Cross-pollination is the transfer of pollen between two different plant varieties or species. This process often raises a question for gardeners: Does the fruit currently growing change immediately if it receives foreign pollen? The answer is complex, depending entirely on the plant’s anatomy and the specific tissues that form the edible part of the fruit.
The Genetic Origins of Fruit Components
Fruit develops primarily from the plant’s ovary wall, which is genetically identical to the parent plant. This surrounding fleshy material, known as the pericarp, is composed entirely of maternal tissue. Because the pollen only contributes half the genetic material to the next generation, it cannot alter the genetic makeup of this existing maternal tissue.
The seed, however, is a different structure entirely, as it is the result of fertilization. Inside the seed is the embryo, which contains the new genetic hybrid that would grow into a new plant if planted. The seed also contains the endosperm, a nutrient-rich tissue that feeds the developing embryo.
For most fruits like tomatoes, peppers, or berries, the edible portion is the maternal tissue, which is genetically protected from the foreign pollen. This is why a cross-pollinated tomato will still taste and look like a tomato of the parent variety.
Immediate Changes Caused by Foreign Pollen (Xenia and Metaxenia)
While the maternal tissue is generally unaffected, there are two distinct phenomena where the pollen’s influence appears immediately in the current fruit or seed. The first, and most commonly observed, is known as Xenia, which describes the direct effect of foreign pollen on the endosperm or embryo.
Corn (maize) provides the most striking example of Xenia because the edible part of the kernel is the endosperm. If a white sweet corn plant is pollinated by a field corn variety with yellow or purple kernels, the resulting kernels on the current cob will immediately show patches of the foreign color or texture. The genetics carried by the foreign pollen directly influence the endosperm tissue, changing the color or converting a sweet kernel to a starchy one in the current season’s harvest.
The second, much rarer phenomenon is Metaxenia, the direct effect of foreign pollen on the surrounding maternal fruit tissue. Unlike Xenia, this effect is hypothesized to be hormonal, triggered by the growth of the newly fertilized endosperm and embryo, influencing the development of the fruit flesh itself.
The date palm is the classic example of Metaxenia, where the pollen source influences the size, shape, and time of fruit ripening. Different pollen varieties can cause the fruit to mature days or weeks earlier or later, a change that is purely physiological rather than genetic. In these specific cases, foreign pollen does affect the fruit they are growing right now.
Practical Applications for Common Garden Crops
The principles of Xenia and Metaxenia translate into practical concerns for certain garden crops, though most common fruits remain unaffected. Corn is the primary crop requiring isolation to prevent immediate changes to the harvest quality. Gardeners growing different corn types, such as sweet corn and popcorn, must ensure adequate distance or staggered planting times to prevent the Xenia effect from reducing sweetness or changing kernel texture.
For the large Cucurbita family, which includes pumpkins, squash, and zucchini, foreign pollen rarely affects the current season’s fruit flesh. A zucchini cross-pollinated by a pumpkin will still produce a perfectly edible zucchini that season. However, if the gardener saves the seeds from that cross and plants them the following year, the resulting hybrid fruit will likely be unpredictable in shape, flavor, and texture.
In tree fruits like apples and pears, cross-pollination is often required for successful fruiting, as many varieties are self-incompatible. While the fruit flesh’s flavor and color are not changed by the foreign pollen, the pollination event influences fruit quality. A higher number of fertilized ovules and seeds results in increased production of growth hormones, leading to larger, better-formed fruit. This subtle Metaxenia-like effect means a poorly pollinated apple may be smaller and misshapen, even if its taste profile remains true to its variety.