T. Fetch

Cereal rust control in Canada

The major cereal crops grown in Canada are wheat (11 Mha), barley (4 Mha), and oat (1.5 Mha). Over 90% of the total cereal production area is in the western provinces of Manitoba, Saskatchewan,and Alberta. Historically, the disease of major concern in wheat was stem rust, caused by Puccinia graminis f. sp. tritici. The first significant stem rust resistant cultivar in Canada was Thatcher, grown extensively from 1939 until the early 1970s. The stem rust resistance in Thatcher was relatively effective, with the exception of susceptibility to race 15B epidemic in the 1950s. Thatcher, however, was very susceptible to leaf rust, caused by Puccinia triticina. Over time, improved resistance to both stem and leaf rust was achieved with the release of cultivars with additional genes for resistance, primarily Sr2, Sr6, Sr7a, Sr9b, Lr13, Lr14a, Lr16, and Lr34. Over the years genetic resistance has adequately controlled stem rust but leaf rust continues to cause significant losses, partially due to changes in the P. triticina population which reduced the effectiveness of resistance genes such as Lr13 and Lr16. Stripe rust on wheat, caused by Puccinia striiformis f. sp. tritici, was historically a problem under irrigation in southern Alberta, but since 2000 it has been found annually in the central Canadian prairies and southern Ontario. The genetic basis of resistance to stripe rust in most Canadian wheat cultivars has not been determined, although Yr18 provides partial resistance in many cultivars. In contrast to wheat, rust diseases have generally not caused concern for barley producers. Stem rust, caused by P. graminis f. sp. tritici, is the primary concern for barley growers, and has been controlled through use of gene Rpg1 since 1947. In 1988 race QCCJ with virulence on Rpg1 was detected in the prairie region but to date has not caused significant economic losses in barley. The resistance gene rpg4 is effective against QCCJ, but no commercial varieties have yet been produced with rpg4. In oat, both stem rust, caused by Puccinia graminis f. sp. avenae, and crown rust, caused by Puccinia coronata f. sp. avenae, have caused significant yield losses. Both rusts have been controlled mainly through host resistance and early planting. Stem rust resistance genes Pg2 and Pg13 have been the most effective and occur in many current oat cultivars. However, in 1998, 2 races, NA67 and NA76, with virulence on both Pg2 and Pg13 were detected in the prairie region. Currently, race NA67 is predominant in the prairie region and thus all Canadian cultivars are susceptible to stem rust. Since the 1980s, improved resistance to crown rust has been achieved through use of resistance derived from Avena sterilis. Pc39 was the first of the genes derived from this wild relative to be deployed in a new cultivar, followed by the release of cultivars possessing both Pc38 and Pc39. These 2 genes remained effective until the early 1990s. From 1994 onward, a series of cultivars with the highly effective Pc68 gene introgressed from A. sterilis were released. Virulence to Pc68 appeared in 2001, and in 2005 cultivars with this gene were severely rusted. The cultivar Leggett with Pc68 plus the highly effective Pc94 gene from the diploid A. strigosa was released in 2004. Rhamnus cathartica, the alternate host of P. coronata, is widespread in Canada and removal of these woody shrubs in the vicinity of oat fields is important to reduce the severity of crown rust. The increased use of fungicides on all cereals in the past 10 years has been fairly effective in rust control but represents an added input cost for producers.

International surveillance of wheat rust pathogens - progress and challenges.

Surveillance of wheat rust pathogens, including assessments of rust incidence and virulence characterization via either trap plots or race (pathotype) surveys, has provided information fundamental in formulating and adopting appropriate national and international policies, investments and strategies in plant protection, plant breeding, seed systems, and in rust pathogen research. Despite many successes from national and regional co-ordination of rust surveillance, few attempts were made to extend rust surveillance to international or even global levels. The Global Cereal Rust Monitoring System was established to address this deficiency. It is underpinned by an information platform that includes standardized protocols for methods and systems used in surveys, preliminary virulence testing, data, sample transmission and management at the field and national and global levels, and includes two web-based visualization tools. While considerable progress has been made towards a global system for monitoring variability in the wheat stem rust pathogen, and linking this to the threat posed by this pathogen to regional wheat production, some challenges remain, including ongoing commitment to support rust surveillance, and the ability to share and compare surveillance data.

