We’ve all been there. Sat eating a piece of fruit, minding our own business, getting on with our day, and then being dumbstruck at the realisation that the delicious fruit you’re eating has no seeds.
How are seedless fruits made? Do all fruits have seeds? Are seedless fruits genetically modified? These questions have crossed everybody’s mind at least once, so today, we’ll demystify this wondrous phenomenon.
Before we begin, this is a BIG topic, so we are only scraping the surface with the information below. We promise to hold your hand throughout this journey and do our best to make sense of the impossible. Let’s start with how fruit is normally formed before getting into the weird and wonderful world of chromosomes, hybridisation, and farmers’ experiments.
How is Fruit Normally Formed?
A simple rule of nature is for a plant to form fruit, it must first form flowers. Inside these flowers, there are male and female parts (or in some plants, there are separate male flowers and female flowers).
Fruit is triggered to form after pollen from a male part of the flower (stamen) comes in contact with the female part of a flower (stigma) resulting in pollination. This forms an embryo in the flower base which is the beginning of a seed!
Once the seed has begun, the flower has completed its job and will either fall off or become a part of the forming fruit.
In zucchinis, the male and female flowers are easily distinguishable. The male flowers have thin stems and the female flowers have the beginnings of an immature fruit at the base. In apples, the male and female parts are within the same flower.
In apples, the male and female parts are within the same flower.
Are Seedless Fruits Genetically Modified?
No, seedless fruits in Australia are not genetically modified (GMO). Farmers have been growing seedless fruits for generations, long before the beginnings of genetic engineering, and several natural methods can result in seedless fruit.
How Are Seedless Fruits Made Naturally?
Lots of seedless fruits result from a random genetic mutation and there are two ways a seedless fruit can develop randomly:
Stenospermocarpy
One way that seedless fruit can be formed is through stenospermocarpy. This is when pollination has triggered fruit development, but the embryos (baby seeds) stop growing before they can mature. The fruit continues to grow but without seeds inside. Sometimes there will be remnants of immature seeds within the fruit. This is common in grapes, watermelons, and avocadoes.
Parthenocarpy
Seedless fruit can also be formed through parthenocarpy. This is when a fruit develops without any pollen being transferred. Without pollen, fertilisation cannot occur and therefore seeds can’t form.
However, if the flower is cross-pollinated with another seed-forming variety, the fruit may contain seeds. This type is common in bananas, pineapples, cucumbers, tomatoes, figs, oranges, grapes, kiwi, blackberries, capsicum, and many others.
Due to the many benefits of seedless fruit, seedless varieties are often selected to grow commercially.
How to Create Seedless Fruit Yourself
There are many ways to multiply a plant without seeds and a common method is to grow them from cuttings. This happens by taking a piece of the parent plant and encouraging it to grow its own roots or grafting it to another rootstock.
The advantage of this is that the new plant is an exact clone of its parent so it will maintain the seedless genetics. This method is used for seedless bananas, grapes, and citrus fruits such as oranges, lemons, and limes.
Non-Chemical Hybridisation
Some seedless plants cannot be grown from cuttings and must be grown from seed instead. These include annual plants such as watermelon and cucumber that can be made seedless through hybridisation which is the cross-breeding between two distinct varieties.
However, not all hybrids are seedless and they must be genetically incompatible for this to occur.
Infertile offspring occurs in nature when two varieties are similar enough to cross-breed but different enough to be genetically incompatible. A common example of this is when breeding a horse with a donkey, the resulting offspring – a mule – will be infertile.
This occurs in the plant kingdom as well, but with plants, infertility means that they do not produce seeds.
In the case of seedless watermelons, farmers cross-bred a diploid (2-chromosome) variety with a tetraploid (4-chromosome) variety. These genetically incompatible varieties produce offspring that is a triploid (3 chromosomes) variety. Plants with odd numbers of chromosomes are sterile because the chromosomes have to match up in pairs during reproduction, which means triploid plants cannot make pollen or seeds.
Chemical Hybridisation
It gets even more interesting here because naturally, melons are all diploid (2 chromosomes) varieties. So, first breeders had to make a tetraploid (4 chromosomes) variety to breed the original melon.
This was achieved through a chemical treatment using Colchicine, a chemical derived from Colchicum Autumnale or as you may know it - autumn crocus. This was originally (and weirdly) used as a treatment for gout but has also been used in horticulture since the 1940s. Today, it’s known to produce varieties with larger leaves and flowers and has been used to breed larger flowered ornamentals.
When Colchicine is applied to plants, it doubles the number of chromosomes, which is how a tetraploid (4 chromosomes) melon variety was first bred. This process doesn’t need to be repeated as the variety is stable, meaning when it is bred with another tetraploid (4 chromosomes) melon, the offspring will all be tetraploids (4 chromosomes).
The seeds from cross-breeding a diploid (2 chromosomes) melon with a tetraploid (4 chromosomes) melon creates a seedless watermelon.
So, as you can see, seedless fruit can occur in many different ways. However, each method is difficult or expensive to reproduce from seed, which is why gardeners often do not get access to seedless varieties.
Grow Fruit at Home
Discover fruit seeds and produce bulbs all year round with Mr Fothergill’s. If you’d like to find out more about our products, how to grow different produce in different seasons, or explore the world of gardening in more detail, drop us a line or check out our garden advice blog!
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