By Dr Nazatul Shima Naharudin
The writer is a lecturer at the Department of Crop Science, Universiti Putra Malaysia and an expert in Plant Breeding and Cytogenetics.
KUALA LUMPUR: When we bite into a fruit and accidentally bite through the seed, the resulting taste can be quite unpleasant. Therefore, seedless fruits are often more favoured than their seeded counterparts. This is especially true for fruits like watermelons, grapes and bananas.
The seed is the result of the fertilisation of plants that reproduce sexually. In the right conditions, a dispersed or planted seed will grow into a new plant.
It is possible for seedless fruits to occur naturally but such instances are rare. This is because the seed is an important structure in the survival of a plant species. Because seedlessness is a naturally occurring trait, fruit plant breeders can select this trait in producing quality plants and fruits without resorting to genetic engineering.
Unfortunately many articles shared on electronic media today call on consumers to avoid seedless fruits because they are deemed genetically modified and are thus GMOs (genetically modified organisms). Such articles often garner so many shares that the information has become viral, leading to the misperception about seedless plants.
Every plant has to undergo a specific growth process and it is the same with the development of seeds.
Any defect that occurs during the process can result in the failure to develop a seed. As such, seedlessness is actually an unfavourable trait, because the plant has lost its ability to propagate!
The development of fruit without fertilisation can be classified as parthenocarpy. This happens when a fruit is produced without fertilisation of ovules (the female reproductive unit in a plant that would develop into a seed).
In seedless plants, the pollination process can produce a hormone to stimulate the contraction of the ovary walls and causes it to thicken and form fruit. However, the fertilisation and seed production process do not happen and as such there are no “traces of seed”. This trait is present in cucumbers and grapes and results in smaller fruits, compared to the seeded variety.
Another type of parthenocarpy called stenospermocarpy may also produce apparently seedless fruit, but the seeds are actually aborted while they are still immature. Thus “traces of seeds” are left behind (these are hollowed seeds, typically white in colour in watermelons).
Seedless fruit plant breeders take advantage of these phenomenon by extracting these developing seeds before it is aborted. They then propagate the plants using tissue culture. This method allows the production of a breed that retains the seedless trait and can pass it on the next generation.
The disruption to the process of seed formation is due to several factors. For plants like watermelon and banana, the seedless breed occurs due to a phenomenon called triploidy. In other words, it has three sets of chromosomes. An odd-numbered set of chromosomes causes an abnormal development of the gamete.
Most organisms have even-numbered sets of chromosomes and as such produce male and female gametes that possess genetic material or DNA that are balanced.
In triploid plants, the formation of gamete cells does not go through a balanced division of genetic materials. This results in the production of defective seeds.
Triploid plants can occur naturally but it can also be artificially created by crossing a diploid parent (two sets of chromosomes) with a tetraploid parent (four sets of chromosomes to produce a triploid breed.
In watermelons, assisted pollination is required for fruit development. Because the pollens from triploid plants are sterile, they must be planted in rows alternating with diploid varieties so that pollination can happen. This will help produce seedless watermelons or watermelons with soft, white seeds.
The extraction of seeds done commercially today can produce fruits that are sweeter, bigger, mature faster and are high in nutrients.
Understanding how seedless fruits are produced prevents consumers from being swayed by misinformation. We can enjoy seedless fruits without worrying about them being GMO products as they are actually formed through a natural breeding process.
(This article is the opinion of the writer.)
