Genetic Relationship of Stripe Rust Resistance Genes Yr34 and Yr48 in Wheat and Identification of Linked KASP Markers.

The Australian continent was free from wheat stripe rust caused by Puccinia striiformis f. sp. tritici until exotic incursions occurred in 1979 and 2002. The 2002 incursion enabled the identification of a new stripe rust resistance gene (Yr34) in the advanced breeding line WAWHT2046. In this study, we developed and validated markers closely linked with Yr34, which is located in the distal region in the long arm of chromosome 5A. Four kompetitive allele-specific polymerase chain reaction (KASP) and three sequence-tagged site (STS) markers derived from the International Wheat Genome Sequencing Consortium RefSeq v1.0 scaffold-77836 cosegregated with Yr34. Markers sun711, sun712, sun725, sunKASP_109, and sunKASP_112 were shown to be suitable for marker-assisted selection in a validation panel of 71 Australian spring wheat genotypes, with the exception of cultivar Orion that carried the Yr34-linked alleles for sunKASP_109 and sunKASP_112. Markers previously reported to be linked with adult plant stripe rust resistance gene Yr48 also cosegregated with Yr34. Wheat genotypes carrying Yr34 and Yr48 produced identical haplotypes for the Yr34-linked markers identified in this study and those previously reported to be linked with Yr48. Phenotypic testing of genotypes carrying Yr34 and Yr48 showed that both genes conferred similar seedling responses to pre-2002 and post-2002 P. striiformis f. sp. tritici pathotypes. Further testing of 600 F2 plants from a cross between WAWHT2046 and RIL143 (Yr48) with P. striiformis f. sp. tritici pathotype 134 E16A+Yr17+Yr27+ failed to reveal any susceptible segregants. Our results strongly suggest that Yr34 and Yr48 are the same gene, and that Yr48 should be considered a synonym of Yr34.

Yr60, a Gene Conferring Moderate Resistance to Stripe Rust in Wheat.

Stripe rust, caused by Puccinia striiformis f. sp. tritici W., is a devastating disease of wheat worldwide. A new stripe rust resistance gene with moderate seedling and adult plant resistance was mapped using an F5 recombinant inbred line (RIL) population developed from the cross of the resistant parent 'Almop' with the susceptible parent 'Avocet'. The parents and RILs were phenotyped for seedling stripe rust response variation in a greenhouse and in field trials at Toluca, Mexico for 2 years. Almop showed moderate levels of resistance at both seedling and adult plant stages compared with the highly susceptible response of Avocet. The distribution of homozygous resistant, homozygous susceptible, and segregating RILs conformed to segregation at a single locus. Seedlings and adult plant responses were correlated, indicating that the same gene conferred resistance at both stages. A bulk segregant analysis approach with widely distributed simple sequence repeat (SSR) markers mapped the resistance gene to the distal region of the long arm of chromosome 4A. The SSR marker wmc776 cosegregated with this gene, whereas markers wmc219 and wmc313 were tightly linked and both located at 0.6 centimorgans. The resistance locus was designated Yr60.

Inheritance and molecular mapping of a gene conferring seedling resistance against Puccinia hordei in the barley cultivar Ricardo.

Genetic studies were undertaken to determine the inheritance and genomic location of uncharacterised seedling resistance to leaf rust, caused by Puccinia hordei, in the barley cultivar Ricardo. The resistance was shown to be conferred by a single dominant gene, which was tentatively designated RphRic. Bulk segregant analysis (BSA) and genetic mapping of an F(3) mapping population using multiplex-ready SSR genotyping and Illumina GoldenGate SNP assay located RphRic in chromosome 4H. Given that this is the first gene for leaf rust resistance mapped on chromosome 4H, it was designated Rph21. The presence of an additional gene, Rph2, in Ricardo, was confirmed by the test of allelism. The seedling gene Rph21 has shown effectiveness against all Australian pathotypes of P. hordei tested since at least 1992 and hence represents a new and useful source of resistance to this pathogen.

Characterisation of a new stripe rust resistance gene Yr47 and its genetic association with the leaf rust resistance gene Lr52.

