Cytogenetic analysis of American chestnut (Castanea dentata) using fluorescent in situ hybridization.
The American chestnut (Castanea dentata), once known as ‘The King of the Forest’ in the Appalachian Mountains of the eastern United States and southeastern Canada, has been all but extirpated by chestnut blight disease caused by an Asiatic bark fungus, Cryphonectria parasitica. A group of scientists at The American Chestnut Foundation has been working since 1983 to develop blight resistant American chestnut by inter-species backcross breeding with the relatively resistant Chinese chestnut (Castanea mollissima). In an effort to facilitate this breeding program we have initiated cytogenetic studies of these two species and their F1 and backcross hybrids. Here we report our successes in preparing somatic chromosomes using enzymatic digestion of American chestnut seedling root tips and demonstrate the quality of the chromosome spreads using fluorescent in situ hybridization with ribosomal DNA probes. Our results show two 18S-28S rDNA sites, one major and one minor, and one 5S rDNA site in American chestnut. This is the first such report for American chestnut and our preliminary results appear similar for Chinese chestnut.