Monosomic analyses of stripe rust and leaf rust resistance genes in winter wheat varieties Lüquyu and Yantar

Summary A set of 21 monosomics of Novosadska Rana-1 was used to locate the rust resistance genes of Lüqiyu, a stripe rust resistant line developed by BAU and Yantar, a leaf rust resistant wheat introduced from Bulgaria. The resistance of the former to p. striiformis race C25 was conditioned by a dominant gene located on chromosome 2B, whereas that of the latter to P. recondita race CL3 was controlled by two complementary dominant genes located on chromosomes 5A and 1D, respectively. The relationship of the stripe rust resistance gene in Lüqiyu to Yr5, Yr7 or Yr _Suwon' all located on chromosome 2B is unknown. The two complementary leaf rust resistance factors in Yantar appear to be new.     

Development and Validation of SCAR Markers Co-Segregating with an Agropyron Elongatum Derived Leaf Rust Resistance Gene Lr24 in Wheat

Summary An Agropyron elongatum-derived leaf rust resistance gene Lr24 located on chromosome 3DL of wheat was tagged with six random amplified polymorphic DNA (RAPD) markers which co-segregated with the gene. The markers were identified in homozygous resistant F₂ plants taken from a population segregating for leaf rust resistance generated from a cross between two near-isogenic lines (NILs) differing only for Lr24. Phenotyping was done by inoculating the plants with pathotype 77-5 of Puccinia triticina. To enable gene-specific selection, three RAPD markers (S1302₆₀₉, S1326₆₁₅ and OPAB-1₃₈₈) were successfully converted to polymorphic sequence characterized amplified region (SCAR) markers, amplifying only the critical DNA fragments co-segregating with Lr24. The SCAR markers were validated for specificity to the gene Lr24 in wheat NILs possessing Lr24 in 10 additional genetic backgrounds including the Thatcher NIL, but not to 43 Thatcher NILs possessing designated leaf rust resistance genes other than Lr24. This indicated the potential usefulness of these SCAR markers in marker assisted selection (MAS) and for pyramiding leaf rust resistance genes in wheat.     

Molecular mapping and detection of the yellow rust resistance gene Yr26 in wheat transferred from Triticum turgidum L. using microsatellite markers

Yellow rust (stripe rust), caused by Puccinia striiformis Westend f. sp. tritici, is one of the most devastating diseases of wheat throughout the world. Wheat-Haynaldia villosa 6AL.6VS translocation lines R43, R55, R64 and R77, derived from the cross of three species, carry resistance to both yellow rust and powdery mildew. An F₂ population was established by crossing R55 with the susceptible cultivar Yumai 18. The yellow rust resistance in R55 was controlled by a single dominant gene, which segregated independently of the powdery mildew resistance gene Pm21 located in the chromosome 6VS segment, indicating that the yellow rust resistance gene and Pm21 are unlikely to be carried by the same alien segment. This yellow rust resistance gene was considered to beYr26, originally thought to be also located in chromosome arm 6VS. Bulked Segregation Analysis and microsatellite primer screens of the population F₂ of Yumai 18 × R55 identified three chromosome 1B microsatellite locus markers, Xgwm11, Xgwm18 and Xgwm413, closely linked to Yr26. Yr26 was placed 1.9 cM distal of Xgwm11/Xgwml8, which in turn were 3.2 cM from Xgwm413. The respective LOD values were 21 and 36.5. Therefore, Yr26 was located in the short arm of chromosome 1B. The origin and distribution of Yr26 was investigated by pedigree, inheritance of resistance and molecular marker analysis. The results indicated that Yr26 came from Triticum turgidum L. Three other 6AL.6VS translocation lines, R43, R64 and R77, also carried Yr26. These PCR-based microsatellite markers were shown to be very effective for the detection of the Yr26 gene in segregating populations and therefore can be applied in wheat breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transfer of rust resistance from Aegilops ovata into bread wheat (Triticum aestivum L.) and molecular characterisation of resistant derivatives

