Question

Explain the different ways by which apomictic seeds can be developed.
Mention one advantage of apomictic seeds for farmers.

Hint:

Think of apomixis as "natural plant cloning inside a seed." Because there is no meiosis and no fusion of gametes, the resulting seed forms a exact genetic carbon copy of the high-performing maternal hybrid parent.

Answer 1

Step 1: Understanding the Question:
The question asks for an explanation of the biological pathways through which apomictic (asexual) seeds develop in flowering plants. It also requires identifying a specific agricultural advantage that these seeds offer to farmers.

Step 2: Key Formula or Approach:
Apomixis is a reproductive mechanism where seeds are formed without going through fertilization. It acts as a mimic of sexual reproduction but preserves the exact genetic composition of the maternal plant.

Step 3: Detailed Explanation:
(a) Mechanisms of Apomictic Seed Development: Apomictic seeds can develop through two primary evolutionary pathways:
1. Apospory Diplospory (Development from an unreduced egg cell): In several plant species, a diploid ($2n$) egg cell is formed without undergoing normal meiotic reduction division. This unreduced diploid egg cell then develops directly into an embryo through mitotic divisions without being fertilized by a male gamete.
2. Adventive Embryony (Development from nucellar or integumentary cells): In many citrus fruit varieties and mango (Mangifera indica), diploid somatic cells belonging to the surrounding maternal tissues—such as the nucellus or integuments—protrude directly into the embryo sac. These somatic cells divide mitotically and develop into fully functional embryos. This often leads to a phenomenon known as polyembryony, where a single seed contains multiple embryos.
(b) Advantage for Farmers: Farmers often grow hybrid crops because they provide high vigor, better resilience, and increased yields. However, if farmers collect seeds from a hybrid crop and plant them the following year, the alleles segregate during sexual reproduction, causing the offspring to lose those specialized hybrid traits. Consequently, farmers must buy expensive hybrid seeds every single season. If these hybrid seeds can be engineered to be apomictic, the embryos develop asexually without fertilization. This prevents genetic segregation, allowing farmers to keep saving and replanting their own high-yielding seeds year after year without losing hybrid performance.

Step 4: Final Answer:
(a) Apomictic seeds develop either by a diploid egg forming without meiosis and developing into an embryo without fertilization, or by surrounding maternal nucellar cells dividing and protruding into the embryo sac.
(b) The main advantage is that hybrid seeds do not segregate their traits, allowing farmers to replant saved seeds year after year without buying new ones every season .