The probationary aspect of the defendant's sentence for violation of the Georgia Controlled Substances Act was revoked on evidence that he sold marijuana to an undercover agent of the Georgia Bureau of Investigation. In his sole enumeration of error and in reliance upon Thornton v. State, 238 Ga. 160 (2) (231 SE2d 729) (1977), the defendant contends that the state should have been required to disclose the identity of an informer whose tip led the agent to him and who was present when the sale took place. See generally Roviaro v. United States, 353 U. S. 53 (77 SC 623, 1 LE2d 639) (1957). Held: