Microsatellite DNA markers are consistently found to be more informative than other classes of markers in hexaploid wheat. The objectives of this research were to develop new primers flanking wheat microsatellites and to position the associated loci on the wheat genome map by genetic linkage mapping in the ITMI W7984 x Opata85 recombinant inbred line (RIL) population and/or by physical mapping with cytogenetic stocks. We observed that the efficiency of marker development could be increased in wheat by creating libraries from sheared rather than enzyme-digested DNA fragments for microsatellite screening, by focusing on microsatellites with the [ATT/TAA]n motif, and by adding an untemplated G-C clamp to the 5'-end of primers. A total of 540 microsatellite-flanking primer pairs were developed, tested, and annotated from random genomic libraries. Primer pairs and associated loci were assigned identifiers prefixed with BARC (the acronym for the USDA-ARS Beltsville Agricultural Research Center) or Xbarc, respectively. A subset of 315 primer sets was used to map 347 loci. One hundred and twenty-five loci were localized by physical mapping alone. Of the 222 loci mapped with the ITMI population, 126 were also physically mapped. Considering all mapped loci, 126, 125, and 96 mapped to the A, B, and D genomes, respectively. Twenty-three of the new loci were positioned in gaps larger than 10 cM in the map based on pre-existing markers, and 14 mapped to the ends of chromosomes. The length of the linkage map was extended by 80.7 cM. Map positions were consistent for 111 of the 126 loci positioned by both genetic and physical mapping. The majority of the 15 discrepancies between genetic and physical mapping involved chromosome group 5.

In children with severe traumatic brain injury, hypothermia therapy that is initiated within 8 hours after injury and continued for 24 hours does not improve the neurologic outcome and may increase mortality. (Current Controlled Trials number, ISRCTN77393684 [controlled-trials.com].).

Stem rust, caused by Puccinia graminis f. sp. tritici, historically was one of the most destructive diseases of wheat and barley. The disease has been under effective control worldwide through the widespread use of host resistance. A number of stem rust resistance genes in wheat have been characterized for their reactions to specific races of P. graminis f. sp. tritici. Adult plant responses to race TTKS (also known as Ug99) of monogenic lines for Sr genes, a direct measurement of the effectiveness for a given gene, have not been investigated to any extent. This report summarizes adult plant infection responses and seedling infection types for monogenic lines of designated Sr genes challenged with race TTKS. High infection types at the seedling stage and susceptible infection responses in adult plants were observed on monogenic lines carrying Sr5, 6, 7a, 7b, 8a, 8b, 9a, 9b, 9d, 9g, 10, 11, 12, 15, 16, 17, 18, 19, 20, 23, 30, 31, 34, 38, and Wld-1. Monogenic lines of resistance genes Sr13, 22, 24, 25, 26, 27, 28, 32, 33, 35, 36, 37, 39, 40, 44, Tmp, and Tt-3 were effective against TTKS both at the seedling and adult plant stages. The low infection types to race TTKS observed for these resistance genes corresponded to the expected low infections of these genes to other incompatible races of P. graminis f. sp. tritici. The level of resistance conferred by these genes at the adult plant stage varied between highly resistant to moderately susceptible. The results from this study were inconclusive for determining the effectiveness of resistance genes Sr9e, 14, 21, and 29 against race TTKS. The understanding of the effectiveness of individual Sr genes against race TTKS will facilitate the utilization of these genes in breeding for stem rust resistance in wheat.

No abstract

The stem rust resistance gene Sr24 is effective against most races of Puccinia graminis f. sp. tritici, including race TTKS (syn. Ug99), and is used widely in commercial wheat cultivars worldwide. In 2006, susceptible infection responses were observed on wheat lines and cultivars carrying Sr24 in a field stem rust screening nursery at Njoro, Kenya. We derived 28 single-pustule isolates from stem rust samples collected from the 2006 Njoro nursery. The isolates were evaluated for virulence on 16 North American stem rust differential lines; on wheat lines carrying Sr24, Sr31, Sr38, and SrMcN; and on a wheat cultivar with a combination of Sr24 and Sr31. All isolates were identified as race TTKS with additional virulence on Sr31 and Sr38. These isolates were divided into two groups: group A (seven isolates and the two control isolates), producing a low infection type, and group B (21 isolates), producing a high infection type on Sr24, respectively. Isolates of group B represented a new variant of race TTKS with virulence to Sr24. Eighteen simple sequence repeat (SSR) markers were used to examine the genetic relationship between these two groups of isolates in race TTKS and five North American races (MCCF, QCCQ, RCRS, RTHS, and TPMK) that are representative of distinct lineage groups. All isolates of race TTKS shared an identical SSR genotype and were clearly different from North American races. The virulence and SSR data indicated that the new variant of race TTKS with Sr24 virulence likely has arisen via mutation within the TTKS genetic lineage. We propose to revise the North American stem rust nomenclature system by the addition of four genes (Sr24, Sr31, Sr38, and SrMcN) as the fifth set. This revision recognizes the virulence on Sr31 and differentiates isolates within race TTKS into two separate races: TTKSK and TTKST, with avirulence and virulence on Sr24, respectively. The occurrence of race TTKST with combined virulence on Sr24 and Sr31 has substantially increased the vulnerability of wheat to stem rust worldwide.