Fertilization of an unreduced egg (2n + n) increases ploidy level and creates a new hybrid. It occasionally occurs in apomictic species but at a frequency too low to be a reliable method for genetic improvement. This investigation was undertaken to determine if 2n + n fertilization could be increased by early pollination. Six buffelgrass, Pennisetum ciliare (L.) Link [syn. Cenchrus ciliaris L.], accessions, five apomicts and one sexual, were self‐pollinated and cross‐pollinated with birdwoodgrass, P. ciliare (L.) Link var. setigerum (Vahl.) Leek, at 3, 2, 1, and 0 d before anthesis. The 2n + n progeny were identified by flow cytometry. DNA content (pg 2C−1) was determined for 1962 self‐pollinated and 3072 cross‐pollinated plants. Twenty‐eight self‐ and 80 cross‐pollinated plants had a higher DNA content and were products of 2n + n fertilization. The overall frequency of 2n + n fertilization when self‐ and cross‐pollinated was 1.4 and 2.6%, respectively. For all protogynous intervals, the frequency ranged from 0 to 5.2% for self‐pollinated plants and 0 to 8.2% for cross‐pollinated plants. When self‐pollinated, there was no correlation between time of pollination and recovery of 2n + n hybrids. When cross‐pollinated, there was a linear relationship between time of pollination and number of 2n + n hybrids recovered. More 2n + n hybrids were recovered from crosses made 2 or 3 d before anthesis. Thus in apomictic buffelgrass, the frequency of 2n + n fertilization can be increased by pollinating early, and in apomictic species where sexual germplasm is not available, this approach has potential to produce new apomictic hybrids.

parent, new genotypes are produced when the reduced egg cells in meiotically derived embryo sacs are fertil-Buffelgrass, Pennisetum ciliare (L.) Link syn ϭ Cenchrus ciliaris ized. Another fertilization event in apomict plants oc-L., is an important warm-season perennial forage grass that is widely grown throughout the arid tropics. It has perfect florets, and emascula-curs when the unreduced egg in an apomictic sac is tion is thought to be required to produce controlled hybrids. This is fertilized by a reduced sperm nucleus. This phenomenon a tedious, difficult undertaking because of the small floret size. The is known as the fertilization of an unreduced egg (2n ϩ flowering behavior of buffelgrass is such that the stigmas are exserted n) or B III hybridization (Bashaw and Hignight, 1990). from the floret prior to anthesis, which is referred to here as the Fertilization of an unreduced egg provides a means for protogynous interval. This investigation was conducted to determine producing new genotypes by the incorporation of whole the duration of the protogynous interval in 447 buffelgrass accessions alien genomes while retaining the entire somatic chroand to ascertain stigma receptivity during the protogynous intervals. mosome complement of the apomictic female parent. Protogynous intervals in a field nursery near College Station, TX, for Bashaw and Hignight (1990) demonstrated that 2n ϩ n all accessions ranged from 1 to 4 d. Six accessions with protogynous intervals ranging from 1 to 3 d were used to investigate stigma receptiv-fertilization can be used to develop unique apomictic ity under both self-and cross-pollinated conditions in a greenhouse.buffelgrass germplasm. Pollen germination and tube growth were observed with fluorescentA range of chromosome numbers has been reported microscopy at different time increments following pollination. Across for buffelgrass with the most common number being all accessions, pollen germinated within 15 min of contacting the 2n ϭ 4x ϭ 36 (Fisher et al., 1954). The species apparently stigma, and pollen tubes grew to the micropyle within 2 to 6 h, deis a segmental allotetraploid because its chromosomes pending on the accession and pollen source. Mean seed set ranged typically pair as one or two quadrivalents and 16 or 14 from 11 to 76% and from 22 to 80% among accessions following selfbivalents during diakinesis of meiosis I. However, it is and cross-pollination, respectively. This investigation revealed that not uncommon to find plants with 2n ϭ 5x ϭ 45 and variation exists for protogynous interval within buffelgrass, and the stigmas are receptive when exserted from the floret and remain re-6x ϭ 54 chromsomes as well as aneuploids of these three ceptive throughout duration of the protogynous interval regardless ploidy levels (Fisher et al., 1954; Bashaw and Higof whether it occurs 3, 2, or 1 d prior to anthesis. These findings night, 1990). demonstrate that protogyny can be used to produced controlled hy-Like most warm-season perennial grasses, buffelgrass brids in sexual b...