Microsatellite variation in Avena sterilis oat germplasm

The Avena sterilis L. collection in the Plant Gene Resources of Canada (PGRC) consists of 11,235 accessions originating from 27 countries and is an invaluable source of genetic variation for genetic improvement of oats, but it has been inadequately characterized, particularly using molecular techniques. More than 35 accessions have been identified with genes for resistance to oat crown and stem rusts, but little is known about their comparative genetic diversity. This study attempted to characterize a structured sample of 369 accessions representing 26 countries and two specific groups with Puccinia coronataavenae (Pc) and Puccinia graminisavenae (Pg) resistance genes using microsatellite (SSR) markers. Screening of 230 SSR primer pairs developed from other major crop species yielded 26 informative primer pairs for this characterization. These 26 primer pairs were applied to screen all the samples and 125 detected alleles were scored for each accession. Analyses of the SSR data showed the effectiveness of the stratified sampling applied in capturing country-wise SSR variation. The frequencies of polymorphic alleles ranged from 0.01 to 0.99 and averaged 0.28. More than 90% of the SSR variation resided within accessions of a country. Accessions from Greece, Liberia, and Italy were genetically most diverse, while accessions from Egypt, Georgia, Ethiopia, Gibraltar, and Kenya were most distinct. Seven major clusters were identified, each consisting of accessions from multiple countries and specific groups, and these clusters were not well congruent with geographic origins. Accessions with Pc and Pg genes had similar levels of SSR variation, did not appear to cluster together, and were not associated with the other representative accessions. These SSR patterns are significant for understanding the progenitor species of cultivated oat, managing A. sterilis germplasm, and exploring new sources of genes for oat improvement.

Attempts to remove gametocidal genes co-transferred to common wheat with rust resistance from Aegilops speltoides

Rust resistance genes (introgressions S24 and S13) transferred to hexaploid wheat from two Aegilops speltoides accessions could not be used commercially due to associated gametocidal (Gc) genes. Crosses to wheat followed by rigorous selection for increased fertility were employed in an attempt to separate the unmapped S24 stem rust resistance from the Gc gene(s). However, improved fertility of the better selections could not be maintained in subsequent generations. Since the S13 introgression (leaf, stripe and stem rust resistances) mapped to chromosome 3A, allosyndetic pairing induction was used in an attempt to remove the Gc gene(s). This produced putative primary recombinants with improved fertility and plant type, the best of which had exchanged a small region of Ae. speltoides chromatin, yet was still associated with (reduced) Gc effects. This selection (04M127-3, which appears to have the Su1-Ph1 suppressor) was then crossed with wheat. Surprisingly, the 04M127-3 gametocidal effect differed drastically from that of the original introgression allowing the recovery of 35 recombinant, leaf rust resistant progeny. Microsatellite and DArT markers showed that each secondary recombinant had exchanged most of the Ae. speltoides chromatin. Although the data suggested that a complex multigenic interaction may govern the gametocidal response, preliminary indications are that the Gc effect had largely been removed and it now seems possible to completely separate the gametocidal genes from the S13 leaf rust resistance gene (here designated Lr66). The associated (S13) stripe rust and stem rust resistance genes were lost during recombination.

