Systematics and evolution of parasitic plants

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Parasitic plants take water and nutrients from other plants called hosts. Some parasitic plants, referred to as “obligate”, depend entirely on their hosts for survival and negatively affect their growth and development. The proposed research program focuses on the species diversity and evolution of Cuscuta (dodder), a taxonomically challenging group of obligate parasitic plants comprising ~ 200 species distributed worldwide. The taxonomical difficulties of Cuscuta arise in part because the morphological variation among species is minimal and hidden inside the small flowers (~ 3 mm long). In addition, the recently documented hybrid formation of species (reticulate evolution) complicates the reconstruction of evolutionary histories. This parasitic group is particularly important because native dodders are keystone species in their ecosystems. However, Cuscuta is also economically important because some of its species are agricultural and horticultural pests that cause major yield losses in numerous crops. *** The first short-term objective of the proposed research is to unravel species-level evolutionary histories within four unstudied groups of Cuscuta, and to uncover the depth and extent of reticulate evolution in two other groups in which we have previously shown that hybrid speciation occurs. We will use molecular and morphological data to understand how species have evolved, based on which we will also revise their taxonomy. New species are likely to be discovered as a part of this research. *** Cuscuta has a pronounced variation of the chromosome number (polyploidy) and the second short-term aim of this research is to elucidate how the extra sets of chromosomes have been acquired and to identify the role that these changes had in the evolution of dodders. Since reticulate evolution and polyploidy often work in tandem, the chromosome data will provide a more thorough understanding of how hybrid species originated.*** The host range is an essential attribute of any parasitic organism and represents the totality of hosts that the parasite can attack. The third short-term objective of this research program aims to characterize for the first time the host range and its evolution in Cuscuta. The study of the host range has been hindered in Cuscuta because most dodders infest many hosts from numerous botanical families. To solve this problem, we will obtain host data from tens of thousands of herbarium specimens, and use novel analytical approaches employed in animal parasites. *** Overall, this research program is part of the ongoing global efforts to catalog life on Earth and understand its natural history and evolution. From a practical point of view, the results will facilitate a better identification and management of both native and pest Cuscuta species from Canada and the rest of the world. Host range results can be used to model and predict the potential expansion of pest dodders.