Ploidy of Seeds from Odd-polyploid American Elm.

Seeds from two odd-polyploid Ulmus americana L., both open-pollinated from surrounding tetraploid trees, were analyzed for nuclear genome size by using flow cytometry. Seeds from the triploid were predominantly aneuploid, with DNA content intermediate between triploid and tetraploid levels, but substantial numbers of tetraploid and pentaploid seeds were observed. No seeds of even ploidy were found in progeny of the pentaploid; seeds of the pentaploid were pentaploid, aneuploid with DNA content intermediate between tetraploid and pentaploid levels, or aneuploid with DNA content intermediate between pentaploid and hexaploid levels. Seeds from both trees often gave two peaks via flow cytometry, indicating the presence of two genetically distinct embryos in the same seed. The frequency of polyembryony in the sample is much higher than the frequency of seeds that yield multiple seedlings, suggesting that the formation of two genetically distinct embryos, followed by abortion of one embryo, is common in elms. [ABSTRACT FROM AUTHOR]