to wheat called Zhong 5 and disease-resistant derivatives of Zhong 5, in a wheat background. Evidence from GISH indicated that Th. intermedium contained seven pairs of St, seven J^S and 21 J chromosomes; three pairs of Th. intermedium chromosomes with satellites in their short arms belonging to the St, J, J genomes and homoeologous groups 1, 1, and 5 respectively. GISH results using different materials and different probes showed that seven pairs of added Th. intermedium chromosomes in Zhong 5 included three pairs of St chromosomes, two pairs of J^S chromosomes and two pairs of St-J^S reciprocal tanslocation chromosomes. A pair of chromosomes, which substituted a pair of wheat chromosomes in Yi 4212 and in HG 295 and was added to 21 pairs of wheat chromosomes in the disomic additions Z1, Z2 and Z6, conferred BYDV-resistance and was identical to a pair of St-J^S tanslocation chromosomes (StJ^S) in Zhong 5. The StJ^S chromosome had a special GISH signal pattern and could be easily distinguished from other added chromosomes in Zhong 5; it has not yet been possible to locate the BYDV-resistant gene(s) of this translocated chromosome either in the St chromosome portion belonging to homoeologous group 2 or in the J^S chromosome portion whose homoeologous group relationship is still uncertain. Among 22 chromosome pairs in disomic addition line Z3, the added chromosome pair had satellites and belonged to the St genome and homoeologous group 1. Disomic addition line Z4 carried a pair of added chromosomes which was composed of a group-7 J^S chromosome translocated with a wheat chromosome; this chromosome was different to 7 Ai-1, but was identical to 7 Ai-2. The leaf rust and stem rust resistance genes were located in the distal region of the long arm, whereas the stripe rust resistance gene(s) was located in the short arm or in the proximal region of the long arm of 7 Ai-2. A pair of J^S-wheat translocation chromosomes, which originated from the WJ^S chromosomes in Z4, was added to the disomic addition line Z5; the added chromosomes of Z5 carried leaf and stem rust resistance but not stripe rust resistance; Z5 is a potentially useful source for rust resistance genes in wheat breeding and for cloning these novel rust-resistant genes. GISH analysis using the St genome as a probe has proved advantageous in identifying alien Th. intermedium in wheat. Received: 17 May 1999 / Accepted: 22 June 1999     

Molecular characterization of a Thinopyrum intermedium group 2 chromosome (2Ai-2) conferring resistance to barley yellow dwarf virus.

The wheat--Thinopyrum intermedium addition lines Z1 and Z2 carry 21 pairs of wheat chromosomes and one pair of Th. intermedium chromosomes (2Ai-2) conferring resistance to barley yellow dwarf virus (BYDV). GISH results using the genomic DNA of Pseudoroegneria strigosa (S genome) as the probe indicated that the 2Ai-2 chromosome in Z1 and Z2 is an S-J intercalary translocation. Most of the 2Ai-2 chromosome belongs to the S genome, except for about one third in the middle region of the long arm that belongs to the J genome. The results of detailed RFLP analyses confirmed that the 2Ai-2 chromosome is extensively homoeologous to wheat group 2 chromosomes. Some new RFLP markers specific to the 2Ai-2 chromosome were identified. A RAPD marker, OP-R16(340), specific to the 2Ai-2 chromosome, was screened. We converted the RAPD marker into a sequence-characterized amplified region (SCAR) marker (designated SC-R16). The study establishes the basis for selecting translocation lines with small segments of the 2Ai-2 chromosome and localizing the BYDV resistance gene when introgressed into a wheat background.     

应用原位杂交及RAPD技术标记抗黄矮病小麦一中间偃麦草染色体异附加系

以生物素（Ｂｉｏｔｉｎ－１６－ｄＵＴＰ）标记中间偃麦草基因组 ＤＮＡ为探针,与抗黄矮病小麦－中间偃麦草染色体异附加系Ｚ６进行原位杂交,鉴定出附加的１对中间偃麦草染色体。对异附加系 Ｚ６和 Ｌ１及它们的小麦亲本进行了 ＲＡＰＤ分析,从 １２０个随机引物中,筛选出 ２个引物可以扩增出附加染色体的特异ＤＮＡ片段,可作为鉴定寻人小麦的中间偃麦草染色质的分子标记。     

Detection of alien chromosomes from S-genome species in the addition/substitution lines of bread wheat and visualization of A-, B- and D-genomes by GISH

