What percentage of Texas grown grape must be in a bottle of wine to claim Texas grown?

Wine labeling regulations in the US are wonderfully thorough and careful to assure that we can trust that labels are properly describing its contents. According to the Alcohol and Tobacco Tax and Trade Bureau, in order to say that a wine is from a specific appelation (country, State, or county), "at least 75% of the wine is produced from grapes grown in the place named."