M. W. Sutherland

The reaction of perhydroxyl radical (HO2) with linoleic, linolenic, and arachidonic acids has been studied in aqueous ethanolic solutions by the stopped flow technique. The corresponding rate constants are 1.2 x 10(3), 1.7 x 10(3), and 3.0 x 10(3) M-1 S-1, respectively. While kinetic results suggest that the HO2 radical reacts with the double allylic H atom of the polyunsaturated fatty acids, thermodynamic approximations indicate that the reaction is exothermic by approximately 10 kcal/mol. The relevance of this reaction to membrane damage observed in biological systems that have been exposed to HO2/O2- radicals is discussed.

Genetic maps were compiled from the analysis of 160–180 doubled haploid lines derived from 3 crosses: Cranbrook Halberd, CD87 Katepwa, and Sunco Tasman. The parental wheat lines covered a wide range of the germplasm used in Australian wheat breeding. The linkage maps were constructed with RFLP, AFLP, microsatellite markers, known genes, and proteins. The numbers of markers placed on each map were 902 for Cranbrook Halberd, 505 for CD87 Katepwa, and 355 for Sunco Tasman. Most of the expected linkage groups could be determined, but 10–20% of markers could not be assigned to a specific linkage group. Homologous chromosomes could be aligned between the populations described here and linkage groups reported in the literature, based around the RFLP, protein, and microsatellite markers. For most chromosomes, colinearity of markers was found for the maps reported here and those recorded on published physical maps of wheat. AFLP markers proved to be effective in filling gaps in the maps. In addition, it was found that many AFLP markers defined specific genetic loci in wheat across all 3 populations. The quality of the maps and the density of markers differs for each population. Some chromosomes, particularly D genome chromosomes, are poorly covered. There was also evidence of segregation distortion in some regions, and the distribution of recombination events was uneven, with substantial numbers of doubled haploid lines in each population displaying one or more parental chromosomes. These features will affect the reliability of the maps in localising loci controlling some traits, particularly complex quantitative traits and traits of low heritability. The parents used to develop the mapping populations were selected based on their quality characteristics and the maps provide a basis for the analysis of the genetic control of components of processing quality. However, the parents also differ in resistance to several important diseases, in a range of physiological traits, and in tolerance to some abiotic stresses.

Radiant frost is a significant production constraint to wheat (Triticum aestivum) and barley (Hordeum vulgare), particularly in regions where spring-habit cereals are grown through winter, maturing in spring. However, damage to winter-habit cereals in reproductive stages is also reported. Crops are particularly susceptible to frost once awns or spikes emerge from the protection of the flag leaf sheath. Post-head-emergence frost (PHEF) is a problem distinct from other cold-mediated production constraints. To date, useful increased PHEF resistance in cereals has not been identified. Given the renewed interest in reproductive frost damage in cereals, it is timely to review the problem. Here we update the extent and impacts of PHEF and document current management options to combat this challenge. We clarify terminology useful for discussing PHEF in relation to chilling and other freezing stresses. We discuss problems characterizing radiant frost, the environmental conditions leading to PHEF damage, and the effects of frost at different growth stages. PHEF resistant cultivars would be highly desirable, to both reduce the incidence of direct frost damage and to allow the timing of crop maturity to be managed to maximize yield potential. A framework of potential adaptation mechanisms is outlined. Clarification of these critical issues will sharpen research focus, improving opportunities to identify genetic sources for improved PHEF resistance.

Doubled haploid populations from 5 carefully selected wheat ( Triticum aestivum L.) crosses were established in order to produce genetic maps. The characterisation of the parental material included pedigree analyses to define the extent of the genetic relationships among the lines and to determine the occurrence of alien chromosome segments that may contribute to segregation distortion. The characterisation of the parents also defined the range of grain quality traits that could be examined in the lines derived from each cross. Populations of up to 321 lines were produced using wide cross-mediated doubled haploid production from F1 plants. Assessment of the lines for heterogeneity was carried out using readily identifiable phenotypic markers and electrophoresis of seed storage proteins, with 2.3–11.6% of the lines being removed from further analysis. Segregation distortion was estimated in several populations where sufficient information from genetic markers was available. In a Sunco/Tasman doubled haploid population, heterogeneity was detected between the first 51 lines and the remainder of the mapping population and this could be traced to F1 plants that were produced from an earlier set of crosses. ?2 tests on the mapping data available for the Cranbrook/Halberd, CD87/Katepwa, and Sunco/Tasman doubled haploid populations revealed segregation distortion at rates of 1.8%, 5.1%, and 12.5% respectively. Whereas the wide-cross doubled haploid protocol does not appear responsible for the bulk of the non-Mendelian segregation observed, several potential sources were identified. In particular, clustering of distorted loci at specific chromosome regions appeared to be associated with the presence of alien introgressions in one of the parents. This was especially marked in the Sunco/Tasman population. Providing such distortions are recognised in the models used, these populations provide powerful tools for extensive mapping studies to determine the genetic factors controlling grain quality traits and other wheat characters of interest.