Transgenic crops are developed by introducing foreign genes into a plant's genome to confer desirable traits. Gene silencing techniques like RNA interference are used to modify gene expression in transgenic plants, often to reduce the expression of specific genes. Cytoplasmic male sterility (CMS) is a maternally inherited trait that prevents the plant from producing viable pollen; it is a crucial tool in hybrid seed production and can be engineered or used in conjunction with genetic modification to facilitate cross-pollination in transgenic development. Budding and grafting, however, are traditional vegetative propagation methods and do not involve genetic modification to create transgenic organisms.