Date of Award

2006

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

School

School of Natural Sciences

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Ian Bennett

Second Advisor

Digby Growns

Abstract

Germination of pollen in vitro is a common technique used to assess the ability of pollen to germinate under a variety of conditions. The ability to determine the viability of a pollen grain, and optimal conditions for maximum germination and storage are important for hybridisation. A means of storing pollen, while maintaining viability, enables inter-species hybridisation between species that are spatially and temporally (flowering time) separated. The ultimate aim of hybridisation is seed set and in order to increase this in a genus renowned for a very low fruit to flower ratio, maximum pollen germination must be obtained. Therefore, by determining the ideal conditions for Grevillea pollen germination on the style (in vivo) using laboratory (in vitro) techniques may allow the highest possible germination and subsequent seed set for an individual species. All Grevillea species displayed a significant -difference (P = <0.001) in pollen germination when pollen was collected and germinated one day before anthesis, the day of anthesis and up to three days post anthesis. Desiccation up to 24 hours before in vitro germination did not produce a difference in germination for G. saccata (P = 0.911), however, G.fililoba, G. pinaster and G. thelemanniana responded significantly within 12 hours of desiccation with increased germination (P = <0.001). The effect of temperature on pollen germination was significant for all species (P = <0.001) with optimum temperatures being species specific. For example, G. thelemanniana displayed its' highest germination at 30 °C, with all other species investigated displaying optimum germination at 25 °C. The storage potential of untreated Grevillea species was low and there was a significant difference (P = <0.001) in germination between freshly collected pollen and that which was stored for approximately seven months. Results suggest that Grevillea pollen may require special treatment to maintain viability during storage as only one species, G. baxeri, showed no difference between treatments (P = 0.064) and lost little viability. Dark conditions during germination in vitro significantly increased pollen germination (P = <0.001) for all species, compared to light conditions. Using Brewbaker and Kwack as the germination medium, without a coverslip during the incubation period, also promoted a general increase in germination with the exception of G. preissii (P = 0.035 and 0.127 respectively). The effect of sucrose content in Brewbaker and Kwack medium was significant for all Grevillea species with an optimum concentration range between 10- 20% depending on the species. Any concentration above 40% sucrose caused germination to drop below 10% for all species. Sucrose was also demonstrated to have the greatest effect on G. fililoba germination when compared to the osmotica mannitol and polyethylene glycol (PEG).

Inter-species hybridisation between three distantly related Grevillea species produced no fruit set. Geitonogamous crosses in G. rhyolitica produced fruit, however, all fruit aborted before maturation. The removal of the stigma and its incompatibility barriers did not encourage fruit set for any of four crosses, geitonogamous or inter-species hybrid. In conclusion, it was found that Grevillea pollen displays the highest germination in vitro when incubated in the dark, without a coverslip, on Brewbaker and Kwack medium containing between 10-20% sucrose. Osmotica such as mannitol and PEG did not increase germination, suggesting that sucrose is primarily a food source for pollen during germination with osmotic balance capabilities that are important for germination. The highest pollen germination was obtained when collected on the day of anthesis for four of the five Grevillea species investigated. Ideal temperature ranged between 22.5-27°C depending on the species, and G. saccata was the only species in the study to show no difference in germination after desiccation prior to germination.

Share

 
COinS