Inheritance and QTL mapping of leaf rust resistance in the European winter wheat cultivar ‘Beaver’

Genetic studies were conducted on an European winter wheat cultivar, Beaver, to determine the mode of inheritance of leaf rust resistance at seedling and adult plant growth stages using a recombinant doubled haploid population, Beaver/Soissons. Greenhouse studies indicated the involvement of genes Lr13 and Lr26 in governing leaf rust resistance at seedling growth stages, whereas, adult plant resistance (APR) in the field with pathotypes carrying virulence individually for Lr13 and Lr26 showed trigenic inheritance for the population. Marker regression analysis of adult plant field data indicated the involvement of six significant QTLs (chromosomes 1B, 3B, 3D, 4B, 4D and 5A) in year 2005, four QTLs (1B, 3B, 4B and 5A) in 2006, and six QTLs (1A, 1B, 3B, 4A, 4B and 5A) in 2007 for reducing leaf rust severity. QTLs on chromosomes 1B, 4B and 5A were considered the most important because of their detection across years, whereas QTLs on chromosomes 1A, 3B, 3D and 4A were either inconsistent or non-significant and unexplained. Based on an association of closely linked markers with phenotypic data, putative single gene stocks were identified for each consistent QTL and crossing was initiated to develop populations segregating for each to permit fine mapping of the identified regions.     

Genetic mapping of seedling and adult plant stem rust resistance in two European winter wheat cultivars

A recombinant inbred line (RIL) population derived from the cross Arina/Forno was field tested for 2 years against Puccinia graminis f. sp. tritici under artificially created epidemic conditions. Both parents showed intermediate adult plant stem rust responses and the RIL population showed continuous variation for this trait. Composite interval mapping identified genomic regions controlling low stem rust response on chromosomes 5B and 7D consistently across all experiments. These genomic regions were named QSr.Sun-5BL and QSr.Sun-7DS and explained on an average 12% and 26% of the phenotypic variation in adult plant stem rust response, respectively. QSr.Sun-5BL mapped close to Xglk0354 and was contributed by Arina. The Lr34-linked markers csLV34 and swm10 were closely associated with QSr.Sun-7DS suggesting the involvement of Lr34 in controlling adult plant stem rust response of cultivar Forno. Additional minor and inconsistent QTLs explaining variation in adult plant stem rust response were identified on chromosome arms 1AS and 7BL. The QTL located on chromosome 7BL corresponded to the stem rust resistance gene Sr17 carried by cultivar Forno. A seedling stem rust resistance gene carried by Arina, SrAn1, was ineffective under field conditions and was mapped on the long arm of chromosome 2A. Genotypes carrying combinations of QSr.Sun-5BL and QSr.Sun-7DS based on positive alleles of the respective closest marker loci Xglk0354 and XcsLV34 or Xswm10 exhibited a lower response than either parent indicating an additive effect of these genes. Transfer of these genes into cultivars carrying Sr2 would provide a more effective and durable resistance against the stem rust pathogen. Markers csLV34 and/or swm10 could be used in marker assisted selection of QSr.Sun-7DS in breeding programs.     

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.     

Molecular mapping of adult plant stripe rust resistance in wheat and identification of pyramided QTL genotypes

The Puccinia striiformis f. sp. tritici (Pst) pathotype, 134 E16A+, detected in 2002 in Australia, produced relatively lower and higher adult plant stripe rust responses, respectively, on cultivars Kukri and Janz in comparison to the pre-2002 Pst pathotype 110 E143A+. Molecular mapping of adult plant stripe rust response variation among 180 Kukri/Janz-derived doubled haploid lines over 4 years, two each with Pst pathotypes 110 E143A+ and 134 E16A+, was performed. QYr.sun-7B and QYr.sun-7D were consistently contributed by Kukri and Janz, respectively. QYr.sun-7D corresponded to the genomic location of Yr18 and QYr.sun-7B remains to be formally named. QYr.sun-1B, QYr.sun-5B, and QYr.sun-6B were detected during more than one season irrespective of the Pst pathotypes used, whereas QYr.sun-3B was identified only during the 2003 crop season. QYr.sun-1A contributed by Janz, and QYr.sun-2A from Kukri, were detected only against Pst pathotypes 110 E143A+ and 134 E16A+, respectively. The DH lines showing better resistance than the either parent carried combinations of 4 to 6 QTL. These lines are currently being used as stripe rust resistance donors in wheat breeding programs.     

