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Potatoes: what are the threats they face and what can we do to save our spuds?
Image by Paul & Kelly Flickr. (CC BY-NC 2.0)
Last year farmers in the UK harvested almost 6 million tonnes of potatoes. But farmers and researchers are concerned that threats including diseases and climate change pose a serious risk to the amount of potatoes we will be able to grow in the future.
Late blight is a fungal-like disease that thrives in wet weather. UK farmers have to spend £20m a year on fungicides to contain the disease. Fields sometimes need to be sprayed as often as 15 times in a growing season which is not only expensive for farmers, but also environmentally unsustainable. Climate change is predicted to impact on potato production and worsen current challenges such as water availability and loss of top soil.
What will reductions in summer rainfall mean for potatoes in the UK? What are the tools available to combat blight and other diseases? Is it going to be possible to create potatoes that are resistant to late blight? What would changing potatoes in this way do to other potato characteristics; would they taste the same? Would they make good chips?
On Monday 22nd June 2015 our expert panel answered your questions.
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JJ: "When potato plants are regenerated from tissue culture, as inevitably occurs during making a GM potato, variants can arise through various poorly defined mechanisms that result in a line that differs from the parental variety in taste, texture, size and also yield. Therefore, we select for 100s of 'independent GM events', each of which has to be tested for whether they properly resemble the parental variety in all characteristics except those for which they were modified. Once multiple lines have been compared, the best is selected, partly in order to ensure that there are no unintended consequences in the released line."
25. "How long would it take for the thing that causes late blight to overcome what ever resistance a potato has to it? Will it be like antibiotic resistance and we'll end up creating more of a problem in the future?" (Jose Rincon)
DC: "Good question - this is critical to the long-term success of conventional or GM methods as Phytophthora infestans is a diverse and evolving threat. If the deployment is planned carefully the lifespan of any resistance gene will be extended and we should avoid the ‘boom and bust’ of the past. Epidemic modelling in different deployment scenarios has shown, for example that it is better to mix varieties in strips in the same field than to plant alternate fields with resistant and less resistant crops (reference). It is important to understand the pathogen population which is why we study this at the James Hutton Institute on a British (work sponsored by AHDB Potatoes) and European (see www.euroblight.net) scale. Poorly planned resistance use could, in theory, make things worse but a strategic approach using optimal combinations of resistances would benefit the industry."
AD: "For efficient water use you have to apply the right volume (not too much or too little) of water at the right time (not too early not too late). Irrigation systems should be designed to apply the desired volume uniformly across the field. Sprinklers are mainly affected by pressure and wind while drip systems are more sensitive to clogging and pipe damage. Both have pros and cons, and both can be efficient if well designed, maintained and matched with good irrigation scheduling. Water use can also be reduced using drought/ scab tolerant varieties. Options such as the use of treated waste water and rain harvesting should also be considered."
23. "Blight resistant genes have been available for years, especially in Hungary during the Cold War. So we know if it alters taste. The price of potatoes will increase since many cannot grow them at a profit and supplies will reduce. Your comments please." (Robin Upton)
GB: "You are referring to the ‘Sarpo’ blight resistant cultivar, the origins of which are not well known. Most late blight genes deployed in breeding come from wild species. These genes are ‘introgressed’ into varieties by crossing, an extremely inexact method which usually means that many undesirable genes are introgressed as well - a phenomenon known as ‘linkage drag’. Wild potato species do not generally produce edible tubers and many of them produce high levels of glycoalkaloids and other noxious compounds. Therefore there is a tendency for varieties with high levels of late blight resistance from wild species to have poor taste and quality. This of course is one of the reasons for using GM to introduce a single blight resistance gene from a potato species and nothing else."
JJ: "When a late blight spore lands on the leaves of a susceptible host under conducive conditions (with high humidity, and not too hot), the spore germinates and the infection starts. Within 4-6 days of growth on the host, the infection produces spore-releasing sporangiophores that carry sporangia. Spores can be blown 50 miles in the wind to propagate the disease-causing organism. It’s not clear how this could be mitigated in a crop grown outside in wet-and-windy UK."
