CHROMOSOME-NUMBER AND NUCLEAR-DNA CONTENT OF SEVERAL SWITCHGRASS POPULATIONS

Information regarding ploidy level of switchgrass (Panicum virgatum L. ) is needed for use of populations in breeding programs and for mainte nance of germplasm. Our objectives were to determine chromosome number and variation in DNA content of several switchgrass populations and t o examine the usefulness flow cytometry techniques for estimating ploi dy level in switchgrass. Chromosome numbers were determined by means o f light microscopy; laser Bow cytometry was used to determine nuclear DNA content. Only octaploid plants were found within 'Blackwell', (Pat hfinder', 'Cave-in-Rock', and 'Trailblazer', all of which were previou sly reported to be hexaploid populations. Average nuclear DNA contents , with ranges in parentheses, were 3.1 (2.7-3.2) pg for verified tetra ploid populations and 5.2 (4.8-5.8) pg for verified octaploid populati ons. Flow cytometry techniques were useful in discriminating between 4 x and 8x plants; ploidy level of plants estimated to be 6x may need to be verified with actual chromosome counts.