From wild crocus to fields of gold

Mystery solved – biologists in Dresden explain the genetic origins of the saffron crocus.

Saffron, the world’s most expensive spice, comes from the stigmas of saffron crocus flowers, Crocus sativus. For many farmers in Mediterranean countries, Kashmir, India, Afghanistan, Iran and Pakistan, saffron production is the main source of income, since the saffron crocus thrives in poor soils that can’t be used for agriculture.

The elusive spice can only be harvested when the flowers bloom, in autumn. Skilled pickers can collect between 60 and 80 grams of stigmas per day, and to yield one kilogram of saffron, between 150,000-200,000 individual flowers must be harvested by hand. The high price tag – up to €30,000 per kilogram – is seen as an attractive prospect by some and saffron is frequently adulterated with substances such as pollen from other flowers.

Flowering autotriploid Crocus sativus with orange stigmas as a source of the spice saffron, in front of DAPI‐stained metaphase chromosomes. Courtesy of Sarah Breitenbach.

But there’s a problem with saffron. The plant is a triploid hybrid – it has three sets of chromosomes, rather than two. The three chromosome sets can’t be distributed evenly during sexual reproduction, effectively making the plant sterile. Although saffron has been cultivated for more than 3,500 years, all the plants worldwide come from daughter bulbs – they are genetically identical. Without knowing saffron’s parentage, conventional breeding isn’t possible.

Controversy has surrounded debate around what the possible parents of the saffron crocus could be for nearly a century. Thomas Schmidt and a team of scientists from TU Dresden embarked on a program of research to solve this mystery, using sequencing and fluorescent in situ hybridisation (FISH) to resolve the composition of the saffron chromosome. Their research – and the answer to the mystery – is published in New Phytologist 222:4 and featured on the front cover.

Schmidt and colleagues have found that the saffron crocus is descended from one species: the wild species Crocus cartwrightianus, found in Greece. The TU Dresden team were able to demonstrate that the genomes of two Crocus cartwrightianus individuals with slight chromosomal differences were fused, thus concluding the search for the origins of this much-admired plant. “The saffron crocus is an autotriploid species arisen from the cross of genetically different cytotypes of the wild Crocus cartwrightianus,” said Thomas Schmidt.

This post contains elements of a TU Dresden press release.

Mike Whitfield
Development Coordinator
The New Phytologist Trust

Read the paper: Schmidt, T., Heitkam, T., Liedtke, S., Schubert, V. and Menzel, G. (2019) Adding color to a century‐old enigma: multi‐color chromosome identification unravels the autotriploid nature of saffron (Crocus sativus) as a hybrid of wild Crocus cartwrightianus cytotypes. New Phytologist, 222: 1965-1980. doi: 10.1111/nph.15715

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