The correct answer is Sternospermocarpy. Seedlessness in grapes is a result of stenospermocarpy. A form of fruit set in grapes, where pollination and fertilization occurs and seeds form, but soon embryo abort. Berries, however, continue to mature and usually contain only rudimentary seeds (Thompson Seedless). The main reason stenospermocarpic seedlessness was not clearly understood up to now.