TH E WOR LD OF GM T POTATO R ESEARCH he Agrobacterium tumefaciens (At) bacterium can induce its host to produce galls in which the bacterium itself thrives. When the plant tissue is heated somewhat the bacterium dies but the plant continues to rapidly multiply cells in the gall. Apparently At has genetically modified its host in a ‘natural’ way. Genetic laboratories worldwide use this to produce genetically modified plants. As a routine procedure the desired gene – let us say the gene from the bacterium - Baccillus thuringienses – (Bt) that leads to the production of a substance that is toxic for insects is isolated, coupled to a selection marker e.g. conveying herbicide resistance, and cloned. Cloning means producing many identical copies. Cloning is done by feeding this isolated gene to yet another bacterium E. coli (also present in human guts) which forms colonies on a medium in a petri dish with each individual E. coli bacterium containing the Bt gene. When there are enough clones of the Bt gene the E. coli is brought into contact with the At bacterium that has the ability to absorb the Bt gene into its genome. Next At is allowed to infect individual plant cells of the crop to be modified and the Bt+marker gene may ‘jump over’ to the genome of the plant and express itself. Only few of the many individual plant cells have received the Bt gene so the regenerated plants are treated with a herbicide so the surviving ones contain the Bt gene. In a recent issue of the American Journal of Potato Research there is an article by Dr Douches of the Michigan State University entitled “Evaluation of transgenic potatoes for resistance to potato tuber worm in the laboratory and field” Potato tuber moth is one of the most serious insect pests of potato and is increasingly becoming a problem in the pacific North West of the united states. The modified Spunta plants contain the Bt gene and all tuber worms (larvae of the tuber moth) died in the lab and field. Late last century another Bt potato was created and introduced to the US market NewLeaf bt containing Russet Burbank resistant to Colorado beetle still authorized in the USA, Russia and Ukraine but withdrawn from the US market. Research and field trials regarding resistance to nematodes, viruses and Phytophthora has also been carried out. Market introduction is close now for the amylopectine varieties Amflora and Amadea of BASF. Here the gene responsible for 20 % of the starch as amylose is blocked saving much energy and chemicals in the starch separation industry. BASF also soon wants to launch a late blight resistant variety Fortuna with two resistance genes from the wild Mexican species Solanum bulbocastanum still with a selection marker (herbicide resistance). BASF and the starch company AVEBE jointly develop a blight resistant starch variety. At Wageningen University we make current varieties resistant against blight by supplying them with a stack of up to 6 genes (see www.durph.nl). These are all from a resistant wild species crossed with a susceptible variety and its offspring’s genome is enzymatically cut up in small fragments that are separated in a gel. The picture shows that a particular band is associated with resistance. From this band the resistance genes are cloned. The DuRPh project does not make use of selection marker genes so albeit the process is GM, the product contains potato genes only, so called cisgenic versus transgenic. At present about 10% of the world arable surface produces GM crops (150 million hectares, five times the global potato production area) such as herbicide tolerant, high oleic acid soybean, herbicide tolerant, high laurate and myristate (edible oil) canola, insect resistant, herbicide tolerant cotton and insect resistant, herbicide tolerant, modified amylase for ethanol production, high-lysine maize. So far no GM potatoes grown but seeing what is in the pipeline, this likely changes. ● Anton Haverkort anton.haverkort@wur.nl Potato World 2011 • number 2 29 Pagina 28
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