Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/8/1999
Publication Date: N/A
Citation: Interpretive Summary: Buffelgrass is an important forage grass grown on approximately 60 million acres of rangelands in the world, including 8 million acres in the south western US and northern Mexico. The grass has more than doubled the live stock carrying capacity in south Texas and is a superior forage in these arid regions. But, it has limitations because it lacks winter hardiness and is susceptible to various diseases and insects. To develop improved germplasm with winter hardiness and disease/insect resistance, controlled hybridization is necessary. However, to produce controlled hybrids, it is necessary to emasculate the small florets by hand, which is a tedious, time consuming, costly, and not necessarily effective approach. In some buffel grass accessions, the flowering behavior is such that the stigmas in the flower emerge from the floret before the anthers. The period between stigma and anther exsertion is called the protogynous interval. If the stigmas are receptive to pollen when they emerge from the floret, this interval could be used to eliminate the need for hand emasculation in producing hybrids. More than 400 buffelgrass accessions were screened and the protogynous interval ranged from 1 to 4 days. The stigmas of six different buffelgrass accessions were pollinated on different days during their protogynous intervals and then examined for pollen germination and pollen tube growth. It was concluded that the stigmas were receptive when exserted from the floret and remained receptive until anthesis, regardless of the protogynous interval. The amount of seed produced from the pollinations confirmed these findings. Thus, buffelgrass accessions with long protogynous intervals can be crossed with other genotypes and produce controlled hybrids without costly, time consuming hand emasculation.
Technical Abstract: Buffelgrass, Pennisetum ciliare (L.) Link syn+Cenchrus ciliaris L., is an important warm-season perennial forage grass that is grown throughout the arid tropics. It has small florets with perfect flowers and emasculation is thought to be required to produce controlled hybrids, which is a tedious sdifficult undertaking because of the small floret size. The flowering behavior of buffelgrass is such that the stigmas are exserted from the floret prior to anthesis. This investigation was conducted to determine the duration of the protogynous interval in 447 buffelgrass accessions and to ascertain stigma receptivity during the protogynous intervals. Protogynous interval for the different buffelgrass accessions ranged from 1.0 to 4.0 d. Six accessions with protogynous intervals ranging from 1 to 3 d were used to investigate stigma receptivity for both self- and cross- pollinated conditions. Pollen germination and tube growth were observed using fluorescent microscopy at different time increments following pollination. Across all accessions, pollen germinated within 15 min of contacting the stigma, and pollen tubes grew to the micropyle within 2 to 6 h. depending on the accession and the pollen source. Mean seed set ranged from 10 to 68% and from 28 to 76% among accessions following self- and cross-pollination, respectively. This study reveals variation exists for protogynous interval within buffelgrass, and the stigmas are receptive when exserted from the floret and remain receptive throughout duration of the protogynous interval regardless of whether it occurs 3-, 2-, or 1-d prior to anthesis. These findings demonstrate that protogyny can be used to produce controlled hybrids in sexual buffelgrass without emasculation.