Effects of polyploidy on secondary chemistry, physiology, and performance of native and invasive genotypes of Solidago gigantea (Asteraceae).

Abstract

Vol 96 No. 4: 762–770, March 2009, doi: 10.3732/ajb.0800200 We have determined that some of the plant cytotypes that we reported in this paper were incorrect. In light of reports that only the tetraploid cytotype of Solidago gigantea occurs in Europe (Schlapfer et al., 2008), we re-examined our ploidy determinations on a subset of our original plants. We grew plants from rhizomes from 15 of our original plants, including all of the surviving European plants that we originally counted as diploid (8 plants), plus 2 US plants that were originally counted as diploid and 5 European plants that were originally counted as tetraploid. Chromosome counts using flower buds revealed that all 15 plants were tetraploid. In an attempt to determine why our original chromosome counts (which were based on root-tip material) were incorrect, we modified our protocol for counting chromosomes from root tips and obtained much sharper images for two of the European plants that were originally counted as diploid. We believe our original counts were incorrect because the chromosomes were not spread sufficiently. Adjacent chromosomes may have overlapped, resulting in undercounts because individual chromosomes were not clearly distinguishable. In our original paper, we generally failed to find significant differences between diploid and tetraploid plants. We now know that this was because many of the plants that were counted as diploid were in fact tetraploid. Based on the literature and our re-analysis, we know that there were no diploid plants in our European sample. We do not know the true frequency of US diploids, but it is surely lower than what we reported. However, we did find that hexaploids differed from diploids/tetraploids in many characteristics, including secondary chemistry, photosynthetic rates, specific leaf area, stomatal density and guard cell length, and the proportion of reproductive biomass invested in infructescences. We believe that our conclusions related to hexaploid plants are valid for the following reasons: (1) Our counts were in error due to undercounting, which would not have affected plants counted as hexaploid, (2) we found hexaploids in the geographic locations where they would be expected to occur, and (3) the hexaploids were morphologically distinguishable from the other plants. We apologize for the errors in our paper, and we regret any inconvenience or difficulties to readers of American Journal of Botany.