Inbreeding depression occurs when individuals mate with closely related individuals, resulting in offspring with reduced fitness and increased susceptibility to diseases. This is because inbreeding increases the chances of inheriting two copies of the same harmful recessive allele, which can have detrimental effects on the organism's phenotype and overall health.
To avoid inbreeding depression, plants have evolved various mechanisms for inbreeding avoidance. These mechanisms can be classified into two main categories:
1.Pre-mating mechanisms: These mechanisms prevent self-pollination or mating between closely related individuals before fertilization occurs.
- Dichogamy: This refers to the temporal separation of male and female sexual functions. For example, some plants have flowers that open at different times for male and female phases, preventing self-pollination.
- Self-incompatibility (SI): This is a genetic mechanism that prevents pollen from fertilizing ovules of the same flower or closely related flowers. SI can be gametophytic (involving the gametophytes) or sporophytic (involving the sporophytes) and is controlled by specific genetic loci.
- Pollen allelopathy: This involves the production of chemical substances by pollen that inhibit the germination or growth of pollen from the same or closely related individuals, preventing cross-pollination.
2.Post-mating mechanisms: These mechanisms prevent the development or survival of inbred offspring after fertilization has occurred.
- Embryo sac abortion: In some cases, the embryo sac may abort after self-fertilization, preventing the development of the embryo.
- Seed abortion: Fertilized ovules may abort at an early stage, resulting in the loss of self-fertilized seeds.
- Self-selective abortion: This refers to the phenomenon where self-fertilized seeds have a lower chance of germination or produce weaker seedlings compared to cross-fertilized seeds.
The evolution of inbreeding avoidance in plants is driven by natural selection. Plants that are more successful in avoiding inbreeding and promoting cross-fertilization have a higher chance of producing viable and vigorous offspring, leading to increased reproductive success and survival of the species. Over time, these mechanisms have become refined and diversified, resulting in the complex and fascinating array of reproductive strategies observed in plants.