An interspecific cross was made to transfer leaf rust and stripe rust resistance from an accession of Aegilops ovata (UUMM) to susceptible Triticum aestivum (AABBDD) cv. WL711. The F₁was backcrossed to the recurrent wheat parent, and after two to three backcrosses and selfing, rust resistant progenies were selected. The C-banding study in a uniformly leaf rust and stripe rust resistant derivative showed a substitution of the 5M chromosome of Ae. ovata for 5D of wheat. Analysis of rust resistant derivatives with mapped wheat microsatellite makers confirmed the substitution of 5M for 5D. Some of these derivatives also possessed one or more of the three alien translocations involving 1BL, 2AL and 5BS wheat chromosomes which could not be detected through C-banding. A translocation involving 5DSof wheat and the substituted chromosome 5M of Ae. ovata was also observed in one of the derivatives. Susceptibility of this derivative to leaf rust showed that the leaf rust resistance gene(s) is/are located on short arm of 5M chromosome of Ae. ovata. Though the Ae. ovatasegment translocated to 1BL and 2AL did not seem to possess any rust resistance gene, the alien segment translocated to 5BS may also possess gene(s) for rust resistance. The study demonstrated the usefulness of microsatellite markers in characterisation of interspecific derivatives. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cytogenetical studies in wheat XIX. Location and linkage studies on gene Yr27 for resistance to stripe (yellow) rust

The stripe (yellow) rust resistance gene Yr27 was located in wheat (Triticum aestivum L.) chromosome 2B and shown to be closely linked to the leaf (brown) rust resistance genes Lr13 and Lr23 in the proximal region of the short arm. Gene Yr27 was genetically independent of Lr16, which is distally located in the same arm. While Yr27 was often difficult to score in segregating seedling populations, it is apparently quite effective in conferring resistance to avirulent cultures under field conditions. The occurrence of Yr27 in Mexican wheat germplasm and the current over-dependence on Yr27 for crop protection in Asia are discussed.     

Variation of characters in near-isogenic lines of wheat with added genes for leaf rust resistance

Summary Using the cultivar Arina as the recurrent parent, six backcrosses were made with two donor lines carrying the leaf rust resistance genes Lr1 and Lr9, respectively. Selection for leaf rust resistance occurred at the seedling stage in the greenhouse; the first plants transferred to the field were BC₆F₄s. Frequency distribution of the 332 Lr1/7 × Arina and the 335 Lr9/7 × Arina lines showed continuous variation for yellow rust resistance and heading date in these leaf rust near-isogenic lines (NILs). Similar results were also obtained for plant height, for resistance to powdery mildew and glume blotch, as well as for baking quality characters in another set of more advanced NILs. The available information on the behaviour of one of the parents of cultivar Arina led to the conclusion that the expressed yellow rust resistance is quantitative and might possibly be durable.     

Wheat chromosome engineering at the 4x level: the potential of different alien gene transfers into durum wheat

Summary With the aim of making the point on feasibility and relative success of alien transfers into durum wheat via chromosome engineering, three transfer works, differing in origin and content of the alien introduction and in the transfer strategy adopted, are described. For the transfer of a powdery mildew resistance gene, Pm13, originating from Aegilops longissima and previously transferred to common wheat chromosome 3B, as well as for that of the leaf rust resistance gene Lr19 and its associated Yp (yellow pigment) gene, deriving from Ag. elongatum and introduced into 7A, the common wheat recombinants were employed as donors, from which the alien segments were homologously transferred into durum genotypes. On the other hand, for the transfer of common wheat chromosome ID seed storage protein genes, ph1 mediated homoeologous recombination was repeatedly induced. This resulted in loss of individuals, including potentially desirable recombinants, probably due to imbalances created by the ph1 condition. However, recovered Gli-D1/Glu-D3 tetraploid recombinants exhibited normal transmission and fertility. Preliminary evidence indicates a normal behaviour also for Glu-D1 5+10 putative recombinants. Similarly, there was no negative impact from the transfer of the Pm13 gene, which has been successfully pyramided into Pm4a durum varieties. On the contrary, transfer of the Ag. elongatum segment showed normal female but almost no male transmission in one durum genotype. This in spite of the fact that the alien segment, proved to be, through in situ hybridization, considerably longer than previously believed, should contain an Sd-1 gene, causing preferential transmission in common wheat. While its behaviour is being checked in other durum genotypes, shortening of the alien segment, through ph1 induced recombination, is also being carried out. Possible causes of the severe negative selection that this alien transfer seemingly encounters at the tetraploid level are discussed.     

Characterization of stem rust resistant derivatives of wheat cultivar Amigo

Summary Originally developed for resistance to greenbug derived from Insave rye, Amigo wheat carries two genes for resistance to stem rust. One of these genes is associated with a rye chromosome 1RS segment carrying the Sec-1 protein marker and presumably greenbug resistance. The second gene which is genetically linked to leaf rust resistance is associated with an Agropyron-derived segment. Rust tests in Canada confirmed that these genes were Sr24 and Lr24. In contrast to Agent and certain 3D/Ag derivatives from Dr. E.R. Sears, the Amigo source of Sr24/Lr24 freely recombined with white seed colour during backcrossing.     

