IELTS Reading: Sentence and Summary Completion

Banking on seeds

Why scientists freeze the world’s crops, and what freezing cannot save

A  For most of the history of agriculture, farmers did not grow a single standard version of a crop. Each region kept its own local varieties, known as landraces, which had been selected over many generations to suit particular soils, climates and tastes. Over the past century, much of that variety has disappeared from farmers’ fields, as growers have switched to a smaller number of high-yielding modern types. The loss matters because old varieties often carry useful traits, such as tolerance of drought or resistance to a particular disease, that plant breeders may one day need. A modern variety that fails when a new pest arrives might be rescued by crossing it with a forgotten relative. Gene banks exist to make sure that such relatives are still available when that day comes.

B  The basic method is surprisingly simple. Seeds are cleaned, dried until they contain very little water, sealed in airtight packets and stored in cold rooms. For the majority of crops, whose seeds are described as orthodox, drying and cooling slow down the chemical processes of ageing, so a sample that might last only a few years on a shelf can remain alive for decades. Storage is not, however, a matter of locking the door and walking away. Staff must test each sample at intervals by trying to germinate a few of its seeds. When too few of them grow, the variety has to be planted again in a field or greenhouse to produce a fresh batch, a process known as regeneration, which is slow and costly.

C  The idea of collecting crop diversity on a large scale owes much to the Russian botanist Nikolai Vavilov. In the 1920s and 1930s he led expeditions across several continents and built up one of the largest seed collections in the world at his institute in Leningrad, now St Petersburg. The collection faced its greatest test during the siege of the city by German forces, which lasted from 1941 to 1944 and caused mass starvation. Staff at the institute hid part of the collection and took turns guarding it. Although they were surrounded by sacks of rice, wheat and other edible seeds, they refused to eat them, and several died of hunger. Vavilov himself did not live to see the end of the war: he had been arrested by the Soviet authorities and died in prison in 1943.

D  The best-known gene bank today was designed for a different kind of emergency. The Svalbard Global Seed Vault, which opened in 2008, is cut into a mountain on a Norwegian island in the Arctic, and its seeds are kept at minus 18 degrees Celsius. It does not breed or regenerate plants, and it does not decide who may use the seeds. Instead, it acts as a backup store for other gene banks, which send duplicate copies of their samples and keep ownership of them; only the depositor can ask for its boxes back. The site was chosen partly because the surrounding permafrost, ground that stays frozen all year, was expected to keep the seeds cold for some time even if the electricity failed.

E  For several years the vault was a precaution that nobody needed. That changed in 2015, when it received its first request for a withdrawal. The International Center for Agricultural Research in the Dry Areas, known as ICARDA, had kept a major gene bank near Aleppo in Syria, but the civil war had forced the centre to move its work to Lebanon. Using the copies it had sent to Svalbard, ICARDA was able to grow its collection again in Lebanon and Morocco, and it later returned fresh duplicates to the vault. The vault itself has also had to adapt. In 2017, after an unusually warm Arctic winter, meltwater entered the entrance tunnel. The seeds were not affected, but the tunnel was later waterproofed: even a store built for disasters is not immune to a changing climate.

F  Freezing has limits that no engineering can remove. Some plants produce what are known as recalcitrant seeds, which die if they are dried, so they cannot be stored in the usual way. Oak, avocado and cocoa are among them. For such species, researchers are developing cryopreservation, in which the tiny embryo is cut from the seed and stored in liquid nitrogen, but the method has to be worked out species by species and success remains uneven. A broader debate concerns what storage actually preserves. Critics argue that a seed held in a freezer stops adapting, while varieties grown year after year in farmers’ fields continue to evolve alongside new pests and climates. Most specialists now appear to see the two approaches as complements rather than rivals, though how funding should be shared between them remains unresolved.