Stripe rust and leaf rust have been major constraints to wheat production in Nepal since the 1960s. Several rust epidemics causing hardship for Nepalese wheat growers were due to race changes. Breeding for rust resistance was initiated with establishment of the National Wheat Research Program in 1972, but concerted searches for durable resistance came later with the introduction of wheat genetic resources from CIMMYT, Mexico. The early wheat varieties Nepal 297, Siddhartha, Vinayak, BL1473, BL 1022 and Annapurna series with leaf rust and stripe rust resistance genes Lr13, Lr23, Lr26 and Yr9, and Yr27 in the 1970s and 1980s succumbed to new races within a few years of release. However, Bhrikuti (CMT/COC75/3/PLO/FURY/ANA) with both major and minor gene combinations (Lr10, Lr14a, Lr26/Yr9/Sr31+ and Lr34/Yr18) and released in 1994 was unaffected by Yr9 virulence in 1997 and Yr27 virulence in 2004. This variety with >20 years of leaf rust and stripe rust protection continues to be the most popular wheat variety in Nepal. Three other varieties, Gautam (Siddhartha/Ning8319//Nepal 297) released in 2004, WK 1204 (SW89-3064/Star) released in 2007, and Pasang Lhamu (PGO/SERI) released in 1997 with Lr16, Lr26/Yr9/Sr31, Lr34/Yr18, Lr46/Yr29, Yr7, and Sr2 also remain resistant. The Ug99 resistant varieties Vijay (NL748/NL837), Danphe(KIRITATI//2*PBW65/2*SERI.1B) and Tilottama (Francolin#1 = Waxwing*2/Vivitsi) also possesses APR to the three rusts. Nepalese wheat researchers work closely with the CIMMYT Global Wheat Program and DRRW/BGRI to utilize knowledge and APR germplasm. Strong networks for participatory varietal selection involving women farmers in both the hills and terai help in faster adoption and in establishing varietal diversity. In summary, Nepalese wheat breeders have successfully used APR in protecting wheat crops.
Primary Author: Thapa, Agriculture Botany Division, Nepal Agricultural Research Council (NARC), Nepal
The discovery of Ug99 stem rust with virulence on most widely grown wheat cultivars worldwide triggered substantial new research on host resistance genes and associated virulence dynamics in the pathogen. Ug99 is mutating and migrating, with eight variants presently known, and has spread throughout eastern Africa, across the Red Sea to Yemen and Iran, and to South Africa. It has been speculated that further movement of Ug99 spores from South Africa to South America could happen on prevailing winds that occur about eight days per month on average. While Ug99 is not yet present in South America, this is a critical entry point into the Western Hemisphere as demonstrated by introduction of soybean rust to Paraguay in 2001. Thus, work was initiated to engage countries in South America to participate in monitoring for its occurrence. Stem rust surveys are currently conducted in Argentina, Brazil, and Uruguay on a regular basis. Each country has a national agricultural institute with adequate to good capacity to perform pathotyping work, but have limitations due to inadequate greenhouse cooling. We will present the current virulence dynamics of Pgt in each country. In addition to surveys for rust, we searched for the presence of Berberis spp. in Brazil. Berberis laurina was abundantly distributed in the Rio Grande du Sul state near the city of Caçapava. Leaves sampled in October displayed low to moderate aecial infections. Determination of the pathogen species infecting B. laurina is currently being determined by physiologic and molecular methods.
The first system describing physiologic specialization in the cereal rust fungi was that by Stakman and Levine (1922) for the wheat stem rust pathogen. Thirty seven biologic forms or “races” were identified using 12 differential wheat lines. Since then, additional variability in physiologic specialization was found and several systems evolved to describe this variation using numbers, letters, or combinations of both. This led to difficulties in comparing races, most often because of differences in the system that is used and the differential lines employed. A system that describes virulence succinctly and allows easilymade comparisons between races is highly desirable. Additionally, differential lines should be monogenic or near-isogenic so that virulence is classified on a genetic basis. Wherever near-isogenic stocks are used, it is vital that the recurrent parent is included. The systems that appear to be best suited to describing virulence with the above parameters are the letter-code and octal nomenclature. Of these, the letter-code system is the most commonly used based on a survey of research scientists working on stem rust. Thus, the letter-code system that uses 20 differential host lines is proposed to describe the nomenclature of Puccinia graminis f. sp. tritici on a worldwide basis. In addition, the source seedstock line for each differential gene is provided.
