Further Studies on Polyploidy in White Ash (Fraxinus Americana L.)

Cytophotometric determinations of DNA-Feulgen levels in individual root tip nuclei from seedlings of white ash (Fraxinus americana L. ) were used to identify diploid, tetraploid, and hexaploid seed sources in naturally occurring forest stands from the mid to southern range of this species in North America. Comparative measurements of white ash nuclei and chicken blood cell nuclei, included with each preparation as an internal reference standard of 2.5 pg DNA per cell, yielded genome size estimates of 3.1 pg, 6 0 pg, and 91 pg for diploid , tetraploid, and hexaploid ash seedlings, respectively. These data also provide evidence for the occurrence of several sub-populations of hypohexaploid, or possibly pentaploid, white ash seed sources in certain collecting localities. Average seed weight correlated well with genome size estimates for individual seed lots and may provide a useful screening procedure for rapid, preliminary identification of putative hexaploid seed sources.