Factors influencing seed production of Phragmites australis

We investigated the seed set rate of a common reed, Phragmites australis (Cav.) Trin. ex Steudel, in the Lake Biwa-Yodo River system in south-western. Japan, and analyzed the factors that influenced seed production. In the 12 populations studied, the seed set rate ranged from 0. 1 to 59.6% (mean 9.7%). Intensive studies in four populations showed that pollen stainability, used to indicate the pollen viability, and the percentage of germinating pollen were high, irrespective of ploidy levels, and seed production proved to be inhibited at any stage leading to ovule development. In a pollination experiment P. australis was shown to be at least partially self-incompatible, and the addition of pollen increased seed set rate. Resource limitation was not found. Pollen limitation brought about by the clonal structure of R australis populations may be the most important factor decreasing seed production. The damage by a thrips, Chirothrips manicatus Haliday, was another factor of reduced seed set rate in some populations. (C) 2002 Elsevier Science B.V. All rights reserved.