Leaf rust is common in wheat worldwide, consistently reducing yields by 5-15% or more. Fungicides are applied to U.S. spring wheat to mitigate crop losses, but combinations of resistance genes can provide less expensive, effective control. We use biparental and association mapping approaches to identify resistance genes in two Minnesota varieties and 3,000 diverse global lines. Six populations developed from selected National Small Grains Collection lines were evaluated for seedling resistance, which has been mapped using bulk segregant analysis. Two populations were developed to map adult plant resistance using recombinant inbred lines. Leveraging large association mapping panels can identify novel variants from the diverse NSGC lines. The results will identify successful gene combinations underlying durable resistance and associated genetic markers. We will explore the utility of association mapping to identify leaf rust resistance genes and evaluate the global distribution of leaf rust resistance to inform worldwide wheat improvement.
Primary Author: Turner, Department of Agronomy and Plant Genetics, University of Minnesota, USA
Wheat varieties with single effective gene for leaf rust resistance often quickly become susceptible because of multiplication of virulent Puccinia triticina genotypes. One of the methods to elongate term of effectiveness is to combine two genes in host genotype. To note, it is impossible to distinguish phenotypically plants or families having one or two genes in hybrid populations; the only method is to use PCR producing DNA markers linked to each gene for resistance. It is not convenient when necessary to analyze thousands plants or especially families of crosses between carriers of certain genes. At inoculation of wheat seedlings having Lr 9, 19, 24, 47, 29 and Sp with rust population from North-West region of Russian Federation all of them were absolutely resistant, so these genes may be considered to be effective in this region. Rust population was multiplied on cv. Leningradka leaf segments placed on cotton wool wetted with solution of maleic acid hidrazide (10 mg/l) + potassium chloride (0.48 g/l) +monosubstituted sodium phosphate (0.66 g/l) and used to infect seedling of the lines constantly poured with the solution. Rare pustules were recorded on each line. Isolates from the line were combined, multiplied and used to infect the lines set. Interaction specificity was shown for carriers of certain genes for resistance and inoculums. We propose to infect seedlings of hybrid wheat populations with mixtures of isolates virulent to first gene and those virulent to second one at use of above-mentioned method to multiply rust and grow plants. Seedlings resistant to that inoculum have both genes for resistance. If we have F3 or later families it is possible to use original population without selection of virulent isolates; in this case the method allowed removing progenies of heterozygous plants. With this approach we developed lines possessing combinations of Lr9+Lr24 and Lr9+Lr47 genes
Primary Author: Tyryshkin, All-Russian Institute of Plant Genetic Resources
Malika', a hard red spring wheat (Triticum aestivum L.) cultivar developed using doubled haploid technology by the Institut National de la Recherche Agronomique (INRA), Morocco, and tested as 06DHBW48, was approved for release in 2016 by the Office National de S?curit? Sanitaire des Produits Alimentaires (ONSSA), Morocco. Malika was selected from the doubled haploids derived from the cross 'Achtar3*//'Kanz'/Ks85-8-4). Achtar and Kanz are Moroccan varieties originating from segregating populations from CIMMYT. Achtar and Kanz are a well adapted to Moroccan conditions but susceptible to the Hessian fly, yellow rusts and some races of leaf rust. 'Achtar' was crossed with it in order to incorporate the Hessian fly resistance, yellow rust resistance and leaf rust resistance and 'Achtar' was crossed with Kanz/Ks85-8-4 having resistance to Hessian fly, yellow rust and leaf rust. Backcrossed 3 times with 'Achtar', and selected lines having resistance to the Hessian fly, yellow rust and leaf rust from the population derived from each backcross. Finally the selected the resistant line was used develop doubled haploids. The doubled haploid lines produced were tested in the laboratory and field for Hessian fly and the rust resistance. The resistant lines were incorporated in the multi-local yield trials and three promising lines with the resistance to Hessian fly, yellow rust and leaf rust and better yield and quality were submitted for registration in the official catalog in 2014. After 2 years of testing (years 2014-15 and 2015-16), one line (06DHBW48) was accepted for the registration and designated as 'Malika'. 'Malika' is a semi-dwarf variety, well adapted to semi-arid regions, early maturing, high yielding, tolerant to drought and resistant to Hessian fly, leaf rust and yellow rust.
