RE SEARCH Salt tolerance studied in depth ‘E gyptians have to dig deeper and deeper to reach the much-needed water for their desert potatoes. In doing so, they are now almost drawing sea water from the salt layers hundreds of metres below the earth’s surface. According to the Food and Agricultural Organisation (FAO), the groundwater of 800 million hectares of agricultural land worldwide is too salty. Salinisation is also on the increase in the coastal areas of Europe, sometimes without people even noticing it. This is why the cultivation of potatoes has stopped in some regions’, Heselmans tells us. ‘Potatoes don’t really like saline soil. In agricultural areas where the soil is turning saline, the cultivation of potatoes has been replaced by a cereal such as barley. This is a crop that is doing very well on saline soils.’ Testing started in time And yet, potatoes may grow in saline soil and even come to full development with salt water. This expectation is hidden in the breeding, Heselmans explains. And this is exactly what C. Meijer B.V. has been doing for years. The adaptability of varieties to stress factors such as drought and salt has been high on the agenda of Meijer’s breeding programme for many years. ‘Already by the late nineties, we’d started testing young stock in the Spanish city of Seville. The early testing in this environment has produced a lot of knowledge about stress tolerance in general. Meijer is now reaping the benefits with varieties such as Melody, Orchestra and Musica. Trials in the province of Zeeland in the Netherlands have also shown that these varieties have a high salt tolerance. No seepage to order Together with the Provincial Executive and the Southern Organisation for Agriculture and Horticulture (ZLTO), Meijer started trials around the towns of Zierikzee and Kerkwerve in 2009. Heselmans: ‘There are plots here that are confronted with WHAT DOES TOO MUCH SALT DO TO THE POTATO PLANT? The researtch article ‘Updating the knowledge on salt tolerance of agricultural crops’ by Alterra Wageningen University provides information about the relationship between salt in the root zone, the crop growth and the crop yield. For example, salt in the root zone of plants such as the potato can lower the absorption of water. The salts increase the osmosis in the roots so they have to ‘work harder’ to absorb the water. Because the water absorption is slower, the stoma closes more quickly, which results in lower yields. Moreover, the plant can poison itself by taking up too much sodium and by disruption of the ion balance. It can also cause a displacement of important minerals. For example, too much sodium causes a shortage of potassium. This effect can be observed by visible burns at the leaf edges. The full report can be downloaded from the Wageningen University Library website www.wageningenur.nl/ library. The salts increase the osmosis in the roots so they have to ‘work harder’ to absorb the water. saline seepage. At a depth of approx. 2 metres, the water is half as salt as seawater itself. This was calculated by Agrowa soil specialists. If there is a shortage of rain, the capillarity of the clay soil can cause the seepage to rise and reach the root zone of the potato plants. To test varieties on these locations it is, of course, a good idea to actually run trials. The problem is, however, that you can’t order the seepage to come up. And just in that first trial year we had a great deal of rain during the growing season. When there’s enough water from the sky, the seepage water won’t come up and you can’t measure any influence of salt on the potato plants. In 2010, though, the growing season was dry and we definitely saw the effects.’ Tolerance in black and white Already by the late nineties, C. Meijer B.V. had started testing young stock for salt tolerance in Spain. In the photos that Heselmans showed during the WPC study meeting, the differences are black and white. A variety such as Melody remains as green as grass and the conventionallygrown variety next to the Melody shows dying haulm. ‘However, it’s not only seepage water that can hinder the 34 Potato World 2013 • number 4 Pagina 33
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