The Evolutionary Origin of Poa annua L.

Abstract

ABSTRACTPoa annua L. (annual bluegrass) is one of the world's most widely distributed plant species and is ecologically and economically important both as a weed and as a forage and turfgrass. Determining the evolutionary origin of Poa anuua would provide valuable insight into understanding its wide distribution and extreme phenotypic variability. The objective of the present study is to use single copy nuclear DNA sequences trx and CDO504 and chrolopast sequences ndhF and trnTLF to discern the evolutionary origin of Poa annua from all other possible origins. Here we show that the homeologous nuclear DNA sequences present within Poa annua are inseparable from their respective orthologs within Poa supina Schrad. (supina bluegrass) and Poa infirma Kunth (weak bluegrass) and therefore could not have been contributed by any other Poa species. We confirm that Poa infirma served as the maternal parent and provide evidence that at least two interspecific hybridizations gave rise to Poa annua. Our data also suggest that the polyploid origin of Poa annua would be considered recent on an evolutionary time scale. Once the parental species of Poa annua have been identified, we were able to reexamine previously published cytological data and present evidence for the genomic designations of Poa infirma as II and Poa supina as SS, making the genomic constitution of the allotetraploid Poa annua as IISS. The results of this research place new emphasis on chromosomal rearrangements that likely took place during the evolution origin of Poa annua.