Cary Fowler once helped build an Arctic vault to save the world’s great variety of crop seeds from extinction. Now, as the State Department’s global envoy for food security, he is trying to plant a new seed in U.S. foreign policy.

Instead of urging developing countries to grow only huge amounts of staple grains, like maize, as American policy has done for decades in Africa, Mr. Fowler is promoting a return to the great variety of traditional crops that people used to grow more of, like cowpeas, cassava and a range of millets.

He calls them “opportunity crops” because they’re sturdy and full of nutrients.

The effort is still in its infancy, with a relatively tiny budget of $100 million. But at a time when climate shocks and rising costs are aggravating food insecurity and raising the risks of political instability, the stakes are high.

Mr. Fowler’s boss, Secretary of State Antony Blinken, said this week at the World Economic Forum in Davos that the idea could be “genuinely revolutionary.”

Traditional crops are more nourishing for people who eat them and for the soils in which they are grown, according to Mr. Fowler, and they are better at withstanding the wild weather delivered by climate change. The problem, he says, is that they’ve been ignored by plant breeders. His goal, through the new State Department initiative, is to increase the agricultural productivity of the most nutritious and climate-hardy among them.

The initial focus is on a half dozen crops in a half dozen countries Africa.

“These crops have been grown for thousands of years in Africa, Mr. Fowler, 74, said in a recent interview. “They’re doing something right. They’re embedded in the culture. They really supply nutrition. If they have yield problems or other barriers to commercialization, frankly, by and large, it’s because we haven’t invested in them.”