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Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a widely distributed species in western north America, and a major economic pest of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). The objectives of this study were to : 1) determine the inheritance of seedling and adult plant resistances in a wheat line PI 294994 ; 2) establish whether greenhouse and field resistances were related ; 3) determine the effect of RWA infestation on the dry matter, grain yield, and harvest index in the crosses Moro/PI 294994 and Hyak/PI 294994 ; 4) determine whether there was a difference in the three traits between different genotypes due to RWA infestation ; and, 5) assess the degree of protection genetic resistance provided in the two crosses. The club wheat cultivars 'Moro' and 4Hyak' were crossed with PI 294994. Progenies from these two crosses were artificially infested with RWA in the field and the crosses were compared for their dry matter, grain yield, and harvest index. Plant reactions of F2 seedlings, F2 adult plants, and F3 seedlings indicated that both seedling and adult plant resistances are controlled by two genes with dominant and recessive mode of inheritance and that plant reactions in the field were the same as those in the greenhouse. Comparison of mean values of dry matter, grain yield, and harvest index showed that the three traits were affected by RWA infestation and genotype in both crosses. Resistant genotypes and noninfested population were comparable with respect to the three traits in Moro/PI 294994 but they were not in Hyak/PI 294994.
Current Trends in Wheat Research is an interdisciplinary book dealing with diverse topics related to recent developments in wheat research. It discusses the latest research activities in biotic and abiotic stress tolerance in wheat. The book contains chapters containing valuable information on wheat diseases, insect pests, drought stress as well as water use efficiency in wheat crops.
This thesis investigates the effect of Russian wheat aphid (RWA: Diuraphis noxia) infestation on the defence responses of the bread wheat line, PI 137739, on a molecular level. PI 137739 is known to contain the RWA resistance gene, Dn1. The study was conducted by utilising and combining a vast array of molecular biological techniques. Chapter 1 introduces the reader to a summary of the resistance responses observed within infested plants. A detailed description of the Russian wheat aphid follows and the genes responsible for RWA resistance in wheat is discussed. A brief report of research performed on the bread wheat genome is given and the biochemical defence responses of plants against insect infestation are discussed. This is followed by a concise description of resistance (R) genes and resistance gene categories in plants. The last discussion concerns microarray technology, a molecular tool utilised during this study. Chapter 2 aims at identifying genes involved in resistance against RWA infestation: specifically, genes containing the conserved nucleotide binding site leucine rich repeat (NBS-LRR) motif. Genomic, as well as complementary DNA (cDNA), was utilised in order to compare functional gene expression in wheat infested with the RWA. This was executed by employing PCR-based methods, single-pass sequencing and basic local alignment search tool (BLAST) analyses. Chapter 3 introduces suppression subtractive hybridisation (SSH) as a tool to further identify NBS-LRR or other resistance-related sequences in RWA infested wheat plants. SSH allows the comparative analysis of differential gene expression in RWA infested and uninfested wheat in order to identify resistance- related genes expressed in the infested, resistant wheat plants. The effect of RWA infestation on wheat resistance responses was examined further in chapter 4 through microarray analysis. The aim was the introduction and establishment of the microarray technique and to test the feasibility of using microarrays for differential gene expression and regulation studies. Microarray slides were assembled in order to monitor the up- and down regulation of genes at different time intervals - day 2, day 5 and day 8 - of RWA infestation. Clones isolated throughout this study were assembled on microarray slides and probed with control and RWA infested RNA. Differential gene regulation was assessed and further confirmed through Northern blot analyses, as well as quantitative real-time PCR. The thesis concludes with a general summary of the results obtained in chapter 5 and future prospects are outlined.
Wheat breeders have achieved significant results over the last fifty years in research on mankind's one of the most important crops. Classical genetic and breeding methods, far broader international cooperation than was experienced in earlier periods, and improvements in agronomic techniques have led to previously unimaginable development in the utilisation of wheat for human consumption. The contribution of wheat researchers is particularly noteworthy since these results have been achieved at a time when the world population has grown extremely dynamically. Despite this demographic explosion, of a proportion never previously experienced, thousands of millions of people have been saved from starvation, thus avoiding unpredictable social consequences and situations irreconcilable with human dignity. Despite these developments in many regions of the world food supplies are still uncertain and the increase in the world's wheat production has not kept pace with the population increase during the last decade. Due to the evils of civilisation and the pollution of the environment there is a constant decline in the per capita area of land suitable for agricultural production. Based on population estimates for 2030, the present wheat yield of around 600 million tonnes will have to be increased to almost 1000 million tonnes if food supplies are to be maintained at the present level.