Search

Acacia mearnsii (black wattle) is a commercially important forestry species in South Africa, grown for its timber and bark. Due to its invasiveness, it is also considered be an alien invader species and for this reason the production of a sterile triploid variety would be highly desirable for South African commercial forestry. Previous research on crosses between diploid and tetraploid parent plants to produce triploid progeny has resulted in poor seed set. One possible barrier preventing seed set could be the effect of temperature and relative humidity, within the isolation bags used during cross-pollination operations. For this reason in 2011 diploid polyads were subjected to various temperature and relative humidity combinations, to simulate conditions recorded within the isolation bags being used in the 2010 flowering season in order to see if the conditions were detrimental to polyad viability. The results showed that when polyads were exposed to extreme temperatures (> 30 °C) and low relative humidities (RH's) (10%), polyad viability and pollen tube development, decreased significantly. In contrast the effect of high RH's in combination with low temperatures for long periods appeared to be beneficial to polyad viability and pollen tube growth. The results also indicated that the Australian Centre for International Agricultural Research (ACIAR) agar germination medium was superior to the Brewbaker and Kwack (BK) 30% agar germination medium for determining polyad viability as it resulted in greater number of pollen tubes per polyad, which were healthier in appearance. The Sigma® DAB peroxidase vital stain test overestimated polyad viability and showed no significant differences between the various treatments, highlighting its unreliability as a test. Polyad viability and pollen tube development were compared across three flowering seasons (2009, 2010 and 2011) and similar trends were apparent with some seasonal differences.

The surface sterilisation procedure is of integral importance to any micropropagation technique. This process should do the least amount of plant damage, whilst reducing microbial contamination to an acceptable level. The objective of this research was to investigate alternative sterilisation agents to the dangerous chemical mercuric chloride (HgCl2), and to determine the effect of sterilant exposure time on shoot apex culture of Acacia mearnsii. Explants were cultured on MS medium supplemented with 2.0 mg l–1 BA and monitored for 21 d for signs of contamination and shooting. Household bleach (NaOCl), diluted 1:3 in water, resulted in decontaminated explant levels not significantly different to the 0.2% HgCl2 treatment and resulted in shoot development levels significantly higher than the 0.2% HgCl2 treatment. There was no significant effect of sterilant exposure time on decontaminated explant levels, whilst the shortest exposure time resulted in significantly higher shooting levels than the other two time periods tested. Keywords: Acacia mearnsii, shoot apex culture, sterilisation agent, vegetative propagation

Acacia mearnsii (black wattle) is a commercially important forestry species in South Africa, grown for its timber as well as its bark. It is, however, also considered to be an alien invader of indigenous vegetation and for this reason the production of a sterile variety would be highly desirable for commercial forestry in South Africa. Previous research on crosses between diploid and tetraploid parent plants to produce triploid progeny has resulted in poor seed set. One possible barrier preventing seed set could be the viability of the pollen used in the cross pollination operations. Thus a study was conducted to test the pollen viability. In vitro agar media germination tests (ACIAR and Brewbaker and Kwack media) were optimised on Acacia podalyriifolia pollen and then used together with vital stain tests (Sigma® DAB peroxidase and p-phenylendiamine) to test pollen germination and viability of A. mearnsii pollen. These were then compared to in vivo pollen germination on the stigma, and were conducted on both diploid and tetraploid pollen mixes. Results showed that the vital stain tests gave significantly (p0.05) between the two agar media germination tests and between the two vital stain tests.