An experimental study of ecological differences in winter growth between sympatric diploid and autotetraploid Dactylis glomerata

1 Previous work on the ecological significance of variation in genome size among plant species would suggest that tetraploid plants, due to their larger genomes and cell size, should show a greater capacity for growth at low temperature than closely related diploids. 2 To test this we determined winter growth and flowering phenology of diploid and autotetraploid genotypes of the Galician subspecies of Dactylis glomerata sampled from north-western Spain. Individual genotypes of each ploidy level were cloned and grown in four contrasting environments. 3 The phyllochron index (i.e. the cumulative temperature necessary for the production of each leaf) was used to asses the kinetics of leaf production during winter and the dates of first panicle emergence and flowering were quantified. 4 Contrary to predictions, diploids produced more leaves in all environments during the winter and very early spring period than did derivative tetraploids. Increased quantities of nuclear DNA do not therefore permit faster winter growth in tetraploids of this subspecies of D. glomerata. 5 However, tetraploids flowered earlier than diploids in all environments, confirming that observed differences in flowering time have a genetic basis in Galician D. glomerata. 6 Our results are compared to previous data and discussed in the context of diploid-polyploid coexistence in sympatric situations.