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All of our crop plants originated in the Vavilovian centers of plant genetic diversity. Following domestication, crop plants went through a period of reduced diversity caused by a domestication bottleneck. The cultivation of crop plants in native habitats where crop plants and their wild relatives grew in close contact created native agroecosystems, which facilitated frequent genetic exchange between crop plants and their wild ancestors, thereby enriching the crop gene pool. These native agroecosystems even produced new crop plants, such as bread wheat. Humans traveled with their crop plants spanning the globe, and the enriched crop gene pools were adapted to diverse habitats, creating landraces that nourished preindustrial agriculture and human civilizations. Genomic research has shown that many of the genes that were exploited in the Green Revolution evolved recently by the active evolutionary processes made possible by functioning native agroecosystems and the selection pressure imposed by various abio...

Phylogenetic relationships of polyploid Aegilops species sharing the U-genome were investigated by analyzing heterochromatin banding patterns of their somatic metaphase chromosomes as revealed by C-banding and fluorescence in situ hybridization (FISH) with the heterochromatin-limited repetitive DNA probes pSc119, pAs1, as well as the distribution of NOR and 5S DNA loci revealed by pTa71 (18S-26S rDNA), and pTa794 (5S rDNA) probes. Seven tetraploid (Ae. triuncialis, Ae. peregrina, Ae. kotschyi, Ae. geniculata, Ae. biuncialis, Ae. columnaris, and 4x Ae. neglecta) and one hexaploid (6x Ae. neglecta) Aegilops species of the U-genome cluster were studied. The Ut and Ct chromosomes of 4x Ae. triuncialis (UtCt) were similar to the diploid donors Ae. umbellulata (U) and Ae. caudata (C). However, the size of the NOR locus on chromosome 5Ut was reduced. Karyotypic analyses confirmed that 4x Ae. peregrina (SpUp) was derived from a hybridization of the diploid species Ae. umbellulata with Ae. longissima, whereas Ae. umbellulata and Ae. sharonensis (or an immediate precursor) were the diploid progenitor species of Ae. kotschyi (SkUk). In both 4x species, the NORs on S-genome chromosomes were inactivated and were accompanied with a decrease or loss of rDNA sequences. Karyotypes of the tetraploid species, Ae. geniculata (UgMg) and Ae. biuncialis (UbMb) differed from each other and from the putative diploid progenitors Ae. umbellulata and Ae. comosa indicating that various types of chromosomal alterations occurred during speciation. Inactivation of major NORs on the M-genome chromosomes, redistribution of 5S rDNA sites, and loss of some minor 18S-26S rDNA loci were observed in Ae. geniculata and Ae. biuncialis. Significant differences in the total amount and distribution of heterochromatin, the number and location of 5S and 18S-26S rDNA loci observed between Ae. columnaris (UcXc)/4x Ae. neglecta (UnXn) and Ae. geniculata/Ae. biuncialis indicate that these species have different origins. Similarities in C-banding and FISH patterns of most Ae. columnaris and 4x Ae. neglecta chromosomes suggest that they were probably derived from a common ancestor, whereas distinct differences of three chromosome pairs may indicate that the divergence of these species was probably associated with chromosomal rearrangements and/or introgressive hybridization. Ae. umbellulata contributed the U genome, however, the source of their second genomes remains unknown. The formation of 6x Ae. neglecta (UnXnNn) was not associated with large modifications of the parental genomes.

Leaf rust, caused by the fungus Puccinia triticina Eriks,is one of the most serious diseases of wheat (Triticum aestivum AABBDD, 2n=6x=42) worldwide. Growing resistant cultivars is an efficient and economical method of reducing losses to leaf rust. Here we report a new leaf rust resistance gene, Lr39, transferred from Aegilops tauschii into common wheat. Lr39 conditions both seedling and adult plant resistance to the leaf rust pathogen. The inter- and intra-chromosomal mapping of the Lr39 gene showed that it is different from all previously described Lr genes. We used monosomic analysis for the inter-chromosomal mapping and wheat microsatellite markers for the intra-chromosomal mapping. The monosomic and ditelosomic analysis indicated that Lr39 is independent of the centromere on the short arm of chromosome 2D. Eight microsatellite markers for 2DS were used for linkage analysis on a population of 57 F2 plants derived from a cross of an Ae. tauschii-derived wheat, cv. Wichita line TA4186 (possessing Lr39), with Wichita monosomics for the D-genome chromosomes. The microsatellite marker analysis confirmed the location of the gene on 2DS. Three markers were polymorphic and linked to the gene. The closest marker Xgwm210 mapped 10.7 cM from Lr39. The location of Lr39 near the telomere of 2DS distinguishes it from the Lr2 and Lr22 loci, which are located on 2DS proximal to Xgwm210.

