Pollen tube growth and seed set in protogynous buffelgrass

Abstract

Buffelgrass, Pennisetum ciliare (L.) Link syn=Cenchrus ciliaris L., is a warm-season perennial forage grass that is widely grown throughout the arid tropics. Because buffelgrass florets are small and perfect-flowered, emasculation and controlled pollination is difficult. This study was conducted to determine the potential to use early pollination of protogynous buffelgrass as a method to enhance hybridization. More than 440 buffelgrass accessions were evaluated under field conditions and the protogynous interval, or time between stigma and anther exsertion7 recorded. Mean protogynous interval ranged from 1.0 to 4.0 days with 15%, 77% and 8% of the accessions having protogynous intervals of between 1.0 and 1.9, 2.0 and 2.9, or greater than 3.0 days. Six accessions (PI 4094077 Pi 409367, Pi 409704, S12103, Pi 315679 and Pi 295657) with mean protogynous intervals ranging from 1.2 to 3.4 days were selected and either self-pollinated or cross-pollinated with birdwoodgrass (Pi 193444) pollen. For each accession pollination began on the day of stigma exsertion with new florets being pollinated daily until anthesis. Pollen germination and pollen-tube growth were observed using fluorescence microscopy. Across all accessions, pollen germinated within 15 minutes of contacting the stigma and reached the micropyle within 2 to 6 hours depending upon accession and method of pollination. No evidence of pollen-stigma incompatibilities were observed. Mean seed set ranged from 1 0 to 68 and from 28 to 76% following self-and cross-pollination respectively. From this study it was concluded that variation exists for Protogynous interval in buffelgrass and that buffelgrass stigmas are receptive to pollen the day of exsertion even if they are one days prior to anthesis.