The chestnut event Darling 58 was developed through Agrobacterium-mediated transformation of the American chestnut tree with vector p35S-OxO containing:

• the oxalate oxidase gene from wheat coding for an enzyme that helps the plant tolerate Cryphonectria parasitica. This enzyme has no direct fungicidal properties, but rather detoxifies oxalic acid (oxalate) produced by the fungus, preventing the acid from killing the chestnut’s tissues.
• an nptII gene cassette as selectable marker.

Darling 58 American chestnut has a single insertion of those two genes. The insertion did not result in any extraneous insertions of vector or other DNA, or deletions of existing DNA compared to the non-transgenic American chestnut isogenic line Ellis.

A preliminary screen for 24-mer sequence matches from the Agrobacterium tumefaciens T-DNA binary vector backbone showed no matches in Darling 58 (or T1 or T2 offspring), confirming that there were no insertions of DNA from this plant pest anywhere in the genome.