Aegilops tauschii is the diploid D-genome progenitor of bread wheat (Triticum aestivum L. em Thell, 2n=6x=42, AABBDD). A genetic linkage map of the Ae. tauschii genome was constructed, composed of 546 loci. One hundred and thirty two loci (24%) gave distorted segregation ratios. Sixty nine probes (13%) detected multiple copies in the genome. One hundred and twenty three of the 157 markers shared between the Ae. tauschii genetic and T. aestivum physical maps were colinear. The discrepancy in the order of five markers on the Ae. tauschii 3DS genetic map versus the T. aestivum 3D physical map indicated a possible inversion. Further work is needed to verify the discrepancies in the order of markers on the 4D, 5D and 7D Ae. tauschii genetic maps versus the physical and genetic maps of T. aestivum. Using common markers, 164 agronomically important genes were assigned to specific regions on Ae. tauschii linkage, and T. aestivum physical, maps. This information may be useful for map-based cloning and marker-assisted plant breeding.

Embryogenesis was analyzed in wheat × maize hybrids using paraffin sectioning. Embryogenesis in wheat × maize hybrids is different from that in self-pollinated wheat plants. Development of the embryo is not accompanied by the formation of an endosperm. The endosperm nuclei remain free in the cytoplasm, fail to advance into the cellular stage, and degenerate at a later time. The antipodal cells quickly degenerate in the fertilized ovaries of wheat × maize hybrids similar to self-pollinated ovaries. The antipodal cells remain normal in unpollinated ovaries. The pre-embryo will abort if it is allowed to develop on the plant, because of a nutritional shortage in the absence of an endosperm. Therefore, embryo rescue is necessary for haploid production from a wheat × maize hybrids. Haploid polyembryos were obtained from spikelet culture of wheat × maize hybrids. The formation of polyembryos is due to the cleavage of the pre-embryo and the effect of 2,4-D. The frequency of haploid embryo production and plant regeneration is affected significantly by maize genotypes, but not by wheat genotypes. The concentration of 2,4-D affects only the size of the embryo.

In order to diversify the genetic base of resistance in hard red winter wheat (Triticum aestivum L.) to leaf rust (caused by Puccinia recondita Rob. ex Desm.), five genes for resistance were transferred from the diploid goatgrass T. tauschii (Coss.) Schmal. to hexaploid wheat lines. One of the derived lines, KS90WGRC10, had a very low infection type when inoculated with 23 cultures of P. recondita. The others, KS91WGRC11, KS92WGRC16, U1865, and U1866, had low to intermediate infection types with three cultures

One hundred and seventy-eight loci have been mapped in Triticum tauschii (Coss.) Schmal. (2n = 14, DD) and Triticum aestivum L. em. Thell. (2n = 42, AABBDD). Thirty-five loci were mapped by aneuploid analysis in T. aestivum. One hundred and fifty-two loci, including 143 restriction fragment length polymorphisms (RFLPs), 8 proteins, and 1 leaf rust resistance gene, were mapped in an F2 population (60 plants) of T. tauschii. One hundred and twenty-seven loci were placed in linkage groups belonging to seven D-genome chromosomes of T. tauschii. The source of the probes was a PstI genomic library of T. tauschii, which gave 13% single-low copy clones. Four restriction endonucleases (DraI, EcoRI, EcoRV, HindIII) gave 75% polymorphism between the two parents. Nineteen clones detected multiloci ranging from two to nine in number. Deletions–insertions and point mutations were equally important for generating RFLPs. A hypervariable sequence was identified, which may have potential use in varietal fingerprinting. One marker was found to be linked to a rust-resistance gene. The map will be useful for determining genetic relationships in the Triticeae and for tagging genes of economic importance.Key words: restriction fragment length polymorphism, Triticum aestivum, leaf rust, isozymes, Aegilops squarrosa.