GB: "There have been attempts to use 'push-pull' and 'trap cropping' (using specific plants to repel or attract pathogens away from the main crop) to prevent insects from damaging potato crops. The best example is Colorado Potato Beetle (CPB), not really a problem in UK right now, where winter wheat has been used as a buffer against CPB. Having said that, researchers found that a physical barrier (wheat, rye) was more effective than a chemical one (tansy, wormwood). In the UK companies have been trying to use species very distantly related to potato to induce the hatch of nematodes in the soil but I don’t think this has been deployed commercially as yet."
20. "According to the latest 7th Edition of McCance and Widdowson’s The Composition of Foods there would appear to have been a small fall in the nutrient content of potato. I would welcome any explanation that you would be able to offer in addition to variation in sampling or season." (Dr Alan Stewart)
GB: "Vitamin C levels in particular are known to be highly variable depending on variety, agronomy, cooking method, storage etc - in fact the factors influencing this are not well understood and we hope to do some research in this area in the next few years. I am very dubious about the apparent fall in Vit C and Folate – were they comparing the same variety in each case? I don’t think there is any real evidence that levels of these nutrients are falling significantly. Potato is still a very good source of these nutrients."
DC: "Many products have been tested but there is only one effective ingredient approved for organic use in Britain – various formulations of copper. Its use, up to the level of 6kg per hectare per year, is permitted on the basis of the major threat to potato crops from blight. Copper does not have a good environmental profile compared to ‘conventional’ fungicides, but its approval is presumably on the basis of its ‘traditional’ use since the 19th century. Resistance incorporated into the potato plants themselves would offer a more environmentally friendly approach to controlling late blight under organic standards."
AD: "It depends largely on your location and on the emission scenario (lots of uncertainty here) used in the climate change projections. Of course changing the climatic conditions in which current diseases develop might encourage or limit their spread. These changes could be humidity, temperature or both combined. It is also important that these changes occur in the right time (period of disease development). However, it is expected that some diseases might disappear or become less relevant, and others might find the new climate optimal conditions to develop. Note also that the micro-climate created by increasing the frequency of irrigating with overhead systems could itself create a favourable environment for late blight (or other disease) if not well managed and controlled."
JJ: "The short answer is, yes, blight is the biggest threat in the UK, and the rest of the world, though cyst nematodes are also important (see Q3). In the humid subtropics, bacterial wilt caused by Ralstonia can be a problem, and there are also many viruses transmitted by insects that reduce yield.
"The weather? Potatoes need plenty of water, so water shortages can also reduce potato yields. However, because of blight, potato production is harder in the moister western side of the UK. If we could control blight, and move production west, we might reduce the water footprint of potato production."
16. "Animal farmers are using increasing amounts of trace elements including selenium, cobalt and zinc to keep their animals healthy, aid growth and immune function. Additionally biosolids contain manganese and other trace elements which might be provided in excess. What influence, if any, could these or other nutrients that are added to the soil influence the risk of late blight and other problems developing in this precious crop." (Dr Alan Stewart)
GB: "I’m a bit out of my comfort zone with this one! I think we know very little about how the use of trace elements and biosolids may impact on how potato plants grow, or how they may affect the reaction of potato to diseases. One for future research! Farmers do have to be careful about using water from natural water courses on potato crops as sometimes they can harbour bacterial pathogens that affect potato. In some cases it has been possible to trace potato pathogens in river water back to discarded tomatoes that were infected."
JJ: "There are no technologies currently available for this. However, the emerging science of investigating the benign organisms that associate with plants – 'the microbiome' – in particular the microbiome associated with roots, may reveal bacterial strains that reduce losses to, for example, cyst nematodes. It’s too early to be sure that this will be helpful, but already companies are being started to develop new products on the basis of this kind of idea, for example (www.agbiome.com)."
