GENETIC CONTAMINATION

Something that is not often considered is the possibility of contamination of the genetic base of a species by plants in cultivation. Orchids South Africa 1999 contained a very disturbing report: "Alien Disa Hybrids on Table Mountain - Implications for Nature Conservation" by Vogelpoel, Cywes, Cywes and Pauw. This paper irrefutably demonstrated that the Disa uniflora gene pool on Table Mountain, here in Cape Town, is in the process of being contaminated. The authors came to the conclusion that "There is good reason to suspect that the plant of D. Kirstenbosch Pride (D. uniflora x D. cardinalis) found in 1988 was the seminal plant resulting from a misguided man-made introduction into the habitat of D. uniflora".
I constructed my own scenario to explain Table Mountain's Disa gene pool contamination and it briefly goes as follows: In the late 1970's or early 1980's there must have been a plant of Disa cardinalis in flower at a place to which a specimen of the red-flower-pollinating Mountain Pride Butterfly (Aeropetes tulbaghia) had access and within flying distance of the aqueduct on Table Mountain, where the contamination of D. uniflora took place. This D. cardinalis was obviously a cultivated specimen, as this species does not occur on the Cape Peninsula and could perhaps have been in an open greenhouse at Kirstenbosch Botanic Gardens, or could have been brought to an orchid show at Kirstenbosch and have been left temporarily in an unguarded crate. The distance from Kirstenbosch to the aqueduct is in the region of two kilometers (a mile and a bit). The plant was visited by a Mountain Pride Butterfly irresistibly attracted to its red colour. The butterfly picked up a pollinarium from the Disa cardinalis, continued with its perambulations and later flew off up Table Mountain to commit its 'crime'.
But it does not finish there, because it is quite feasible that by a similar mechanism, a far more insidious form of contamination may already have taken place, or may yet occur. It is most certainly possible that our butterflies could come into contact with advanced hybrids of D. uniflora or D. uniflora clones from other areas or those containing genetic material from other areas and carry this foreign material up the mountain, creating cases of genetic contamination which would not be readily detectable. As the discrete populations of Disa uniflora are in the process of evolving as we speak, perhaps towards distinct subspecies, contamination of plants in one area with the genetic material of plants from another area is possibly more damaging than it would appear superficially.
Shortly after submitting an article concerning this for publication in Orchids South Africa 2000, I was pleased to see a letter published in Veld & Flora, the Journal of the Botanical Society of South Africa (86(2): 90, June 2000) written by Dr Piet Vorster of Stellenbosch University under the headline: "Genetically modified indigenous plants are a threat to our indigenous flora". Amongst other things he said: "There are numerous examples of crop plants which were developed and grown in areas where their wild progenitors were indigenous, and where the genetically modified plants contaminated their progenitors to extinction".
In my idealised world, no-one would be permitted to hybridise with local species, or be allowed to introduce fertile species or hybrid plant material into any area where a natural species population may be jeopardised.

© 2003-2009 Greig Russell

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