A. Sunflowers reproduce their offspring with seeds, which is sexual reproduction. The common propagation method of grapes is cutting, which is asexual reproduction. A is wrong.

B, potatoes are propagated by stems of vegetative organs, and the common propagation method of grapes is cutting, which is asexual propagation. B is right.

C, potatoes are propagated by vegetative stems, which is asexual reproduction, and corn is propagated by seeds, which is sexual reproduction. C error.

D. Common propagation methods of peach trees include cutting. For vegetative reproduction, and sorghum uses seeds to reproduce offspring, which belongs to sexual reproduction, D error.

So choose: B.