Genotypic and environmental effects on lupin seed composition

Currently, white lupin (Lupinus albus L.) is gaining importance due to its high nitrogen fixation capability and potential in sustainable crop production systems. Even though research conducted in Australia, Chile, Germany, New Zealand, and Portugal has indicated lupin's positive potential as human and animal food, such information from Virginia and adjoining areas of the United States is not available. In addition, effects of growing environment and genotypes on lupin seed composition need to be characterized to evaluate lupin's potential as a food and feed crop. Towards this end, seed of 12 lupin genotypes produced in Maine (USA) and Virginia (USA) were compared to determine genotypic and environmental effects on contents of protein, sugar, oil, various fatty acids, amino acids, and minerals. The protein content of dry seed was not affected by growing environment. However, growing environment had significant effects on contents of total sugar, amino acids, oil, fatty acids, and minerals. Significant variation existed among 12 lupin genotypes for various traits when composition of seed produced in Virginia was evaluated. The results indicated that site-specific evaluation of adapted lupin genotypes for chemical composition should be included in efforts to evaluate lupin's overall potential as a food or feed crop.     

Cytogenetic studies in wheat XIX. Chromosome location and linkage studies of a gene for leaf rust resistance in the Australian cultivar 'Harrier'

Monosomic analysis indicated that a seedling leaf rust resistance gene present in the Australian wheat cultivar ‘Harrier’(tentatively designated LrH) is located on chromosome 2A. LrH segregated independently of the stripe rust resistance gene Yr1 located in the long arm of that chromosome, but failed to recombine with Lr17 located in the short arm. LrH was therefore designated Lr17b and the allele formerly known as Lr17 was redesignated as Lr17a. The genes Lr17b and Lr37 showed close repulsion linkage. Tests of allelism indicated that Lr1 7b is also present in the English wheats ‘Dwarf A’(‘Hobbit Sib’), ‘Maris Fundin’ and ‘Norman’. Virulence for Lr17b occurs in Australia, and pathogenicity studies have also demonstrated virulence in many western European isolates of the leaf rust pathogen. Despite this, it is possible that the gene may be of value in some regions if used in combination with other leaf rust resistance genes.     

Aspects of wheat rust research in Australia

A National Wheat Rust Control Program, that has operated in Australiasince 1975, provides national pathotype surveys for the three rustpathogens, undertakes ongoing searches for new sources of resistance andcarries out genetic analyses of these sources, and provides rust screeningand germplasm enhancement support for breeders. The program wasexpanded in the 1980s to address problems arising from the introductionof wheat stripe rust. A new form of stripe rust, described as barley grassstripe rust, was first detected in 1998. Although virulent on some wheatseedlings this new rust appears to be a greater threat to barley. Molecularmarkers are expected to make an increasing impact on our ability to selectthe gene combinations needed to enhance the durability of resistance.     

Relationship between wheat rust resistance genes Yr1 and Sr48 and a microsatellite marker

A recombinant inbred line population derived from a cross between the winter wheat cultivars Arina and Forno was used to study the genetic relationship between genes Yr1 and SrAn1 in chromosome 2AL. Yr1 from Forno showed repulsion linkage (16·5 cM) with SrAn1 carried by Arina and was proximal to SrAn1 . Based on the chromosomal location of SrAn1 with respect to Yr1 and its ineffectiveness against the Australian Puccinia graminis f. sp. tritici pathotype 34-1,2,7 +  Sr38 , it was concluded that SrAn1 is distinct from Sr21 and was designated as Sr48 . An attempt was made to map more markers in the distal region of chromosome 2AL in order to determine the precise location of Sr48 . Unfortunately none of the markers tested mapped between Yr1 and Sr48 , with the latter being the most distal locus. However, close linkage was identified between Yr1 and the PCR-based molecular marker stm673acag. Genotyping with stm673acag amplified a 120-bp fragment in eight of nine genotypes carrying Yr1 . Avocet S was the only line tested without Yr1 that also amplified the 120-bp product. A 124-bp product was amplified in 40 Australian wheat cultivars known to lack Yr1. These results suggest that stm673acag could be used for marker assisted selection of Yr1 . Genotypes carrying both Yr1 and Sr48 were identified.     

Temperature-sensitive wheat stem rust resistance gene Sr15 is effective against Puccinia graminis f. sp. tritici race TTKSK

The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty-two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature-sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker-assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less-desirable TTKSK-effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.