Definition of Parthenocarpy
Parthenocarpy could be defined as a process by which fruits are produced without the process of fertilization of ovules. A parthenocarpic fruit is devoid of embryo and endosperm and therefore does not have any seeds. That is why they are also known as seedless or virgin fruits.
The process was first introduced in 1902. During the cultivation of plants, Parthenocarpy is introduced alongside a range of plant hormones which parthenocarpic fruits include Gibberellic acid. This results in the maturation of the ovary without fertilization, leading to the products of big and pulpy fruits. Parthenocarpic fruit examples include Banana, pineapple, cucumber, watermelon etc.
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What are the Types of Parthenocarpy?
Parthenocarpy can be classified into three different categories
Vegetative parthenocarpy
Stimulative parthenocarpy
Stenospermocarpy
Vegetative Parthenocarpy
This type of Parthenocarpy takes place without pollination which results in no seed production within seeds. It can be seen in pears and figs to name a few.
Stimulative Parthenocarpy
This also takes place without pollination, however, there is the usage of an external stimulator. This can be the ovipositor of a wasp inserted into the ovary of a flower or the application of plant growth regulators into unisexual flowers which are observed inside the syconium. (Syconium is a flask-shaped structure line with unisexual flowers.)
Stenospermocarpy
This is a unique type of parthenocarpy where fertilization does take place and the seed begins to develop but it eventually aborts. There’s a seed trace that can be observed within the fruit and it can be outlined where seed development was terminated. This type of Parthenocarpy can be seen in seedless grapes and watermelons.
Breeders of seedless fruits take advantage of underdeveloped seeds before they are aborted. These partially developed seeds are removed from the fruit and grown into plants using tissue culture techniques. The seedless trait is passed on to both parents which assist in the production of a high yield of seedless offspring.
Explanation of Parthenocarpy with an Example
The following summary explains how parthenocarpy takes place in Stenospermocarpy using seedless watermelons as an example. Stenospermocarpy takes place due to several reasons. One of them is having three sets of chromosomes. Whilst most organisms have even numbers of chromosomes so the resulting pollen and egg cells also receive the same, seedless watermelons having three sets of chromosomes in each cell. These cells are known as triploids and when they form pollen and egg cells, they do not receive an equal set of chromosomes. The information needed to produce a viable cell is not available due to this reason and therefore results in the abortion of seed development. Triploid organisms are naturally developed or they can produce by crossing a diploid cell with a tetraploid cell which results in a triploid cell. Triploid pollens are poorly formed and since they cannot germinate diploid varieties are interplanted to induce fruit production with underdeveloped seeds. In seedless watermelons, the traces of seeds are visibly seen. It should also be mentioned that stenospermocarpy seedlessness in fruits is due to a naturally occurring point mutation in the part of the grape chromosome which is responsible for seed development.
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Diagrammatic Representation of Parthenocarpy
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What are the Advantages and Disadvantages of Parthenocarpy?
Parthenocarpy has its advantages and disadvantages. Both are briefly explained below.
Advantages:
It is very much popular amongst horticulturists. Seedless fruits are more preferred for the production of jams, sauces and fruit drinks. This process also increases the fleshy part of fruits. The process also allows a grower to keep pests and insects away from crops without using pesticides. As there is no need for pollinating insects, plants can be covered to prevent harmful insects from attacking the crops.
Disadvantages:
Parthenocarpy can also be chemically induced and in such cases, it is harmful to the plant and fruit yields. For example, early application of phytohormones such as auxins before the flowering period or the opening of the flower bud (also known as anthesis) can damage the flowers which lead to abortion to abortion of seed and fruit drop.
Benefits of Parthenocarpy
It produces seedless, fleshy fruitsIt reduces the cost of cultivation
It helps in increase in crop yield with the use of pesticides
Natural plant growth regulators are used which helps in the production of larger fruits
Reduces the usage of chemical pesticide to prevent attacks from harmful insects.
Natural and Artificial Parthenocarpy
Natural parthenocarpy is a type of parthenocarpy that occurs due to natural causes such as male sterility, adverse environmental conditions, the absence of pollinizers and pollinators, etc.
Artificial parthenocarpy is a type of parthenocarpy that is done by artificial means.
Artificial parthenocarpy can be done through irradiated pollen and with the spray of plant growth hormones such as auxin and Gibberellins that help in the growth of the fruits.
What is Parthenogenesis?
Parthenogenesis is defined as a process in which a new individual develops without the fertilization of an ovum. It takes place in invertebrates and some lower plants. In this process, male and female gametes are formed but they do not fuse and therefore it is also called incomplete sexual or asexual reproduction. The offspring is haploid and a clone of a female. The offspring cannot reproduce sexually. Parthenogenesis occurs naturally in queen bees. The unfertilized egg of queen bee develops to form male drones having a haploid set of chromosomes. Parthenogenesis can also be done artificially in mammals to produce identical offspring.
Significance of Parthenogenesis
Parthenogenesis is an important process due to the following reasons:
It can help to know the sex of an individual for example: in honey bees, wasps etc, the process helps to know sex of newly formed offspring.
