Genetic Diversity among Elite Sorghum Inbred Lines Assessed with Simple Sequence Repeats

phisms among 36 sorghum lines were equally low for profiles obtained by means of 30 RAPD primers or 29 DNA markers are being increasingly utilized in cultivar developRFLP probes. Vierling et al. (1994) found 73 RAPD ment, quality control of seed production, measurement of genetic diversity for conservation management, varietal identity, and to assist primers discriminated among sorghum lines but those in maintenance of intellectual property protection (IPP). The use of data did not allow lines to be associated into groupings simple sequence repeats (SSRs) for variety profiling can provide high that reflected pedigrees. Associations among 34 lines discrimination, with excellent reproducibility at less cost than for determined by 19 RFLP probes, 21 RAPD primers, and restriction fragment length polymorphisms (RFLPs). The objective 41 ISSRs were markedly different and dependent on of this study was to evaluate the potential utility of SSR technology the source of molecular profile data (Yang et al., 1996). for applications in research, product development, seed production, Ahnert et al. (1996) reported a study of 105 sorghum and genetic resource conservation management for sorghum. Fifty inbreds that used 104 RFLP probes which showed genetically diverse elite sorghum [Sorghum bicolor (L.) Moench] higher levels of polymorphism and associations of lines inbreds were used to compare the discrimination abilities of 15 SSR that were congruent with pedigree information and primers with 104 RFLPs and to compare the associations among lines revealed by these molecular data and by pedigrees. RFLP data allowed breeder classifications of germplasm. Brown et al. all lines to be uniquely identified; two lines could not be distinguished (1996) in an explorative study surveyed diversity among by the SSR data. The mean polymorphism information content (PIC) 13 temperate adapted sorghum lines and four diverse values were 0.62 (RFLPs) and 0.58 (SSRs). Correlations for pairwise genotypes using approximately 30 SSRs. Seventeen molecular profile distances with pedigree distances among the mainprimer pairs revealed polymorphisms. Taramino et al. tainer female (B) lines were 0.52 and 0.53 for RFLP and SSR data, (1997) used 13 SSRs to reveal moderate to high levels respectively; data for the male parental restorer (R) lines were 0.41 of diversity among a group of nine sorghum lines of and 0.47. This set of SSRs could be used to help genetic conservation different racial classification and from different geomanagement and to support IPP. Data from additional SSRs that graphic origins. collectively cover more of the genome will be required for applications The limited sampling of germplasm in these previous to assist in breeding. studies hinders an assessment of the ability of SSRs to detect genetic variation in sorghum. Few (9–13) inbred lines were included and they may not adequately repreD genetic markers are being increasingly sent the gene pool of many breeding programs. Furtherutilized in cultivar development, quality control of more, comparisons of discrimination abilities and associseed production, measurement of genetic diversity for ations of germplasm that stem from the use of various conservation management, varietal identification, and molecular profiling methodologies are confounded by intellectual property protection (IPP). Previously rethe use of different inbred lines. Therefore, the potential ported methods to characterize inbred lines of sorghum utility of SSRs as a molecular profiling technology to include RFLPs (Tao et al., 1993; Vierling et al., 1994; aid in research and product development of sorghum Ahnert et al., 1996; Yang et al., 1996), randomly ampliremains to be evaluated. fied polymorphic DNA (RAPD) (Tao et al., 1993; VierThe objective of this study was to determine the poling et al., 1994; Yang et al., 1996), inter-simple sequence tential utility of SSR technology for applications in rerepeats (ISSR) (Yang et al., 1996), and SSRs or microsearch, product development, seed production, intellecsatellites (Brown et al., 1996; Taramino et al., 1997). tual property protection (IPP), and genetic resources Each of these classes of molecular markers has characconservation management for sorghum. To accomplish teristics affecting comprehensivity of genome coverage, this goal, we report molecular profile and pedigree data discrimination ability, reproducibility, speed, and cost for a set of 50 elite sorghum lines. We assessed the of data generation and scoring that impact applications discrimination ability of data obtained from RFLP of the individual technologies by plant breeders and conprobes and from SSR loci and we compare associations servators. among inbred lines that are revealed by these data with Tao et al. (1993) found that overall levels of polymorassociations that would be expected on the basis of known pedigrees. We also discuss the cost effectiveness J.S.C. Smith, Pioneer Hi-Bred International, Inc., Research Technology Services, 7300 NW 62nd Avenue PO Box, 1004, Johnston, IA of acquiring SSR data with respect to the potential use 50131-1004; S. Kresovich, M.S. Hopkins, S.E. Mitchell, and R.E. Dean, of this technology by researchers, breeders, and conserPlant Genetic Resources Conservation Unit, USDA/ARS, 1109 Exvators. periment Street, Griffin, GA 30223-1797; W.L. Woodman, and M. Lee, Iowa State Univ., 1553 Agronomy Building, Ames, IA 50011; K. Porter, Pioneer Hi-Bred International, Inc., Sorghum Research, MATERIALS AND METHODS 501 E. Pioneer Road, Plainview, TX 79072. Received 6 March 1998. We established a test array of 50 elite sorghum inbred lines *Corresponding author ([email protected]). that had already been characterized by RFLPs (Ahnert et al., 1996). Inbreds were selected so that they would collectively Published in Crop Sci. 40:226–232 (2000).