Evaluation of Avena spp. Accessions for Resistance to Oat Stem Rust

Oat stem rust, caused by Puccinia graminis f. sp. avenae, can cause significant yield losses in the eastern prairie region of western Canada. Currently, the predominant race of P. graminis f. sp. avenae in this region is NA67. Few genes confer resistance to NA67, and none are present in any oat cultivars registered for production in Canada. To detect lines exhibiting resistance to race NA67, we evaluated 9,978 accessions from 22 Avena spp. in field nurseries from 2001 to 2004. In all, 35 accessions were highly resistant and 12 were moderately resistant, comprised mostly of the species A. strigosa. Seventy-one accessions had an intermediate response, comprised mostly of A. abyssinica, A. barbata, A. sterilis, and A. vaviloviana. All other accessions (9,860 = 98.8%) were susceptible to race NA67. Some highly resistant accessions were found to have been incorrectly classified previously as hexaploid species A. sativa or A. sterilis, and were confirmed by chromosome counts to be diploid or tetraploid. The most promising source of novel stem rust resistance is from the diploid species A. strigosa. Transfer of resistance from diploid and tetraploid species to A. sativa is very difficult, but the lines identified in this study should prove useful as new sources of resistance to oat stem rust.

Major Gene for Field Stem Rust Resistance Co-Locates with Resistance Gene Sr12 in 'Thatcher' Wheat.

Stem rust, caused by Puccinia graminis (Pgt), is a damaging disease of wheat that can be controlled by utilizing effective stem rust resistance genes. ‘Thatcher’ wheat carries complex resistance to stem rust that is enhanced in the presence of the resistance gene Lr34. The purpose of this study was to examine APR in ‘Thatcher’ and look for genetic interactions with Lr34. A RIL population was tested for stem rust resistance in field nurseries in Canada, USA, and Kenya. BSA was used to find SNP markers associated with reduced stem rust severity. A major QTL was identified on chromosome 3BL near the centromere in all environments. Seedling testing showed that Sr12 mapped to the same region as the QTL for APR. The SNP markers were physically mapped and the region carrying the resistance was searched for sequences with homology to members of the NB-LRR resistance gene family. SNP marker from one NB-LRR-like sequence, NB-LRR3 co-segregated with Sr12. Two additional populations, including one that lacked Lr34, were tested in field nurseries. NB-LRR3 mapped near the maximum LOD for reduction in stem rust severity in both populations. Lines from a population that segregated for Sr12 and Lr34 were tested for seedling Pgt biomass and infection type, as well as APR to field stem rust which showed an interaction between the genes. We concluded that Sr12, or a gene closely linked to Sr12, was responsible for ‘Thatcher’-derived APR in several environments and this resistance was enhanced in the presence of Lr34.

Inheritance of resistance to oat stem rust in the cultivars Ronald and AC Gwen

Mitchell Fetch, J. and Fetch Jr., T. 2011. Inheritance of resistance to oat stem rust in the cultivars Ronald and AC Gwen. Can. J. Plant Sci. 91: 419–423. Oat stem rust, caused by Puccinia graminis Pers. f. sp. avenae Eriks. and E. Henn., causes sporadic epidemics and yield losses in Manitoba and eastern Saskatchewan. Oat (Avena sativa L.) cultivars registered for production in this area possess resistance to stem rust, but their genetic composition is unknown. Race TJJ (NA67), first detected in 1998, is virulent on most Pg genes; thus, it is desirable to know the gene(s) that are present in currently grown oat varieties. The hulled cultivar Ronald and the hulless cultivar AC Gwen were selected for characterization of inheritance of stem rust resistance, and crossed to the susceptible cultivar Triple Crown. Race BLD (NA1) was used to evaluate F1 plants and F2 populations. All F1 plants were resistant, indicating the presence of at least one dominant gene. Pooled F2 populations fit a 13:3 (resistant:suscep...

