3. The development of sporophyte directly from gametophytic tissue without fusion of gametes is termed as
   (1) Apogamy (2) Apospory
   (3) Adventive embryony (4) Apomixis

The development of a sporophyte directly from gametophytic tissue without the fusion of gametes is termed as Apogamy.

Therefore, the correct answer is:

(1) Apogamy.

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Introduction

In plant reproduction, apogamy is a specialized form of asexual reproduction where the sporophyte generation develops directly from gametophytic tissue, circumventing the usual sexual fusion of gametes. This process leads to the formation of new sporophytes genetically identical to the parent gametophyte, and is especially observed in certain ferns and bryophytes.

Definition and Mechanism of Apogamy

• Apogamy refers to the development of a sporophyte (diploid phase) from gametophyte cells without fertilization or fusion of sperm and egg.

• The sporophyte can develop from any cell of the gametophyte except gametes themselves, such as synergids or antipodal cells.

• This process bypasses meiosis and syngamy, allowing propagation without genetic recombination.

Distinction from Related Terms

• Apospory (Option 2): The development of a gametophyte directly from sporophyte tissue without meiosis, opposite to apogamy.

• Adventive embryony (Option 3): Formation of embryos directly from somatic cells like nucellus or integument, a form of apomixis but distinct from apogamy.

• Apomixis (Option 4): A broader term encompassing both apogamy, apospory, and other asexual seed formation methods; apogamy is a specific type within this category.

Biological Significance of Apogamy

• Apogamy allows plants to reproduce asexually under unfavorable sexual reproduction conditions, maintaining genotypes that confer survival advantages.

• It is a valuable mechanism in plant breeding and propagation for producing uniform crop varieties.

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Summary Table: Key Features of Apogamy

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Conclusion

Apogamy is the term for the development of the sporophyte directly from the gametophytic generation without gamete fusion. It is a unique reproductive strategy that enables asexual propagation in plants, distinct from apospory and other forms of apomixis.