|Mueller Warrant, George|
Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/1999
Publication Date: 7/10/2000
Interpretive Summary: DNA "fingerprints" were used to study the genetic diversity of annual bluegrass plaguing grass seed farmers of western Oregon. The DNA markers showed this weed to be highly diverse. Although enough differences existed that we were able to distinguish between groups such as collection sites and dates, most of the diversity occurred within our collections. This is much the same pattern as would be seen in measure- ments of human diversity, and implies that annual bluegrass outcross frequently instead of always self-pollinating. High initial diversity coupled with long-term resupply of genotypes from the seed bank must have been factors in maintaining genetic diversity of this weed despite intensive use of herbicides. Knowledge of the genetic diversity of Willamette Valley P. annua will help in formulating more effective strategies for managing this herbicide-resistant weed.
Technical Abstract: Genetic diversity of Poa annua populations collected from western Oregon grass seed fields was surveyed using 18 randomly amplified polymorphic DNA (RAPD) markers. Markers from 1357 individual plants from 47 pop- ulations collected from three sampling dates (fall, winter and spring) at 16 sites were used to measure genetic diversity within and among pop- ulations. Site histories varied from how low to high herbicide selection pressure, and some sites were subdivided by three years of differing post-harvest residue management. Gene diversity statistics, simple frequency of haplotype occurrence, and analysis of molecular variance revealed the presence of significant variability in P. annua among sites, collection dates within sites and within collection dates. Nei gene diversity statistics and population differentiation parameters indicated that P. annual populations were highly diverse. Mean Nei gene diversity (h) for all 47 populations was 0.241 and total diversity (HT) was 0.245. A greater proportion of this diversity however, was within populations (HS=0.209) than among populations (GST=0.146). When populations were grouped by season of collection, within group diversity was HS=0.241, while among group diversity was GST=0.017. When populations were grouped by site, within group diversity was HS=0.224, while among group diversity was GST=0.087. Populations collected from fields with histories of high herbicide selection pressure showed low differentiation among collection dates with GST as low as 0l016, whereas those collected from fields with low herbicide selection pressure showed greater differentiation among collection dates, with GST as high as 0.125.