Predicting agronomic performance of barley using canopy reflectance data

The ability to accurately and rapidly predetermine agronomic performance would be desirable in most plant breeding programs. Remote sensing of canopy reflectance is a quick and nondestructive method that may be useful in the estimation of agronomic performance. Studies were conducted at Fargo and Langdon, North Dakota, to determine the effectiveness of a multispectral radiometer in estimating yield, kernel plumpness (KP), and 1000-kernel weight (TKW) in barley. Canopy reflectance was measured in eight (500–850 nm) discrete narrow-wavelength bands. Three types of reflectance models were evaluated: simple models using one to four wavelengths, simple ratio and normalized difference vegetation indices (NDVI) using green, red, and near-infrared wavelengths, and soil-adjusted vegetation indices (SAVI). The relationship between canopy reflectance and agronomic performance was significantly influenced by environment, growth stage, and plant genotype. Grain yield was best estimated near GS73 (0.84 < R2 < 0.92) at ...

Genetics and mapping of seedling resistance to Ug99 stem rust in winter wheat cultivar Triumph 64 and differentiation of SrTmp, SrCad, and Sr42

Key MessageResistance to Ug99 stem rust in Triumph 64 was conferred bySrTmpon chromosome arm 6DS and was mapped to the same position asSrCadandSr42, however, the three genes show functional differences.AbstractStem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is an important disease of wheat that can be controlled by effective stem rust resistance (Sr) genes. The emergence of virulent Pgt races in Africa, namely Ug99 and its variants, has stimulated the search for new Sr genes and genetic characterization of known sources of resistance. Triumph 64 is a winter wheat cultivar that carries gene SrTmp, which confers resistance to Ug99. The goals of this study were to genetically map SrTmp and examine its relationship with other Sr genes occupying a similar chromosome location. A doubled haploid (DH) population from the cross LMPG-6S/Triumph 64 was inoculated with Ug99 at the seedling stage. A single gene conditioning resistance to Ug99 segregated in the population. Genetic mapping with SSR markers placed SrTmp on chromosome arm 6DS in a region similar to SrCad and Sr42. SNP markers developed for SrCad were used to further map SrTmp and were also added to a genetic map of Sr42 using a DH population (LMPG-6S/Norin 40). Three SNP markers that co-segregated with SrTmp also co-segregated with SrCad and Sr42. The SNP markers showed no difference in the map locations of SrTmp, SrCad, and Sr42. Multi-race testing with DH lines from the Triumph 64 and Norin 40 populations and a recombinant inbred-line population from the cross LMPG-6S/AC Cadillac showed that SrTmp, SrCad, and Sr42 confer different spectra of resistance. Markers closely linked to SrTmp are suitable for marker-assisted breeding and germplasm development.

Races of Puccinia graminis on wheat, oat, and barley in Canada in 2009 and 2010

Abstract Stem rust, caused by Puccinia graminis, is an important disease on wheat, oat, and barley crops worldwide. Because the disease is primarily controlled in Canada using resistant cultivars, determining the virulence structure in pathogen populations is necessary for the early detection of novel virulent races. Surveys of wheat (Triticum aestivum), oat (Avena sativa), and barley (Hordeum vulgare) fields and trap nurseries were conducted in 2009 and 2010 across Canada to provide information on incidence and severity of stem rust infection, and to identify the virulence structure in the pathogen populations. Stem rust was not found on cultivated wheat, and was at trace levels in oat and barley fields in both years. Race QFCSC of P. graminis f. sp. tritici was dominant in 2009 (88.0% of all samples), and was the only race detected in Canada in 2010. Races MCCFC, RFCSC, and TPMKC were found at low levels (<5%) in 2009. Thirteen races of P. graminis f. sp. avenae were found in 2009, with TGD (30.4%), TJN (16.2%), TGN (14.9%), TJJ (11.2%), TJS (9.9%), and TGB (8.6%) the most frequent. Twelve races of P. graminis f. sp. avenae were found in 2010, and TGN (27.3%), TGB (19.8%), TGD and TJN (14.0% each), and TJS (9.9%) were the most frequent. Race TJJ, which is virulent on all Canadian oat cultivars and was first detected in 1998, fell to only 5.2% frequency (total samples) in 2010. One new race (TJL) was detected in three samples from Manitoba in 2009, but is avirulent to gene Pg13 and does not pose a threat to oat production in Canada.