Genetic diversity among elite sorghum inbred lines assessed with DNA markers and pedigree information

The amount of genetic diversity in parental lines of commercial sorghum [Sorghum bicolor (L.) Moench] hybrids is unknown, yet such comprehensive knowledge could improve the effectiveness of future hybrid development programs. Restriction fragment length polymorphisms (RFLPs) and pedigree data were used to investigate the genetic relationships in a group of 58 fertility restorer (R) and 47 sterility maintainer (B) elite sorghum inbred lines. The objectives of this study were to (i) assess the level of genetic variation for RFLPs in these Lines, (ii) estimate genetic similarity (GS) based on RFLPs and pedigree information for R- and B-Lines, and (iii) examine the agreement between RFLP-based GS and coancestry coefficient (f) for related (f > 0) pairs of inbreds. R-lines, derived mainly from Feterita and Zera-zera, and B-lines, mostly from kafir germplasm, were analyzed for RFLPs with 104 DNA probes. A total of 326 patterns of RFLP bands was observed, with 276 being common to both R- and B-lines, 32 unique to R-Lines, and 18 unique to B-lines. On average, 3.6 patterns per clone-enzyme combination were found for R-lines and 3.0 for B-lines. Average GS based on RFLPs was 0.67 for R-lines and 0.76 for B-lines, indicating more diversity within the R-group. The average for R-lines was 0.08 and for B-lines 0.07. Cluster analysis of GS estimates from the entire set (105) of inbreds revealed separate groups for R- and B-lines in agreement with parental types, pedigree information, and the classification system used by breeders. R-lines clustered into two main groups, one derived mainly from Feterita and the other from Zera-zera. B-lines were grouped into different sub-clusters. GS and f were positively correlated for R-lines (r = 0.46) and for B-lines (r = 0.43), suggesting that RFLP data may help quantify the degree of relatedness in elite sorghum germplasm.