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Cryopreservation – Safeguarding crops for millennia

Crop diversity is vital to ensure our current and future food security. Yet, climate change, pests and diseases, unsustainable farming practices and many other factors are threatening this diversity. That’s why we need to safeguard it. Crops are often conserved through their seeds. But what happens to crops that don’t produce seeds or their seeds cannot be easily stored, such as banana, potato and cassava? They are conserved as collections of field plants or small plantlets in test tubes. While in the short term these conservation methods are very effective, in the long term they are expensive and time-intensive. If we want to safeguard these crops for hundreds or thousands of years, we need another conservation method: cryopreservation. Cryopreservation is the storage of biological material at ultra-low temperatures. So why do we want to store something at ultra-low temperatures? The main reason is that we want to store something for long times and for this we need to arrest all biological, physical and chemical processes that a plant is performing, and this we can do by exposing it at ultra-low temperatures. And the temperature that we are using is -196 °C, which is the temperature of liquid nitrogen. Cryopreservation is all about avoiding the formation of ice crystals. If you expose something to very low temperatures, a biological tissue will form ice crystals. Ice crystals are lethal because they are damaging membrane structures, so your cell will die. The solution is to withdraw enough water from the cell, so your cell water will not crystallize but form a glass. So first what we need is in vitro plants. In vitro plants are plants which are grown in glass test tubes. From these in vitro plants we have to excise the growing point, so it’s what we call scientifically the meristem. From a very small meristem of one millimeter we can regenerate a whole new plant. The second step is exposing the meristem to solutions with a very high concentration of different compounds so water is gently withdrawn from the cells. When we have these tissues with lower water content and plunge these in liquid nitrogen, we have extreme rapid freezing and this is also avoiding the formation of ice crystals. So then we have a tissue which is stored in liquid nitrogen undamaged. Bioversity International is extensively using cryopreservation to back up its collection of banana varieties at the International Transit Centre hosted at the Catholic University of Leuven, Belgium. With more than 1,500 banana samples, technically called accessions, the International Transit Centre is the world’s largest collection of banana germplasm. The number of samples that we have cryopreserved until now is 948, which represents about 65% of the collection that we have in vitro. During the last 15 years we have gained an enormous experience with cryopreservation and cryopreservation protocols, but also the management of such cryopreserved collections. The cryopreservation method that we developed for banana, which we call droplet vitrification, is applicable to many other crops like potato, sweet potato, cassava, taro, thyme. So now the collections at the International Potato Centre, they are using the same method as we have developed for banana. Crops like banana, potato, sweet potato and cassava are important for the food and nutrition security and livelihoods of hundreds of millions of people. Their global production reaches more than 1 billion tons a year and is worth at least 100 billion US dollars. For these crops there is no global backup and many existing plant collections are at risk, due to financial restrictions, natural disasters or disruption caused by conflicts. Our dream is in fact to establish a big CryoVault, where people from all over the world can place their backup, their cryopreserved material in a safe way. Infact this is a bit comparable to the Svalbard Vault where seeds from all over the world are conserved in a hole in the mountain in Svalbard, Norway. So we would like to establish something similar not for seeds but for cryopreserved tissues. By creating such a cryopreservation facility, we would be able to store crops like banana, like potato, like sweet potato. And by combining both facilities we can conserve all crops for future generations.

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