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 balance acquisition priorities with the constrained level of financial support that is dedicated to long-term maintenance of collections. As such, understanding Low variation is partitioned among accessions is essential for effective management. It is generally recognized that most large collections exhibit 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) were assayed with 15 simple sequence repeat (SSR) markers. Genotyping was performed with fluorescent primers with five primer sets in each of three multiplex polymerase chain reactions (PCRs) and automated allele sizing. A total of 96 individuals were analyzed, five plants from each of 19 Orange accessions and one individual from an elite inbred Line,'RTx430'. The SSR markers 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 redundant groups (involving a total of five entries) were found among the 19 Orange accessions evaluated. The molecular variance analysis (AMOVA) showed that 90% of the total genetic variation was partitioned among accessions, while one-tenth of the variation resulted from genetic differences between individual plants within accessions. The variance analysis also indicated that it should be possible to reduce the number of Orange accessions held by NPGS by almost half without seriously jeopardizing the overall amount of genetic variation contained in these holdings. This study demonstrated that a limited number of SSR markers can be used in a cost-efficient manner to rapidly assess variation in accessions of Orange sorghum.