CHLOROPLAST DNA AND NUCLEAR-DNA CONTENT VARIATIONS AMONG CULTIVARS OFSWITCHGRASS, PANICUM-VIRGATUM L

Switchgrass, Panicum virgatum L.,, is a native, cross-pollinated, morp hologically diverse species with an array of ploidy levels and ecotype s, Switchgrass is found throughout most of the USA and Canada, primari ly east of the Rocky Mountains and south of Hudson Bay, The objective of this research was to determine if chloroplast DNA (cpDNA) restricti on fragment length polymorphisms (RFLPs) occur among switchgrass culti vars and experimental strains that differ in ploidy level or ecotype c lassification, Eighteen switchgrass cultivars or experimental strains representative of reported ecotypes, ploidy levels, and the geographic al range of switchgrass were surveyed for cpDNA polymorphisms by means of four restriction endonucleases and 20 sorghum cpDNA probes, One po lymorphism was detected which was associated with the lowland-upland e cotype classification, The lowland cultivars contained a restriction s ite change that was not present in the upland cultivars, The two cytot ypes discovered have been designated as the U (upland) or L (lowland) cytotype, The lowland cultivars had 3 pg DNA/nuclei as measured by Bow cytometry while the upland types had either 3 or 6 pg DNA/nuclei. The re were no cpDNA polymorphisms among the upland cultivars regardless o f ploidy level as measured by DNA content, These results demonstrate t hat cpDNA differs among switchgrasses and that this variation is assoc iated with ecotype variation but not with nuclear DNA content.