Leave no crops behind: the case for cryopreservation

This year’s World Food Prize was awarded to two pioneers of crop diversity conservation: Geoff Hawtin and Cary Fowler. Both have been tireless champions of genebanks – including the eleven that are run by CGIAR centers – and they were the driving force behind the creation of the iconic Svalbard Global Seed Vault.

They have helped ensure that hundreds of thousands of crop varieties are safely conserved to give farmers and scientists options as they strive to grow nutritious food in a changing climate.

But not all crops are equal.

Storing plant diversity as seeds is relatively straightforward. Once they have been collected, sorted and cleaned of diseases, orthodox seeds can be dried out, packed in a sealed container and stored in a cold room (typically at -18°C).

Sadly, this technique does not work for many of the plants we eat. The list includes five of humanity’s ten most important crops – potato, cassava, sweetpotato, yam and banana – and several plants that both farmers and consumers would sorely miss if we could no longer grow them, such as cacao, coffee, coconut, apple, pineapple and orange, among many others.

Global annual production of crops that cannot be conserved as seed is estimated to be worth at least US$100 billion annually.

“Conserving crop diversity is work in progress. While there is still much to be done with seed crops, we need to make a special effort to secure the clonal and other crops that are harder to conserve.”

Geoff Hawtin, 2024 World Food Prize winner

The diversity of these crops has traditionally been looked after as plants and trees in the field. This on farm conservation will always be important. It ensures that the diversity is being used and consumed, and it allows the plants to continue to evolve to changing conditions. Due to the complexity of conservation of these crops, many genebanks also maintain their diversity in controlled experimental fields.

But it leaves the plants vulnerable to threats ranging from diseases and land use changes to cyclones and war.

Many collections have already been wiped out. In Togo, up to 37% of yam cultivars are believed to have been lost, and in Samoa, the national taro collection was destroyed by leaf blight.

An alternative, complementary approach is to conserve these crops as tiny plantlets in test tubes in genebanks, often under “slow growth” conditions.  This in vitro technique makes it possible to bring diversity together in one place, making it much easier to use in research and breeding.

However, the plantlets outgrow their test tubes after periods of one to three years and so must be frequently cut back and transplanted into new tubes. This means the samples are vulnerable if staff cannot easily access collections, as happened in many genebanks during Covid-19 lockdowns. It also means that they are under significant risk of contamination and/or mixture, due to intensive manipulation.

Due to these challenges, as many as 100,000 unique examples of crop diversity are at risk of being lost. We urgently need another solution to protect this diversity and ensure that it is available to future generations.

That solution is cryopreservation.

This technique, developed in the medical world, makes it possible to store plant material in liquid nitrogen at -196°C. The ultra-low temperatures halt cell metabolism, meaning that samples can be stored for decades and potentially centuries.

The material is stored safely in metal tanks, comparable to big thermos flasks, and is protected from the risks inherent to field or in vitro conservation. Cryopreservation also saves a lot of space – a tank the size of a wine barrel can hold thousands of samples.

And while there are significant up-front costs in getting the material into storage, there are major savings over the longer term. When compared to in vitro conservation, the initial outlay is recovered in between 5 and 15 years, depending on the crop.

Cryopreservation also provides a viable, efficient way of backing up the collections stored in genebanks. Rather than multiplying and replacing plantlets kept in test tubes as safety duplicates every year, the cryopreserved material can be duplicated just once and then kept in a cryo hub in another location.

That would offer these hard-to-conserve crops a similar level of protection to that which Svalbard provides for seeds. We would be able to recover and regenerate any lost material as happened when ICARDA’s collections were damaged by conflict in Syria.

CGIAR centers are already using cryopreservation to protect crop diversity, including:

• 4,500 varieties of potato and 550 of sweetpotato at the International Potato Center (CIP)
• 1,350 types of banana at the Alliance of Bioversity and CIAT
• 400 samples of cassava and 100 of yam at the International Institute of Tropical Agriculture (IITA)

This is as much a triumph of logistics as of technology. These centers have shown that it is possible to line up all the necessary pieces: a regular supply of liquid nitrogen; just-in-time delivery of good quality, clean plant material; and highly-trained teams to excise and store the samples.

The CIP team have developed detailed protocols and step-by-step guidance for potatoes, just as the Alliance of Bioversity and CIAT team have done for banana. Other CGIAR genebanks are following suit on cassava and yam.

A model approach has also been developed for partnering with communities to rescue and conserve crop diversity from farmers’ fields.

In a project funded by the UK Darwin Initiative, farmers’ sweetpotato varieties in Zambia and Mozambique are gathered for disease cleaning in a phytosanitary hub. The cleaned material is then multiplied up by national partners and disease-free planting material is returned to the farmers for planting, with the unique samples sent for long-term conservation in a cryo hub.

These examples show that cryopreservation can be successfully implemented and offers a long-term solution. The next step is to develop a global movement to scale up and protect hard-to-conserve crop diversity before too many more varieties are lost forever.

“CGIAR and others have shown that it is possible to translate the science of cryopreservation into something tangible. The next step is to roll it out across the globe. If we forget about cryopreservation, in the long run it will be much more expensive to conserve these crops.”

Stefan Schmitz, Executive Director of the Crop Trust

CGIAR centers have started this process by creating regional hubs known as Centers of Cryopreservation Excellence in Latin America (CIP), Africa (IITA) and Europe (Alliance of Bioversity & CIAT).

The Latin American hub has already hosted workshops to share expertise with more than 10 national partners, notably with Ecuador and Chile who have built their own national cryobanks since the beginning of the initiative. These two countries are already preparing cryopreserved samples of key crops for safety back-up at CIP. And in a project funded by GIZ and with the support of the Crop Trust, CIP recently unveiled a Cryo Vault in Lima, Peru with space for 70,000 safety back-up copies.

These are major steps forward, providing a model for international collaboration on cryopreservation.

But if we are to protect the diversity of hard-to-conserve crops around the world, we need to accelerate our efforts. A Feasibility Study in 2017 concluded that a “major global initiative is urgently needed to accelerate the development and implementation of crop cryopreservation”. More than seven years later, there remains a lot to do to realise that vision.

If we make the up-front investment now and work together as a community, we can protect thousands of crop varieties that are currently at risk of extinction.

To feed a growing population in a changing climate, we need all the options we can get.