Wheat Stem Rust Race Research Articles

The importance of plant health to food security

Rapid food price rises have highlighted serious concerns about food security globally and have had a huge impact on achieving Millennium Development Goal 1. Since 2007, an estimated 100 million more people have fallen into absolute poverty. Most live in developing countries where low incomes (less than $1 per day) make it difficult to access food. Access to sufficient food for dietary needs and food preferences defines food security. However, whilst price rises have brought food security into sharp focus, underlying problems need to be addressed. Over the last three to four decades, there has been chronic under-investment in agriculture at all levels. Development aid to agriculture has declined and often in-country policies do not support the sector. Low crop yields are common in many developing countries and improved productivity is vital to reducing rural poverty and increasing food security. Whilst the causes of low productivity are complex, one major contributory factor is crop losses due to plant health problems. Often accurate information on the extent of these losses is missing but estimates of 30–40% loss annually from “field to fork” are common. Any future solution regarding improved global food security must address these losses and that means improving plant health. Two trans-boundary diseases, wheat stem rust race Ug99 and Coffee Wilt Disease of Coffea are highlighted. CABI has a number of plant health initiatives and one radical approach (Global Plant Clinic) involves partnership with in-country services to deliver plant health advice to farmers at the point of demand. Such innovations are entirely consistent with a proposed new “Green Revolution” which would need to be “knowledge intensive”.

Haplotype diversity of stem rust resistance loci in uncharacterized wheat lines

Stem rust is one of the most destructive diseases of wheat worldwide. The recent emergence of wheat stem rust race Ug99 (TTKS based on the North American stem rust race nomenclature system) and related strains threaten global wheat production because they overcome widely used genes that had been effective for many years. Host resistance is likely to be more durable when several stem rust resistance genes are pyramided in a single wheat variety; however, little is known about the resistance genotypes of widely used wheat germplasm. In this study, a diverse collection of wheat germplasm was haplotyped for stem rust resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr36, Sr40, and 1A.1R using linked microsatellite or simple sequence repeat (SSR) and sequence tagged site (STS) markers. Haplotype analysis indicated that 83 out of 115 current wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT) likely carry Sr2. Among those, five out of 94 CIMMYT spring lines tested had both Sr2 and Sr25 haplotypes. Five out of 22 Agriculture Research Service (ARS) lines likely have Sr2 and a few have Sr24, Sr36, and 1A.1R. Two out of 43 Chinese accessions have Sr2. No line was found to have the Sr26 and Sr40 haplotypes in this panel of accessions. DArT genotyping was used to identify new markers associated with the major stem resistance genes. Four DArT markers were significantly associated with Sr2 and one with Sr25. Principal component analysis grouped wheat lines from similar origins. Almost all CIMMYT spring wheats were clustered together as a large group and separated from the winter wheats. The results provide useful information for stem rust resistance breeding and pyramiding.

Genetics and mapping of stem rust resistance to Ug99 in the wheat cultivar Webster

New races of wheat stem rust, namely TTKSK (Ug99) and its variants, pose a threat to wheat production in the regions where they are found. The accession of the wheat cultivar Webster (RL6201) maintained at the Cereal Research Centre in Winnipeg, Canada, shows resistance to TTKSK and other races of stem rust. The purpose of this study was to study the inheritance of seedling resistance to stem rust in RL6201 and genetically map the resistance genes using microsatellite (SSR) markers. A population was produced by crossing the stem rust susceptible line RL6071 with Webster. The F(2) and F(3) were tested with TPMK, a stem rust race native to North America. The F(3) was also tested with TTKSK. Two independently assorting genes were identified in RL6201. Resistance to TPMK was conferred by Sr30, which was mapped with microsatellites on chromosome 5DL. The second gene, temporarily designated SrWeb, conferred resistance to TTKSK. SrWeb was mapped to chromosome 2BL using SSR markers. Comparison with previous genetic maps showed that SrWeb occupies a locus near Sr9. Further analysis will be required to determine if SrWeb is a new gene or an allele of a previously identified gene.

