|February 06, 2020|
After 2,000 years, these seeds have finally sprouted
|Their names are Adam, Jonah, Uriel, Boaz, Judith, and Hannah, and their ages are---well, actually, this one's a bit complicated.|
Adam, Jonah, Uriel, Boaz, Judith, and Hannah are date-palm trees, and although they were all planted in recent years, the seeds from which they germinated all came from ancient archaeological sites. These seeds, according to radiocarbon dating, were about 2,000 years old. They had waited two millennia to sprout.
The seeds of Judean date palms turn out to have remarkable longevity. A team led by Sarah Sallon, which planted these six trees, first tried in 2005 to germinate a 2,000-year-old seed from the ancient fortress of Masada. To the surprise and delight of Sallon and her colleagues, it sprouted, and they named that first date-palm tree Methuselah, who in the Bible lived to the age of 969.
"I was so not expecting it," says Sallon, a doctor at Hadassah Medical Center who got interested in date palms as medicinal plants. At the time, the team didn't even think to take basic measurements, such as seed weight or size, for comparison with modern date seeds. So after the success of Methuselah, they decided to try again, but more systematically. After all, was Methuselah a fluke, or were lots of date seeds viable after 2,000 years?
An archaeologist at the Hebrew University of Jerusalem allowed Sallon to sift through dusty boxes of plant material recovered from some of Israel's most famous archaeological sites. She found plenty of seeds for her purpose. "They were in all various stages of disintegration," Sallon says. "But some were in beautiful condition." She picked 32 of the best-preserved seeds, and her collaborator Elaine Solowey planted them at a kibbutz in southern Israel. Solowey soaked the seeds in water and applied commercial plant hormones and fertilizer, but the protocol for planting them was essentially no different than for modern seeds.
Five of the six seeds that ultimately sprouted came from either Masada, the site of a famous siege in 74 b.c. that is said to have ended with the mass suicide of Masada's defenders, or the Qumran Caves, best known as the site of the Dead Sea Scrolls. (A sixth came from caves at Wadi Makukh.) At 2,000 years old, the seeds are in fact contemporaries of these ancient events. Around the time Romans were laying siege to Masada and the Dead Sea Scrolls were being written, these seeds were being formed.
"It's quite remarkable this team of researchers managed to germinate seeds of that age," says Oscar Alejandro Pérez-Escobar, who studies ancient dates at the Royal Botanic Gardens, Kew. The fact that the team has done it not just once but now seven times suggests that ancient seeds could be used to resurrect genes that disappeared after thousands of years of breeding. "These ancient seeds might represent lost genetic diversity we don't see any more," Pérez-Escobar says. As date-palm growers adapt to climate change and battle pests and diseases, they might want to tap into the pool of ancient genes hidden in archaeological archives.
Why date-palm seeds can remain viable for so long, no one is quite sure. The seeds are physically tough and, because they are adapted to the desert, especially tolerant of drying out. But Sallon also points to the environment where they were found, near the Dead Sea. The Dead Sea is the lowest place on Earth's land. That means it has an especially thick layer of atmosphere to protect from cosmic radiation that could damage the seeds.
To understand how Adam, Jonah, Uriel, Boaz, Judith, and Hannah are related to more modern date palms, the team also analyzed genetic markers from the seedlings. The seedlings were genetically quite different from one another. Methuselah and Adam were most closely related to eastern varieties now found in the Arabian Gulf; Hannah and Judith to modern Iraqi varieties; and Uriel, Boaz, and Jonah to modern Moroccan varieties. The ancient seeds were also bigger and heavier than modern varieties.
Sallon helped name the seedlings. After Methuselah, she decided to continue with the biblical theme. Adam sprouted in the fall, around Rosh Hashanah, the Jewish new year, which celebrates the creation of the world and of Adam and Eve. She originally named the tree Eve, but switched to Adam after genetic markers revealed that it was a male tree. Judith came up a few months later, around Hanukkah, and was originally named Judah for the hero of the Hanukkah story, Judah Maccabee. Two more seedlings germinated around the spring harvest festival of Shavuot, when the Book of Ruth is traditionally read. So Sallon named those trees after Ruth and Boaz, Ruth's second husband---until genetic analysis revealed that Ruth was also male. So Sallon changed the name to Uriel, after, this time, her own son.
Methuselah is now mature enough to produce pollen, and he's actually become a father. Solowey used him to pollinate a modern female, and they made dates. The two female date palms from ancient seeds, Judith and Hannah, have not yet reached sexual maturity, so no ancient date fruits have been resurrected yet.
And even when they do, Sallon explains, the fruits they bear are unlikely to be identical to the ones that people grew and ate 2,000 years ago. Once growers found a date palm with all the qualities they liked, they likely kept "cloning" that single palm by taking cuttings. Farmers do the same thing today with apple and pear varieties. Sexual reproduction---crossing a male and female tree---scrambles genetic lineages and introduces uncertainties. It's the same reason an apple seed from a Pink Lady at the grocery store is unlikely to yield perfect Pink Ladies when planted in your backyard. Ancient DNA can be resurrected, but re-creating the exact taste of an ancient fruit would be much harder.