The release of the bermudagrass (Cynodon spp.) triploid hybrid ‘Tifgreen’ revolutionized southeastern U.S. golf course greens. Off-types within this cultivar began to be identified soon after the initial plantings, and through the last 50 years, many of the best performing off-types have been released as new cultivars. Examination of some of the most popular somatic mutants with a new set of 47 simple sequence repeat (SSR) markers and 23 previously discovered genomic SSR markers identified five polymorphic fragments (as compared with ‘Tifgreen’) among three cultivars, TifEagle, MiniVerde, and Tifdwarf. Each polymorphism appears to be a slight increase/decrease in microsatellite repeat number and the polymorphic fragments are unique for each cultivar. Two polymorphic fragments were identified that were unique to ‘Tifdwarf’, one polymorphic fragment was unique to ‘TifEagle’, and two polymorphic fragments were unique to ‘MiniVerde’. Furthermore, three of the five polymorphic markers display an additional allele only in the shoot tissue but not in the root tissue of ‘TifEagle’ and ‘Tifdwarf’. This finding suggests that ‘TifEagle’ and ‘Tifdwarf’ are somatic chimeras. This set of SSR markers identifies repeatable polymorphic fragments among multiple ‘Tifgreen’-derived cultivars and gives insight into the nature of the mutations that exist within ‘Tifgreen’.
Karen R. Harris-Shultz, Brian M. Schwartz, and Jeff A. Brady
Karen R. Harris-Shultz, Brian M. Schwartz, Wayne W. Hanna, and Jeff A. Brady
Genetic linkage maps of bermudagrass (Cynodon spp.) species using 118 triploid individuals derived from a cross of T89 [C. dactylon (2n = 4x = 36)] and T574 [C. transvaalensis (2n = 2x = 18)] were enriched with expressed sequence tags-derived simple sequence repeat (EST-SSR) markers. Primers were developed from 53 ESTs containing SSRs producing 75 segregating markers from which 28 could be mapped to the T89 and T574 genetic maps. With the addition of previously generated marker data, 26 T89 linkage groups and eight T574 linkage groups were formed using a log-of-odds (LOD) value of 4.0. The T89 and T574 linkage maps spanned 1055 cM and 311.1 cM and include 125 and 36 single-dose amplified fragments (SDAFs), respectively. Many of the SDAFs displayed disomic segregation and thus T89 may be a segmental allotetraploid or an allotetraploid. The additional EST-SSR markers add value to the maps by increasing marker density and provide markers that can be easily transferred to other bermudagrass populations. Furthermore, EST-SSRs can be immediately used to assess genetic diversity, identify non-mutated cultivars of bermudagrass, confirm pedigrees, and differentiate contaminants from cultivars derived from ‘Tifgreen’.
Karen R. Harris, Brian M. Schwartz, Andrew H. Paterson, and Jeff A. Brady
Thirty-one partial bermudagrass (Cynodon spp.) disease-resistance gene analogs (BRGA) were cloned and sequenced from diploid, triploid, tetraploid, and hexaploid bermudagrass using degenerate primers to target the nucleotide binding site (NBS) of the NBS–leucine-rich repeat (LRR) resistance gene family. Alignment of deduced amino acid sequences revealed that the conserved motifs of the NBS are present and all sequences have non-Drosophila melanogaster Toll and mammalian interleukin-1 receptor (TIR) motifs. Using a neighbor-joining algorithm, a dendrogram was created and nine groups of deduced amino acid sequences from bermudagrass could be identified from those sequences that span the NBS. Four BRGA markers and 15 bermudagrass expressed sequence tags (ESTs) with similarity to resistance genes or resistance gene analogs were placed on a bermudagrass genetic map. Multiple BRGA and EST markers mapped on T89 linkage groups 1a and 5a and clusters were seen on T89 19 and two linkage groups previously unidentified. In addition, three primers made from BRGA groups and ESTs with similarity to NBS-LRR resistance genes amplify NBS-LRR analogs in zoysiagrass (Zoysia japonica or Z. matrella) or seashore paspalum (Paspalum vaginatum). This gives evidence of conservation of NBS-LRR analogs among the subfamilies Chloridoideae and Panicoideae. Once disease resistance genes are identified, these BRGA and EST markers may be useful in marker-assisted selection for the improvement of disease resistance in bermudagrass.