Resistant or immune to grafting; incapable of being successfully grafted onto another plant or tissue.
From graft (from Old French grafte) combined with proof (from Old French preuves, meaning tested or verified). The compound describes something that has been 'tested' against grafting.
Plant breeders discovered that some rootstocks are naturally graftproof—the biochemistry just rejects foreign tissue—which taught us that incompatibility exists even in plants, similar to organ rejection in humans.
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