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EUROPEAN-SEED.COM I EUROPEAN SEED I 33 FUNGICIDECONSUMPTION Each season several sometimes up to 15 sprays with fungicides are needed to keep late blight under control. With 1400 tonnes of active sub- stance a year the Dutch potato sector is a leader in fungicide consumption and the late blight disease costs Dutch growers over 100 million euros in crop protection and losses every year. Global average losses due to late blight are estimated to be around 22 per cent. LIFE CYCLE OF THE LATE BLIGHT FUNGUS Late blight is caused by the oomycete pathogen Phytophthora infestans. It is notable for having both an asexual and sexual life cycle. P. infestans reproduces asexually predominantly and spreads via zoospores but in certain locations of the world the sexual cycle is dominant and there it spreads via oospores. The zoospores can travel easily on the wind when the weather is cool and moist and can rapidly infect neighboring fields and continue to produce more spores there. In the absence of the oospore stage Phytophthora infestans survives between potato crops as mycelium in infected tuber The oospores have a much tougher cell wall and can survive in the soil for years. TRADITIONAL PLANT BREEDING Genetic modification that remains within the species is termed cisgenesis as opposed to transgenesis in which DNA is used from a dif- ferent species or bacteria. Transgenic maize and soya beans with genes from bacteria and viruses have given rise to many questions and much debate over the past 20 years about the risks to humans and the environment. Cisgenesis avoids some of those objec- tions as the result is much closer to the outcome of conventional plant breeding. Haverkort By using cisgenesis we wanted to keep a link with traditional plant breed- ing. Cisgenesis is somewhat trickier and more expensive because selecting the right modi- fied plants is a little more difficult. In the course of the project the research- ers tracked down 15 resistance genes in wild potato species. Those genes enable a plant to recognise Phytophthora causing a rapid immune response on first contact so that the pathogen is unable to get a foot in the door. But resistance is never permanent. Organisms are constantly evolving and so new strains of Phytophthora could emerge over the years that even resistant plants are unable to cope with. The potato plant no longer recog- nises its attacker so the infection can take hold. Breaking through the plants immune system is a great deal harder however if it has multiple resistance genes. That is why the researchers created a chain of two or three different resist- ance genes and inserted them in the DNA of the potato cells. The plants that grow from these cells undergo extensive testing not just for their resistance to the disease but also to check that they are similar to the original vari- ety in all other respects. This method was used to create Phytophthora-resistant versions of three potato varieties Premire Dsire and Aveka. Field trials produced convincing results. This does not mean pesticides are completely redundant says Haverkort. It would be possi- ble to do without pesticides entirely but when the foliage turns yellow in the autumn levels of resistance are low too and Phytophthora could get an opportunity to attack. Then it is a good idea to spray the plants once or twice. It is also possible that Phytophthora will gradually evolve and therefore bypass one of the resist- ance genes that is another reason for spraying occasionally says Haverkort. There will always be a need to closely monitor developments in Phytophthora just as there will be for switching potato variants whenever Phytophthora looks like bypassing a resistance gene. You need plenty of substi- tutes on the bench so to speak the same potato variety but with a different combina- tion of resistance genes every time. In this way Phytophthora is given little opportunity to adapt to the new combination of genes. If it looks as if a resistance gene has been cracked that variant will not be used for a few years. The Phytophthora strains that cracked the resist- ance will gradually lose that property again. If the resistance gene is brought back into action in the field a few years later it will therefore be effective once more. Haverkort You can make sure that you retain control of Phytophthora and prevent your resistance genes from becom- ing worthless by monitoring the situation and alternating 15 resistance genes in various com- binations. IMPRESSIVE SIGHT I visited the trial fields and they were an impressive sight says Tanja van Oers the chair of the DuRPh supervisory committee and a senior policy officer in the Plant Supply Chain and Food Quality Department in the Ministry of Economic Affairs. You see the resistant potato plants growing with hardly any pesticides while the standard varieties die off. The ministry is very enthusiastic about what has been developed within DuRPh says Van Oers. It is a good example of a technique that is contributing to food security and sus- tainability and it can be applied using the existing table potato varieties. So you could make varieties resistant within a few years. This also fits in with one of the ministrys goals which is to reduce the use of pesticides. Sharon Dijksma the former State Secretary for Economic Affairs attended a talk by the researchers says Van Oers. She said then that she hoped the private sector would continue with the application of cisgenic techniques in producing resistant potato vari- eties. Van Oers The development phase was funded by the ministry. Now it is up to the pri- vate sector to take this further. The technology has advanced far enough to enable cisgenic potato varieties to be brought onto the market quickly. We want to hear from companies how they intend making use of these results. We can appreciate that Wageningen would like to continue with this research perhaps this will be possible in collaboration with the private sector. You could for instance consider fund- ing through the top sector system with the government supplying part of the funding but with the private sector taking the lead. But if cisgenesis is to become truly appealing to the private sector for example to potato breeding companies then it will need to lose the GMO genetically modified organism label says Robert Graveland head of RD at potato breeding company HZPC the largest producer of seed potatoes in the Netherlands. The company from the town of You see the resistant potato plants growing with hardly any pesticides while the standard varieties die off. ANTON HAVERKORT