Genetic control of esterase-6 isozymes in hexaploid wheat and rye

Summary The EST-6 leaf esterase phenotypes from euploid, nullisomic-tetrasomic and rye chromosome addition and substitution lines of common wheat were determined using polyacrylamide gel electrophoresis. Evidence is presented to demonstrate that Est-6 is a new set of genes, that are expressed in the leaf. The Est-6 gene set were clearly distinguished from the Est-5 genes which are expressed in the grain. The three homoeoallelic loci, Est-A6, Est-B6 and Est-D6, were located on chromosomes 3A, 3B and 3D. An Est-R6 gene was located on chromosome 6R is involved in rye. Some considerations concerning homoeology between homoeologous group 3 of wheat and the rye chromosome 6R are made.     

Molecular tagging of the yellow rust resistance gene Yr10 in common wheat, P.I.178383 (Triticum aestivum L.)

A microsatellite marker, Xpsp3000, located on the end of chromosome 1BS was linked with the yellow rust resistant gene, Yr10, with a distance 1.2 cM. It could be used in marker assisted selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

Avena fatua L. subsp. fatua v. glabrata Peterm. subv. pseudo-basifixa Thell. as a source of crown rust resistance genes

Summary An accession of Avena fatua L. subsp. fatua v. glabrata Peterm. subv. pseudo-basifixa Thell. (A. fatua L. CS Sel. No. 1), collected in Czechoslovakia in 1971, was found to be resistant to a wide range of crown rust races. Analyses of crosses of this oat with cvs. Weikuss, Leanda, Mona, Rodney A, Rodney B, Rodney M, Dodge and K 316 indicated that the resistance of A. fatua CS Sel. No. 1 is conditioned by one recessive gene which is in interaction with one partially dominant gene with additive effect. The expression of rust reaction was affected by temperature. The crown rust resistance genes of A. fatua L. CS Sel. No. 1 were non-allelic with stem rust resistance genes Pg-2 (A) and Pg-4(B).     

The reaction of x Tritordeum and its Triticum spp. and Hordeum chilense parents to rust diseases

Summary Hexaploid and octoploid tritordeums and their parents Hordeum chilense and Triticum spp. were screened for resistance to isolates of wheat and barley yellow and brown rusts. All H. chilense lines were highly resistant to both wheat and barley brown rust, few lines were susceptible to wheat yellow rust while susceptibility to barley yellow rust was common. In general the resistance of tritordeum is predominantly contributed by the wheat parent and apparently the genes for resistance in H. chilense are inhibited in their expression by the presence of the wheat genome.Abbreviations WYR wheat yellow rust - WBR wheat brown rust - BYR barley yellow rust - BBR barley brown rust     

Chromosome locations of leaf rust resistance genes in selected tetraploid wheats through substitution lines

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F₁ double monosomic individuals selected at metaphase I. Segregating F₂ individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.     

Cytogenetic studies in wheat XVII. Monosomic analysis and linkage relationships of gene Yr15 for resistance to stripe rust

Summary The highly effective stripe rust resistance gene, Yr15, derived from Triticum dicoccoides, was located in chromosome 1BS. Yr15 showed linkage of 0.30 (34 cM) with Yr10 and 0.07 with the centromere. Yr15 was preferentially transmitted relative to its alternate allele.     

Resistance in spelt wheat to yellow rust

Summary Seven spelt wheat accessions of different origin were hybridized with the susceptible bread wheat cultivar Taichung 29 in order to study the genetics of their resistance to yellow rust (Puccinia striiformis Westend. f. sp. tritici). One Iranian and five European accessions were found to carry Yr5 of Triticum aestivum ssp. spelta var. album, whereas a factor for resistance in the Iranian accession 415 was confirmed to be genetically distinct from Yr5. The alleles for resistance in each of the accessions studied showed a monogenic dominant mode of inheritance. Twenty-eight spelt wheat accessions, including those studied for their resistance to yellow rust, were subjected to polyacrylamide-gel-electrophoresis to study variation for gliadin storage protein patterns. Thirteen distinct patterns were revealed, implying the presence of duplicates within the studied spelt wheat collection.     

The effect of transfers of alien genes for leaf rust resistance on the agronomic and quality characteristics of wheat

Summary Nine transfers of leaf rust (Puccinia recondita Rob. ex Desm.) resistance to wheat (Triticum aestivum L.) from Agropyron elongatum Host. Beauv., Triticum speltoides Tausch and rye (Secale cereale L.) were backcrossed up to 10 times to commercial wheat cultivars. The objective was to study the effect of the transfers on agronomic and quality characters and to make them available in desirable genetic backgrounds. The results varied greatly for different transfers. In four cases no promising material was obtained even after nine backcrosses. However, for the remaining five transfers material with potential as a new cultivar was obtained.     

Use of a synthetic hexaploid Triticum miguschovae for transfer of leaf rust resistance to common wheat

Summary Triticum miguschovae, a genome addition synthetic, was used as a source for transfer of leaf rust (Puccinia recondita tritici) resistance to common wheat. This synthetic, developed from two wild species Triticum militinae and Aegilops squarrosa, proves a valuable donor of the genes for leaf rust resistance. Leaf rust resistance was transferred from T. miguschovae by both dominant and recessive genes. Stable lines phenotypically similar to their recurrent parents Kavkaz and Bezostaya 1 but differing from them in a high level of leaf rust resistance were obtained. The genes for resistance in 3 selected lines differed from each other and from the known effective genes Lr9, Lr19, and Lr24. The resistance of one of them (line 1229) is controlled by two complementary interacting genes located on chromosome 7B and 1D was revealed by monosomic analysis.     

The inheritance of stem rust and leaf rust resistance in some Ethiopian wheat collections

Summary Common and durum wheat populations obtained from Sweden and originally collected in Ethiopia were screened for resistance to steum rust and leaf rust. Resistant selections of common wheat were crossed and backcrossed with either stem rust susceptible RL6071, or leaf rust susceptible Thatcher. Genetic studies, based largely on tests of backcross F₂ families, showed that four of the selections had in common a recessive gene SrA. Plants with this gene were resistant (1⁺ infection type) to all stem rust races tested. This gene was neither Sr26 nor Sr29. The resistance of other selections, based on tests with an array of rust isolates, was due to various combinations of Sr6, 8a, 9a, 9d, 9c, 11, 13, 30, and 36. One of the selections had linked genes, Lr19/Sr25. Another selection had a dominant gene for resistance (;1 infection type) to all the races of leaf rust. With the possible exception of this gene for leaf rust resistance and SrA, no obviously new resistance was found.     

Evaluation of seedling and adult plant resistance in European wheat cultivars to Australian isolates of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

A set of 105 European wheat cultivars was assessed for seedling resistance and adult plant resistance (APR) to stripe (yellow) rust in greenhouse and field tests with selected Australian isolates of Puccinia striiformis f. sp. tritici (Pst). Twelve cultivars were susceptible to all pathotypes, and among the remainder, 11 designated seedling genes (Yr1, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr27, Yr32, YrHVII and YrSP) and a range of unidentified seedling resistances were detected either singly or in combination. The identity of seedling resistance in 43 cultivars could not be determined with the available Pst pathotypes, and it is considered possible that at least some of these may carry uncharacterised seedling resistance genes. The gene Yr9 occurred with the highest frequency, present in 19 cultivars (18%), followed by Yr17, present in 10 cultivars (10%). Twenty four cultivars lacked seedling resistance that was effective against the pathotype used in field nurseries, and all but two of these displayed very high levels of APR. While the genetic identity of this APR is currently unknown, it is potentially a very useful source of resistance to Pst. Genetic studies are now needed to characterise this resistance to expedite its use in efforts to breed for resistance to stripe rust. Colin R. Wellings seconded from NSW Department of Primary Industries.     

Postulation of resistance genes to yellow rust in wild emmer wheat derivatives and advanced wheat lines from Nepal

Summary Seedlings of 38 wild emmer derivatives, and a total of 53 advanced wheat varieties/lines introduced from the International Maize and Wheat Improvement Centre (CIMMYT) or other sources, Nepalese breeding lines and local cultivars were inoculated with 18 different yellow rust isolates to postulate yellow rust resistance genes (Yr). Many wild emmer wheat derivatives used were resistant to all isolates indicating the presence of undescribed genes. Some derivatives carried Yr9, Yr6 and/or YrSU. Genes Yr1, Yr2, Yr6, Yr7, Yr8, Yr15, YrSU and YrA+ are no longer effective in Nepal; Yr4, Yr5, Yr9, Yr10, YrSP and YrSD are still effective; the effectiveness of Yr3 remains unclear. This study shows that stripe rust resistance in seedling stage of most Nepalese cultivars and advanced materials is based on Yr9 with combinations of Yr2, Yr6, Yr7, and YrA+, of which only Yr9 is still effective in Nepal. In many countries Yr9 has lost its effectiveness. Therefore the introduction of new Yr-genes from wild emmer wheat in Nepalese cultivars is highly important.