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Scottsville, South Africa

Van Wilgen B.W.,South African Council for Scientific and Industrial Research | Dyer C.,Institute for Commercial Forestry Research | Hoffmann J.H.,University of Cape Town | Ivey P.,South African National Biodiversity Institute | And 7 more authors.
Diversity and Distributions | Year: 2011

Aim A range of approaches and philosophies underpin national-level strategies for managing invasive alien plants. This study presents a strategy for the management of taxa that both have value and do harm. Location South Africa. Methods Insights were derived from examining Australian Acacia species in South Africa (c.70 species introduced, mostly >150years ago; some have commercial and other values; 14 species are invasive, causing substantial ecological and economic damage). We consider options for combining available tactics and management practices. We defined (1) categories of species based on invaded area (a surrogate for impact) and the value of benefits generated and (2) management regions based on habitat suitability and degree of invasion. For each category and region, we identified strategic goals and proposed the combinations of management practices to move the system in the desired direction. Results We identified six strategic goals that in combination would apply to eight species categories. We further identified 14 management practices that could be strategically combined to achieve these goals for each category in five discrete regions. When used in appropriate combinations, the prospect of achieving the strategic goal will be maximized. As the outcomes of management cannot be accurately predicted, management must be adaptive, requiring continuous monitoring and assessment, and realignment of goals if necessary. Main conclusions Invasive Australian Acacia species in South Africa continue to spread and cause undesirable impacts, despite a considerable investment into management. This is because the various practices have historically been uncoordinated in what can be best described as a strategy of hope. Our proposed strategy offers the best possible chance of achieving goals, and it is the first to address invasive alien species that have both positive value and negative impacts. © 2011 Blackwell Publishing Ltd.


Beck-Pay S.L.,Institute for Commercial Forestry Research
South African Journal of Botany | Year: 2012

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. © 2012 South African Association of Botanists.


Beck-Pay S.L.,Institute for Commercial Forestry Research
South African Journal of Botany | Year: 2012

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 (p< 0.05) higher pollen viability than the agar germination tests and were more in agreement with the results from the pollen germination rate on the stigma. For both the diploid and tetraploid pollen mixes tested, there were no significant differences (p> 0.05) between the two agar media germination tests and between the two vital stain tests. © 2011 Elsevier B.V.


Beck-Pay S.L.,Institute for Commercial Forestry Research
South African Journal of Botany | Year: 2012

A study of the reproductive biology of black wattle (. Acacia mearnsii de Wild) was conducted, specifically with regard to the compatibility of the diploid. ×. tetraploid cross to produce a triploid variety, together with identifying ways of increasing triploid seed production. Fluorescent microscopy was used to determine pollination and fertilisation rates and to identify any pre-zygotic barriers at the stigma, style and ovary. Both diploid and tetraploid families were tested as maternal parents to establish if this was imperative to producing a triploid. Morphological measurements were documented in order to determine any incompatibilities in the cross to produce a triploid. The . in vivo results showed that successful fertilisation of the ovary was possible whether one used a diploid or tetraploid maternal parent. When the maternal parent was a tetraploid, however, the pollination rate (polyads adhering to the stigma) and ovary fertilisation rates were significantly (. p<. 0.05) greater. Morphological measurements and observations also revealed that tetraploid floral parts were significantly (. p<. 0.05) larger than the diploids. The morphological size differences between the diploid and tetraploid polyads and pistils did not appear to influence the fertilisation of the ovaries and thus did not pose any identifiable barrier in the cross to produce a triploid. When considering the results from the cross to produce a triploid (2n. ×. 4n or 4n. ×. 2n), the diploid polyads were significantly (. p<. 0.05) more vigorous and suitable in fertilising the tetraploid ovaries as opposed to the reverse. Possible pre-zygotic barriers at the stigma, style or ovary were investigated and the only area that could be identified limiting seed production was within the ovary. © 2011 Elsevier B.V.


Acacia mearnsii (black wattle) is grown commercially in South Africa for its timber and bark. However, the invasive nature of the species has resulted in it being considered an alien invader and for this reason research has been aimed at producing a sterile triploid variety that would be highly desirable for the South African commercial forestry industry. Tetraploids were successfully induced by soaking germinating diploid seeds in colchicine. Seed from these tetraploids was used to establish a field trial, where crossing diploid with tetraploid parent plants only produced diploid and tetraploid progeny and failed to produce any triploid progeny. Control-crossed seed set between diploids is generally low in A. mearnsii and, together with the possibility of an unstable tetraploid population, this could be reducing the chances of producing triploid seed. Thus identification and confirmation of stability within the existing advanced-generation tetraploid population (aged 10-11 years) was critical to ensure the production of sterile triploids. Flow cytometry was used to determine the stability of the ploidy of leaf vegetative tissues, whereas polyad and ovule size measurements were used to determine the stability of ploidy of the reproductive tissues. Results from the study revealed that the tetraploidy of within the leaf vegetative tissue was stable. For both the ovule and polyad size measurements, a size range was determined for diploids and tetraploids and, within the population under investigation, no overlap was apparent. This allowed for the conclusion that the advanced-generation tetraploid population was stable and that the absence of triploid progeny must be because of post-zygotic reproductive barriers within the ovary. © 2013 Copyright NISC (Pty) Ltd.

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