Dissertation Research: Dispersed Introgression Between Yucca baccata and Y. schidigera (Agavaceae)

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Hybridization has long been important to plant breeding and the production of crop plants. Less well understood, however, is the importance of hybridization in the evolution of wild plants. In part this is because it can be difficult to detect and document the occurrence of hybridization events and to distinguish genetic novelties introduced from another species from natural genetic variation arising within a species by mutation processes. Recently, new and powerful molecular methods for analyzing directly the DNA of plants have made possible a broad analysis of this problem. Graduate student Hanson under the guidance of Dr. Loren Rieseberg of the Rancho Santa Ana Botanic Garden is studying a presumptive case of repeated hybridization events (termed introgression) between two species of yuccas of the American Southwest. Protein markers are being assayed by electrophoresis, and variation in nuclear ribosomal and plastid DNA is being analyzed by enzymatic restriction-sites. Several related yucca species are also being studied to infer the phylogenetic relationships among species in this group, in order to determine whether the two hybridizing species have shared a recent common ancestor. Recent ancestry can also lead to a pattern of shared genetic markers that could be confused with hybridization. The range of protein and DNA markers to be studied, from both nuclear and chloroplast genomes, will help distinguish between recent common ancestry and current introgression. The study will thus advance understanding of hybridization in natural plant populations, and will help in the training of a young plant scientist.