Barley Stem Rust Resistance Genes: Structure and Function

Rusts are biotrophic pathogens that attack many plant species but are particularly destructive on cereal crops. The stem rusts (caused by Puccinia graminis) have historically caused severe crop losses and continue to threaten production today. Barley (Hordeum vulgare L.) breeders have controlled major stem rust epidemics since the 1940s with a single durable resistance gene Rpg1. As new epidemics have threatened, additional resistance genes were identified to counter new rust races, such as the rpg4/Rpg5 complex locus against races QCCJ and TTKSK. To understand how these genes work, we initiated research to clone and characterize them. The Rpg1 gene encodes a unique protein kinase with dual kinase domains, an active kinase, and a pseudokinase. Function of both domains is essential to confer resistance. The rpg4 and Rpg5 genes are closely linked and function coordinately to confer resistance to several wheat (Triticum aestivum L.) stem rust races, including the race TTKSK (also called Ug99) that threatens the world's barley and wheat crops. The Rpg5 gene encodes typical resistance gene domains NBS, LRR, and protein kinase but is unique in that all three domains reside in a single gene, a previously unknown structure among plant disease resistance genes. The rpg4 gene encodes an actin depolymerizing factor that functions in cytoskeleton rearrangement.

Genetic comparison of Ug99 with selected South African races of Puccinia graminis f.sp. tritici

Using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) marker analyses, the genetic structure of selected South African wheat stem rust races was compared with Ug99. SSR analysis divided the population into two distinct groups with 24.5% similarity between them. A local race, UVPgt55 (North American race notation TTKSF), grouped with Ug99 (TTKSK) with a 100% similarity. When AFLP data were included, the same groups were found, but with an increased similarity of 66.7%. Although the SSR data were unable to distinguish between all individual isolates, the AFLP data alone and in combination with the SSR data discriminated between the isolates. The grouping of individual isolates resembled the pathogenicity profile of the different races. On the basis of its similarity with Ug99, it was concluded that UVPgt55 was most probably an exotic introduction into South Africa, whereas the other races specialized locally through mutational adaptation.

Durable resistance to wheat stem rust needed

The recent outbreak of a new wheat stem rust race capable of parasitizing many commercial wheat cultivars highlights the need for durable disease resistance in crop plants. More advanced breeding approaches using quantitative disease resistance genes and resistance gene pyramids are being used to combat wheat stem rust and other diseases, though widespread adoption of these breeding methodologies is needed to maintain resistance efficacy. Advances in understanding the molecular basis of plant disease resistance at both host and nonhost levels offers further possibilities for stem rust resistance using biotechnological approaches. However, truly durable resistance to wheat stem rust and other phytopathogens seems an unlikely prospect in the face of continually evolving pathogen populations.

A walk on the wild side: mining wild wheat and barley collections for rust resistance genes

