Bold strategy to defeat potato blightAn innovative way to control potato late blight with fewer chemicals is being developed by Sainsbury Laboratory scientists based at the John Innes Centre on the Norwich Research Park. They plan to introduce different resistance genes from wild potato species into single potato varieties, helping to limit the spread of the disease. Potato late blight is highly contagious, and is the most important disease of potatoes in the UK and worldwide. It infects the plant under humid conditions, causing the tubers to rot and the leaves to die. The disease can be severe enough to wipe out entire crops, shown dramatically in Ireland in the 1840s, where late blight caused the infamous Irish Potato Famine. Until three decades ago, the disease was manageable using fungicides and potato varieties bred for resistance. But in the late 1970s, a big outbreak of the disease in the USA proved uncontrollable; late blight was back with a vengeance. Crucially, two different mating types of the disease were found for the first time – when they met, they crossed with each other and generated new strains that could quickly become immune to chemical sprays and infect resistant crop varieties. The approach taken by scientists in the Sainsbury Laboratory is different to that used by conventional plant breeders. Instead of introducing one major resistance gene into the variety, they plan to use a number of genes that, at the crop level, would work together to slow the progression of the disease across the field. The use of multiple genes, providing several different lines of defence, reduces the risk of the disease defeating a single resistance gene and devastating the whole crop. Using wild relatives of potatoes from South and Central America, some of which cannot be crossed with potato, the scientists are looking for the genes that will protect these varieties from late blight. Once they have found them, they plan to engineer these genes into a single commercial potato cultivar, with individual plants carrying different resistance genes. The theory is that a single crop would be made up of a variety of plants that are identical, except they would each carry one of a number of resistance genes. Overall, there would be at least five different resistance genes present in the crop; but they wouldn’t all be in every plant. This would make life much harder for the disease – even if it was able to overcome the resistance in one plant, the next one it tried to infect would have a completely different defence system to beat. The particular advantage for farmers is that the crop would be identical in all other ways. Similar approaches in crops such as rice have involved farmers planting different varieties within the same field, in an attempt to reduce the spread of disease. But although different varieties offer a range of resistance strategies, the final crop contains non-identical products, which might cause problems later, for example, during processing. As usual, the pace of discovery isn’t rapid. So far, the Sainsbury Laboratory researchers have discovered three genes they think might be useful. And as they have worked through a high proportion of the available material in European germplasm banks, hopes are high that varieties kept in American collections might contain new resistance genes. Once enough genes have been found, new varieties with multiple resistance to late blight might be a real possibility. © Dr Belinda Clarke 2003 This Article originally appeared as part of the "Science
on your Doorstep" series, published in the Eastern Daily Press
1st March 2003
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