GB: "Growing potatoes is quite a conservative business, with many long-established varieties topping the UK list in terms of the area on which they are grown. For example, Maris Piper, an old UK variety, still tops the list with ~15% of the total area and the relatively ancient King Edward is still in the top 10! Other top varieties are ones like Markies, Lady Rosetta, and Hermes, all important for the potato processing industry. Hardly any of the varieties grown in the UK have any resistance to current late blight populations, the disease being controlled by spraying at 1-2 week intervals in the summer months. There is some nematode resistance in UK varieties, mainly against the so called ‘golden nematode’. This situation highlights the need for late blight resistant cultivars (or varieties), to reduce the reliance on sprays. With climate change we are also starting to think about resistance to aphid-transmitted viruses, which will become more of a problem if the climate warms up a degree or two."
GB: "The prospects for such developments are not good. A potato-tomato fusion (TomTato) was released a couple of years ago but this was not a true hybrid. It was achieved by grafting the stem of a tomato onto the root of a potato, in fact such ‘grafts’ are used a lot for research purposes. However you cannot cross a potato with an aubergine or a tomato using normal breeding practices to produce a true hybrid. It is possible to use cell culture techniques to make such fusions but these are usually unbalanced genetically and not used for food production. The potato tuber is a storage organ so any hybrid would potentially suffer fruit quality issues due to the plant sending resources to the tuber."
JJ: "We are putting in resistance to potato late blight disease and to potato cyst nematode. The potatoes will also accumulate lower levels of reducing sugar and asparagine, which can make acrylamide after high temperature cooking, and they will also be less prone to damage caused by bruising. You can read more about the tuber quality traits at www.simplotplantsciences.com. The European Food Safety Authority has recently recommended minimizing acrylamide in the diet, at it potentially increases the risk of developing cancer."
GB: "Sweet potato is not actually a potato at all. It is a plant very closely related to the ornamental Morning Glory, and is not grown in the UK. Sweet potato certainly has its own disease threats but is not threatened by potato late blight."
AD: "It depends on your location and on the future projections. Generally speaking, areas that are currently too wet or too cold for potato production might (i.e. northern and western part of the UK) in the future as result of warmer and drier climate become suitable. Also in these areas, the length of the growing season (planting to harvesting) might become long enough for the plant to accumulate the needed dry matter for higher yield."
JJ: "There are already non-GM blight resistant potatoes such as Sarpo Mira, but these are currently not favored commercially (see here and also here). The Sarvari Research Trust continues to try to breed varieties that combine blight resistance with other desirable traits. They point out, with some justification, that they are under-resourced for this challenging task. Breeding is very important, but in my view, where other technologies such as GM can help, they should not be excluded."
Professor Jonathan Jones: "Eight to ten years from now; 2024 at the earliest. This year we will make the DNA constructs that carry the traits into the potato, and next year we will conduct our first field trial of the lines that emerge from this pipeline. We will spend at least three years identifying elite lines in which we have introduced all the traits we want, and in which the other desirable properties of the variety are maintained. In years three to six, we will gather additional data to verify the performance of the lines and gather data to seek regulatory approval for the new line. If after year six we can submit a dossier to seek regulatory approval, we might have approval two years later."
DC: "Yes – in theory this approach would work but to do it on a commercial scale would be very expensive and I do not imagine there would be an appetite for the extra area of glass or polytunnels required. The 'soft fruit' area of the UK is, for example, almost 10,000 hectares with a high proportion under cover. Now consider the visual impact of growing a further 121,000 hectares (current British areas of potatoes) under glass or plastic. Incidentally, the main advantage of covering the crop would not be to prevent contact but to manage moisture levels to prevent any spores from infecting the crop."
GB: "Flavour is a very complex trait and is quite far down the list of traits selected in potato breeding programmes. However, as most new potato varieties come from crosses between two older varieties you rarely get a horrible tasting potato! As a staple crop potatoes generally have a relatively ‘bland’ flavour although there are significant differences in how various varieties taste. Texture is very important in determining our overall sensory impression of a potato. Obviously how potatoes are prepared makes a big difference and some varieties have been bred for specific purposes- boiling, roasting, baking etc. Potato processing companies have very special requirements. Ultimately it comes down to the chemical composition of the tubers – the right amount of water, the right amount of starch and other sugars. Nowadays consumers are much more sophisticated and smaller bags of potatoes with particular characteristics are becoming very popular, especially as sales of larger bags of potatoes drop somewhat due to the overall drop in consumption of fresh potatoes in the UK."
