POLLEN STORAGE AND BREEDING SYSTEM IN RELATION TO CONTROLLED POLLINATION OF 4 SPECIES OF ACACIA (LEGUMINOSAE, MIMOSOIDEAE)

Pollen of Acacia auriculiformis, A. iteaphylla, A. karroo and A. mangium was stored at 25, 5, -18 or -196-degrees-C, for up to three years, and its viability tested by pollen staining, in vivo pollen tube growth or by pod set one month after hand pollination. The effectiveness of staining methods using 2,3, 5-triphenyltetrazolium chloride (TTC), 5-bromo-4-chloro-3-indole-beta-galactoside (X-Gal) and fluorescein diacetate (FDA) to predict pollen viability was investigated. All of the staining methods gave variable results, but the TTC and X-Gal tests were found to be particularly unreliable. FDA staining of pollen gave the best indication of its ability to germinate on the stigma and penetrate ovules. Pollen stored for up to three days at 25-degrees-C retained the ability to penetrate ovules following hand pollination, and of that stored for three years at 5-degrees-C, 19% of the grains fluoresced with FDA. Pollen stored at -18-degrees-C for one year retained the ability to penetrate ovules and produce pod set, and of that stored for three years 23% of the grains fluoresced with FDA. Pollen stored at -196-degrees-C for one year retained the ability to penetrate ovules and produce pod set, but thawing and refreezing of the pollen reduced viability to zero. It was concluded that the most successful and convenient method of pollen storage was vacuum drying followed by storage at -18-degrees-C. The Australian species of Acacia investigated, A. iteaphylla, A. auriculiformis and A. mangium, all had protogynous flowers, with stigma receptivity preceding anther dehiscence, such that flowers could be reliably hand pollinated. The African species A. karroo had protandrous flowers, with stigmas unreceptive at anthesis, but receptive at 5 days after anther dehiscence. Deposition of self pollen on the stigma prior to attainment of receptivity rendered hand pollination of this species unreliable.