21. Given below are statements regarding apomixis, i.e. asexual reproduction through seeds

1. Sporophytic apomicts often produce a mix of clonal and sexual progeny
   B. In gametophytic apomixis, the unreduced central cell gives rise to apomictic embryo
   C. In pseudogamy the endosperm is formed in the absence of fertilization
   D. Apomixis can potentially be used to maintain hybrid vigour over many generations
   Which one of the following options represents the combination of all correct statements?
   (1) A and C (2) B and C
   (3) C and D (4) A and D

The correct combination of statements regarding apomixis in plants is:

(4) A and D

Explanation:

• (A) Sporophytic apomicts often produce a mix of clonal and sexual progeny — Correct. In sporophytic apomixis (adventive embryony), embryos arise from somatic cells alongside sexually formed embryos, leading to mixed progeny.​

• (D) Apomixis can potentially be used to maintain hybrid vigour over many generations — Correct. Apomixis allows clonal propagation through seeds, preserving hybrid vigor by bypassing meiosis and fertilization.​

• (B) In gametophytic apomixis, the unreduced central cell gives rise to apomictic embryo — Incorrect. Generally, the apomictic embryo arises from the unreduced egg cell. The central cell forms endosperm, occasionally needing fertilization (pseudogamy).​

• (C) In pseudogamy, the endosperm is formed in the absence of fertilization — Incorrect. In pseudogamy, fertilization of the central cell is required for endosperm formation while the embryo is apomictic.​

Introduction

Apomixis enables asexual seed formation, bypassing fertilization, and offers enormous potential for agricultural innovation by fixing desirable traits. Among its types, sporophytic apomixis is notable for producing both clonal and sexual progeny. Understanding these mechanisms and their impact on hybrid vigor maintenance is vital in plant breeding.

Sporophytic Apomixis and Mixed Progeny

• Sporophytic apomixis or adventive embryony occurs when embryos develop directly from somatic ovule tissues, such as the nucellus, alongside sexually derived embryos.​

• This leads to seeds with both clonal and sexual embryos, resulting in variation in progeny.​

Apomixis and Hybrid Vigor

• Apomixis bypasses genetic reshuffling of sexual reproduction, maintaining hybrid vigor by producing genetically identical seeds across generations.​

• This characteristic could revolutionize crop improvement by stabilizing heterosis effects.​

Clarification of Other Concepts

• In gametophytic apomixis, the apomictic embryo arises usually from the unreduced egg cell rather than the central cell (B incorrect).​

• Pseudogamy requires fertilization of the central cell for endosperm development, contradicting the statement that endosperm forms without fertilization (C incorrect).​

Summary Table: Validity of Apomixis Statements

Conclusion

Statements (A) and (D) accurately describe sporophytic apomixis producing mixed progeny and the ability of apomixis to preserve hybrid vigor, respectively. Statements (B) and (C) are incorrect in describing embryo origin and endosperm formation.