This process can help to eliminate variations from populations
It is an easy and stable process of reproduction.
It can be used to develop beneficial mutant characteristics in organisms
It can help to control non-adaptive combination of genes
Difference between Parthenocarpy and Parthenogenesis
Parthenocarpy and parthenogenesis are an alternative form of reproduction that occur without fertilization. Parthenocarpy helps in the formation of fruits without seeds and parthenogenesis is a process in which an unfertilized ovum forms a new individual. The new individual is a clone of the female and is mostly haploid.
You can know the differences between parthenocarpy and parthenogenesis from the table given below:
FAQs on Parthenocarpy
1. What is parthenocarpy, and what are some common examples of parthenocarpic fruits?
Parthenocarpy is the biological process where fruit develops without the fertilization of ovules. This results in the formation of fruit that lacks viable seeds. Such fruits are often called 'virgin fruits'. Common examples of fruits that can be produced through parthenocarpy include bananas, pineapples, cucumbers, and certain varieties of watermelon and grapes.
2. What are the main types of parthenocarpy found in plants?
Parthenocarpy is generally classified into three main types based on its mechanism:
- Vegetative Parthenocarpy: This type occurs without the need for any pollination stimulus. The fruit develops naturally without fertilization, as seen in some varieties of pears and figs.
- Stimulative Parthenocarpy: In this type, pollination or another stimulus is required to initiate fruit development, but fertilization does not happen. The stimulus can be from non-viable pollen or even a physical one.
- Stenospermocarpy: This is a unique type where fertilization actually occurs, but the embryo aborts at a very early stage. This results in fruits with tiny, undeveloped seed traces, like those found in 'seedless' grapes.
3. Which hormones are commonly used to artificially induce parthenocarpy?
Plant growth regulators, or hormones, are frequently used in horticulture to induce parthenocarpy. The most common hormones used for this purpose are auxins and gibberellins. Spraying these hormones on the flowers at the right stage can trigger the ovary to develop into a fruit without the need for fertilization, often resulting in larger, fleshier fruits.
4. What is the key difference between parthenocarpy and parthenogenesis?
The key difference lies in the final product. Parthenocarpy is the development of a fruit without fertilization. In contrast, parthenogenesis is the development of a complete organism or individual from an unfertilized egg. For example, a seedless banana is a product of parthenocarpy, while the development of male drones in honeybees from unfertilized eggs is an example of parthenogenesis.
5. How does parthenocarpy differ from apomixis?
Parthenocarpy and apomixis are both forms of asexual reproduction in plants but differ in their outcome. Parthenocarpy results in the formation of a seedless fruit because the ovary develops without fertilization. Apomixis, on the other hand, is the formation of a viable seed without fertilization. In apomixis, the resulting seed is genetically identical to the mother plant.
6. What are the major commercial advantages of growing parthenocarpic fruits?
Commercially, parthenocarpy offers several significant advantages:
- It produces seedless fruits, which are highly preferred by consumers for direct consumption and for making jams, sauces, and juices.
- It increases the yield and quality of fruits, especially in conditions where pollination is poor or absent.
- It allows growers to protect plants with nets since they don't need to rely on insect pollinators, thereby reducing pest damage without extensive pesticide use.
7. Why are fruits produced by parthenocarpy always seedless?
Fruits produced by true parthenocarpy are seedless because the fundamental process of seed formation is skipped. A viable seed develops from an ovule only after it has been fertilized by pollen, leading to the formation of a zygote (the embryo) and endosperm (the nutritive tissue). Since parthenocarpy is defined by the absence of fertilization, the ovules never develop into seeds, resulting in a seedless fruit.
8. Can artificially inducing parthenocarpy have any disadvantages?
Yes, while commercially beneficial, artificially induced parthenocarpy can have disadvantages. If plant hormones like auxins are not applied at the correct time or concentration (e.g., before the flower bud opens), they can damage the flowers, leading to the abortion of both the seed and the fruit. From an ecological standpoint, widespread cultivation of genetically uniform parthenocarpic crops can reduce plant biodiversity, potentially making the species more vulnerable to diseases.
9. How does stenospermocarpy, as seen in seedless grapes, differ from true parthenocarpy?
The primary difference lies in the event of fertilization. In true parthenocarpy, no fertilization occurs at all. In stenospermocarpy, pollination and fertilization do happen, and an embryo begins to form. However, this embryo aborts at a very early stage of development, failing to mature into a viable seed. This is why 'seedless' grapes produced this way still contain tiny, soft, and edible seed traces inside.
10. From an evolutionary perspective, what is the purpose of natural parthenocarpy?
Natural parthenocarpy can be seen as an evolutionary 'backup plan' for plants. It ensures fruit production and dispersal even when conditions for sexual reproduction are not met. In environments with a scarcity of pollinators or adverse weather conditions that hinder pollination, parthenocarpy guarantees that the plant can still produce fruit. This ensures the survival and propagation of the parent plant, even if it's unable to produce genetically diverse offspring through seeds in that cycle.
