(b) Distinguish between polyembryony and parthenocarpy. Classify parthenocarpy and add a note on its significance.

Distinction between Polyembryony and Parthenocarpy

Polyembryony and parthenocarpy are distinct biological phenomena in plant reproduction, differing fundamentally in their definition, mechanism, and outcome.

Feature	Polyembryony	Parthenocarpy
Definition	The development of more than one embryo within a single ovule or seed.	The development and maturation of a fruit without prior fertilization of ovules.
Process Involves	Embryo and seed formation.	Fruit development, independent of sexual reproduction and successful seed set.
Fertilization Status	Typically involves fertilization, with multiple embryos arising from various sources (zygote cleavage, nucellus, synergids, etc.). In some cases, embryos may arise sexually or asexually.	Occurs without fertilization; hence, no fusion of male and female gametes is involved in fruit initiation.
Seed Presence	Seeds are always present, containing multiple embryos.	Fruits are typically seedless or contain non-viable rudimentary seeds.
Genetic Outcome	Embryos can be genetically identical (clonal, e.g., from nucellar cells) or genetically diverse (e.g., from multiple fertilized archegonia).	The fruit's genetic makeup is determined by the maternal plant, as no genetic contribution from pollen is involved in fruit development.
Examples	Citrus (orange, lemon), mango, onion, Pinus, some orchids.	Banana, pineapple, seedless grapes, seedless watermelon, cucumber, certain varieties of oranges and figs.

Classification of Parthenocarpy

Parthenocarpy can be classified based on its natural occurrence and the mechanism of its induction:

1. Natural Parthenocarpy

This type occurs spontaneously in plants without any human intervention. It can be further sub-classified:

• Vegetative Parthenocarpy: Fruit development occurs entirely in the absence of pollination stimulus. The ovary develops into a fruit without any need for external triggers.
  • Examples: Some varieties of bananas, seedless cucumbers, navel oranges.
• Stimulative Parthenocarpy: This type requires a stimulus, such as pollination (even by non-viable pollen) or mechanical irritation, to initiate fruit development. However, fertilization itself does not occur.
  • Examples: Seedless grapes (where rudimentary seeds may be present due to early embryo abortion, a condition sometimes called stenospermocarpy), some varieties of watermelon.
• Genetic Parthenocarpy: Occurs due to specific genetic mutations or hybridization that inherently lead to seedless fruit production.
  • Examples: Certain varieties of citrus, cucurbits.

2. Induced (Artificial) Parthenocarpy

This involves the artificial inducement of seedless fruit development through external means:

• Hormone-Induced Parthenocarpy: Application of plant growth regulators (phytohormones) such as auxins, gibberellins, or cytokinins to flowers can stimulate the ovary to develop into a fruit without fertilization.
  • Examples: Commercial production of seedless tomatoes, grapes, and cucumbers often utilizes this method.
• Other Induced Methods: This can include using irradiated pollen, genetic engineering techniques (e.g., expressing auxin biosynthesis genes), or manipulating environmental conditions (e.g., low temperatures) in some cases.

Significance of Parthenocarpy

Parthenocarpy holds immense significance in agriculture, horticulture, and the food industry due to the desirable characteristics of seedless fruits:

• Enhanced Consumer Preference and Market Value: Seedless fruits are highly preferred by consumers for their convenience, ease of consumption, and improved texture. This translates into higher market value and commercial demand for such produce. Examples include seedless grapes, watermelons, and citrus varieties.
• Increased Crop Yield and Quality:
  • Reliable Fruit Set: Parthenocarpy ensures fruit production even in conditions where natural pollination is poor or absent (e.g., adverse weather, scarcity of pollinators, or in greenhouses). This leads to more predictable and consistent yields.
  • Reduced Cultivation Costs: Decreased reliance on pollinators can reduce the need for their management and protection, potentially lowering cultivation costs.
  • Higher Edible Portion: The absence of seeds means a larger proportion of the fruit is edible, which is beneficial for both fresh consumption and processing into products like jams, jellies, and juices.
  • Larger Fruit Size: Artificial induction of parthenocarpy often leads to the production of larger and pulpy fruits due to the hormonal stimulus.
• Pest and Disease Management:
  • Reduced susceptibility to diseases that can be transmitted during pollination or through genetic combinations during seed formation.
  • Seedless fruits may be less attractive to certain pests that feed specifically on seeds, potentially reducing pesticide use.
• Extended Growing Seasons and Geographical Range: Parthenocarpic plants can produce fruits outside their normal growing season or in environments where natural pollinators are scarce or climatic conditions are unfavorable for fertilization. This allows for year-round production in controlled environments.
• Facilitates Food Processing: Seedless fruits simplify industrial processing for juices, purees, canned fruits, and other products, as there is no need for seed removal.
• Advancements in Plant Breeding: Understanding the genetic and hormonal mechanisms of parthenocarpy allows breeders to develop new seedless varieties through conventional breeding or biotechnological approaches, such as genetic engineering to introduce or enhance parthenocarpic traits. Recent research, as highlighted in "Trends in Plant Science" (2024), explores molecular mechanisms involving transcription factors and phytohormones like auxin and gibberellin to further leverage parthenocarpy for yield stability under climate change.