Pathenocarpy

When learning about fruit formation, we have all gone through fertilisation. Most fruits develop following the fertilisation process wherein a male gamete (pollen) fuses with a female gamete (ovule). But, under certain conditions, like environmental factors, hormonal treatments, or genetic modifications, fruits can develop without fertilisation.

Parthenocarpy (Gr. parthenos, virgin; karpos, fruit) is fruit development without fertilisation. Pollination may or may not occur, but fertilisation is absent. In 1902, F. Noll introduced this process of fruit production, where the parthenocarpic fruits lack viable seeds.

Processes of Parthenocarpy

The process of developing parthenocarpic fruits is carried out by

Natural Parthenocarpy

Under adverse environmental conditions or in the absence of pollinators, seedless fruits develop spontaneously, without needing external treatment.
It is also found in plants which are self-incompatible or dioecious, and the fruits just develop without fertilisation.

Examples include bananas and certain varieties of orange.

Artificial Parthenocarpy

The plants are treated with specific chemicals and growth hormones (like auxin and gibberellin) to stimulate the ovaries to develop seedless fruits.
Sometimes, irradiated pollen stimulates ovary growth and leads to parthenocarpic fruit.

Example: Squash, cucumber, tomato, etc.

Types of Parthenocarpy

Based on the mode of stimulation, the process of parthenocarpy can be classified into two types ^[b] -

Vegetative Parthenocarpy

Does not rely on external factors and develops seedless fruits due to the absence of pollination.

Example: Banana

Stimulative Parthenocarpy

Fertilisation is not needed, but the presence of external stimuli (like the insertion of the ovipositor of a wasp into the ovary of a flower or the application of phytohormones into unisexual flowers) results in the formation of a seedless fruit.

Example: Fig (with wasp oviposition) or cucumber (with hormones)

Stenospermocarpy ^[c]: A Special Type of Parthenocarpy

Stenospermocarpy is a special form of seedlessness, not true parthenocarpy, where fertilisation occurs but the seed aborts. The trace of the seed could be observed within the fruit, and it can be determined when the seed development terminated.

Example: Seedless grapes and watermelons.

Advantages of Parthenocarpy

Lead to higher, consistent yields due to little to no reliance on pollination and environmental conditions.
Results in improved fruit quality and better taste and texture.
In stenospermocarpy, breeders use embryo rescue and tissue culture to propagate plants before the seed aborts. The seedless trait is passed on to the offspring.

Disadvantages of Parthenocarpy

Parthenocarpy can reduce genetic diversity since it limits the natural genetic recombination that occurs during sexual reproduction.
The resulting fruits do not contain seeds.
Dependency on the external factors (growth regulators, environment) is high, increasing production cost, which sometimes makes the process unsustainable.

Summary

Parthenocarpy is the formation of seedless fruits without fertilisation. It can occur naturally or be induced artificially by hormones or treatments. This process improves fruit quality. It is widely used in crops like banana, tomato, cucumber, and grapes for commercial benefits.

Frequently Asked Questions

Q1. How does parthenocarpy differ from apomixis?

A.Parthenocarpy results in seedless fruits, but apomixis produces seeds without fertilisation.

Q2. How does parthenocarpy differ from parthenogenesis?

A.Parthenocary is the development of seedless fruit, whereas parthenogenesis is the development of an entire organism from an unfertilised egg. Example of parthenocarpy – banana; example of parthenogenesis – male honeybees (drones).