Puccinia graminis f. sp. tritici (Pgt) is one of the most destructive pathogens of wheat. Fungal secreted proteins termed effectors play an important role in modulating the host cellular environment and suppressing the plant defense response to enable fungal growth. They also become targets of plant resistance (R) proteins. We have taken a genomics approach to initially identify candidate effectors. We have built a draft genome for a founder Australian Pgt isolate of pathotype (pt.) 21-0 (collected in 1954) by next generation DNA sequencing. A combination of reference-based assembly using the genome of the previously sequenced North American Pgt isolate CDL 75-36-700-3 (p7a) and de novo assembly resulted in a 92 Mbp reference genome for Pgt isolate 21-0. This draft genome was subsequently used to build a pan-genome based on five Australian Pgt isolates. Transcriptomes from germinated urediniospores and haustoria were separately assembled for pt. 21-0 and comparison of gene expression profiles showed differential expression in ~10% of the genes in germinated urediniospores as well as haustoria. A total of 1,924 secreted proteins were predicted from the 21-0 transcriptome, of which 586 were classified as haustorial secreted proteins (HSPs). We are currently exploring effector gene expression during infection of wheat to reduce this candidate list based on a common expression profile identified for Avr genes in the flax rust fungus. Comparison of 21-0 with two presumed clonal field derivatives (collected in 1982 and 1984) that had evolved virulence on four additional resistance genes (Sr5, Sr11, Sr27, SrSatu) identified mutations in 13 HSP effector candidates. These candidate effectors are being assessed for recognition in wheat accessions with the corresponding R genes using a bacterial type three secretion delivery system based on an engineered Pseudomonas fluorescence strain (Upadhyaya NM et al. Mol Plant Microbe Interact 27:255-264).
Primary Author: Upadhyaya, CSIRO Agriculture, Canberra, Australia
The Green Revolution involved the deployment of reduced height (Rht) genes to generate shorter wheat varieties with increased grain yields. It also contributed to a reduction in genetic diversity in the modern gene pool. Therefore, the pre- Green Revolution tall wheat landraces may provide a reservoir of genetic variation for economic traits such as rust resistance. Considering the breakdown of a suite of rust resistance genes through the emergence of currently predominant pathotypes (e.g. Ug99 and high temperature adapted isolates of the stripe rust pathogen) after three decades of Green Revolution, the discovery, characterisation and deployment of diverse sources of resistance remains a high priority. We have screened the Watkins wheat landrace collection and discovered, characterised and formally named a suite of new rust resistance genes including Yr47, Yr51, Yr57, Yr63 and Sr49. In addition, genotypes carrying potentially new genes for resistance to three rust pathogens are currently being investigated by students from seven nations representing three continents (Australia, Asia and Africa). Yr47, Yr51, Yr57 and Lr52 have been backcrossed into modern cultivars including the widely adapted cultivar PBW343 (Atilla) using markers developed in our research program. Development of triple rust resistant derivatives in modern wheat backgrounds is in progress. Stocks carrying Yr47, Yr51, Yr57 and Lr52 have been mutated to facilitate cloning of these loci for their eventual use in development of multi-gene cassettes for transformation.
Primary Author: Urmil Bansal, The University of Sydney, Plant Breeding Institute, Australia
Association mapping detects correlations between genotypes and phenotypes in a sample of individuals based on the linkage disequilibrium and can be used to uncover new genetic variation among germplasm collections. Two hundred and five landraces collected by the English botanist A. Watkins in the 1920s were screened for rust response variation under field conditions during three crop seasons. An integrated map of 350 polymorphic DArT markers was developed. Association mapping identified the involvement of several genomic regions in controlling resistance to three rust diseases. Seven, eight and nine genomic regions, respectively, appeared to carry yet uncharacterized leaf rust, stripe rust and stem rust resistance. Three dimensional analyses indicated genetic association of leaf rust and stripe rust resistance in some accessions, whereas no such association was observed between stem rust resistance and resistance to either of the other two rust diseases. A new stripe rust resistance locus, Yr47, has been named.
Primary Author: Urmil Bansal, The University of Sydney, Plant Breeding Institute, Australia
Leaf rust is endemic to all wheat-growing regions of the world. Resistance to leaf rust in wheat cultivars is controlled either by all stage resistance (ASR) or by adult plant resistance (APR) genes. Although deployment of single ASR genes can provide high levels of resistance, these are usually overcome by virulence in pathogen populations. In contrast, individual APR genes often provide low levels of resistance and combinations of three to four genes are necessary to achieve adequate resistance for crop protection. This kind of APR has proven to be durable. APR gene Lr48 in a single plant selection of Condor (CSP44) was mapped on chromosome 2BS and was flanked by markers gwm429b (6.1 cM, distal) and barc7 (7.3 cM, proximal) (Bansal et al. 2008, Theor. Appl. Genet. 117:307-312). The present study was planned to identify markers more closely linked to Lr48. Selective genotyping by 90K Infinium Assay identified 27 SNP markers linked with Lr48. The SNP sequences were used to design Kompetitive Allele-Specific Primers (KASP). Eleven KASP markers showing clear clustering were genotyped on a RIL population using the CFX96 Touch™ real-time PCR detection system (Biorad, USA). KASP marker IWB72894 co-segregated with Lr48.
Primary Author: Vallence Nsabiyera, The University of Sydney, Plant Breeding Institute, Australia