Presence of triploids among oak species

Polyploids, organisms that have multiple sets of chromosomes, are common in certain plant and animal taxa. However, there are only a few reports of intraspecific ploidy variation within the genus Quercus. The aim of the study was to investigate the suspected ploidy level of two oaks that have unusual microsatellite banding patterns.

Polyploidy was investigated by using microsatellite analysis, stomata length measurements and nuclear DNA content estimation by flow cytometry.

Each putative triploid tree has patterns of microsatellite variation unexpected for diploid genomes, with up to three alleles at some loci, significantly longer stomata and 1.5 times more DNA per nucleus compared with diploids.

To our knowledge, this report contains the first evidence for triploidy in Q. petraea and confirmation of this phenomenon in Q. robur. Regardless of the positive or negative aspects of the presence of triploid oaks in forest stands, it is of value to be able to screen for them. This study demonstrates that nuclear microsatellites and estimation of DNA content by flow cytometry can readily be used for this purpose.