Direct introgression of genes from diploid Aegilops squarrosa L into hexaploid wheat (Tnticum aestivumL.) is an efficient way of developing stable, hexaploid lines with unique, useful genes. 39 such lines derived front direct crosses to determine the effects of Ac. squarrosa germplasm were field-tested on productivity. Whereas some lines were agronomically inferior to the recurrent parent, others periormed at an equall or better level. In addition to the larget traits (Hessian-fly and leaf-rust resistance), other traits, including soilborne-mosaic-virus resistance and protein concentration, were improved.

Wild relatives of common wheat, Triticum aestivum, are an important source for disease and pest resistance. Recently we reviewed the status of wheat-alien translocations conferring resistance to diseases and pests (45). Since then, several new transfers were reported and markers linked to resistance genes identified. Here we present an update of the available information on wheat-alien translocations.

Wild relatives of wheat are useful sources of alien resistance genes for wheat breeding. The objective of this review is to document research on the evaluation, transfer, and molecular analysis of alien resistance to wheat leaf rust especially in Aegilops tauschii, the diploid D-genome donor of common wheat. Nine named resistance genes (Lr1, Lr2, Lr15, Lr21, Lr22, Lr32, Lr34, Lr39, and Lr42) occur in the D genome. Twelve new leaf rust resistance genes have been documented in Ae. tauschii. The south-west Caspian Sea region is the centre of genetic diversity for seedling resistance. Adult-plant resistance is widespread in all geographic regions and should be exploited more in the future. Lr1 and Lr21 have been cloned and are typical NBS-LRR genes. The recent documentation of cryptic introgressions of Lr57/Yr40 from Ae. geniculata and Lr58 from Ae. triuncialis offers exciting possibilities for transferring alien genes without linkage drag. Both Lr21 and Lr34 presumably arose during or following the origin of common wheat ~8000 years ago. Leaf rust resistance genes often are located towards the physical ends of wheat chromosomes. These regions are known to be high in recombination, and this may explain their rapid rate of evolution.

The wild diploid wheat Triticum tauschii (syn. Aegilops squarrosa) is a valuable genetic resource for improvement of pest resistance in hexaploid wheat (T. aestivum). A collection of 219 T. tauschii accessions, obtained from Kyoto University, Japan, and representing most of the species' geographic range, was screened for reaction to four diseases: leaf rust (caused by Puccinia recondita f. sp. tritici), stem rust (caused by P. graminis f. sp. tritici), powdery mildew (caused by Blumeria graminis f. sp. tritici [syn. Erysiphe graminis f. sp. tritici]), and tan spot (caused by Pyrenophora tritici-repentis) (.)

Gill, B. S., Raupp, W J , Sharma, H. C., Browder, L. E., Hatchett, J. H., Harvey, T. L., Moseman, J. G., and Waines, J G 1986. Resistance in Aegilops squarrosato wheat leafrust, wheat powdery mildew, greenbug, and Hessian fly. Plant Disease 70:553-556. Sixty accessions of Aegilops squarrosa (= Triticum tauschii Schmal) were evaluated for resistance to leaf rust (Paccinia reconditaf. sp. lrirlci) culture PRTUS6; powdery mildew (Erysiphe graminis f. sp. tritici),composite cultures ABK, 127, YUMA CC, and Asosan; greenbug (Schizaphis graminum) biotype E; and Hessian fly (Mayetiola destructor) biotype D. Thirty-two accessrons were resistant to the leaf rust pathogen, 3l to the powdery mildew pathogen, and 34 to the greenbug; 24 were homozygous and I 6 were segregating for resistance to the Hessian fly. Multiple resistance was widespread and six accessions were resistant to both pathogens and both insects Resistance varied from immune to moderate reactions. Because A. squarrosaisthe donor ofthe D genome in common wheat, this species can be readily exploited in breeding wheats for pest resrstance Common or bread wheat (Triticum aestivum L. emend. Thell) is an allohexaploid (AABBDD) of recent origin (about 8,000 yr) between a tetraploid wheat ?i turgidum L. (AABB) and Aegilops squarrosa L. e f. Muschii [DD]) (14). Presumably, initial hybridization was restricted to a narrow range of genotypes of each species, thus the genetic diversity of today's wheats primarily accumulated during the culture and spread of bread wheat into the Mediterranean region, Africa, India, China, and elsewhere. During this expansion. further introgression may have occurred with il, turgidum but not with A. squarrosa because of the latter's strong cross-incompatibility with bread wheat.