Two Iranian common wheat landraces AUS28183 and AUS28187 from the Watkins collection showed high levels of seedling resistance against Australian pathotypes of leaf rust and stripe rust pathogens. Chi-squared analyses of rust response segregation among F(3) populations derived from crosses of AUS28183 and AUS28187 with a susceptible genotype AUS27229 revealed monogenic inheritance of leaf rust and stripe rust resistance. As both genotypes produced similar leaf rust and stripe rust infection types, they were assumed to carry the same genes. The genes were temporarily named as LrW1 and YrW1. Molecular mapping placed LrW1 and YrW1 in the short arm of chromosome 5B, about 10 and 15 cM proximal to the SSR marker gwm234, respectively, and the marker cfb309 mapped 8-12 cM proximal to YrW1. LrW1 mapped 3-6 cM distal to YrW1 in two F(3) populations. AUS28183 corresponded to the accession V336 of the Watkins collection which was the original source of Lr52. Based on the genomic location and accession records, LrW1 was concluded to be Lr52. Because no other seedling stripe rust resistance gene has previously been mapped in chromosome 5BS, YrW1 was permanently named as Yr47. A combination of flanking markers gwm234 and cfb309 with phenotypic assays could be used to ascertain the presence of Lr52 and Yr47 in segregating populations. This investigation characterised a valuable source of dual leaf rust and stripe rust resistance for deployment in new wheat cultivars. Transfer of Lr52 and Yr47 into current Australian wheat backgrounds is in progress.

Development of wheat lines carrying stem rust resistance gene Sr39 with reduced Aegilops speltoides chromatin and simple PCR markers for marker-assisted selection.

The use of major resistance genes is a cost-effective strategy for preventing stem rust epidemics in wheat crops. The stem rust resistance gene Sr39 provides resistance to all currently known pathotypes of Puccinia graminis f. sp. tritici (Pgt) including Ug99 (TTKSK) and was introgressed together with leaf rust resistance gene Lr35 conferring adult plant resistance to P. triticina (Pt), into wheat from Aegilops speltoides. It has not been used extensively in wheat breeding because of the presumed but as yet undocumented negative agronomic effects associated with Ae. speltoides chromatin. This investigation reports the production of a set of recombinants with shortened Ae. speltoides segments through induction of homoeologous recombination between the wheat and the Ae. speltoides chromosome. Simple PCR-based DNA markers were developed for resistant and susceptible genotypes (Sr39#22r and Sr39#50s) and validated across a set of recombinant lines and wheat cultivars. These markers will facilitate the pyramiding of ameliorated sources of Sr39 with other stem rust resistance genes that are effective against the Pgt pathotype TTKSK and its variants.

Genetic mapping of adult plant leaf rust resistance genes Lr48 and Lr49 in common wheat.

Hypersensitive adult plant resistance genes Lr48 and Lr49 were named based on their genetic independence of the known adult plant resistance genes. This study was planned to determine genomic locations of these genes. Recombinant inbred line populations derived from crosses involving CSP44 and VL404, sources of Lr48 and Lr49, respectively, and the susceptible parent WL711, were used to determine the genomic locations of these genes. Bulked segregant analyses were performed using multiplex-ready PCR technology. Lr48 in genotype CSP44 was mapped on chromosome arm 2BS flanked by marker loci Xgwm429b (6.1 cM) and Xbarc7 (7.3 cM) distally and proximally, respectively. Leaf rust resistance gene Lr13, carried by the alternate parent WL711, was proximal to Lr48 and was flanked by Xksm58 (5.1 cM) and Xstm773-2 (8.7 cM). Lr49 was flanked by Xbarc163 (8.1 cM) and Xwmc349 (10.1 cM) on chromosome arm 4BL. The likely presence of the durable leaf rust resistance gene Lr34 in both CSP44 and VL404 was confirmed using the tightly linked marker csLV34. Near-isogenic lines for Lr48 and Lr49 were developed in cultivar Lal Bahadur. Genotypes combining Lr13 and/or Lr34 with Lr48 or Lr49 were identified as potential donor sources for cultivar development programs.

Determinants of IQ profile in children with idiopathic generalized epilepsy.

To determine the IQ profile of children with epilepsy and the influence of various epilepsy-related variables on IQ scores, we studied 50 children with idiopathic generalized epilepsy of > 1-year duration, 25 of their siblings, and 30 healthy controls. IQ assessments were made with Malin's Indian modification of the Wechsler Intelligence Scale for Children. The mean +/- SD IQ scores of children with epilepsy (85.6 +/- 12) and their siblings (93.2 +/- 11) were significantly lower than those of the controls (101.6 +/- 9). The IQ scores of the children with epilepsy were also significantly lower than those of their siblings (p < 0.05). The IQ scores showed a significant correlation with socioeconomic status (SES) score (r = 0.33), a history of status epilepticus (r = -0.38), duration of seizure disorder (r = -0.31), and total number of seizures (r = -0.31). On multiple regression analysis, status epilepticus emerged as the most significant variable, accounting for 14% variance, followed by SES score (9% variance), duration of seizure disorder (6% variance), and sex of the child (5% variance). Genetic or environmental factors that probably lead to cognitive deficit in children with epilepsy and their siblings require further study.