Molecular evidence for an interfamilial laminarialean cross

When generating kelp hybrid crosses in vitro, small blades are frequently s een in single-sex cultures of microscopic gametophytes as well as in putati ve hybrid crosses. We demonstrate a polymerase chain reaction (PCR)-based m ethod that quickly determines the presence/absence of possible parental gen omes in the observed blades. ITSI nrDNA fragments that varied in length in a species-specific way were amplified. Amplification products from possible hybrid blades, apogamic blades and parental gametophytes were compared on agarose gels. Using these methods, we were able to identify a number of apo gamic blades (i.e. formed directly hom gametophytic cells) as well as a tru e hybrid sporophyte blade in crosses between Alaria marginata (Alariaceae) and Lessoniopsis littoralis (Lessoniaceae), members of two separate familie s of the Laminariales. To our knowledge this is the first genotypic confirm ation of a hybrid kelp.