A modified approach based on the GISH technique for detecting introgressed chromosomes/chromosome arms from closely related S-genome species to wheat genome and for visualization of A-, B- and D-genomes of Triticum aestivum L. (genome AABBDD, 2n = 6x = 42) is presented. For detecting alien chromosomes we investigated two lines of bread wheat, one is an addition line with a pair of chromosome No. 4 short arms from Aegilops searsii (4SsS) and a wheat substitution line with a pair of chromosomes No. 6 from Ae. longissima (6S1). A hybridization mixture consists of two differently labelled DNAs, one from the line used for chromosome spread preparations, and the second from origin species of alien chromosomes. The latter adds different color in the regions of its hybridization showing the presence of alien chromosomes by creating a strong and easily detected combined signal. For discriminating A-, B-, and D-genome chromosomes, the hybridization mixture of differently labelled total DNA from Ae. tauschii--the proposed progenitor of D-genome (detected red) and T. dicoccoides (genome AABB) (detected green) were used. The high temperature of hybridization allows high precision annealing of chromosome/probe sequences and at the same time it sharpens differences between reassociation kinetics of eu- and heterochromatin revealing chromosome substructure. A pre-annealing step increases probe specificity. As a result, we observed brown chromosomes of A-genome, banded green chromosomes of B-genome and red chromosomes of D-genome. Inter genomic invasion of the sequences from A/B-genomes to D-genome has been detected.     

Characterization of a Wheat- wheatgrass Translocation Line by FISH

The genomic DNA of wheatgrass (Agropyron intermedium (Host) P.B. = Elytrigia intermedia (Host) Nevski = Thinopyrum intermedium (Host) Barkworth and Dewey) was labelled with biotin-16-dUTP as a probe, and genomic DNA of common wheat ( Triticum aestivum L. ) "Chinese Spring" was used for blocking. Wheat-wheatgrass line 33 was examined by fluorescence in situ hybridization (FISH) technique. The terminal regions of a pair of chromosomes showed green fluorescent signals. It has been concluded that chromosome segrnents containing alien genes of wheatgrass are located at the terminal regions of wheat chromosomes in wheat-wheatgrass line 33, and the translocated segments were small. Wheat-wheatgrass line 33 has been proved to be a translocation line with chromosome segments of wheatgrass translocated to the terminal regions of wheat chromoSomes.     

Disomic Thinopyrum intermedium addition lines in wheat with barley yellow dwarf virus resistance and with rust resistances.

Zhong 5 is a partial amphiploid (2n = 56) between Triticum aestivum (2n = 42) and Thinopyrum intermedium (2n = 42) carrying all the chromosomes of wheat and seven pairs of chromosomes from Th. intermedium. Following further backcrossing to wheat, six independent stable 2n = 44 lines were obtained representing 4 disomic chromosome addition lines. One chromosome confers barley yellow dwarf virus (BYDV) resistance, whereas two other chromosomes carry leaf and stem rust resistance; one of the latter also confers stripe rust resistance. Using RFLP and isozyme markers we have shown that the extra chromosome in the Zhong 5-derived BYDV resistant disomic addition lines (Z1, Z2, or Z6) belongs to the homoeologous group 2. It therefore carries a different locus to the BYDV resistant group 7 addition, L1, described previously. The leaf, stem, and stripe rust resistant line (Z4) carries an added group 7 chromosome. The line Z3 has neither BYDV nor rust resistance, is not a group 2 or group 7 addition, and is probably a group 1 addition. The line Z5 is leaf and stem rust resistant, is not stripe rust resistant, and its homoeology remains unknown.     

Genome analysis of Elytrigia pycnantha and Thinopyrum junceiforme and of their putative natural hybrid using the GISH technique.

Genomic in situ hybridization (GISH), using genomic DNA probes from Thinopyrum elongatum (Host) D.R. Dewey (E genome, 2n = 14), Th. bessarabicum (Savul. & Rayss) A. Love (J genome, 2n = 14), Pseudoroegneria stipifolia (Czern. ex Nevski) Love (S genome, 2n = 14), and Agropyron cristatum (L.) Gaertner (P genome, 2n = 14), was used to characterize the genome constitution of the polyploid species Elytrigia pycnantha (2n = 6x = 42) and Thinopyrum junceiforme (2n = 4x = 28) and of one hybrid population (2n = 5x = 35). GISH results indicated that E. pycnantha contains S, E, and P genomes; the first of these was closely related to the S genome of Ps. stipifolia, the second was closely related to to the E genome of Th. elongatum, and the third was specifically related to A. cristatum. The E and P genomes included 2 and 10 chromosomes, respectively, with S genome DNA sequences in the centromeric region. GISH analysis of Th. junceiforme showed the presence of two sets of the E genome, except for fewer than 10 chromosomes for which the telomeric regions were not identified. Based on these results, the genome formula SSPsPsEsEs is proposed for E. pycnantha and that of EEEE is proposed for Th. junceiforme. The genomic constitution of the pentaploid hybrid comprised one S genome (seven chromosomes), one P genome (seven chromosomes), and three E genomes (21 chromosomes). The E and P genomes both included mosaic chromosomes (chromosomes 1 and 5, respectively) with the centromere region closely related to S-genome DNA. On the basis of these data, the genome formula SPSESEE is suggested for this hybrid and it is also suggested that the two species E. pycnantha and Th. junceiforme are the parents of the pentaploid hybrid.     

