Hormones that "wake up" dormant tubers

IITA, iNew

Only patience could make yams ready for planting, until IITA researchers found that the same chemical solution used to make poinsettia plants shrink can make yams grow. They have identified a hormone that can “wake up” dormant tubers and accelerate propagation cycles of this vital food source.

Yam is the dominant food crop in West Africa, but unlike other staple crops such as cassava, most yam varieties can only be harvested once annually, even though they mature in as few as 8 to 10 months even teve. New plants are usually grown using seed yams from the previous year's crop but this takes time. After being harvested, the tubers lie dormant for three months before sprouting; and until the yams sprout, they won't grow into new plants. This awkward growing cycle means farmers all produce at the same time, glutting the market for a few months until the supply runs out and prices skyrocket.

While improved yam propagation methods exist, changing the growing cycle remains a challenge. Previous research showed that a growth regulating plant hormone called gibberellin could increase yam dormancy time for food storage purposes. So an IITA scientist, whose work is funded by the Japanese Ministry of Foreign Affairs, tried the reverse. He treated tubers with a solution containing gibberellin inhibitors, which was already manufactured for creating dwarf-sized versions of plants such as poinsettias and strawberries. The results were groundbreaking. Using select water yam varieties, he found that soaking the tubers for 24 hours reduced dormancy time from three months to just a single month.

“The power to induce sprouting in dormant yam opens up many possibilities,” says IITA yam physiologist Dr Hironobu Shiwachi. “This means we can change the growing period to meet market demand and can more easily disseminate improved varieties.”

With sufficient water supply, yam can now be grown twice a year. Additionally, field tests in Nigeria have shown that there is potential in certain areas for crop rotation with rice. Off season yam cultivation will help reduce market fluctuations, ensuring better prices for farmers and more yams for all West Africans.


March 2004