Response to wheat dwarf virus in wild and domesticated wheat : genetic resources of evolutionary and environmental origins

Sammanfattning: Wild and domesticated plants are constantly exposed to a variety of pathogens, which may trigger an arms race in evolution of defense strategies in the plant and development of virulence in the pathogen. The outcome of the interaction depends on the intensity of reciprocal selection between the interacting species, which may vary over space and time, explained as the geographic mosaic theory of coevolution. While wild crop relatives may have evolved resistance or tolerance to many pathogens, the same pathogens cause damage on crops. Studies on coevolving interactions between wild host plants and pathogens can therefore provide important knowledge for identifying genetic resources for crop improvement among wild relatives. This PhD thesis focuses on an interesting interaction between Wheat dwarf virus (WDV), the leafhopper vector Psammotettix alienus and the wild and domesticated wheats (Triticum spp.). There is no known resistant wheat cultivar and severe incidences of WDV have occurred in Europe, Africa and Asia. The overall aim is to contribute to the development of improved cereal cultivars through the understanding of variation in response to WDV in wild wheat relatives (Aegilops spp., Triticum spp.), and to identify potential genetic resources. Inspired by the geographic mosaic theory of coevolution a diverse set of wild wheat relatives with different geographical, environmental, and genetic origins, directly or indirectly involved in the evolution of bread wheat was studied for response to WDV in this host plant-vector-virus interaction. Some findings are: i) wild wheat relatives had different response patterns during growth, including susceptibility, partial resistance and tolerance, ii) the response at early plant development was related to variation in onset of systemic infection and WDV accumulation in the plant, iii) differences in response were affected by the environment from which the wild relatives originate, iv) in contrast to what was expected, domestication and other genetic bottlenecks during wheat evolution have not resulted in a general increase in susceptibility in cultivated wheats, v) potential genetic resources were identified in Aegilops species carrying the D genome and of particularly interest was Ae. tauschii, one of the ancestors to hexaploid bread wheat. These findings can be directly applied in pre-breeding of wheat. This research also provided insights into a host-vector-virus interaction of interest for plant defense and coevolution.

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