Determination of the origin of the cold-adapted populations of barnyard grass (Echinochloa crus-galli) in eastern North America: a total-evidence approach using RAPD DNA and DNA sequences

This survey attempts to establish the origin of cold-adapted populations of barnyard grass (Echinochloa crus-galli (L.) Beauv.) in North America using molecular techniques, including random amplified polymorphic DNA (RAPD) an d two types of sequences: chloroplast intron (trnL (UAA)) and rDNA nuclear spacer (ITS 1). There exists many possible scenarios to explain the origin of E. crus-galli in eastern Canada (Quebec), but we dwelled on two particul ar hypotheses, which are not mutually exclusive. The first hypothesis stipu lates that the populations originated only from Europe, whereas the second implies that native subtropical and warm-temperate populations migrated fro m the south towards northern regions. To assess the likelihood of these hyp otheses, the genetic distance matrices obtained from RAPD markers, nuclear, and chloroplastic sequences were combined and tested against the competing models. A principal coordinate analysis was used to discriminate among pop ulations sampled from three different regions (i.e., Quebec, American east coast, and western Europe) and an analysis of molecular variance (AMOVA) de tected a significant genetic structure among these populations (F-ST = 0.11 0, p < 0.05). Pairwise comparisons further indicated that European populati ons were significantly different from all other populations, whereas North American populations were not different from one another. The combined sequ ences revealed eight different haplotypes. Six populations were characteriz ed by unique haplotypes, while one haplotype was shared by 3 of the 12 Nort h American populations. The last and most common haplotype was observed in 9 of the 18 populations from all three regions. The tests computed thus sup ported the second hypothesis suggesting that the cold-adapted populations o f eastern Canada are probably derived from other North American populations rather than European populations.