Leaf rust, stem rust, and stripe rust are among the most important diseases of wheat and barley worldwide and are best controlled using genetic resistance. To increase the diversity of rust resistance in wheat and barley, a project was initiated to identify and characterise rust resistance genes from the wild species of Aegilops sharonensis (Sharon goatgrass) and Hordeum vulgare ssp. spontaneum (wild barley), respectively. One hundred and two accessions of Sharon goatgrass from Israel and 318 Wild Barley Diversity Collection (WBDC) accessions from the Fertile Crescent, Central Asia, North Africa, and the Caucasus region were evaluated for resistance to leaf rust, stem rust, and/or stripe rust. Sharon goatgrass exhibited a wide range of infection types (ITs) in response to leaf rust, stem rust, and stripe rust. The percentage of resistant accessions in Sharon goatgrass was 58.8–78.4% for leaf rust, 11.8–69.6% for stem rust, and 46.1% for stripe rust, depending on the race used and the plant growth stage. Genetic studies with Sharon goatgrass revealed oligogenic resistance to leaf rust and stem rust. Wild barley also exhibited a wide range of ITs to leaf rust and stem rust; however, the overall frequency of resistance was lower than for Sharon goatgrass. The percentage of resistant accessions in wild barley was 25.8% for leaf rust and 5.7–20.1% for stem rust, depending on the race used. Resistance to the new virulent stem rust race TTKS (i.e. Ug99), present in eastern Africa, was found in both Sharon goatgrass (70% of accessions) and wild barley (25% of 20 accessions tested). Association mapping for stem rust resistance was applied in the WBDC using Diversity Arrays Technology (DArT) markers. Using the highly conservative P value threshold of 0.001, 14 and 15 significant marker associations were detected when the number of subpopulations (K value) was set for 10 and 8, respectively. These significant associations were in 9 and 8 unique chromosome bins, respectively. Two significant marker associations were detected for resistance to the wheat stem rust race MCCF in the same bin as the rpg4/Rpg5 complex on chromosome 7(5H). The presence of a major stem rust resistance gene in this bin on chromosome 7(5H) was validated in a bi-parental mapping population (WBDC accession Damon × cv. Harrington) constructed with DArT markers. The results from this study indicate that Sharon goatgrass and wild barley are rich sources of rust resistance genes for cultivated wheat and barley improvement, respectively, and that association mapping may be useful for positioning disease resistance genes in wild barley.

Development of PCR markers for the selection of wheat stem rust resistance genes Sr24 and Sr26 in diverse wheat germplasm

The use of major resistance genes is the most cost-effective strategy for preventing stem rust epidemics in Australian wheat crops. The long-term success of this strategy is dependent on combining resistance genes that are effective against all predominant races of the pathogen, a task greatly assisted by the use of molecular markers linked to individual resistance genes. The wheat stem rust resistance genes Sr24 and Sr26 (derived from Agropyron elongatum) and SrR and Sr31 (derived from rye) are available in wheat as segments of alien chromosome translocated to wheat chromosomes. Each of these genes provides resistance to all races of wheat stem rust currently found in Australia . We have developed robust PCR markers for Sr24 and Sr26 (this study) and SrR and Sr31 (previously reported) that are applicable across a wide selection of Australian wheat germplasm. Wheat lines have recently become available in which the size of the alien segments containing Sr26, SrR and Sr31 has been reduced. Newly developed PCR-markers can be used to identify the presence of the shorter alien segment in all cases. Assuming that these genes have different gene-for-gene specificities and that the wheat industry will discourage the use of varieties carrying single genes only, the newly developed PCR markers will facilitate the incorporation of two or more of the genes Sr24, Sr26, SrR and Sr31 into wheat lines and have the potential to provide durable control to stem rust in Australia and elsewhere.

Prevalence and Distribution of Common Barberry, the Alternate Host of Puccinia graminis, in Minnesota.

A federal and state program operated from 1918 until the 1980s to eradicate common barberry (Berberis vulgaris), the alternate host of Puccinia graminis, from the major areas of cereal production in the United States. Over 500 million bushes were destroyed nationally during the program, approximately 1 million in Minnesota. Some sites in Minnesota where barberry bushes were destroyed remained in the "active" class when eradication was phased out in the 1980s. Active sites were defined as those on which there was still a possibility of emergence of barberry seedlings or sprouts arising from the parent bush. In the present study, from 1998 to 2002, 72 of the approximately 1,200 active sites in Minnesota were surveyed. Areas within 90 m of mapped locations of previously destroyed bushes were searched carefully at each site. Reemerged barberry plants were found on 32 sites. The reproductive status and GPS coordinates were recorded for each reemerged bush. More than 90% of the barberry bushes were found in counties with less than 400 ha of wheat per county, mostly in southeastern Minnesota, but one bush was found in a major wheat-producing county in northwestern Minnesota. Reemergence of barberry may serve as a source of new wheat stem rust races in future epidemics.