5. "I've heard that summer rainfall is predicted to fall due to climate change, how will this affect potato production? Will it mean we have to use more irrigation? What will that mean for water security?" (Chelsea Snell)
AD: "Warmer and drier summers will mean higher water stress and lower yields for rain-fed potatoes. Irrigated crops will need more irrigation to cope with the rainfall shortage and to maintain the same yield. Rain-fed production/quality may decrease and become uncertain (large inter-annual variability), and economically non-viable, unless it’s shifted to irrigated production. In areas where water resources are scarce/not available, the viability of the farming business and the sustainability of the environment might be at risk. However, areas that are currently too wet might, in the future, become suitable for production."
Dr Andre Daccache: "Many spores and pathogens can be transmitted by water or encouraged by humidity. Plants irrigated with overhead (sprinkler) systems are more susceptible to foliar diseases (which affect leaves) than those irrigated with systems (i.e. drip/surface) where leaves remain dry and pesticides/fungicides are not washed away. Over-irrigation and water logging can suffocate plant roots and cause diseases such as powdery scab, blackleg or tuber cracking. On the other hand, irrigation is an effective method to control common scab disease, one of the main diseases affecting the UK potato industry. Therefore, irrigation can both spread and control diseases depending on how the water is applied (type of system and uniformity level) and managed (irrigation scheduling)."
3. "How serious is the threat? The original potato in South America was poisonous to humans. But plant breeding made it edible. So who could be against a bit more plant breeding, to combat late blight?" (FourMark)
Dr Glenn Bryan: "There are many serious threats to potato production. There are many pests and diseases that can destroy or otherwise damage potato crops. The best examples, from a UK perspective, are ‘cyst nematodes’, tiny worms that live on the roots, and late blight, the air borne pathogen that caused the Great Famine in Ireland. These problems are currently controlled by use of chemicals, but these are threatened due to changing environmental legislation. The deployment of plant (actually from a different type of wild potato) ‘resistance’ genes via GM technology is a potentially very powerful and benign technology for keeping one step ahead of the disease pathogen, that has been shown to work in field trials. This could have an impact in reducing the amount of chemical sprays needed on potato crops. Use of these genes via conventional breeding is possible but in an outbred crop such as potato, extremely slow."
DC: "Several fungal diseases infect potatoes, Alternaria (early blight) on the foliage and many that cause scabs or other blemishes on the tubers. These can be a problem for yield but below-ground problems are mostly a quality issue in the pre-packed fresh potato market. The principal ‘fungal’ problem is the destructive potato late blight pathogen (see Q1). P.infestans arrived in Europe a lot later than potato itself but has had the greatest impact of any plant disease. It prompted the famine in Ireland and other parts of western Europe and the ensuing socio-political upheaval and mass emigration.
"Since the first wave of disease in 1845 a series of pathogen migrations have occurred – each displacing the previous pathogen strain with more aggressive and damaging strains. In the drought year of 1976, for example, new strains of the pathogen were imported into Europe on potatoes from Mexico. Scientists are continuing to track the pathogens to support the best disease management practices. The most recent change is presented here."
Dr David Cooke: "Late blight is a disease caused by a moisture loving algal-like pathogen called Phytophthora infestans. Its airborne spores infect leaves, stems and tubers causing significant crop losses. Under optimal conditions on susceptible potatoes it can infect, produce new spores and spread with a few days. A few such disease cycles generate devastating epidemics on the foliage. Destruction of the leaves lowers tuber yield (because less sunlight can reach the crop) whereas tuber infection causes rotting and lowers quality. Fortunately there are many effective fungicides and some disease resistant varieties that allow the disease to be managed in most cases. The pathogen population is however dynamic; P. infestans has generated resistance to some fungicides and evolved to overcome some disease resistant varieties. The battle continues..."
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