Chemically induced brown midrib (bmr) mutants sorghum (Sorghum bicolor (L.) Moench) were characterized with regard to phenotype, fiber composition, and in vitro dry matter disappearance (IVDMD). The recessive bmr genes produced brown pigmentation in the leaf midrib and stem of mature plants. Pigmentation varied among mutants in intensity, time of appearance, and degree of fading as plants matured.Stem and leaf samples of mutant and normal plants were analyzed in the laboratory to determine percent cell wall constituents (CWC), acid detergent fiber, (ADF), cellulose, hemicellulose, permanganate lignin (PL), vitro dry matter, and in vitro cell wall constituent disappearance (IVDMD and IVCWCD). Ten of the 13 mutants had significantly less stem lignin than the normal counterparts. Reductions in lignin ranged from 5 to 51% in stems and from 5 to 25% in leaves. In the case of other fiber components, only occasional differences were observed between normal and mutant plants. Increases in IVDMD and IVCWCD of as much as 33 and 43%, respectively, were associated with the presence of bmr genes.Variation among mutants in lignin concentration probably indicates that several different bmr genes were involved. Similarities between the bmr genes of sorghum and the bm genes of maize (Zea mays L.) suggest the possible existence of similar genes in other grasses, although their identification may be more complicated because of polyploidy.

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 develop- RFLP 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

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.

Sixty‐three sorghum [Sorghum bicolor (L.) Moench] hybrids that are, or have been, widely used in the United States were profiled using 167 simple sequence repeat (SSR) markers. Genetic distance and cluster analysis determined that 43 (68%) of the hybrids formed seven groupings, with each group containing hybrids commercialized by a single breeding organization. Groupings were also reflective of known pedigrees. Hybrids released by different organizations were not very closely associated with one exception of two hybrids. Groupings had limited association with the decade that the hybrid was released. Numbers of alleles per locus have been constant during the past three decades with gain in new alleles being balanced by loss of other alleles. Hybrids released during the 2000s showed the least number of new alleles compared to the previous two decades. Much of the SSR allelic diversity that was introduced via the Sorghum Conversion Program that converted tropical germplasm to be day‐length neutral has been deployed on U.S. farms. Continued monitoring of genetic gain and genetic diversity are important components of sustainable plant breeding strategies.