Analysis of the Long‐term Dynamics of Stem and Leaf Rusts of Wheat in North America Using a Time‐series Approach

AbstractHistorical data on wheat stem rust in the US and wheat leaf rust in Canada were analysed using a time‐series approach to detect patterns in their long‐term dynamics. Three sets of historical data were analysed, the first of which described the annual appearance of wheat‐stem rust in six regions of the western Mississippi Basin from 1921 to 1961. Models developed from these data had significant autocorrelation components of AR(1) or AR(2), indicating that the date of disease appearance in 1 year wasstatistically related to the dates of appearance in the previous 1–2 years. The series of six regions were spatially significantly correlated with each other. Values of the cross‐correlation coefficient increased from 0.20 to 0.83 as the distance between, two regions decreased. The second data set represented relative diversity of physiological races of wheat stem rust from 1918 to 1982. Analysis suggested that a change in race diversity may occur in the US every 5–6 years, based on AR(5) and AR(6) patterns. The third data set had two series on the phenotypes of leaf rust in the eastern and prairie regions of Canada. Analysis indicated that there was a 2‐year autoregressive component AR(2) in each of these two time series. Analysis further suggestedthat the prairie population differed from the eastern population in having a 4‐year moving average component, MA(4), in the majority of individual races.

Reaction of 578 Spring Spelt Wheat Accessions to 35 Races of Wheat Stem Rust

A survey of spelt wheat accessions (Triticum aestivum ssp. spelta L.) was made to characterize their reactions to stem rust (Puccinia graminis Rob. ex Desm. f. sp. tritici). Spelt wheat genotypes cross readily with bread wheat (Triticum aestivum L.) and could be used as donor parents in bread wheat breeding programs. Because of the paucity of information on their reaction to stem rust in the literature, the objectives of this study were to: (i) screen spelt accessions for possible new sources of resistance to wheat stem rust, and (ii) postulate and confirm the presence of known genes for resistance to stem rust. Infection‐type data from seedlings artificially infected with stem rust were used to postulate Sr genes present in 578 spring spelt accessions from the USDA National Small Grain Collection. Conventional genetic studies were used to confirm the hypothetical resistance genotypes derived from infection‐type data. Genetic studies confirmed the presence of postulated genes for resistance Sr9e, Sr9f, Sr18, SrLC, and SrMcN; Sr9g was absent. Other genes for resistance postulated to be present included Sr9a, Sr9d, Srl0, Sr15, Sr17, Srl9, and Sr20. Infection‐type data proved the absence of Sr5, Sr6, Sr8a, Sr9b, Sr11, Sr13, Sr14, Sr16, Sr24, Sr25, Sr26, Sr29, Sr36, and SrTmp in these spelt accessions. Several unidentified genes that were postulated to be present may provide useful levels of resistance when transferred in combinations to bread wheat.

Detergent-soluble polypeptides extracted from uredospores of four physiologic races of Puccinia graminis f. sp. tritici

Dormant uredospores of four isolates, each belonging to different physiologic races of wheat stem rust (Puccinia graminis f. sp. tritici) were extracted with a buffer containing the detergents Nonidet P40 and sodium dodecylsulphate. The polypeptides in the extracts were separated by two-dimensional isoelectric focusing-polyacrylamide gel electrophoresis. More than 290 separate polypeptides were detected. More than 270 were the same in all races while 18 varied between races. Separate extracts prepared from different batches of uredospores of the same race had the same polypeptides, while extracts prepared from different races consistently contained unique combinations of the 18 polypeptides that varied between races.

