Apomixis has been reported in eastern gamagrass [Tripsacum dactyloides (L.) L.I, but considerable uncertainty exists concerning the mechanism of apomixis involved. Because of this and the recent interest in improving the grass by breeding, this study was undertaken to characterize apomixis in eastern gamagrass. Megasporogenesis and embryo sac development were observed in ovules of eight eastern gamagrass genotypes: five diploid pistillate plants (2n = 2x = 36), two triploid (2n = 3x = 54) accessions, and one tetraploid (2n = 4x = 72) accession. The triploid and tetraploid accessions were apomictic. In these three, the megaspore mother cell enlarged; but rather than undergoing meiosis, the cell remained meiotically inactive. The only apparent changes were continued cell elongation and vacuolation. Eventually, the nucleus of the elongated megaspore mother cell divided mitotically and subsequently produced an 8‐nucleate embryo sac, which appeared similar to a Polygonum type sac. The embryo developed parthenogenetically. Pollination or fertilization was necessary for endosperm development, which indicates pseudogamy. The diploid plants reproduced by normal sexual means. After the first mitotic division, there was no difference in the appearance between the apomictic and sexual embryo sacs. These findings confirm that the apomictic mechanism in eastern gamagrass is diplospory of the Antennaria type followed by pseudogamy.

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All known sources of lehmann lovegrass, Eragrostis lehmanniana Nees, reproduce by apomixis, which precludes hybridization and conventional genetic research. This study was conducted to locate sexual germplasm and describe the reproductive process in lehmann lovegrass. Purported diploid germplasm was grown in pots in a greenhouse. Chromosome number was determined and embryo sac development was studied and compared with another lehmann lovegrass accession. Self fertility, open‐pollinated seed set, and mode of reproduction by progeny test were evaluated. Three accessions were diploid (2n = 2x = 20) and two were tetraploid (2n = 4x = 40). Triploid plants (2n = 3x = 30), discovered in the primarily diploid accessions, probably resulted either from the union of reduced and unreduced gametes or from fertilization of diploid plants by pollen from nearby tetraploid lehmann lovegrass. Diploid plants were sexual (i.e., megaspores were produced) and required cross pollination for seed set. Triploid and tetraploid plants were facultative diplosporous apomicts. Progeny tests were not conclusive. Although some diploid plants were clearly different from others, morphological differences were not sufficient to clearly and easily differentiate genetic from environmental variation. This is the first report of sexual reproduction in E. lehmanniana. This sexual germplasm will be essential to future genetic research with lehmann lovegrass.

Apomixis can hinder plant improvement if sexual or apomictic germ plasm of the appropriate ploidy level, required for effective manipulation of apomixis, is not available. To develop needed germ plasm and increase knowledge of apomixis in Tripsacum dactyloides, diploid (2n = 2x = 36) sexual plants were crossed with a highly apomictic triploid (2n = 3x = 54) accession in an attempt to transfer apomixis from a polyploid to the diploid level. The fertility of most hybrids was very low, 69% had 10% or less seed set. A selected subset of 48 hybrids, including most of the more fertile plants, was studied cytologically. The chromosome number of these hybrids ranged from 2n = 36 to 2n = 54. All but 3 of 46 of the 48 hybrids showed indications of apomictic development. Those with near-diploid chromosome numbers were primarily sexual. Highly apomictic hybrids, based on percent diplosporous ovules, had 43 or more chromosomes. Fertility of these hybrids was not related to chromosome number. Fertility of sexual to moderately apomictic plants was reduced as chromosome number increased. Apomixis in T. dactyloides is facultative. Backcrosses are needed to develop germ plasm with a high level of apomixis and near-diploid chromosome numbers.Key words: eastern gama-grass, chromosome number, fertility, mode of reproduction, germ plasm.