The seedless grapes found in grocery stores are not the result of genetic engineering, but rather a naturally occurring genetic mutation that has been cultivated and refined by horticulturists over centuries. This characteristic originates from a change in the grapevine’s reproductive process, which was then intentionally exploited to produce fruit more appealing to consumers. The process of creating and maintaining these varieties involves a unique biological mechanism, specialized agricultural propagation, and careful management to achieve the large, uniform berries we expect today.
The Biological Origin of Seedlessness
The phenomenon that produces commercial seedless grapes is called stenospermocarpy, a trait where the fruit develops after fertilization, but the seeds fail to mature. The grapes are not truly seedless; they contain tiny, soft, undeveloped seed remnants that are unnoticeable when eaten. The process begins normally, with pollination and fertilization taking place, which is necessary to trigger the initial development of the fruit.
Shortly after fertilization, however, the developing embryo within the seed prematurely aborts its growth, typically within two to four weeks. This cessation of growth leaves behind a small trace or rudiment of the seed. This early abortion is linked to a specific change in the grapevine’s genetic code that regulates seed development. The presence of these rudimentary seeds is beneficial, as their initial development helps stimulate the surrounding fruit tissue to grow to a larger size than truly seedless fruits.
Growing New Vines Without Seeds
Since stenospermocarpic grapes do not produce viable seeds, new vines cannot be grown from the fruit in the traditional way. To ensure the seedless trait is maintained, growers rely entirely on vegetative propagation, a method of cloning the parent plant.
This technique involves taking hardwood cuttings, or canes, from an existing seedless vine during its dormant season. The cuttings are treated and planted to encourage root growth. Because the new plant is grown from a piece of the original vine, it is genetically identical to the parent, ensuring the resulting fruit will also be seedless. This cloning process allows growers to maintain the specific desirable traits of popular cultivars like Thompson Seedless across generations.
How Growers Maximize Size and Quality
While the genetic mutation makes the grapes seedless, the resulting berries are often naturally smaller than their seeded counterparts. To produce the large, plump, and uniform grapes consumers expect, commercial growers apply the plant hormone Gibberellic Acid (GA). The application of GA does not induce seedlessness, but rather enhances the size and shape of the fruit that is already genetically seedless.
Gibberellic Acid is a plant growth regulator that promotes cell elongation and division in the developing fruit. Growers spray the grape clusters with GA multiple times throughout the season, adjusting the concentration based on the desired outcome. An early application helps thin the cluster, creating more space for the remaining berries to grow and preventing crowding. Subsequent applications during and after the fruit set phase promote the increase in berry size and improve the overall uniformity of the cluster, making the final harvest commercially viable.