Where do your carrots come from? They may be grown locally, but 50% of the world’s carrot seeds come from New Zealand. Crop breeding is more than just collecting seeds. In controlled conditions male and female lines of carrots are interbred to produce hybrid offspring. These seeds are sold around the world to farms that want carrots with known characteristics, instead of a genetic pot pourri. But wild carrots can cause trouble, by cross-breeding with the domesticated varieties and introducing undesirable traits.
To find out how big a threat this is, Asharp Godwin and colleagues examined the reproductive behaviour of both wild and cultivated carrots. They found that the wild carrots are always ready to reproduce, and it’s a problem that might grow as the climate warms.
At Massey University in New Zealand, Godwin and colleagues grew 360 carrots, half wild and half cultivated, under controlled conditions. The goal was to understand what triggers the plants to flower, because flowering is when the genetic mixing happens. One common trigger is the cold.
In nature, plants often use a cold period as a trigger so that when it passes, the plants flower for spring, a process called vernalisation. Some of the plants got the full twelve weeks, some got just four weeks and some no cold at all. The team were aware the age of the plants could affect their responses, so the plants themselves were a mixture of 4-week youngsters, 8-week adolescents, and 12-week mature plants.
Combining the different plants with the different “winters” allowed the scientists to build up a picture of how the plants react to the seasons. They measured everything – how many plants flowered, how quickly they flowered, how many survived the winter, and even counted the flowers and branches on each plant.
Godwin and colleagues found that the wild carrots were survivors, with survival rates ranging between 94.9% and 100% over winter. If the wild plants survived, they flowered, with the team recording a 100% flowering rate across all the treatment combinations. In contrast, the cultivated carrots had only a 66% to 98% survival rate. Another difference was in the flowering.
The mature carrots flowered if they had 12 weeks of vernalisation. 87% of the adolescent carrots flowered with 12 weeks of vernalisation, and even 8% of the juvenile carrots flowered with the same treatment. But none of the other cultivated carrots flowered. There had to be twelve weeks of cold.
The results show that wild carrots pose a serious threat to hybrid seed production. If your cultivated carrots are capable of flowering, then wild carrots definitely are. Crossing of genetic material between the two populations poses a threat to growers aiming to supply the best quality seeds to farmers. Godwin and colleagues add that milder winters will lead to even more survival of overwintering wild carrots.
They conclude that control of wild carrots is critical for success. “[W]ild carrots have a more competitive advantage over male lines of cultivated carrots in attracting and rewarding pollinators due to the development of more umbels, branches and taller floral stalks.” Therefore they argue that wild carrots should be weeded as soon as possible after winter, to ensure seed quality in cultivated crops. This isn’t just in New Zealand, but anywhere where carrots are grown to supply seeds.
Godwin A, Pieralli S, Sofkova-Bobcheva S & McGill C. 2025. Natural genetic adaptation allows flexible reproductive behaviour: the case of wild carrot (Daucus carota L. subsp. carota) vs cultivated carrot (Daucus carota L. subsp. sativus). Crop & Pasture Science 76, CP24320. https://doi.org/10.1071/CP24320
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