Pollen morphological features and impact of temperature on pollen germination of various Pinus species
South African Journal of Botany
Sappi Forests Research, Shaw Research Centre, PO Box 473, Howick 3290, South Africa; Res. Ctr. Plant Growth and Devmt., School of Botany and Zoology, Univ. KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
The aim of this study was to determine if differences in pollen morphology and response to temperature treatments were apparent among seven Pinus species used in an inter-specific hybridisation programme. The seven species included were: P. caribaea, P. elliottii, P. greggii, P. oocarpa, P. patula, P. radiata and P. tecunumanii. This study showed that pollen from the seven Pinus species displays the structure typical of the Pinaceae, having no visibly distinguishing structural characteristics. Differences in pollen grain diameter, measured across the distal region of the grain, were found among species and among different clones of Pinus patula. The mean grain diameters ranged from 42μm (P. patula) to 50μm (P. radiata). Within P. patula they ranged between 42μm and 47μm. Different species responded differently to temperature treatments of dry-stored and re-hydrated germinating pollen. Pollen stored at low humidity (below 10%) could tolerate relatively high temperatures up to 80°C, and still maintain some level of viability. P. caribaea and P. greggii maintained viability of 19 and 33%, respectively, after treatment at 80°C. The 90°C treatment resulted in zero viability for the three species investigated: P. caribaea, P. greggii and P. patula. In contrast to dry-stored pollen, re-hydrated pollen germinated in vitro at different temperatures, had lower levels of tolerance. Optimal germination occurred at 32°C and steadily declined for all species as the temperature was increased until 44°C at 2°C increments. P. caribaea, P. patula and P. tecunumanii still germinated, albeit at low levels at 40°C, but no germination occurred above 42°C. Differences in pollen tube length were observed between different species incubated at 30°C for 72h. P. caribaea displayed the longest tube length (242μm) while some clones of P. patula had the shortest pollen tubes (92μm). Morphological features cannot be used to distinguish among the species studied, but there were differences in tolerance levels to temperature treatments of dry-stored and re-hydrated pollen among these species. Copyright © NISC Pty Ltd.
coniferous tree; pollen; temperature effect; Pinaceae; Pinus caribaea; Pinus elliottii; Pinus greggii; Pinus oocarpa; Pinus patula; Pinus radiata; Pinus tecunumanii