New Wheat Lines with Known Resistance Genes for Identification of Indian Wheat Stem Rust Races

New Wheat Lines with Known Resistance Genes for Identification of Indian Wheat Stem Rust Races

Physiologic races of wheat stem rust in Canada from 1919 to 1969

The races of wheat stem rust found in Canada and identified by the "standard" and "formula" methods are described. Seven races or race groups made up 90.8% of the isolates. In 1964 a new system of race identification was introduced. It makes use of virulence formulas consisting of the numbers of effective resistance genes in the numerator and ineffective genes in the denominator. Resistance genes Sr6, Sr8, Sr9a, Sr9b, and Sr13 confer resistance to most isolates obtained since 1964, but no single gene confers resistance to all isolates. Experience shows that 250 isolates per year are sufficient to establish the trends of prevalence of the main races. The detection of rare, new combinations of virulence requires screening varieties carrying combinations of resistance genes. The main races in the past 50 years have been 56 and 15B. Race 56 is uniform with a single subrace but 15B is variable with many subraces. There is no evidence that unnecessary virulence is harmful or that "stabilizing selection" is operative in Canada, nor is there evidence that virulence on resistance genes Sr6 and Sr11 is harmful to the rust.

Observations on growth of selected australian races of wheat stem rust in axenic culture

Attempts were made to grow Puccinia graminis Pers. f.sp. tritici (Australian races 126-ANZ-6,7; 16-ANZ-1,6,7; 21-ANZ-2,3,7; 1 11-ANZ-2,3,7) in axenic culture using modifications of the techniques described by Williams, Scott & Kuhl (1966) and Williams, Scott, Kuhl & Maclean (1967) . Mycelium of race 126-ANZ-6,7 grew in culture but the colonies were small and became deeply pigmented. Uredospores of the other races germinated but failed to differentiate beyond the germ-tube stage. Different cultural techniques and media tried, including the addition of ascorbic acid and glutathione, were not successful in maintaining extensive growth. Discoloration of the colonies and medium was closely associated with loss of viability of the fungus and different phenolic compounds were observed in unpigmented and pigmented colonies. Germination of uredospores was inhibited on pigmented areas of the medium.

The component fatty acids of oils found in spores of plant rusts and other fungi. II.

The oils extracted from the spores of 17 species of rusts have been analyzed by gas–liquid chromatography. The spore oils of six species of Puccinia, three species of Cronartium, one species each of Frommea, Hemileia, Phragmidium, and Uromyces contained cis-9, 10-epoxyoctadecanoic acid but it was absent from two species of Gymnosporangium, one species of Puccinia, and one of Uromyces. The Puccinia species include eight races of wheat stem rust which had very similar fat compositions. The different spore forms of wheat and oat stem rust from both the alternate hosts were also quite similar in fat composition. The oils of the spores from the alternate hosts for one of the Gymnosporangium species were similar but for the other species there were marked differences.

PHYSIOLOGIC SPECIALIZATION OF WHEAT STEM RUST IN CANADA, 1919 TO 1955

From 1919 until shortly after 1930 the races of wheat stem rust most prevalent in Canada were: race 21, the race group 3-18-36, and the race group 17–29 which again assumed importance from 1940 to 1948. Race 49 was widely prevalent from 1927 to 1932. Race 56, first found in Canada in 1931, was the predominant race from 1934 to 1949. Race 15B, discovered shortly before 1940 and first found in Canada in 1946, was predominant from 1950 to 1955.The influence of changes in the wheat varieties under cultivation on the rust race population is discussed and it is postulated that a north-to-south movement of rust spores late in the summer plays an important part in the perpetuation of races selectively propagated in northern areas.Recently, biotypes of certain races have become important in relation to varieties now in cultivation and new varieties in the course of production. Methods of identification of such biotypes by means of accessory differential hosts are discussed in relation to the breeding or rust-resistant varieties.A brief account is given of races identified from collections of aecia from barberry.

Pharmacology of the alkaloids of Aspidosperma oblongum A. DC.

Pharmacology of the alkaloids of Aspidosperma oblongum A. DC.