The imposing 100-foot American chestnut tree that once dominated forests in the eastern U.S. may soon return, fortified by a new resistance to an Asian fungus. That blight essentially wiped out the tree during the past century, altering entire forest ecosystems. Scientists are releasing a sixth-generation hybrid this year for planting in several locations, confident that it will show the resistance of its hardy Chinese cousin.

The hybridization began decades ago, when breeders crossed the American and Chinese chestnuts to obtain the resistance genes.

The sixth generation should now have about 94 percent American character and “should have high resistance to the blight,”

If the sixth generation shows the required resistance, Fitzsimmons foresees chestnut trees being available in garden centers in about 25 years. And with oaks in decline because of gypsy moth infestation, the reemergence of hardy chestnuts would provide prodigious quantities of nuts for animals and valuable biodiversity.