The release of ‘Tifgreen’ bermudagrass in 1956 launched the era of vegetatively propagated turfgrasses using a production method that preserved the initial hybrid vigor of new cultivars barring genetic instability (Hanna and Anderson, 2008). ‘Tifgreen’ originated from a cross between an Egyptian Cynodon transvaalensis introduction and a common bermudagrass (Cynodon dactylon) from a North Carolina golf course green (Hein, 1961). This cultivar can be mowed daily at a plant height of 4.7 mm, which at the time of its release represented a breakthrough in putting green quality. The ability to uniformly mow ‘Tifgreen’ at lower heights spurred golf courses across the southeast to replace their common bermudagrass greens (Hanna and Anderson, 2008).
Well-defined areas with noticeable differences in plant morphology (i.e., plant color, leaf size, and internode length) were observed on ‘Tifgreen’ putting surfaces soon after its release. Several of these “off-types” were isolated from putting greens in Florence, SC, and Sea Island, GA, and further evaluated at lower mowing heights than ‘Tifgreen’ could tolerate. The term off-type refers to a plant that has a different growth habit, density, texture, and color that disrupts uniformity in monoculture plantings (Capo-chichi et al., 2005).The off-type selected from Florence Country Club was released as ‘Tifdwarf’ (Burton, 1966; Elsner, 1966) and became one of the most widely used grasses on greens in the warmer regions of the world.
Off-types found in ‘Tifgreen’ or ‘Tifdwarf’ make up the latest generation of bermudagrass for putting greens. These cultivars include Champion, Classic Dwarf, FloraDwarf, Jenson, Jones Dwarf, MiniVerde, MS Supreme, Pee Dee 102, Quality, Reesegrass, and TifEagle (Harris-Shultz et al., 2010; McCarty and Canegallo, 2005). ‘Champion’, ‘FloraDwarf’, ‘Jones Dwarf’, ‘MiniVerde’, ‘MS Supreme’, ‘Tifdwarf’, and ‘TifEagle’ were highly genetically similar to ‘Tifgreen’ when DNA fingerprinting was used and appear to be somatic mutants (Capo-chichi et al., 2005; Harris-Shultz et al., 2010; Wang et al., 2010). Although many cultivars have been derived from ‘Tifgreen’ and ‘Tifdwarf’, most mutations are deleterious. Inconsistencies in appearance, playability, response to environmental conditions (i.e., nutrient and water availability), herbicide application, etc., have resulted in severe problems and millions of dollars in loss to the golf course industry and sod farms (Caetano-Anolles et al., 1997).
Off-types in bermudagrass can be generated by either clonal variation or by contamination from an unrelated bermudagrass through seed germination or sprig introduction. Clonal variation can be the result of epigenetic modification in response to the environment, from the presence of plant pathogens, or, more commonly, from mutations that occur during growth (Pelsy, 2010). Genetic mutations can be induced by chemicals such as herbicides that affect microtubule formation during mitosis (Capo-chichi et al., 2005) or can occur at random by a natural process such as transposon activity and problems with DNA repair (Leroy and Leon, 2000; Wessler, 2001). A mutation in one cell of a layer of the shoot apical meristem increases by mitosis and produces a mutated sector (Hocquigny et al., 2004). These plants are periclinal chimeras because one or two entire cell layers of the apical meristem are genetically distinct from the adjacent layers. Periclinal chimeras are often stable and can be maintained by vegetative propagation of stems (Dermen, 1960) and are common in long-lived clonally propagated crops (Franks et al., 2002).
Grapes (Vitis vinifera), like bermudagrass, have cultivars that are maintained by vegetative propagation to create clones that are genetically identical to the parent plant assuming that no somatic mutation occurred in the regenerating cells that gave rise to the clone, yet similar to bermudagrass, grape clones as well as many species propagated vegetatively for commercial horticulture often display phenotypic variation (Gill et al., 1995; Pelsy, 2010). When microsatellite markers were used among clones from many grape cultivars (which are diploids), three to four alleles were detected (Franks et al., 2002; Hocquigny et al., 2004). This increase in allele number was the result of expansion or contraction of the repeat motif in a cell layer of grape forming a periclinal chimera (Hocquigny et al., 2004). When the cell layers of the periclinal chimera ‘Pinot Meunier’ were separated by somatic embryogenesis, the regenerated plants not only had distinct genotypes, but had novel phenotypes as compared with the parental plant (Franks et al., 2002). It has been noted that it is easy to miss instances of microsatellite chimerism because minor peaks/bands are often generated (Franks et al., 2002). The genotypes of the cell layers in grape have been determined by studying the roots and sexual progeny because both are descended from the L2 inner tissues and the leaf is derived from L1 and L2 of the plant meristem (Thompson and Olmo, 1963). To our knowledge, the number of cell layers in the tunica of the shoot apical meristem of bermudagrass has not been determined. In monocots, the numbers of tunica cell layers vary from one to four with one and two predominating (Khurana et al., 2004). For example, the shoot apex of wheat (Triticum aestivum) consists of both the L1 and L2 cell layers (Simmonds, 1997), whereas the shoot apex of maize (Zea mays) is composed of one layer of L1-derived cells (Jackson and Hake, 1997).
The close genetic similarity of cultivars within the ‘Tifgreen’ family has made it very difficult to distinguish each cultivar from one another using morphological and DNA fingerprinting methods (Harris-Shultz et al., 2010). This creates problems in the protection of cultivar proprietary rights and plant stock certification. The objectives of this study were to identify SSR markers that can distinguish between genotypes in the ‘Tifgreen’ family and to characterize these polymorphisms in each ‘Tifgreen’-derived cultivar.
Boutin-Ganache, I., Raposo, M., Raymond, M. & Deschepper, C.F. 2001 M13-tailed primers improve the readability and usability of microsatellite analyses performed with two different allele-sizing methods Biotechniques 31 25 28
Brown, R.M., Brown, M.A. & Brown, J.D. 1997 Champion dwarf bermudagrass. Plant Patent PP9888 U.S. Patent and Trademark Office Washington, DC
Caetano-Anolles, G., Callahan, L.M. & Gresshoff, P.M. 1997 The origin of bermudagrass (Cynodon) off-types inferred by DNA amplification fingerprinting Crop Sci. 37 81 87
Capo-chichi, L.J.A., Goatley, J.M., Philley, W., Krans, J., Davis, D., Kato, A. & van Santen, E. 2005 Dinitoaniline-induced genetic changes in bermudagrass Crop Sci. 45 1504 1510
Clemson University 2009 Turfgrass directory 2009 19 Oct. 2010 <http://www.clemson.edu/public/regulatory/plant_industry/fertilizer_seed/images/turfdir09.pdf>
Elsner, J.E. 1966 Effect of fertility level, cutting height and soil top-dressing on Tifgreen and Tifdwarf bermudagrass MS thesis, Univ. of Georgia Athens, GA
Franks, T., Botta, R. & Thomas, M.R. 2002 Chimerism in grapevines: Implications for cultivar identity, ancestry and genetic improvement Theor. Appl. Genet. 104 192 199
Hanna, W.W. & Anderson, W.F. 2008 Development and impact of vegetative propagation in forage and turf bermudagrasses Agron. J. 100 S103 S107
Harris, K.R., Schwartz, B.M., Paterson, A.H. & Brady, J.A. 2010 Identification and mapping of nucleotide binding site-leucine-rich repeat resistance gene analogs in bermudagrass J. Amer. Soc. Hort. Sci. 135 74 82
Harris-Shultz, K.R., Schwartz, B.M., Hanna, W.W. & Brady, J.A. 2010 Development, linkage mapping and utilization of microsatellites in bermudagrass J. Amer. Soc. Hort. Sci. 135 511 520
Hocquigny, S., Pelsy, F., Dumas, V., Kindt, S., Heloir, M.-C. & Merdinoglu, D. 2004 Diversification within grapevine cultivars goes through chimeric states Genome 47 579 589
Jackson, D. & Hake, S. 1997 Morphogenesis on the move: Cell-to-cell trafficking of plant regulatory proteins Curr. Opin. Genet. Dev. 7 495 500
Kamps, T.L., Williams, N.R., Ortega, V.M., Chamusco, K.C., Harris-Shultz, K.R., Scully, B.T. & Chase, C.D. 2011 DNA polymorphisms at bermudagrass microsatellite loci and their use in genotype fingerprinting Crop Sci. doi: 10.2135/cropsci2010.08.0478
Khurana, J.P., Tripathi, L., Kumar, D., Thakur, J.K. & Malik, M.R. 2004 Cell differentiation in shoot meristem: A molecular perspective 367 401 Srivastava, P.S., Narula A. & Srivastava S. Plant biotechnology and molecular markers Anamaya Publishers New Delhi, India
Kim, C., Jang, C.S., Kamps, T.L., Robertson, J.S., Feltus, F.A. & Paterson, A.H. 2008 Transciptome analysis of leaf tissue from bermudagrass (Cynodon dactylon) using a normalized cDNA library Funct. Plant Biol. 35 585 594
Leonard, J.M., Bollmann, S.R. & Hays, J.B. 2003 Reduction of stability of Arabidopsis genomic and transgenic DNA-repeat sequences (microsatellites) by inactivation of AtMSH2 mismatch-repair function Plant Physiol. 133 328 338
Leroy, X.J. & Leon, K. 2000 A rapid method for detection of plant genomic instability using unanchored-microsatellite primers Plant Mol. Biol. Rpt. 18 283a 283g
Li, Y., Korol, A.B., Fahima, T. & Nevo, E. 2004 Microsatellites within genes: Structure, function, and evolution Mol. Biol. Evol. 21 991 1007
Marcotrigiano, M. 2000 Herbivory could unlock mutations sequestered in stratified shoot apices of genetic mosaics Amer. J. Bot. 87 355 361
Rozen, S. & Skaletsky, H.J. 2000 Primer3 on the WWW for general users and for biologist programmers 365 386 Krawetz, S. & Misener S. Bioinformatics methods and protocols: Methods in molecular biology Humana Press Totowa, NJ
Simmonds, J.A. 1997 Mitotic activity in wheat shoot apical meristems: Effect of dissection to expose the apical dome Plant Sci. 130 217 225
Wang, Z., Wu, Y., Martin, D.L., Gao, H., Samuels, T. & Tan, C. 2010 Identification of vegetatively propagated turf bermudagrass cultivars using simple sequence repeat markers Crop Sci. 50 2103 2111