Registration of SG4X‐1 Germplasm of Eastern Gamagrass

SG4X-1 (Reg. no. GP-71, P1 591482) is a fertile, sexually reproducing gynomonoecious tetraploid (2n = 4x = 72) eastern gamagrass (Tripsacum dactyloides formaprolificum Dayton & Dewald) (1). SG4X-1 was developed by chromosome doubling of a gynomonoecious diploid (2n = 2x = 36), GSF-I (P1 483447) and was released by the USDA-NRCS Big Flats Plant Materials Center and Cornell University in December 1995. Callus cultures from P1 483447 were initiated from immature inflorescences of eastern gamagrass on Murashige and Skoog (MS) medium (2) with 2 mg L" of 2,4-dichlorophenoxy acetic acid. The callus cultures were initiated and maintained in the dark on this medium and then subcultured to MS medium with 3 mg L" of benzyladenine (BA) for 6 d in the dark to initiate shoot development. Callus cultures were then transferred to MS medium without growth regulators under continuous light for shoot development. Shoots were then placed on MS medium with 3 mg L" BA to induce the development of microtillers. Young, freshly divided microtillers were transferred onto MS medium with 3 mg L~' of BA, and 5 mL of a 20-umol L" solution of amiprophos-methyl (Bayer AG, Germany) were pipetted over the shoots to induce polyploidy. These shoots were incubated in the dark for 4 d. The shoots were then rinsed and subcultured on MS medium with 3 mg L" of BA for 2 wk under light conditions before being transferred to MS medium with 1 mg L" of indoleacetic acid for rooting. The induced tetraploid plant, P1 591482, was analyzed by flow cytometry (3) and was found to have a DNA content of 16.5 pg nucleus", compared with 8.1 pg nucleus" for a diploid control. The induced tetraploid plant was confirmed by root tip counts to have 72 chromosomes. To ascertain the mode of reproduction of this induced tetraploid plant, a testcross was made to a known diploid, selection 9051292. The nuclear DNA contents for the parents of the testcross were 15.9 pg nucleus" for induced tetraploid P1 591482 and 8.5 pg nucleus" for the diploid selection 9051292. The average DNA content of the 10 offspring evaluated was 12.7±0.6pg nucleus". This value is intermediate between the diploid and tetraploid value, indicating that the progeny are triploid, as expected from a sexual cross. The flow cytometry results were verified by chromosome counts using root tips. All progeny had 54 chromosomes except for one that had a variable number between 36 and 54. SG4X-1 eastern gamagrass is vegetatively similar to GSF-I. It is semiprostrate in growth habit with relatively narrow dark-green leaves. The inflorescence exhibits the gynomonoecious form with no modification to the inflorescence or seed, in spite of the increased ploidy level. It is fertile with 43% seed set. It differs from other tetraploids by being able to reproduce sexually instead ofapomictically and by having the gynomonoecious inflorescence with 20 times more pistil-bearing florets than the monoecious inflorescence. SG4X-1 will be useful to plant breeders and geneticists for studying the inheritance of gynomonoecy and apomixis at the tetraploid level and for manipulating apomixis in eastern gamagrass breeding programs. The germplasm will be maintained vegetatively. Limited quantities of vegetative material may be obtained from the Big Flats Plant Materials Center, Corning, NY. Recipients of plant material are asked to make appropriate recognition of the source if SG4X-1 is used in the development of a new germplasm or cultivar.