CROPS

How seedless fruits are made and propagated

Thumbnail: (Adam Kontor/Pexels)

By JAMES TABABA

Seedless fruits are a popular and convenient choice for many consumers, but have you ever wondered how they are developed? Contrary to popular belief, seedless fruits do not occur naturally. In fact, they are created through a variety of specialized techniques. Here are some methods on how seedless fruits are developed and propagate.

Sterile hybridization

Sterile hybridization is a specialized breeding technique used to produce seedless fruit. Unlike traditional breeding methods that rely on pollination to create offspring, sterile hybridization involves crossing two plants that are incapable of producing viable seeds. This results in a sterile hybrid plant that produces fruit without the development of seeds.

Watermelons are normally diploid, meaning they have two sets of chromosomes. However, to create a seedless watermelon, plant breeders cross a diploid watermelon with a tetraploid watermelon. Tetraploid watermelons have four sets of chromosomes, which is twice the number of a diploid.

Tetraploid watermelons are produced using a process called colchicine treatment. Colchicine is a naturally occurring chemical that is extracted from the crocus plant. When applied to the growing tips of watermelon plants, colchicine disrupts the normal process of cell division, resulting in cells with double the normal number of chromosomes.

When the diploid watermelon is crossed with the tetraploid watermelon, the resulting offspring has three sets of chromosomes, which is an odd number. This odd number of chromosomes makes the resulting plant sterile and unable to produce viable seeds.

However, the resulting plant is still able to produce fruit, since the process of making fruit does not require viable seeds. The fruit of the triploid plant is therefore seedless and can be enjoyed without the hassle of removing seeds.

To propagate these seedless watermelons, plant breeders use vegetative propagation methods such as cutting, grafting or tissue culture. This allows them to produce more plants with the desirable trait of seedlessness, without relying on seed production.

Polyploidy

Polyploidy and sterile hybridization are related concepts, but they are not exactly the same. Polyploidy can occur naturally, such as in some plant species, but it can also be induced through artificial methods like colchicine treatment. In contrast, sterile hybridization is always an intentional breeding technique used to create sterile hybrid plants for specific purposes like seedless fruit production.

Polyploidy is a genetic condition in which an organism has more than two complete sets of chromosomes in its cells. The seedless Cavendish banana is the most commonly consumed banana variety worldwide, and it is seedless due to polyploidy. 

Many citrus fruits, such as seedless oranges, lemons, and limes, are also seedless due to polyploidy. The seedless varieties were developed by selecting plants with natural mutations that resulted in seedlessness, and then breeding those plants to create seedless varieties.

Seedless grapes are another example of plants that have been developed through polyploidy. Like with bananas and citrus, seedless grapes were developed through selective breeding, with breeders selecting plants with natural mutations that resulted in seedlessness and then breeding those plants to create seedless varieties.

Gibberellic acid treatment

Gibberellic acid is a plant hormone that regulates different aspects of plant growth and development. It can also stimulate the development of seedless grapes.

To produce seedless grapes with gibberellic acid treatment, plant breeders use a technique called gibberellic acid-induced parthenocarpy. In this technique, the plant is treated with gibberellic acid during early fruit development. 

The gibberellic acid causes the ovules, part of the flower that develops into seeds, in the grape flower to develop into fruit, even in the absence of pollination.

Normally, grapes are produced from a fertilized ovule, where the ovule is pollinated by pollen and develops into a seed. However, with gibberellic acid treatment, the ovules can develop into fruit without the need for fertilization, resulting in seedless grapes.

After the gibberellic acid treatment, the grapes are usually covered with bags or netting to prevent insects from entering and pollinating the flowers. This ensures that the resulting grapes remain seedless.

While gibberellic acid treatment can produce seedless grapes, it is important to note that the grapes will not be triploid like those produced by sterile hybridization. Instead, they will be diploid, like normal grapes, but will lack seeds due to the absence of fertilization.

Vegetative propagation

Vegetative propagation is a method of asexual reproduction that results in the production of new plants that are genetically identical to the parent plant.

In some cases, vegetative propagation can be used to produce seedless fruit. This is because certain plants have the ability to produce fruit without fertilization, a process called parthenocarpy. Parthenocarpic fruit can be seedless, or may contain small, undeveloped seeds that are not viable.

One way to propagate seedless fruit through vegetative propagation is by taking cuttings from the parent plant and rooting them to form new plants. The resulting plants will be genetically identical to the parent plant and will also produce seedless fruit, as long as the parent plant is parthenocarpic.

Another method of vegetative propagation that can produce seedless fruit is grafting. The scion, a piece of a branch from the desired plant, will eventually grow into a new plant that is genetically identical to the parent plant. If the parent plant was parthenocarpic and produced seedless fruit, then the new plant will also produce seedless fruit.

An example of a crop that can be made seedless through vegetative propagation is grape. Some grape varieties are naturally parthenocarpic, meaning they can produce fruit without fertilization. However, the seeds in the fruit are generally small and underdeveloped, and the fruit is considered seedless. To propagate seedless grapes, cuttings from the parent plant can be taken and rooted to produce new plants that will also produce seedless fruit.

While the methods used to produce seedless fruits can be effective, there are also some drawbacks to consider. Seedless fruit varieties often have limited genetic diversity, as they cannot be propagated through seed. This can make them more susceptible to diseases and pests, and can also limit the ability of farmers to adapt to changing environmental conditions.

In addition, some may argue that seedless fruits may be lower in nutrition than their seeded counterparts, as seeds are often a rich source of vitamins, minerals, and other nutrients. Furthermore, seedless fruit varieties can be more expensive to produce than seeded varieties.

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