[Biology Class Notes] on Parthenocarpy Pdf for Exam

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.

What are the Types of Parthenocarpy?

Parthenocarpy can be classified into three different categories

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.

Diagrammatic Representation of Parthenocarpy

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 ca
  n 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: