Dedication to Robert Alexander McIntosh

Euphytica, 2000

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.

Crop Science, 2000

partial control which is unsatisfactory under high disease pressure. Consequently, both are best combined with Stripe (yellow) rust, caused by Puccinia striiformis West., is an other slow-rusting genes (Ma and Singh, 1996; Singh important constraint to wheat production in cool environments. With the purpose of identifying genes for resistance to the disease, a RFLP and Huerta-Espino, 1997). mapping population of recombinant inbred lines developed from Identification and characterization of minor slowa synthetic [Triticum turgidum L. ϫ Aegilops tauschii (Coss.) rusting resistance genes is difficult by classical methods. Schmal.] ϫ T. aestivum L. cv. 'Opata 85' cross was visually evaluated Recently, RFLP maps of wheat chromosomes were confor seedling infection type in three greenhouse inoculation tests and structed (Van Deynze et al., 1995; Nelson et al., 1995a, for adult-plant disease severity in four field tests at Celaya and Toluca, b, c; Marino et al., 1996) in a population of recombinant Mexico. A previously unidentified gene from Ae. tauschii, designated inbred lines (RILs) developed from a synthetic as Yr28, was located on chromosome arm 4DS. Although Yr28 hexaploid ϫ bread-wheat cross. This genetic material strongly influenced seedling resistance, it showed a strong effect in has been used to characterize and map resistance genes adult plants at only the warmer of the two field sites. A second gene for other diseases (Nelson et al., 1995b, 1997, 1998; Faris showed high environmental sensitivity in seedling tests, with resistance associated with Opata marker alleles near the adult-plant resistance et al., 1997). The synthetic parent was reported to carry (APR) gene Yr18 on chromosome arm 7DS. Gene Yr18, known to YR resistance (Ma et al., 1995) and should be a source be present in Opata, strongly reduced disease response in field trials of valuable genetic diversity for bread wheat cultivar imand was tightly linked with leaf-rust resistance gene Lr34. Three other provement. regions from Opata on chromosome arms 3BS, 3DS, and 5DS were The objective of this study was to identify wheat chroalso associated with APR. mosomal regions carrying stripe rust resistance genes effective at seedling and adult-plant stages by using the available mapping population and RFLP map.

International Journal of Experimental Research and Review (IJERR) , 2016

Wheat, staple food of billions and one of the major crops in volume, is an excellent source of nutrition and income. However, its susceptibility to rust poses a constant threat to sustainable production and hence food security itself. Wheat rust is the most urgent problem regarding the production of this irrevocably important crop. While cultural measures could lower down the extent of the infection, it isn't a permanent solution. Breeding for durable resistance is by far the most dependable solution to the problem. However even this has had many setbacks of pathogen evolution, climate change and other factors. Linked DNA markers show promise for achieving race-specific resistance genes in combinations aimed at their longevity. However, a national deployment strategy is inevitable for its success. The most promising activity so far is breeding for cultivars carrying durable resistance genes based on both minor and additive gene effect. However, using genetic engineering still faces the sentimental opposition of the public against genetically modified organisms. A lot has been done and a lot is to be done in order to grow rust free wheat in our fields. The paper discusses in brief about the major milestones and ongoing attempts regarding wheat breeding for rust resistance.

Crop Science, 2003

cultivars by the use of the ph1 gene (Riley and Chapman, 1958) that promotes homeologous chromosome Rust resistance genes Lr37, Sr38, and Yr17 are located within a recombination. The ph1 mutation has been extensively segment of Triticum ventricosum (Tausch) Cess. chromosome 2NS translocated to the short arm of bread wheat chromosome 2AS. Char-used to incorporate new disease resistance genes in acterization of this chromosome segment by 13 restriction fragment wheat from wild Triticeae species such as T. monococlength polymorphism (RFLP) markers indicated that the 2NS translocum L., T. speltoides (Tausch) Gren., and T. ventricosum cation replaced approximately half of the short arm of chromosome (McIntosh et al., 1995; Friebe et al., 1996; Dubcovsky 2A (distal 25-38 centimorgans, cM). The objective of this study was et al., 1998). to develop polymerase chain reaction (PCR) assays based on RFLP The Yr17, Lr37, and Sr38 rust resistance genes, which marker cMWG682 to facilitate the transfer of this cluster of rust confer resistance in wheat against stripe rust (caused by resistance genes into commercial wheat (Triticum aestivum L.) culti-Puccinia striiformis West. f. sp. tritici), leaf rust (caused vars. DNA sequence was obtained from the A-, B-, D-, and N-alleles by Puccinia triticina Eriks), and stem rust (caused by of cMWG682 and was used to design N-allele specific primers. The Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn.), 2NS fragment amplified by PCR primers cosegregated with the presence of the RFLP-2NS band in all backcross populations. A cleaved respectively, have been used by breeders in different amplified polymorphic sequence (CAPS) was used to develop a parts of the world (Dyck and Lukow, 1988; McIntosh marker for the 2A-allele. This marker can be used to differentiate et al., 1995; Robert et al., 1999; Seah et al., 2000). These homozygous and heterozygous plants carrying the 2NS translocation linked resistance genes were initially introgressed in the in the final cycle of backcross introgression or in screenings for homowinter bread wheat 'VPM1' from Triticum ventricosum zygous plants in segregating populations. Finally, a third PCR assay (Maia, 1967) and are located in a 2NS/2AS translocation was developed by means of TaqMan technology as a high-throughput (Bariana and McIntosh, 1993;. alternative for selection of the 2NS/2AS translocation in large segre-Rust races with virulence to Yr17 and Lr37 have been gating populations in breeding programs that have access to real time identified in different countries (Robert et al., 1999; PCR equipment. These molecular markers were used to develop four J. Kolmer unpublished data) but this gene cluster still hard red spring isogenic lines homozygous for the 2NS chromosome segment. One of the isogenic lines, derived from 'Anza,' did not show provides resistance to a wide range of races and is useful the expected resistance in spite of the presence of all the RFLP in combination with other rust resistance genes. markers for the 2NS chromosome segment. Analysis of F 1 hybrids Molecular markers have been developed to accelerate suggested that a suppressor of the Lr37 gene is present in Anza. These the transfer of these genes into commercial cultivars. isogenic lines will provide a valuable tool to test the effects of the Robert et al. (1999) developed a dominant SCAR (selarge 2NS translocation on quality and agronomic performance.

Cereal Research Communications

Bulk segregant analysis (BSA) was used to identify molecular markers associated with yellow rust disease resistance in wheat (Triticum aestivum L.). DNAs isolated from the selected yellow rust tolerant and susceptible F2 individuals derived from a cross between yellow rust resistant and susceptible wheat genotypes were used to established a “tolerant” and a “susceptible” DNA pool. The BSA was then performed on these DNA pools using 230 markers that were previously mapped onto the individual wheat chromosomes. One of the SSR markers (Xgwm382) located on chromosome group 2 (A, B, D genomes) was present in the resistant parent and the resistant bulk but not in the susceptible parent and the susceptible bulk, suggesting that this marker is linked to a yellow rust resistance gene. The presence of Xgwm382 was also tested in 108 additional wheat genotypes differing in yellow rust resistance. This analysis showed that 81% of the wheat genotypes known to be yellow rust resistant had the Xgwm...

Journal of Applied Genetics, 2007

Adult plant resistance (APR) to stripe rust in three European (Pegaso, Victo and Aztec) and four New Zealand cultivars (Weka, Kopara, Kokart and Takahe) was characterised using hybrid analysis and tests of allelism. In agreement with earlier work, the APR in most of these cultivars appeared to be controlled by two or more genes with additive effects. It was suggested that heavy selection pressure should be avoided in early generations in breeding programs utilising APR, because lines in which APR genes are heterozygous may display lower levels of resistance due to the incompletely dominant and interactive nature of many APRs. Such lines are capable of generating more resistant progenies following selfing. It was also demonstrated that it is possible to misclassify F 2 plants as susceptible if APR genes are in a heterozygous condition, especially in the case of gene(s) conferring intermediate levels of resistance. The presence of a common APR gene in Kopara and Takahe, and perhaps Weka, was suggested because all shared a common parent in their pedigree and no susceptible plants were observed in F 2 populations derived from intercrossing them. The difficulties inherent in conducting genetic studies on APRs and the need for large population sizes for such studies were emphasised.

2012

The molecular characterization and genetic diversity of 10 wheat genotypes was investigated using 34 polymorphic simple sequence repeats screened primers. About thirty-one loci were found. Lr-19 gene was present in all 10 wheat genotypes that cause resistance against wheat rust. Iqbal-2000 and Ufaq showed the highest genetic diversity between each other giving a genetic similarity of 96.34% and a minimum genetic diversity was observed between Lasani-08 and Bhakar which showed the dissimilarity of about 66.64%. The current study found that all of the genotypes could distinguish and characterize by SSR makers, new screened primers could be used for study and can also be used in different saturated regions for further research. Lr-19 is a wheat rust resistant gene and present in all ten genotypes. This gene causes resistance against rust diseases.

Australian Journal of Agricultural Research, 1977

The wheat cultivars Agent and Agatha each possess closely linked genes for resistance to Puccinia graminis tritici and P. recondita derived from Agropyron elongatum. The genes in Agent, located in chromosome 3D, were designated Sr24 and Lr24. The gene in Agatha for resistance to P. graminis tritici was designated Sr25 and is linked with Lr19 in chromosome 7D. Both Agent and Agatha possess additional genes for resistance to certain cultures of P. graminis tritici. Sr24 is considered a valuable source of resistance for wheat-breeding purposes, but Sr25 conferred an inadequate level of resistance to adult plants. A translocation from an A. elongatum chromosome to wheat chromosome 6A, present in Australian cultivars Eagle, Kite and Jabiru, carries a third gene, Sr26, for stem rust resistance.

Euphytica, 1996

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 YrlO and 0 .07 with the centromere. Yr15 was preferentially transmitted relative to its alternate allele .