Genetic redundancy and diversity among 'orange' accessions in the US National Sorghum Collection as assessed with simple sequence repeat (SSR) markers

Plant genetic resources conservation is a challenge based on the need to ba lance acquisition priorities with the constrained level of financial suppor t that is dedicated to long-term maintenance of collections. As such, under standing Low variation is partitioned among accessions is essential for eff ective management. It is generally recognized that most large collections e xhibit varying levels of genetic redundancy. To address this issue, all of the sorghum [Sorghum bicolor (L.) Moench] accessions identified as 'Orange' presently maintained by the U.S. National Plant Germplasm System (NPGS) we re assayed with 15 simple sequence repeat (SSR) markers. Genotyping was per formed with fluorescent primers with five primer sets in each of three mult iplex polymerase chain reactions (PCRs) and automated allele sizing. A tota l of 96 individuals were analyzed, five plants from each of 19 Orange acces sions and one individual from an elite inbred Line,'RTx430'. The SSR marker s provided substantial genetic resolution among the Orange entries. Average heterozygosity estimates were low, and phenetic analyses (neighbor-joining dendograms) were generally consistent with known historical relationships among accessions. Most accessions were genetically distinct, but two redund ant groups (involving a total of five entries) were found among the 19 Oran ge accessions evaluated. The molecular variance analysis (AMOVA) showed tha t 90% of the total genetic variation was partitioned among accessions, whil e one-tenth of the variation resulted from genetic differences between indi vidual plants within accessions. The variance analysis also indicated that it should be possible to reduce the number of Orange accessions held by NPG S by almost half without seriously jeopardizing the overall amount of genet ic variation contained in these holdings. This study demonstrated that a li mited number of SSR markers can be used in a cost-efficient manner to rapid ly assess variation in accessions of Orange sorghum.