Variation inPoa annuaL. from the North of Scotland

Summary A collection of 200 accessions of Poa annua L. from the north of Scotland showed considerable phenotypic variation. Thirty-five of the accessions were perennial and eight produced viviparous inflorescences. Open- and self- pollinated seed was obtained from 112 and 75 accessions respectively and the progeny seedlings obtained from these were assessed. For a number of morphological characters the mean value was similar in open-and self-pollinated families, but the former exhibited higher total variability and a lower proportion of variation due to differences between families. Combinations of three characters were capable of distinguishing between pairs of open- and self-pollinated families in over 95% of cases. The three characters were not the same for the two groups but growth habit and longest culm length (plant height) were common. Cluster analysis of the progeny families resulted in a large number of small clusters and single distinct families. In the open-pollinated group a large cluster containing over half the families was identifiable as P. annua var. annua. The results support the interpretation that P. annua is a largely self-pollinated species, but some outcrossing does occur. It is thus likely that P. annua exists as a large number of relatively homozygous lines, each reasonably well adapted but not very plastic in its response.