Mapping of a BYDV resistance gene fromThinopyrum intermedium in wheat background by molecular markers

The wheat line H960642 is a homozygous wheat-Thinopyrum intermedium translocation line with resistance to BYDV by genomicin situ hybridization (GISH) and RFLP analysis. The genomic DNA ofTh. intermedium was used as a probe, and common wheat genomic DNA as a blocking in GISH experiment. The results showed that the chromosome segments ofTh. intermedium were transferred to the distal end of a pair of wheat chromosomes. RFLP analysis indicated that the translocation line H960642 is a T7DS-7DL-7XL translocation by using 8 probes mapped on the homoeologous group 7 in wheat. The translocation breakpoint is located between Xpsr680 and Xpsr965 about 90–99 cM from the centromere. The RFLP markers psr680 and psr687 were closely linked with the BYDV resistance gene. The gene is located on the distal end of 7XL around Xpsr680 and Xpsr687.     

Mapping of a BYDV resistance gene from Thinopyrum intermedium in wheat background by molecular markers

The wheat line H960642 is a homozygous wheat-Thinopyrum intermedium translocation line with resistance to BYDV by genomicin situ hybridization (GISH) and RFLP analysis. The genomic DNA ofTh. intermedium was used as a probe, and common wheat genomic DNA as a blocking in GISH experiment. The results showed that the chromosome segments ofTh. intermedium were transferred to the distal end of a pair of wheat chromosomes. RFLP analysis indicated that the translocation line H960642 is a T7DS-7DL-7XL translocation by using 8 probes mapped on the homoeologous group 7 in wheat. The translocation breakpoint is located between Xpsr680 and Xpsr965 about 90–99 cM from the centromere. The RFLP markers psr680 and psr687 were closely linked with the BYDV resistance gene. The gene is located on the distal end of 7XL around Xpsr680 and Xpsr687. Project supported by the 863 program and the National Natural Science Foundation of China (Grant No. 39680027).     

Identification of Blue-grained Wheat Translocation Lines Using Fluorescence in Situ Hybridization

The blue-grained wheat substitution line (blue 58) originated from wild hybridization between Triticum aestivum L. and Agropyron elongatum (Host) Beauv= Elytrigia elongatum (Host) Nevski= Thinopyrum ponticum (Host) Barkworth and Dewey (2n=10x=70) was irradiated and four translocation lines were screened by fluorescence in situ hybridization from the offsprings. The results obtained include the following: (1) both the two translocation lines, 9906 and 9902, have 42 chromosomes. The length of the translocated blue-grained segment was approximately one-third of the short-arm and one-half of the long-arm of the translocated wheat chromosome in 9906 and 9902, respectively, and the blue-grained translocated segment in 9902 was located on D genome; (2) both 9915 and 9904 have 44 chromosomes. One pair of chromosomes was translocated and two chromosomes from Th. ponticum were added in 9903, while two pairs of chromosomes were translocated in 9904 by blue-grained wheat segment. The location and application of blue-grained wheat translocation lines were discussed.     

Characterization of derivatives from wheat-Thinopyrum wide crosses

Partial amphiploids are lines that contain 42 (38-42) wheat and 14 (14-18) alien chromosomes. They are derived by backcrossing wheat onto hybrids between wheat and either Thinopyrum intermedium (6x) or Th. ponticum (10x). GISH analysis has shown that, with possibly one exception, the alien genomes (chromosome sets) in partial amphiploids are found to be hybrids i.e. composed of chromosomes from more than one alien genome. The individual partial amphiploids are meiotically stable and nearly perfectly fertile, but hybrids between different lines were characterized by varying numbers of unpaired chromosomes and consequently variable degrees of sterility. Translocated chromosomes involving different Thinopyrum genomes or Thinopyrum and wheat genomes were found in partial amphiploids and consequently in the addition lines derived from them. Partial amphiploids have proven to be an excellent tertiary gene pool for wheat improvement, containing resistance to biotic stresses not present in wheat itself. Resistance to Barley Yellow Dwarf Virus (BYDV) and Wheat Streak Mosaic Virus (WSMV) have been found in partial amphiploids and addition lines derived from both Th. intermedium and Th. ponticum. Excellent resistance to Fusarium head blight has been found on a Th. intermedium chromosome that had substituted for chromosome 2D in wheat. Genes for resistance to leaf rust and stem rust have already been incorporated into wheat and tagged with molecular markers.