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Genetic Engineering to Combat Asia Soybean Rust Disease

written by: Sonal Panse•edited by: Paul Arnold•updated: 6/22/2009

Soybeans are grown the world-over and are economically very important. Genetically-engineered cultivars may protect the several billons worth soybean farming industry from devastating diseases like the Asia soybean rust (ASR).

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    Asia Soybean Rust (ASR)

    Asia soybean rust (ASR) is a fungal disease that can have a devastating effect on the economically important soybean crop farming industry. ASR is caused by a highly virulent fungus called Phakopsora pachyrhizi. The fungus, as the name indicates, originated in Asia, but manifest destiny has brought it to the American continent in the new millennium.

    The fungal infection is spread by wind-blown spores. The spores grow on the soybean leaves in the form of rust colored pustules and cause the leaves to fall off. This means the plant cannot synthesise food and thereby cannot develop healthy soybean pods. ASR disease spreads rapidly and in only a matter of weeks can wipe out nearly 80% of a soybean crop.

    So far, a variety of fungicides have been found to be pretty potent against the Asia soybean rust. However, with prolonged use, it has been found that some of the primary chemical compounds in the fungicides seem to get less effective against the fungus. This may be as a result of the fungi developing an immunity against them. In which case, stronger or newer fungicides are required, or the crop has to be sprayed with fungicide several times instead of just once or twice to get rid of the rust disease. Fungicides are not inexpensive, so repeated spraying naturally increases the overall farming costs. Another factor is the negative impact on the environment from repeated fungicide use.

    In the long run, using fungicides may not be the viable solution to the rust problem. The more practical answer may lie in using soybean cultivars that have been genetically engineered to become resistant to the Asian soybean rust disease.

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    Genetic Engineering Benefits

    Researchers from the Agricultural Research Service (ARS), working together with researchers from Iowa State University (ISU) and Brazil, have discovered soybean genes that are resistant to Asia soybean rust.

    After mapping the soybean genome, the researchers found that there were five areas, Rpp1, Rpp2, Rpp3, Rpp4 and Rpp5, that helped the soybean plant resist an ASR attack. Further research that included comparisons between resistant and susceptible cultivars led to the identification of the ASR-resistant Rpp4C4 gene in the Rpp4 region.

    Once they have identified and isolated ASR-resistant genes, researchers can either combine these genes into one line by the gene pyramiding process, or make a gene construct by recombining the selected genes by genetic engineering in the lab.

    Gene pyramiding is a selective breeding process where different specimens with the required genes are crossed until you can get all these genes in a single specimen.

    Making a gene construct is a much quicker process and so more preferred these days. In this type of plant genetic engineering, the combined gene construct is cloned to produce a good number of copies and these copies are then injected or inserted with a bacterium vector into the embryonic soybean plant tissue. The genetically engineered plants with the required genetic traits are then developed and cultivated.

    This way you have soybean cultivars that have several genes that are resistant to the Asia soybean rust disease. Proponents of this technology believe that widespread use of such genetically modified ASR-resistant cultivars will bring down production costs; fungicides may still be needed, but in smaller amounts. It will bode well for farmers, manufacturers and consumers as well as for the environment.