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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.
Spatially explicit RWA density models will enable management actions to be focused on locations and times when the risk of economic damage is high. Use of this research for forecasting spatially explicit RWA densities, as well as increasing knowledge on initial and boundary conditions, will facilitate directed scouting, precision agricultural techniques, and within-field management practices for control of RWA. Adoption of these practices and techniques has the potential to reduce pesticide inputs, allow for more judicious use of resistant cultivars (when they become available), increase natural enemy refuges, and reduce pesticide exposure to agricultural workers and consumers.
The Russian wheat aphid Diuraphis noxia (Kurdjumov) is a serious pest of world cereal grain crops, primarily barley and wheat. A phenotypic characteristic of D. noxia feeding, leaf rolling, creates a leaf pseudo gall which protects aphids, making it difficult to treat infested plants with insecticides or biological control agents. Therefore, the use of D. noxia-resistant crops is a desirable aphid management tactic. Because of the development of virulent D. noxia biotypes, the identification of new sources of barley and wheat resistance is necessary. Virus-induced gene silencing (VIGS) utilizes the plant defense system to silence viruses in inoculated plants. The accumulation of virus RNA in plants triggers the defense system to silence sequences homologous to the introduced virus and sequences of interest from a plant are inserted into the virus and silenced along with the virus. The VIGS method was tested to determine the ability of barley stripe mosaic virus (BSMV) to serve as a VIGS vector in wheat plants containing the Dnx gene for resistance to D. noxia. Dnx leaves with silenced BSMV virus yielded D. noxia populations that were significantly no different from populations produced on healthy Dnx leaves. Thus, BSMV silencing does not interfere with Dnx resistance. Several different methods were examined to determine how best to confine aphids to the silenced leaf, and a modified plastic straw cage was chosen as the optimum cage type. Microarray and gene expression data were analyzed to select two NBS-LRR type disease resistance protein genes - TaAffx. 104814.1.S1_at and TaAffx. 28897.1.S1 - (NBS-LRR1 and NBSLRR2), in order to assess their role in Dnx resistance. NBS-LRR1 and NBSLRR2 were silenced by inoculating leaves of Dnx plants with barley stripe mosaic virus (BSMV) containing sequences of each gene. Controls included Dnx and Dn0 plants inoculated with BSMV and non-BSMV inoculated plants. Aphids were allowed to feed on control and treatment plants to assess aphid population and mean weight of aphids surviving at the end of the experiment. There were no differences among treatments based on aphid population, but there were significant differences the mean weights of aphids reared on several different treatments.
Diuraphis noxia is an insect pest on barley and wheat in Ethiopia. Yield losses of barley can reach up to 79%. Control is through use of resistant barley cultivars. Biotypes can render control with resistance uncertain. In this book it was indicated that no biotypic variation exist in RWA clones on barley in Ethiopia. Susceptibility of one resistant wheat line (Dn4) to the Ethiopian RWA clones indicated biotypic differences between American and Ethiopian RWA clones. Anholocyclic life cycle of RWA in Ethiopia, dependence on land races and fact that barley land races show tolerance to RWA support the finding of no biotypic variation in the Ethiopian RWA clones. It was also indicated in the same book that molecular markers like mtDNA, two microsatellite loci and dnaN and ptrpE genes of the bacterial endosymbiont Buchnera did not reveal genetic variation among worldwide collections of RWA. Only a single substitution was found in the pseudogene (ptrpE) in the Turkish populations. Amercian populations did not reveal a different genetic pattern compared to Ethiopian ones. The absence of genetic variation could be due to the recent and fast spread 0f the insect from its origin.