Knowledge of the genome of Phytophthora makes it possible to identify potato plants which are resistant to the pathogen much more quickly. To do so scientists use not the pathogen itself but the bacteria combined with a piece of Phytophthora DNA.
Plants do not make it easy for fungi and oomycetes (like Phytophthora) to penetrate their defences. In order to get in, the pathogens use hundreds of different substances. A plant can often prevent an infection by detecting one of these substances. Such a plant is resistant, and the gene that recognises the relevant substance is called a resistance gene.
Plant breeders have been looking for resistance genes in potato plants for more than a century. Their task has been made much easier now that scientists have mapped exactly which substances Phytophthora needs to infect plant tissues.
Detecting resistance genes
For this purpose, scientist Vivianne Vleeshouwers deploys collections of bacteria which comprise the harmful compounds (effectors) of Phytophthora. Injecting them into a potato allows her to see within a few days whether the plant will exhibit an immune response, shown by the plant developing brown spots in the location where the bacterium was injected. “This allows us to search for resistance much faster than before, when we applied Phytophthora to leaves. The results were far more difficult to interpret then, as many plants can be resistant in a variety of ways, some making them completely, and others only partially, resistant. Now we can immediately see which type of resistance we are dealing with.”
Professor Hermsen found an interesting resistance gene in a wild plant in the 1960s, which could not interbreed with the potato. It took thirty years of cross-breeding to get the gene into the potato by way of other plant species. “Our technique allowed us to find the same gene in a plant that does interbreed with the potato,” Vleeshouwers underlines. “This knowledge could have saved thirty years in the creation of new resistant potato varieties.”