American chestnut (Castanea dentata) is a native keystone species that was
nearly eradicated by chestnut blight caused by the fungal pathogen,
Cryphonectria parasitica. A new approach to producing American chestnut
trees with enhanced blight resistance is through Agrobacterium-mediated
transformation. This report describes the progress towards producing a
blight-resistant American chestnut tree.

The transgenic American chestnut ‘Darling4,' which expresses a wheat
oxalate oxidase gene, exhibited an intermediate blight resistance. It was
found to be more resistant than American chestnut but less resistant to
Chinese chestnut (Castanea mollissima), the source of the resistance genes.
Enhanced resistance was first observed in an assay of young chestnuts grown
indoors. It was then confirmed with traditional stem inoculations on
field-grown trees.

Pollen from ‘Darling4′ were also used to produce transgenic T1 seedlings.
The T1 seedlings expressed the enhanced resistance trait. This is vital for
propagation and development of transgenics since outcrossed transgenic
seedlings have several advantages over tissue-cultured plantlets. These
advantages include increased genetic diversity and faster initial growth.

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