The roots then continue to send up shoots that are once again attacked by the blight and die back before they reach maturity, repeating the cycle.
[4] Chestnut blight damages trees by producing oxalic acid, which lowers the pH in the cambium and kills plant tissues.
[13] Presence of the transgenic oxalate oxidase gene in the genome of the American chestnut has little effect on photosynthetic or respiratory physiology.
Infection experiments on cut leaves show that the lesion sizes can be reduced to around or below the level of the blight-resistant Chinese chestnut, suggesting that the potted plant may be resistant too.
[15][16] In 2014, SUNY ESF reported that the "Darling4" transgenic event produced an intermediate level of resistance between American and Chinese chestnuts.
[11] In January 2020, the researchers submitted a deregulation petition for the Darling 58 variant, with a public comment period ending October 19, 2020.
[20] In 2022, SUNY-ESF scientists reported that a different promoter, win3.12 from the eastern cottonwood, allows the expression levels of OxO to remain low in basal conditions, but increase under wound or infection.
In laboratory bioassays, win3.12-OxO lines showed elevated disease tolerance similar to that exhibited by blight-resistant Chinese chestnut.
[9] The SUNY ESF is continuing to seek federal approval to distribute seeds to the public without the support of TACF.